Modular fuel cell assembly

Abstract

A propulsion system is provided, including: a gas turbine engine including a combustion section having a combustor; and a modular fuel cell assembly. The modular fuel cell assembly includes: a first fuel cell string including a first processing unit and a first fuel cell stack including first fuel cells defining an outlet configured to provide output products from the first fuel cells to the combustor; and a second fuel cell string including a second processing unit and a second fuel cell stack including second fuel cells defining an outlet configured to provide output products from the second fuel cells to the combustor.

Description

Technical Field

[0001] This disclosure relates to systems and methods for operating fuel cell components, gas turbine engines, or both. Background Technology

[0002] A gas turbine engine generally consists of a turbine and a rotor assembly. Gas turbine engines (such as turbofan engines) can be used for aircraft propulsion. In the case of a turbofan engine, the turbine includes a compressor section, a combustion section, and a turbine section in a sequential flow sequence, and the rotor assembly is configured as a fan assembly.

[0003] During operation, air is compressed in the compressor and mixed with fuel in the combustion section and ignited to generate combustion gases, which flow downwards through the turbine section. The turbine section extracts energy from the combustion gases to rotate the compressor section and fan assembly, thereby powering the gas turbine engine and propelling the aircraft containing this gas turbine engine during flight.

[0004] At least some gas turbine engines include fuel cell components that can operate in conjunction with them. Attached Figure Description

[0005] The complete and feasible disclosure of this disclosure, including its best mode, is set forth in the specification with reference to the accompanying drawings, for those skilled in the art, wherein:

[0006] FIG. 1 This is a cross-sectional view of a gas turbine engine according to an exemplary aspect of this disclosure.

[0007] FIG. 2 This is a perspective view of the integrated fuel cell and burner assembly according to this disclosure.

[0008] FIG. 3 yes FIG. 2 A schematic axial view of an exemplary integrated fuel cell and burner assembly.

[0009] FIG. 4 This is a schematic diagram of a fuel cell assembly according to an exemplary aspect of the present disclosure, the fuel cell being incorporated into... FIG. 2 An exemplary integrated fuel cell and burner assembly.

[0010] FIG. 5 This is a schematic diagram of a gas turbine engine including an integrated fuel cell and burner assembly, according to an exemplary aspect of this disclosure.

[0011] FIG. 6 This is a schematic diagram of a propulsion system according to another exemplary embodiment of the present disclosure.

[0012] FIG. 7 is a schematic diagram of a fuel cell assembly according to an example embodiment of the present disclosure.

[0013] FIG. 8 is a schematic diagram of a fuel cell assembly according to another example embodiment of the present disclosure.

[0014] FIG. 9 is a flow diagram graphically depicting interrelationships of various aspects of a fuel cell assembly integrated into a gas turbine engine.

[0015] FIG. 10 is a flow diagram of a method for operating a propulsion system according to example aspects of the present disclosure.

[0016] FIG. 11 is a flow diagram of a method for determining fuel cell leak diagnostic information according to example aspects of the present disclosure.

[0017] FIG. 12 is a flow diagram of example aspects of a method for determining fuel cell leak diagnostic information related to an off-engine leak. FIG. 11

[0018] FIG. 13 is a flow diagram of example aspects of a method for determining fuel cell leak diagnostic information related to a cross leak. FIG. 11

[0019] FIG. 14 is a flow diagram of a method for determining carbon deposition diagnostic information according to example aspects of the present disclosure.

[0020] FIG. 15A is a reporting module according to example aspects of the present disclosure.

[0021] FIG. 15B is an inventory and maintenance table according to example aspects of the present disclosure.

[0022] FIG. 16 is a flow diagram of a method for operating a propulsion system according to another example embodiment of the present disclosure.

[0023] FIG. 17 is a flow diagram of a model-based control method according to example aspects of the present disclosure.

[0024] FIG. 18 is a flow diagram of a modified fuel cell model according to example aspects of the present disclosure.

[0025] FIG. 19 is a perspective view of an integrated fuel cell and combustor assembly according to the present disclosure.

[0026] FIG. 20 ​​is a schematic diagram of a propulsion system according to another example embodiment of the disclosure.

[0027] FIG. 21 is a schematic diagram of a propulsion system according to yet another example embodiment of the disclosure.

[0028] FIG. 22 is a method of operating a propulsion system including modular fuel cell assemblies.

[0029] FIG. 23 One embodiment of a multi-gas sensing system according to one embodiment is shown.

[0030] FIG. 24 A system layout of a multi-gas sensing system according to one embodiment is shown. FIG. 23 A sensing circuit of the multi-gas sensing system shown.

[0031] FIG. 25 A system layout of a multi-gas sensing system according to one embodiment is shown.

[0032] FIG. 26 A flow diagram of one embodiment of a method for sensing multiple different gas analytes using a multi-gas sensing system according to one embodiment is shown.

[0033] FIG. 27 A plot of the electrical response of individual sensing elements of a multi-gas sensing system according to one embodiment is shown.

[0034] FIG. 28 A plot of the electrical response in the analyzed electrical response of individual sensing elements of a multi-gas sensing system shown in FIG. FIG. 27 A plot of the electrical response in the analyzed electrical response of individual sensing elements of a multi-gas sensing system shown in FIG.

[0035] FIG. 29 A plot of the response of a metal oxide sensing element to a gas of interest according to one embodiment is shown.

[0036] FIG. 30 A plot of the quantification of gas concentration using dielectrically excited gas detection according to one embodiment is shown.

[0037] FIG. 31 The effect of water vapor on resistance and dielectrically excited response over a range of relative humidity is shown.

[0038] FIG. 32 A plot of the operation of a multi-gas monitor under dynamic wind conditions according to one embodiment is shown.

[0039] FIG. 33 A plot of the response of a sensing element to hydrogen and methane according to one embodiment is shown.

[0040] FIG. 34FIG. 13 illustrates a graph of quantification of gas concentration using dielectrically excited gas detection, according to one embodiment. DETAILED DESCRIPTION

[0041] Reference will now be made in detail to the current embodiments of the present disclosure, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations

[0042] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, to the extent that the

[0043] For purposes of the description hereinafter, the terms "upper", "lower", "vertical", "horizontal", "top", "bottom", and derivatives thereof shall relate to the embodiments as they are oriented in the drawing figures. However, it is to be understood that the embodiments can assume various alternative orientations and, unless otherwise specified, the specific

[0044] As used herein, the terms "first", "second", and "third" can be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components.

[0045] The terms "forward" and "aft" refer to relative positions within a gas turbine engine or vehicle and refer to the normal operating attitude of the gas turbine engine or vehicle. For example, with respect to a gas turbine engine, forward refers to a position closer to the engine inlet and aft refers to a position closer to the engine nozzle or exhaust.

[0046] The terms "upstream" and "downstream" refer to the relative direction with respect to fluid flow in a fluid pathway. For example, "upstream" refers to the direction from which the fluid flows, and "downstream" refers to the direction to which the fluid flows.

[0047] Unless specified otherwise herein, the terms "coupled", "fixed", and the like, refer to either a direct connection between components or an indirect connection via one or more intermediate components or features.

[0048] The singular forms "a", "an", and "the" include plural references unless the context clearly dictates otherwise.

[0049] The term“at least one” in the context of“at least one of A, B, and C” or“at least one of A, B, or C” means A alone, B alone, C alone, or any combination of A, B, and C.

[0050] Approximating language as used throughout the specification and claims is applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is directed. Accordingly, a value modified by a term or terms, such as“about,”“approximately,” and“substantially,” are not limited to the precise value specified. In at least some instances, the approximating language can correspond to the precision of an instrument for measuring the value or the precision of the methods or machines for constructing or manufacturing the components and / or systems. For example, the approximating language can refer to a margin of error within 1%, 2%, 4%, 10%, 15%, or 20%. These approximating margins can apply to individual values, to any one of the endpoints of a range, or to the range of endpoints as a whole.

[0051] Ratios, concentrations, amounts, and other numerical data can be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. As an example, a range of“1 to 10” should be interpreted to include not only the explicitly recited limits of 1 and 10, but also the individual numbers 2, 3, 4, 5, 6, 7, 8, and 9, as well as sub-ranges such as 1-6, 4-8, 2-4, 3- 5, and 1-3, etc. In this example, the range of ratios begins with the number 1 and ends with the number 10.

[0052] “Third flow” as used herein refers to a non-primary gas flow that is capable of adding fluid energy to produce a small amount of total propulsion system thrust. The pressure ratio of the third flow can be higher than the pressure ratio of the primary propulsion flow (e.g., a bypass or propeller driven propulsion flow). Thrust can be produced through a dedicated nozzle or by mixing the gas flow through the third flow with the primary propulsion flow or core gas flow (e.g., into a common nozzle).

[0053] In certain example embodiments, the operating temperature of the gas flow through the third flow can be lower than the maximum compressor discharge temperature of the engine, and more specifically, can be lower than 350 degrees Fahrenheit (such as lower than 300 degrees Fahrenheit, such as lower than 250 degrees Fahrenheit, such as lower than 200 degrees Fahrenheit, and at least as high as ambient temperature). In certain example embodiments, these operating temperatures can facilitate heat transfer to or from the gas flow through the third flow and the separate fluid flow. Further, in certain example embodiments, the gas flow through the third flow can contribute less than 50% of the total engine thrust (and at least, for example, 2% of the total engine thrust) when operating in takeoff conditions, or more specifically, in sea level rated takeoff power, static flight speed, 86 degrees Fahrenheit ambient temperature operating conditions.

[0054] Further, in certain example embodiments, the above-described example percentage contribution to total thrust, by way of airflow aspects (e.g., airflow, mixing, or exhaust properties) of the third stream, and thereby, can be adjusted passively during engine operation or purposefully modified through the use of engine control features such as fuel flow, motor power, variable stator, variable inlet guide vanes, valves, variable exhaust geometry, or fluidic features to adjust or optimize overall system performance under a wide range of potential operating conditions.

[0055] The term "turbomachine" refers to a machine that includes one or more compressors, a heat generating section (e.g., a combustion section), and one or more turbines that together generate a torque output.

[0056] The term "gas turbine engine" refers to an engine that has a turbomachine as all or a portion of its power source. Example gas turbine engines include turbofan engines, turboprop engines, turbojet engines, turboshaft engines, and the like, as well as hybrid electric versions of one or more of these engines.

[0057] The terms "low" and "high," or their respective comparative forms (e.g., more "low" and more "high," where applicable), when used in conjunction with compressor, turbine, shaft, or spool components, and the like, each refer to relative speeds within the engine, unless otherwise noted. For example, a "low turbine" or "low speed turbine" defines a component that is configured to operate at a lower rotational speed (such as a maximum allowable rotational speed) than a "high turbine" or "high speed turbine" at the location in the engine.

[0058] As will be discussed in greater detail below, a fuel cell is an electrochemical device that can convert chemical energy from a fuel, such as hydrogen, into electrical energy through an electrochemical reaction of the fuel with an oxidant, such as oxygen contained in the atmosphere. A fuel cell system can be advantageously used as an energy supply system because, when compared to at least certain existing systems, a fuel cell system can be considered environmentally superior and efficient. To improve system efficiency and fuel utilization and reduce external water usage, a fuel cell system can include an anode recirculation loop. Because a single fuel cell can only generate about 1 V of voltage, multiple fuel cells can be stacked together, which can be referred to as a fuel cell stack, to generate a desired voltage. Fuel cells can include solid oxide fuel cells (SOFCs), molten carbonate fuel cells (MCFCs), phosphoric acid fuel cells (PAFCs), and proton exchange membrane fuel cells (PEMFCs), which are generally named after their respective electrolytes. Each of these fuel cells can have certain benefits in the form of a preferred operating temperature range, power generation capability, efficiency, and the like.

[0059] Reference is now made to the drawings, wherein like numerals refer to like elements throughout, FIG. 1A schematic cross-sectional view of an engine according to an exemplary embodiment of the present disclosure is provided. The engine can be integrated into a vehicle. For example, the engine can be an aircraft engine integrated into an aircraft. However, alternatively, the engine can be any other suitable type of engine for any other suitable vehicle.

[0060] In the depicted embodiment, the engine is configured as a high-bypass turbofan engine 100. As... FIG. 1 As shown, the turbofan engine 100 defines an axial direction A (extending parallel to the centerline axis 101 provided for reference), a radial direction R, and a circumferential direction (extending around the axial direction A; not shown in the diagram). FIG. 1 (As shown in the figure). Typically, the turbofan engine 100 includes a fan section 102 and a turbine 104 disposed downstream of the fan section 102.

[0061] The depicted exemplary turbine 104 generally includes a substantially tubular housing 106 defining an annular inlet 108. The housing 106 surrounds, in a series flow relationship: a compressor section including a boost or low-pressure (LP) compressor 110 and a high-pressure (HP) compressor 112; a combustion section 114; a turbine section including a high-pressure (HP) turbine 116 and a low-pressure (LP) turbine 118; and an exhaust nozzle section 120. The compressor section, combustion section 114, and turbine section together at least partially define a core airflow path 121 extending from the annular inlet 108 to the exhaust nozzle section 120. The turbofan engine further includes one or more drive shafts. More specifically, the turbofan engine includes a high-pressure (HP) shaft or spool 122 drivingly connecting the HP turbine 116 to the HP compressor 112, and a low-pressure (LP) shaft or spool 124 drivingly connecting the LP turbine 118 to the LP compressor 110.

[0062] In the depicted embodiment, fan section 102 includes a fan 126 having a plurality of fan blades 128 spaced apart and coupled to disk 130. The plurality of fan blades 128 and disk 130 are rotatable together about a centerline axis 101 via LP shaft 124. Disk 130 is covered by a rotatable front hub 132, which is aerodynamically shaped to facilitate airflow through the plurality of fan blades 128. Furthermore, an annular fan housing or outer nacelle 134 is configured to circumferentially surround at least a portion of fan 126 and / or turbine 104. Nacelle 134 is supported relative to turbine 104 by a plurality of circumferentially spaced outlet guide vanes 136. A downstream section 138 of nacelle 134 extends over the outer portion of turbine 104 to define a bypass airflow passage 140 therebetween.

[0063] In this way, it will be understood that the turbofan engine 100 generally includes a first flow (e.g., a core airflow path 121) and a second flow extending parallel to the first flow (e.g., a bypass airflow passage 140). In some exemplary embodiments, the turbofan engine 100 may further define a third flow, for example, extending from the LP compressor 110 to the bypass airflow passage 140 or to the environment. With this configuration, the LP compressor 110 may generally include a first compressor stage configured as a ducted intermediate fan and a downstream compressor stage. The inlet of the third flow may be located between the first compressor stage and the downstream compressor stage.

[0064] Still referencing FIG. 1 The turbofan engine 100 additionally includes an accessory gearbox 142 and a fuel delivery system 146. The fuel delivery system 146 may be an aircraft fuel supply unit, such as an aircraft fuel supply unit for an aircraft propulsion system. In the illustrated embodiment, the accessory gearbox 142 is located within the shroud / casing 106 of the turbine 104. Additionally, it will be understood that for... FIG. 1 In the schematically depicted embodiment, accessory gearbox 142 is mechanically coupled to one or more shafts or spools of turbine 104 and is rotatable with one or more shafts or spools of turbine 104. For example, in the depicted exemplary embodiment, accessory gearbox 142 is mechanically coupled to HP shaft 122 via a suitable gear train 144 and is rotatable with HP shaft 122. Accessory gearbox 142 can provide power to one or more suitable accessory systems of turbofan engine 100 during at least some operations and can further provide power back to turbofan engine 100 during other operations. For example, in the illustrated embodiment, accessory gearbox 142 is coupled to starter motor / generator 152. Starter motor / generator can be configured to draw power from accessory gearbox 142 and turbofan engine 100 to generate electricity during some operations and can provide power back to accessory gearbox 142 and turbofan engine 100 (e.g., to HP shaft 122) during other operations to add mechanical work back to turbofan engine 100 (e.g., for starting turbofan engine 100).

[0065] Furthermore, the fuel delivery system 146 generally includes a fuel source 148 (such as a fuel tank) and one or more fuel delivery lines 150. One or more fuel delivery lines 150 supply fuel flow through the fuel delivery system 146 to the combustion section 114 of the turbine 104 of the turbofan engine 100. As will be discussed in more detail below, the combustion section 114 includes an integrated fuel cell and combustor assembly 200. In the described embodiment, one or more fuel delivery lines 150 supply fuel flow to the integrated fuel cell and combustor assembly 200.

[0066] However, it will be appreciated that FIG. 1 The exemplary turbofan engine 100 depicted in FIG. 1 is schematically illustrated as a direct drive fixed pitch turbofan engine, in other embodiments, the gas turbine engine of the present disclosure can be a geared gas turbine engine (i.e., include a gearbox between the fan 126 and the shaft (such as the LP shaft 124) that drives the fan), can be a variable pitch gas turbine engine (i.e., include a fan 126 having a plurality of fan blades 128 that are capable of rotating about their respective pitch axes), etc. Moreover, although the exemplary turbofan engine 100 includes a ducted fan 126, in other exemplary aspects, the turbofan engine 100 can include a non-ducted fan 126 (or open rotor fan) without the nacelle 134. Furthermore, although not depicted herein, in other embodiments, the gas turbine engine can be any other suitable type of gas turbine engine, such as a marine gas turbine engine.

[0067] Reference is now made to FIG. 2 schematically illustrated is a portion of a combustion section 114 including an integrated fuel cell and combustor assembly 200 used in the gas turbine engine 100 of FIG. 1 described above with respect to FIG. 1 the turbofan engine 100 as a turbine fan engine 100.

[0068] It will be appreciated that the combustion section 114 includes a compressor diffuser nozzle 202 and extends generally in an axial direction A between an upstream end and a downstream end. The combustion section 114 is fluidly coupled to the compressor section at the upstream end via the compressor diffuser nozzle 202 and is fluidly coupled to the turbine section at the downstream end.

[0069] The integrated fuel cell and combustor assembly 200 generally includes a fuel cell assembly 204 FIG. 2 depicted only partially in FIG. 3 to FIG. 5The combustor 206 includes an inner liner 208, an outer liner 210, a dome assembly 212, a shroud assembly 214, a swirler assembly 216, and a fuel flow line 218. The combustion section 114 generally includes a housing 220 radially outward of the combustor 206 to surround it, and an inner housing 222 radially inward of the combustor 206. The inner housing 222 and the inner liner 208 define an inner passage 224 therebetween, while the outer housing 220 and the outer liner 210 define an outer passage 226 therebetween. The inner housing 222, the outer housing 220, and the dome assembly 212 together at least partially define the combustion chamber 228 of the combustor 206.

[0070] The dome assembly 212 is positioned near the upstream end of the combustion section 114 (i.e., closer to the upstream end than the downstream end) and includes an opening (not labeled) for receiving and retaining the swirler assembly 216. The swirler assembly 216 also includes an opening for receiving and retaining the fuel flow line 218. The fuel flow line 218 is further coupled to a fuel source 148 disposed radially R outside the housing 220 (see [link to fuel source 148]). FIG. 1 It is configured to receive fuel from fuel source 148. In this way, fuel flow line 218 can be fluidly connected to the reference above. FIG. 1 Describes one or more fuel delivery pipelines 150.

[0071] The swirler assembly 216 may include a plurality of swirlers (not shown) configured to swirl the compressed fluid before it is injected into the combustion chamber 228 to generate combustion gases. In the illustrated embodiment, the shroud assembly 214 is configured to hold the inner liner 208, the outer liner 210, the swirler assembly 216, and the dome assembly 212 together.

[0072] During operation, the compressor diffuser nozzle 202 is configured to direct compressed fluid 230 from the compressor section to the combustor 206, wherein the compressed fluid 230 is configured to mix with fuel within the cyclone assembly 216 and burn within the combustion chamber 228 to generate combustion gases. The combustion gases are supplied to the turbine section to drive one or more turbines of the turbine section (e.g., high-pressure turbine 116 and low-pressure turbine 118).

[0073] During operation of the gas turbine engine 100 including the integrated fuel cell and combustor assembly 200, a flame within the combustion chamber 228 is sustained by a continuous flow of fuel and air. To provide for ignition of the fuel and air, for example, during start-up of the gas turbine engine 100, the integrated fuel cell and combustor assembly 200 further includes an igniter 231. The igniter 231 can provide a spark or initial flame to ignite a fuel and air mixture within the combustion chamber 228. In certain example embodiments, the integrated fuel cell and combustor assembly 200 can additionally include a dedicated fuel cell igniter 233 (depicted in dashed line). In particular, for embodiments of the integrated fuel cell and combustor assembly 200 in which the fuel cell assembly 204 includes a fuel cell stack (as described below), the dedicated fuel cell igniter 233 is positioned downstream of at least a portion of the fuel cell stack. In this manner, the dedicated fuel cell igniter 233 can more effectively combust output products of the fuel cell stack. FIG. 2

[0074] As described above and FIG. 2 As described above and

[0075] For the described embodiments, the fuel cell assembly 204 is configured as a solid oxide fuel cell ("SOFC") assembly, with the first fuel cell stack 232 configured as a first SOFC fuel cell stack and the second fuel cell stack 234 configured as a second SOFC fuel cell stack (each having a plurality of SOFCs). It will be appreciated that SOFCs are generally electrochemical conversion devices that produce electricity directly through oxidation of a fuel. Generally, fuel cell assemblies, and in particular fuel cells, are characterized by the electrolyte material used. The SOFCs of the present disclosure can generally include a solid oxide or ceramic electrolyte. Such fuel cells generally exhibit high overall thermoelectric efficiency, long-term stability, fuel flexibility, and low emissions.

[0076] ​Further, the example fuel cell assembly 204 further includes a first power converter 236 and a second power converter 238. The first fuel cell stack 232 is in electrical communication with the first power converter 236 by a first plurality of power supply cables (not labeled), and the second fuel cell stack 234 is in electrical communication with the second power converter 238 by a second plurality of power supply cables (not labeled).

[0077] The first power converter 236 controls current drawn from the corresponding first fuel cell stack 232, and can convert power from direct current ("DC") power to DC power at another voltage level or alternating current ("AC") power. Similarly, the second power converter 238 controls current drawn from the second fuel cell stack 234, and can convert power from DC power to DC power at another voltage level or AC power. The first power converter 236, the second power converter 238, or both, can be electrically coupled to an electrical bus, such as the electrical bus 326 described below.

[0078] The integrated fuel cell and combustor assembly 200 further includes a fuel cell controller 240 in operable communication with the first power converter 236 and the second power converter 238 to, for example, send and receive communications and signals therebetween. For example, the fuel cell controller 240 can send current or power setpoint signals to the first power converter 236 and the second power converter 238, and can receive voltage or current feedback signals, for example, from the first power converter 235 and the second power converter 238. The fuel cell controller 240 can be constructed in the same manner as the fuel cell controller 240 described below with reference to FIG. 5

[0079] It will be appreciated that, in at least certain example embodiments, the first fuel cell stack 232, the second fuel cell stack 234, or both, can extend substantially 360 degrees in a circumferential direction C of the gas turbine engine (i.e., a direction extending about a centerline axis 101 of the gas turbine engine 100). For example, referring now to FIG. 3 , a simplified cross-sectional view of the integrated fuel cell and combustor assembly 200 is depicted in accordance with example embodiments of the present disclosure. Although only the first fuel cell stack 232 is depicted in FIG. 3 , the second fuel cell stack 234 can be constructed in a similar manner.

[0080] As shown, the first fuel cell stack 232 extends about the combustion chamber 228 in the circumferential direction C, completely surrounding the combustion chamber 288 in the illustrated embodiment about the centerline axis 101. More specifically, the first fuel cell stack 232 includes a plurality of fuel cells 242 arranged along the circumferential direction C. In FIG. 3 ​The fuel cell 242 visible in the image can be a single ring of fuel cell 242, wherein fuel cells 242 are stacked together along the axial direction A (see [link]). FIG. 2 ( ), to form a first fuel cell stack 232. In another example, multiple additional rings of fuel cell 242 may be placed on top of each other to form a first fuel cell stack 232 extending along the centerline axis 101.

[0081] The following will explain this in more detail; please refer to [reference needed]. FIG. 5 In the first fuel cell stack 232, fuel cell 242 is positioned to receive exhaust air 244 from, for example, a compressor section and fuel 246 from a fuel delivery system 146. Fuel cell 242 uses the air 244 and at least some of the fuel 246 to generate an electric current and guides partially oxidized fuel 246 and unused portion of air 248 radially toward the centerline axis 101 into combustion chamber 228. Integrated fuel cell and combustor assembly 200 combusts the partially oxidized fuel 246 and air 248 in combustion chamber 228 into combustion gases, which are then guided downstream into a turbine section to drive or assist in driving one or more turbines therein.

[0082] In addition, now refer to FIG. 4 Provided as FIG. 2 A schematic perspective view of the first fuel cell stack 232 of the integrated fuel cell and burner assembly 200. The second fuel cell stack 234 can be formed in a similar manner.

[0083] The depicted first fuel cell stack 232 includes a casing 250 having a combustion outlet side 252 and a side 254 opposite to the combustion outlet side 252, a fuel and air inlet side 256 and a side 588 opposite to the fuel and air inlet side 256, and sides 260 and 262. Sides 260, 258, and 254 are... FIG. 4 It is not visible in the 3D image.

[0084] It will be appreciated that the first fuel cell stack 232 can include a plurality of fuel cells that are stacked side-by-side, for example, from one end of the first fuel cell stack 232 (e.g., the fuel and air inlet side 256) to the other end of the first fuel cell stack 232 (e.g., side 258). Thus, it will be further appreciated that the combustion outlet side 252 includes a plurality of combustion outlets 264, each combustion outlet from a fuel cell in the first fuel cell stack 232. During operation, combustion gases 266 (also referred to herein as “output products”) are directed out of the housing 250 from the combustion outlets 264. As described herein, the combustion gases 266 are generated using fuel and air that is not consumed by the fuel cells within the housing 250 of the first fuel cell stack 232. The combustion gases 266 are provided to the combustor 228 and, during operation, are combusted to generate combustion gases that are used to generate thrust for the gas turbine engine 100 (and the carrier / aircraft in combination with the gas turbine engine 100).

[0085] The fuel and air inlet side 256 includes one or more fuel inlets 268 and one or more air inlets 270. Optionally, one or more of the inlets 268, 270 can be on the other side of the housing 250. Each of the one or more fuel inlets 268 is fluidly coupled with a source of fuel for the first fuel cell stack 232, such as a hydrogen-containing gas or one or more pressurized containers of a fuel processing unit described further below. Each of the one or more air inlets 270 is fluidly coupled with a source of air for the fuel cell, such as air discharged from a compressor section and / or an air processing unit also described further below. The one or more inlets 268, 270 separately receive fuel and air from external sources of fuel and air and separately direct the fuel and air into the fuel cell.

[0086] In certain example embodiments, FIG. 2 to FIG. 4 The first fuel cell stack 232 can be constructed in a similar manner as one or more of the example fuel cell systems (labeled 100) described in U.S. Patent Application Publication No. 2020 / 0194799 Al, filed December 17, 2018, the entirety of which is incorporated by reference herein. It will be further appreciated that the second fuel cell stack 234 can be constructed in a similar manner as the first fuel cell stack 232, or alternatively, can be constructed in any other suitable manner. FIG. 2 The first fuel cell stack 232 can be constructed in a similar manner as one or more of the example fuel cell systems (labeled 100) described in U.S. Patent Application Publication No. 2020 / 0194799 Al, filed December 17, 2018, the entirety of which is incorporated by reference herein. It will be further appreciated that the second fuel cell stack 234 can be constructed in a similar manner as the first fuel cell stack 232, or alternatively, can be constructed in any other suitable manner.

[0087] Referring now to FIG. 5 Operation of the integrated fuel cell and combustor assembly 200 according to example embodiments of the present disclosure will be described. More specifically, FIG. 5A schematic of a gas turbine engine 100 and integrated fuel cell and combustor assembly 200 according to embodiments of the present disclosure is provided. In certain example embodiments, the gas turbine engine 100 and integrated fuel cell and combustor assembly 200 can be constructed in a similar manner as one or more of the example embodiments described in U.S. Patent No. 10, 1 12, 1 10, which is incorporated by reference herein in its entirety. FIG. 1 to FIG. 4

[0088] Accordingly, it will be appreciated that the gas turbine engine 100 generally includes a fan section 102 having a fan 126, an LP compressor 1 10, an HP compressor 1 12, a combustion section 1 14, an HP turbine 1 16, and an LP turbine 1 18. The combustion section 1 14 generally includes an integrated fuel cell and combustor assembly 200 having a fuel cell assembly 204 and a combustor 206.

[0089] The propulsion system including the gas turbine engine 100 further includes a fuel delivery system 146. The fuel delivery system 146 generally includes a fuel source 148 and one or more fuel delivery lines 150. The fuel source 148 can include a supply of fuel (e.g., a hydrocarbon fuel, including, for example, a carbon neutral fuel or a synthetic hydrocarbon) for the gas turbine engine 100. Further, it will be appreciated that the fuel delivery system 146 further includes a fuel pump 272 and a flow splitter 274, and the one or more fuel delivery lines 150 include a first fuel delivery line 150A, a second fuel delivery line 150B, and a third fuel delivery line 150C. The flow splitter 274 splits a fuel flow from the fuel source 148 and the fuel pump 272 into a first fuel flow through the first fuel delivery line 150A to the fuel cell assembly 204, a second fuel flow through the second fuel delivery line 150B also to the fuel cell assembly 204 (and, in particular, to an air handling unit described below), and a third fuel flow through the third fuel delivery line 150C to the combustor 206. The flow splitter 274 can include a series of valves (not shown) to facilitate this splitting of the fuel flow from the fuel source 148, or, alternatively, can have a fixed geometry. Additionally, for the illustrated embodiment, the fuel delivery system 146 includes a first fuel valve 151 A associated with the first fuel delivery line 150A (e.g., to control the first fuel flow), a second fuel valve 151 B associated with the second fuel delivery line 150B (e.g., to control the second fuel flow), and a third fuel valve 151 C associated with the third fuel delivery line 150C (e.g., to control the third fuel flow).

[0090] ​The gas turbine engine 100 further includes a compressor bleed system and an airflow delivery system. More specifically, the compressor bleed system includes an LP bleed air duct 276 and an associated LP bleed air valve 278, an HP bleed air duct 280 and an associated HP bleed air valve 282, an HP outlet air duct 284 and an associated HP outlet air valve 286.

[0091] The gas turbine engine 100 further includes an airflow supply duct 288 (in airflow communication with an airflow supply 290) and an associated air valve 292, which is also in airflow communication with the airflow delivery system, for providing compressed airflow to the fuel cell assembly 204 of the integrated fuel cell and combustor assembly 200. The airflow supply can be, for example, a second gas turbine engine configured to provide cross-bleed air, an auxiliary power unit (APU) configured to provide bleed air, a ram air turbine (RAT), an ambient location (e.g., free stream air), etc. The airflow supply can be a supplement to the compressor bleed system if the compressor air source is insufficient or unavailable.

[0092] The compressor bleed system (and the airflow supply duct 288) is in airflow communication with the airflow delivery system for providing compressed airflow to the fuel cell assembly 204, as will be explained in greater detail below.

[0093] Still referring to FIG. 5 The fuel cell assembly 204 of the integrated fuel cell and combustor assembly 200 includes a fuel cell stack 294, which can be configured in a similar manner as, for example, the first fuel cell stack 232 described above. The fuel cell stack 294 is schematically depicted as a single fuel cell having a cathode side 296 (also referred to herein as "cathode 296"), an anode side 298 (also referred to herein as "anode 298"), and an electrolyte 300 (also referred to as an electrolyte layer) positioned therebetween. It will be generally understood that the electrolyte 300 can conduct negative oxygen ions from the cathode side 296 to the anode side 298 during operation to generate an electrical current and electrical power.

[0094] Briefly stated, it will be understood that the fuel cell assembly 204 further includes a fuel cell sensor 302 configured to sense data indicative of a fuel cell assembly operating parameter, such as a temperature of the fuel cell stack 294 (e.g., the cathode side 296 or the anode side 298 of a fuel cell), a pressure within the fuel cell stack 294 (e.g., within the cathode side 296 or the anode side 298 of a fuel cell), and / or a composition (e.g., a chemical composition) of an output product from the fuel cell assembly 204. In this manner, it will be understood that, in certain example embodiments, the fuel cell sensor 302 can be a gas sensor, such as a multi-gas sensor.

[0095] The anode side 298 can support an electrochemical reaction that generates electricity. Fuel can be oxidized in the anode side 298 via diffusion through the electrolyte 300, utilizing oxygen ions received from the cathode side 296. This reaction can generate heat, vapor, and electricity in the form of free electrons in the anode side 298, which can be used to power energy-consuming devices (such as one or more additional electrical devices 328 described below). Oxygen ions can be generated using electrons returning from the energy-consuming device to the cathode side 296 via oxygen reduction of the cathode oxidant.

[0096] The cathode side 296 can be coupled to a cathode oxidant source, such as atmospheric oxygen. The cathode oxidant is defined as the oxidant supplied to the cathode side 296, which is used by the fuel cell system to generate electricity. The cathode side 296 can be permeable to oxygen ions received from the cathode oxidant.

[0097] Electrolyte 300 can be connected to both the anode side 298 and the cathode side 296. Electrolyte 300 allows oxygen ions to pass from the cathode side 296 to the anode side 298, and can have very low conductivity or no conductivity to prevent free electrons from passing from the cathode side 296 to the anode side 298.

[0098] The anode side of a solid oxide fuel cell (such as anode side 298 of fuel cell stack 294) can be made of nickel / yttrium oxide-stabilized zirconium oxide (Ni / YSZ) cermet. Nickel in the anode side serves as a catalyst for fuel oxidation and as a current conductor. During normal operation of fuel cell stack 294, the operating temperature can be greater than or equal to about 700°C, and the nickel (Ni) in the anode retains its reduced form due to the continuous supply of primarily hydrogen fuel gas. Alternatively, the anode side may include a small amount of nickel, or may be completely or substantially nickel-free.

[0099] The fuel cell stack 294 is located downstream of the LP compressor 110, the HP compressor 112, or both. Furthermore, from the above regarding... FIG. 2 As will be understood from the description, fuel cell stack 294 may be coupled to or otherwise integrated with the bushings (e.g., inner liner 208 or outer liner 210) of burner 206. In this way, fuel cell stack 294 may also be arranged upstream of combustion chamber 228, which integrates fuel cell and burner assembly 200, and further upstream of HP turbine 116 and LP turbine 118.

[0100] like FIG. 5 As shown, the fuel cell assembly 204 also includes a fuel processing unit 304 and an air processing unit 306. The fuel processing unit 304 can be any suitable structure for generating a hydrogen-rich fuel stream. For example, the fuel processing unit 304 may include a fuel reformer or a catalytic partial oxidation converter (CPO). x), for producing a hydrogen-rich fuel stream for fuel cell stack 294. Air handling unit 306 can be any suitable structure for raising the temperature of air provided thereto to a temperature high enough to achieve fuel cell temperature control (e.g., about 600°C to about 800°C). For example, in the depicted embodiment, air handling unit includes a pre-burner system that operates based on a fuel stream through second fuel delivery line 150B, configured to raise the temperature of air through combustion, for example, during transient conditions such as start-up, shut-down, and abnormal situations.

[0101] In the depicted example embodiment, fuel handling unit 304 and air handling unit 306 are manifolded together within a housing 308 to provide conditioned air and fuel to fuel cell stack 294.

[0102] It should be appreciated, however, that fuel handling unit 304 can additionally or alternatively include any suitable type of fuel reformer, including but not limited to a catalytic partial oxidizer, an autothermal reformer, or a steam reformer, which can require an additional steam inlet stream with a higher hydrogen composition at the reformer outlet stream. Additionally or alternatively, fuel handling unit 304 can also include a reformer integrated with fuel cell stack 294. Similarly, it should be appreciated that air handling unit 306 can alternatively be a heat exchanger or another device for raising the temperature of air provided thereto to a temperature high enough to achieve fuel cell temperature control (e.g., about 600°C to about 800°C). FIG. 5

[0103] As described above, the compressor discharge system (and air flow supply conduit 288) is in air flow communication with an air flow delivery system for providing compressed air flow to fuel cell assembly 204. The air flow delivery system includes an anode air flow conduit 310 and associated anode air flow valve 312 for providing air flow to fuel handling unit 304, a cathode air flow conduit 314 and associated cathode air flow valve 316 for providing air flow to air handling unit 306, and a cathode bypass air conduit 318 and associated cathode bypass air valve 320 for providing air flow directly to fuel cell stack 294 (or more precisely, to the cathode side 296 of the fuel cell). Fuel delivery system 146 is configured to provide a first fuel stream to fuel handling unit 304 through first fuel delivery line 150A, and to provide a second fuel stream to air handling unit 306 through second fuel delivery line 150B (e.g., as fuel for a pre-burner system, if provided).

[0104] Fuel cell stack 294 outputs electrical power as fuel cell power output 322. In addition, fuel cell stack 294 directs cathode air exhaust and anode fuel exhaust (both not labeled for clarity) into combustion chamber 228 of combustor 206.​

[0105] In operation, the air handling unit 306 is configured to heat / cool a portion of the compressed air entering through the cathode airflow conduit 314 to generate a handled air to be directed into the fuel cell stack 294 to facilitate the fuel cell stack 294 to function. The air handling unit 306 receives a second fuel stream from the second fuel delivery line 150B and can, for example, combust such second fuel stream to heat the received air to a desired temperature (e.g., about 600°C to about 800°C) to facilitate the fuel cell stack 294 to function. The air handled by the air handling unit 306 is directed into the fuel cell stack 294. In embodiments of the present disclosure, as shown, the cathode bypass air conduit 318 and the air handled by the air handling unit 306 can be combined into a combined air stream to be fed into the cathode 296 of the fuel cell stack 294.

[0106] Further, as FIG. 5 As shown in embodiments of the present disclosure, the first fuel stream through the first fuel delivery line 150A is directed to the fuel handling unit 304 for generating a hydrogen-rich fuel stream (e.g., to optimize the hydrogen content of the fuel stream) to also be fed into the fuel cell stack 294. It will be appreciated, and as discussed below, that the air (handled air and bypass air) stream to the fuel cell stack 294 (e.g., the cathode side 296) and the fuel from the fuel handling unit 304 to the fuel cell stack 294 (e.g., the anode side 298) can facilitate power generation.

[0107] As the inlet air for the fuel cell stack 294 can only come from the upstream compressor section without any other separately controlled air source, it will be appreciated that the inlet air for the fuel cell stack 294 discharged from the compressor section can be subject to air temperature variations occurring at different flight phases. Merely as an illustrative example, air within a particular location in the compressor section of the gas turbine engine 100 can work at 200°C during idle, 600°C during takeoff, 268°C during cruise, etc. This type of temperature variation of the inlet air directed to the fuel cell stack 294 can cause significant thermal transient issues (or even thermal shock) to the ceramic materials of the fuel cell stack 294, which can range from cracking to failure.

[0108] Accordingly, by fluidly connecting the air handling unit 306 between the compressor section and the fuel cell stack 294, the air handling unit 306 can be used as a control device or system to maintain the air processed by the air handling unit 306 and directed into the fuel cell stack 294 within a desired operating temperature range (e.g., plus or minus 100°C, or preferably plus or minus 50°C, or plus or minus 20°C). In operation, the temperature of the air provided to the fuel cell stack 294 (relative to the temperature of the air discharged from the compressor section) can be controlled by controlling the fuel flow to the air handling unit 306. By increasing the fuel flow to the air handling unit 306, the temperature of the air stream to the fuel cell stack 294 can be increased. By decreasing the fuel flow to the air handling unit 306, the temperature of the air stream to the fuel cell stack 294 can be decreased. Alternatively, no fuel can be delivered to the air handling unit 306 to prevent the air handling unit 306 from increasing and / or decreasing the temperature of the air discharged from the compressor section and directed into the air handling unit 306.

[0109] Further, as depicted in dashed lines, the fuel cell assembly 204 further includes an air stream bypass conduit 321 extending around the fuel cell to allow a portion or all of the air stream conditioned by the air handling unit 306 (and combined with any bypass air through conduit 318) to bypass the cathode side 296 of the fuel cell and directly enter the combustion chamber 228. The air stream bypass conduit 321 can be in thermal communication with the fuel cell. The fuel cell assembly further includes a fuel bypass conduit 323 extending around the fuel cell to allow a portion or all of the reformed fuel from the fuel handling unit 304 to bypass the anode side 298 of the fuel cell and directly enter the combustion chamber 228.

[0110] As briefly mentioned above, the fuel cell stack 294 converts the anode fuel stream from the fuel processing unit 304 and the air processed by the air processing unit 306 sent to the fuel cell stack 294 into electrical energy in the form of DC current, i.e., the fuel cell power output 322. This fuel cell power output 322 is directed to the power converter 324 in order to convert this DC current into DC or AC current that can be effectively utilized by one or more subsystems. In particular, for the depicted embodiment, power is provided from the power converter to an electrical bus 326. The electrical bus 326 can be an electrical bus dedicated to the gas turbine engine 100, an electrical bus of an aircraft incorporating the gas turbine engine 100, or a combination thereof. The electrical bus 326 is in electrical communication with one or more additional electrical devices 328, which can be a power source, a power sink, or both. For example, the additional electrical devices 328 can be an electrical storage device (such as one or more batteries), an electrical machine (a generator, an electric motor, or both), an electrical propulsion device, etc. For example, the one or more additional electrical devices 328 can include a starter motor / generator of the gas turbine engine 100.

[0111] Still referring to FIG. 5 , the gas turbine engine 100 further includes a sensor 330. In the depicted embodiment, the sensor 330 can be configured to sense data indicative of a flame within the combustion section 114 of the gas turbine engine 100, or some other parameter indicative of an operating condition of the gas turbine engine. The sensor 330 may, for example, be a temperature sensor configured to sense data indicative of an outlet temperature of the combustion section 114, an inlet temperature of the turbine section, an exhaust temperature, or a combination thereof. Additionally or alternatively, the sensor 330 can be any other suitable sensor, or any suitable combination of sensors, configured to sense one or more gas turbine engine operating conditions or parameters, including data indicative of a flame within the combustion section 114 of the gas turbine engine 100.

[0112] Further, as FIG. 5 further illustratively depicts, the propulsion system, an aircraft including the propulsion system, or both include a controller 240. For example, the controller 240 can be a standalone controller, a gas turbine engine controller (e.g., a full authority digital engine controller or FADEC controller), an aircraft controller, a supervisory controller of the propulsion system, a combination thereof, etc.

[0113] The controller 240 is operably connected to various sensors, valves, etc. within at least one of the gas turbine engine 100 and the fuel delivery system 146. More specifically, for the depicted example aspect, the controller 240 is operably connected to valves of the compressor discharge system (valves 278, 282, 286), valves of the airflow delivery system (valves 312, 316, 320), and valves of the fuel delivery system 146 (splitter 274, valves 151A, 151B, 151C), as well as the sensors 330 of the gas turbine engine 100 and the fuel cell sensors 302. As will be understood from the following description, the controller 240 can be in wired or wireless communication with these components. In this manner, the controller 240 can receive data from various inputs (including the gas turbine engine sensors 330 and the fuel cell sensors 302), can make control decisions, and can provide data (e.g., instructions) to various outputs (including the valves of the compressor discharge system that control the discharge of airflow from the compressor section, the airflow delivery system that directs the airflow discharged from the compressor section, and the fuel delivery system 146 that directs the flow of fuel within the gas turbine engine 100).

[0114] With particular reference to the operation of the controller 240, in at least certain embodiments, the controller 240 can include one or more computing devices 332. The computing devices 332 can include one or more processors 332A and one or more memory devices 332B. The one or more processors 332A can include any suitable processing device, such as a microprocessor, microcontroller, integrated circuit, logic device, and / or other suitable processing devices. The one or more memory devices 332B can include one or more computer- readable media, including, but not limited to, non-transitory computer-readable media, RAM, ROM, hard drives, flash drives, and / or other memory devices.

[0115] One or more memory devices 332B can store information accessible by the one or more processors 332A, including computer-readable instructions 332C that can be executed by the one or more processors 332A. Instructions 332C can be any set of instructions that when executed by the one or more processors 332A, cause the one or more processors 332A to perform operations. In some embodiments, instructions 332C can be executed by the one or more processors 332A to cause the one or more processors 332A to perform operations such as any operations and functionalities the controller 240 and / or computing device 332 are structured to perform, operations for operating a propulsion system (e.g., methods 700, 800, 900, 1000, 1100, 1300) as described herein, and / or any other operations or functionalities of the one or more computing devices 332. Instructions 332C can be software written in any suitable programming language or can be implemented in hardware. Additionally, and / or alternatively, instructions 332C can be executed in logically and / or virtually separate threads on processor 332A. Memory devices 332B can further store data 332D that is accessible to the one or more processors 332A. For example, data 332D can include data indicative of power flow, data indicative of gas turbine engine 100 / aircraft operating conditions, and / or any other data and / or information described herein.

[0116] Computing device 332 also includes a network interface 332E structured to communicate, for example, with other components of gas turbine engine 100 such as valves of the compressor discharge system (valves 278, 282, 286), valves of the air flow delivery system (valves 312, 316, 320), and valves of the fuel delivery system 146 (splitter 274, valves 151A, 151B, 151C), as well as sensors 330 of gas turbine engine 100 and fuel cell sensors 302, in conjunction with an aircraft incorporating gas turbine engine 100, etc. Network interface 332E can include any suitable components for interfacing with one or more networks, including, for example, transmitters, receivers, ports, controllers, antennas, and / or other suitable components. In this manner, it will be appreciated that network interface 332E can utilize any suitable combination of wired and / or wireless communication networks.

[0117] The technology discussed herein makes reference to computer-based systems, actions taken by such computer-based systems, and information sent and received by such computer-based systems. It will be appreciated that the inherent flexibility of computer-based systems allows for a great variety of possible configurations, combinations, and divisions of tasks and functionality between and among components. For instance, processes discussed herein can be implemented using a single computing device or multiple computing devices working in combination. Databases, memories, instructions, and applications can be implemented on a single system or distributed across multiple systems. Distributed components can operate sequentially or in parallel.

[0118] It will be appreciated that the gas turbine engine 100, the example fuel delivery system 146, the example integrated fuel cell and combustor assembly 200, and the example fuel cell assembly 204 are provided by way of example only. In other embodiments, the integrated fuel cell and combustor assembly 200 and the fuel cell assembly 204 can have any other suitable configuration. For example, in other example embodiments, the fuel cell assembly 204 can include any other suitable fuel processing unit 304. Additionally or alternatively, for example when the combustor of the gas turbine engine 100 is configured to combust a hydrogen fuel, and the fuel delivery assembly 146 is configured to provide a hydrogen fuel to the integrated fuel cell and combustor assembly 200, and in particular to the fuel cell assembly 204, the fuel cell assembly 204 can not require a fuel processing unit 304.

[0119] Reference is now made to FIG. 6 , which provides a schematic illustration of a propulsion system according to another example embodiment of the present disclosure. The example propulsion system generally includes a propulsor, a turbomachine 104 operable to drive the propulsor to generate thrust during operation, and a fuel cell assembly 204 configured to add power to the propulsor, the turbomachine 104, or both.

[0120] In particular, for embodiments of FIG. 6 , the propulsion system is configured in a similar manner to the example propulsion system of FIG. 5 . In this manner, it will be appreciated that the propulsor and the turbomachine 104 together form a gas turbine engine 100, with the propulsor being configured as a fan section 102 having a fan 126 that is driven by the turbomachine 104 to generate thrust. Similarly, for the illustrated embodiment, the fuel cell assembly 204 is integrated into the gas turbine engine 100. More particularly, for the illustrated embodiment, the turbomachine 104 includes a combustion section 114 having a combustor 206, and the fuel cell assembly 204 includes a fuel cell stack 294 having a fuel cell, with the fuel cell defining an exit location to remove an output product from the fuel cell and to provide the output product to the combustor 206.

[0121] The fuel delivery system 146 of the propulsion system is configured to provide a fuel flow to the combustor 206 through a combustor fuel delivery line 150C (described above as the third fuel line 150C), and is further configured to provide a fuel flow to the fuel cell assembly 204 through a fuel cell assembly 204 (“FCA”) fuel delivery line 150A (described above as the first fuel line 150A).

[0122] For embodiments of FIG. 6In the depicted example embodiment, the fuel cell assembly 204 further includes a gas flow delivery system and a fuel processing unit 304. As will be appreciated from the above discussion, the fuel processing unit 304 can be configured as a fuel reformer. The fuel processing unit 304 is configured to receive a gas flow from the gas flow conduit 334 of the gas flow delivery system and a fuel flow from the FCA fuel delivery line 150A. The fuel processing unit 304 is further configured to provide the fuel flow to the fuel cells of the fuel cell stack 294 through a first fuel cell fuel delivery line 336 of the fuel cell assembly 204, and can further bypass the fuel cells of the fuel cell stack 294 by providing the fuel flow directly to the combustor 206 through a second fuel cell fuel delivery line 338 of the fuel cell assembly 204.

[0123] Notably, to achieve the desired level of health monitoring, maintenance guidance, control, and / or fault detection of the gas turbine engine 100, the fuel cell assembly 204, or both, the propulsion system further includes gas sensors 350 (generally "350", individually labeled 350A-F in FIG. 6 the gas turbine 104, the fuel cell assembly 204, or both, for sensing gas composition data of a fluid flow into or to the gas turbine 104, the fuel cell assembly 204, or both. As used herein, the term "gas composition data" generally refers to data related to the identification of one or more gases within a fluid flow and the percentage of the one or more gases within the fluid flow (e.g., the percentage of the fluid flow that is gas A, where "gas A" refers to one of the gases disclosed herein). Unless otherwise specified, the gas composition percentages provided herein refer to volume percentages.

[0124] More particularly, for the depicted example embodiment, the gas sensors 350 are configured as multi-gas sensors, such that the gas composition data includes data indicative of at least two gas compositions. The at least two gas compositions can be two gas compositions within the same fluid flow or within multiple fluid flows.

[0125] Still more particularly, for the depicted embodiment, the propulsion system includes a plurality of multi-gas sensors.

[0126] In particular, for the depicted embodiment, the propulsion system includes a fuel gas sensor 350A configured to sense gas composition data of a fuel flow provided to the combustor 206 through the combustor fuel delivery line 150C. In particular, for the depicted embodiment, the fuel gas sensor 350A is positioned in line with the combustor fuel delivery line 150C of the fuel delivery system 146.

[0127] As schematically depicted in circle 6A, fuel gas sensor 350A is a multi-gas sensor having a sensing circuit 352 with one or more sensing elements 354; a management circuit 356; and one or more processors 358. Management circuit 356 is structured to excite the one or more sensing elements 354 with an alternating current at one or more frequencies, and is further structured to measure one or more electrical responses of the one or more sensing elements 354 in response to exciting the sensing elements with the alternating current at the one or more frequencies. Management circuit 356 is structured to determine one or more characteristics of the sensing circuit 352. The one or more processors 358 are structured to receive the one or more electrical responses of the one or more sensing elements 354 and the one or more characteristics of the sensing circuit 352. The one or more processors 358 are further structured to determine gas composition data based on the one or more electrical responses of the one or more sensing elements 354 and the one or more characteristics of the sensing circuit 352. Reference is made below to FIGS. 7A-7C for a more detailed description of this configuration. FIG. 23 to FIG. 32 A more detailed description of this configuration is provided.

[0128] It will be appreciated, however, that in other example embodiments, any other suitable gas sensor technology or multi-gas sensor technology can be used, as discussed in more detail below.

[0129] Still referring to the close-up in circle 6A, as described above, fuel gas sensor 350A is positioned in alignment with combustor fuel delivery line 150C of fuel delivery system 146. In this manner, it will be appreciated that one or more sensing elements 354 of sensing circuit 352 of fuel gas sensor 350A can be directly exposed to the flow of fuel through combustor fuel delivery line 150C during operation of the propulsion system.

[0130] It will be appreciated that by sensing gas composition data of the flow of fuel provided to combustor 206, changes in the flow of fuel provided to combustor 206 can be determined and accounted for by control of gas turbine engine 100, fuel cell assembly 204, or both. For example, in certain example aspects, gas turbine engine 100 can be structured to receive aviation fuel, sustainable fuel, or a combination thereof during operation. Regardless, by sensing the gas composition data, changes in the fuel composition or changes in other characteristics of the fuel (which can simply be caused by receiving fuel from a different fuel tank of fuel delivery system 146) can be determined and operation of gas turbine engine 100, fuel cell assembly 204, or both can be adjusted to account for such changes. The changes can account for different heating values / enthalpy of the fuel.

[0131] Still referring to FIG. 6The propulsion system further includes an airflow gas sensor 350B operable with the airflow delivery assembly for sensing gas composition data of the airflow to the fuel processing unit 304 through the airflow delivery assembly (and more specifically, through the airflow conduit 334). In this manner, the airflow gas sensor 350B can be configured to sense gas composition data of the airflow including a percentage of oxygen within the airflow, a percentage of nitrogen within the airflow, a percentage of air impurities (e.g., carbon dioxide, sulfur, etc.) within the airflow, etc. Such gas composition data can be used to control, for example, the fuel cell assembly 204 by allowing a specific volume of oxygen to be provided to the fuel processing unit 304, the fuel cell stack 294, or both. Further, such gas composition data can be used to inform a baseline for determining fuel cell leaks and fuel cell diagnostic information, as described below.

[0132] Additionally, the propulsion system includes a first fuel cell gas sensor 350C operable with the fuel flow through the first fuel cell fuel delivery line 336 and a second fuel cell gas sensor 350D operable with the fuel flow through the second fuel cell fuel delivery line 338. In this manner, the first fuel cell gas sensor 350C can be configured to sense gas composition data of the fuel flow at a location downstream of the fuel processing unit 304 and upstream of the fuel cell, and the second fuel cell gas sensor 350D can be configured to sense gas composition data of the fuel flow at a location downstream of the fuel processing unit 304 and upstream of the combustor 206 bypassing the fuel cell and the fuel cell stack 294. The gas composition data sensed by the first fuel cell gas sensor 350C, the second fuel cell gas sensor 350D, or both can include a percentage of hydrogen within the fuel flow to determine, for example, a heating value of the fuel / enthalpy of the fuel. Other gas composition data of the first fuel cell gas sensor 350C, the second fuel cell gas sensor 350D, or both include carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), light hydrocarbons such as C2-C4; nitrogen (N2), steam, ammonia (NH3), non-volatile particulate matter (PM) and volatile PM, other major components in the fuel, other minor components in the fuel, other components in the fuel, etc.

[0133] Further, the propulsion system includes an output product gas sensor 350E and an oxygen sensor 350F. The output product gas sensor 350E is configured to sense gas composition data of an output product stream from the fuel cells of the fuel cell stack 294 at a location downstream of the fuel cells and upstream of the combustor 206. The oxygen sensor 350F can be configured to sense gas composition data of a fluid surrounding the fuel cell stack 294, such as an oxygen content of the fluid surrounding the fuel cell stack 294 (e.g., for leak detection and diagnostics), a flammable gas (such as hydrogen) content of the fluid surrounding the fuel cell stack 294 (e.g., as a safety sensor), etc.

[0134] As with the first and second fuel cell gas sensors 350C and 350D, the output product gas sensor 350E can be configured to sense gas composition data, including a percentage of hydrogen within the output product. This can again allow for determination of a heating value of the output product / how much enthalpy is provided from the fuel cells to the combustor 206, e.g., for control of the fuel cell assembly 204, the gas turbine engine 100, or both.

[0135] Additionally or alternatively, the output product gas sensor 350E can be configured to sense gas composition data indicative of a percentage of H2O within the output product, a percentage of carbon dioxide within the output product, a percentage of nitrogen within the output product, etc. Such gas composition data can be used for control of the fuel cell assembly 204, the gas turbine engine 100, or both, e.g., for emissions purposes and / or for determination of health information of the fuel cell assembly 204 (e.g., for diagnosing leak information within the fuel cell assembly 204, etc.).

[0136] Referring now to FIG. 7 , a close-up schematic view of a fuel cell of the fuel cell stack 294 in the example fuel cell assembly 204 of FIG. 6 is depicted with the output product gas sensor 350E. Notably, for the described embodiment, the fuel cell assembly 204 further includes a housing portion 360 that at least partially surrounds the fuel cell, and although not depicted, the fuel cell stack 294 includes the fuel cell. The housing portion 360 can be formed by one or more walls positioned around the fuel cell (and the fuel cell stack 294). For example, when FIG. 7 the example fuel cell of FIG. 2 is incorporated into the fuel cell assembly 204 depicted in FIG. 2 and described above, the housing portion 360 can be positioned between the outer liner 210 and the outer shell 220 to protect the fuel cell stack 294 from the airflow through the outer passageway 226 (see

[0137] Further, for embodiments of the fuel cell stack 200E, the gas sensor 350E is configured to sense gas composition data from the output product stream of the fuel cell, and more particularly, gas composition data from the output product stream of the cathode 296 and the output product stream of the anode 298, as well as gas composition data of a fluid 362 (e.g., a gas) surrounding the fuel cell, and more particularly, gas composition data of the fluid 362 surrounding the fuel cell within the housing portion 360. As used herein, this fluid 362 is considered a fluid stream. FIG. 7 Further, for embodiments of the fuel cell stack 200E, the gas sensor 350E is configured to sense gas composition data from the output product stream of the fuel cell, and more particularly, gas composition data from the output product stream of the cathode 296 and the output product stream of the anode 298, as well as gas composition data of a fluid 362 (e.g., a gas) surrounding the fuel cell, and more particularly, gas composition data of the fluid 362 surrounding the fuel cell within the housing portion 360. As used herein, this fluid 362 is considered a fluid stream.

[0138] In particular, the gas sensor 350E includes a node 364 exposed to the output product stream from the cathode 296, a node 366 exposed to the output product stream from the anode 298, and a node 368 exposed to the fluid 362 surrounding the fuel cell. The gas composition data sensed from the output product gas sensor 350E can be used to determine health information of the fuel cell assembly 204, and further can be used to diagnose a fault or anomaly within the fuel cell assembly 204, such as a leak within the fuel cell assembly 204.

[0139] For example, as will be explained in greater detail below, in instances where the gas stream provided to the cathode 296 will not include any carbon dioxide or H2O and these are the constituents present in the anode 298 during operation, the presence of carbon dioxide, H2O, or both in the output product from the cathode 296 can indicate a cross-over leak 370 (depicted in dashed lines in FIG. 37B) from the anode 298 to the cathode 296. FIG. 7 Similarly, an increase in the flow rate of the output product from the cathode 296 in the absence of an increase in the flow rate of the gas stream provided to the cathode 296 can indicate a cross-over leak 370 from the anode 298 to the cathode 296.

[0140] For example, when the percentage of carbon dioxide in the output product from the cathode 296 is greater than 0, such as greater than 0 and up to about 1%, this can indicate a cross-over leak 370 from the anode 298 to the cathode 296. Similarly, when the percentage of H2O in the output product from the cathode 296 is greater than 0, such as greater than 0 and up to about 5%, such as up to about 3%, this can also indicate a cross-over leak 370 from the anode 298 to the cathode 296. Alternative methods for diagnosing a cross-over leak 370 from the anode 298 to the cathode 296 can be based on trends in these detected gas compositions, rather than their absolute values. For example, if any of the percentage of CO2, the percentage of H2O, or the flow rate of the output product from the cathode 296 increases, the controller (e.g., the controller 240 of the fuel cell stack 200E) can determine a cross-over leak 370 from the anode 298 to the cathode 296, and for example, provide an alert indicating this cross-over leak 370. FIG. 6 ​

[0141] Similarly, for example, where the fuel stream provided to the anode 298 can not contain any nitrogen, the presence of nitrogen within the output product from the anode 298 can indicate cross-leakage 372 from the cathode 296 to the anode 298 (depicted in dashed lines in FIG. 3B; the term "cross-leakage" is synonymous with "cross- leakage"). Similarly, where a corresponding increase in the fuel stream to the anode 298 is not present, an increase in the flow rate of the output product from the anode 298 can also indicate cross-leakage 372 from the cathode 296 to the anode 298. FIG. 7

[0142] For example, when the percentage of nitrogen in the output product from the anode 298 is greater than 0, such as greater than 0 and up to about 1%, this can indicate cross-leakage 372 from the cathode 296 to the anode 298. Alternative methods for diagnosing cross-leakage 372 can be based on trends in these detected gas compositions, rather than their absolute values. If the nitrogen gas concentration or the anode 298 exhaust flow rate increases, the controller can determine that there is cross-leakage 372 from the cathode 296 to the anode 298, and for example, provide an alert indicating this cross-leakage 372.

[0143] Further, for example, the gas composition data sensed by the gas sensor 350E can further include the percentage of oxygen (O2) in the fluid 362 surrounding the fuel cell. Sensing data related to the percentage of oxygen in the fluid 362 surrounding the fuel cell can also be provided to the controller, and the controller can be configured to determine fuel cell leak diagnostic information further in response to such sensing data. For example, if the percentage of oxygen in the fluid 362 surrounding the fuel cell is decreasing, and further if the percentage of oxygen in the fluid 362 surrounding the fuel cell is greater than the percentage of oxygen in the output product from the cathode 296, this can indicate off-board leakage 374 from the cathode 296. Further, for example, if the percentage of oxygen in the fluid 362 surrounding the fuel cell is decreasing, and further if the percentage of oxygen in the fluid 362 surrounding the fuel cell is less than the percentage of oxygen in the output product from the cathode 296, this can indicate off-board leakage 376 from the anode 298.

[0144] It will be appreciated, however, that while for the embodiment of FIG. 3B the output product gas sensor 350E is positioned within the housing portion 360, in other example embodiments the output product gas sensor 350E can instead be positioned outside of the housing portion 360. FIG. 7 FIG. 8 ​​Such a configuration is depicted in the example embodiments of FIG. 3. Like or similar numbers can refer to like or similar parts. It will be appreciated that with such a configuration, a separate gas sensor 350F can be provided within the housing portion 360 for detecting the percentage of oxygen within the fluid 362 that surrounds the fuel cell.

[0145] Referring back to FIG. 6 It will be appreciated that with one or more of the above configurations, the included gas sensor(s) 350 can be exposed to relatively harsh environments during operating conditions of the propulsion system. For example, as will be appreciated from the foregoing description, the propulsion system is generally configured as an aerospace propulsion system. In order for the gas sensor 350 described herein to operate in the desired manner, the gas sensor 350 needs to be configured to sense (and be capable of sensing) gas composition data of the fluid flow into or to the turbine 104, the fuel cell assembly 204, or both, during flight operations (e.g., takeoff, climb, cruise, descent, landing) of the propulsion system. Moreover, it will be appreciated that the gas sensor 350 described herein will be positioned within the housing of the turbine 104 (or “under the hood”; see, e.g., FIG. 3) of the integrated fuel cell and combustor 206 assembly 200, which is located within the casing 106 of the turbine 104. The under-the-hood environment can be relatively harsh during flight operations of the propulsion system. FIG. 1

[0146] Thus, it will be appreciated that during normal operating conditions (e.g., takeoff, climb, cruise, descent, landing) of the propulsion system, the gas sensor 350 can be positioned within an environment within the turbine 104, the fuel cell assembly 204, or both, that has a temperature of at least 200°C. For example, in certain example embodiments, during normal operating conditions of the propulsion system, the gas sensor 350 can be positioned within an environment within the turbine 104, the fuel cell assembly 204, or both, that has a temperature of at least 400°C and up to 1000°C. Such operating temperature ranges can include FIG. 6 to FIG. 8 For example, various locations within the fuel cell assembly 204 (e.g., between the fuel processing unit 304 and the fuel cell stack 294, between the fuel cell stack 294 and the combustor 206, within or around the housing portion 360, etc.) can be at a temperature between 450°C and 1000°C, such as a temperature between 600°C and 900°C, during normal operating conditions. Similarly, various locations along the combustor fuel delivery line 150C can be at a temperature of at least 200°C and up to 650°C, such as a temperature between 300°C and 500°C, and at a pressure between 100 bar and 300 bar, during normal operating conditions. The gas sensor 350 described herein is configured to be able to withstand these environments.

[0147] ​Furthermore, it will be understood that one or more exemplary gas sensors 350 described herein can be configured to sense gas composition data including one or more of the following: H2%, CO%, CO2%, CH4%, H2O%, N2%, NH3%, percentage of non-volatile particulate matter, and percentage of volatile particulate matter. In particular, for at least some of the exemplary gas sensors 350 described herein, the gas sensor 350 can be configured as a multi-gas sensor, which is configured to sense gas composition data including two or more of the following: H2%, CO%, CO2%, CH4%, H2O%, N2%, NH3%, percentage of non-volatile particulate matter, and percentage of volatile particulate matter.

[0148] Furthermore, it will be understood that at least the gas sensor 350 can be configured to withstand the aforementioned environment and sense desired gas composition data during normal operating conditions of the propulsion system, while being relatively small and lightweight. In particular, one or more exemplary gas sensors 350, and especially, the sensing elements disclosed herein (see, for example...) FIG. 6 The sensing element 354 in the gas sensor 350 may have a length less than about 20 mm (“mm”) multiplied by a width less than about 20 mm multiplied by a thickness less than about 20 mm (i.e., less than about 20 mm × 20 mm × 20 mm). For example, in some exemplary aspects, the sensing element of the gas sensor 350 may have a size less than about 10 mm × 10 mm × 10 mm, such as less than about 5 mm × 5 mm × 5 mm, for example, less than about 4 mm × 4 mm × 2 mm. Further, the sensing element of the gas sensor 350 may have a weight of less than 50 grams. For example, in some exemplary aspects, the sensing element of the gas sensor 350 may have a weight of less than 25 grams, such as less than 10 grams, such as less than 5 grams, such as less than 1 gram, such as less than 0.1 grams. Reference is made below. FIG. 23 to FIG. 32 Further details are provided regarding an exemplary gas sensor 350 technology capable of operating within the disclosed environment, sensing the disclosed gas composition data, and having the disclosed size and / or weight.

[0149] Further, it will be appreciated that a gas sensor 350 including one or more of these example aspects can allow the gas sensor 350 to be positioned in or proximate to a fluid stream from which gas composition data is sensed. In particular, a gas sensor 350 including one or more of these example aspects can allow the gas sensor 350 to be separated from a fluid line by no more than about 100 millimeters, the fluid line having a fluid stream flowing into or to the turbine 104, the fuel cell assembly 204, or both. For example, in certain example embodiments, the gas sensor 350 can be separated from the fluid line by no more than about 50 millimeters, such as no more than about 20 millimeters. More particularly, in at least certain example aspects, a gas sensor 350 including one or more of these example aspects can allow the gas sensor 350 to be positioned in alignment with a fluid line (such as the fluid delivery line 150C) providing a fluid stream flowing into or to the turbine 104, the fuel cell assembly 204, or both (see, e.g., FIG. 6C), such that the gas sensor 350 is not separated from the fluid line. FIG. 6

[0150] Referring now to FIG. 6, FIG. 9 a flow diagram 600 is provided. The flow diagram 600 generally graphically depicts the interrelation of various aspects of a fuel cell assembly integrated into a gas turbine engine. Aspects described with respect to the flow diagram 600 of FIG. 6 can generally be applicable to one or more of the example gas turbine engines 100 and fuel cell assemblies 204 described herein, e.g., with reference to FIG. 9 FIG. 1 to FIG. 8

[0151] More particularly, the flow diagram 600 relates to the interrelation of a fuel cell assembly having a fuel processing unit 602 and a fuel cell stack 604. The fuel processing unit 602 can include a fuel reformer or catalytic partial oxidation converter (CPOx) for producing a hydrogen-rich fuel stream for the fuel cell stack 604. Further, the gas turbine engine can include a combustor 606 and a shaft-driven compressor 608. The shaft-driven compressor 608 can be, for example, a high pressure compressor. As will be appreciated, the shaft-driven compressor 608 can be driven by a turbine that extracts power from combustion gases generated by the combustor 606 during operation.

[0152] As will be appreciated, the fuel cell assembly defines a plurality of fuel processing unit FIG. 9 ​​​The fuel processing unit input parameters 610 are further defined by the fuel processing unit 602 (abbreviated as "FPU" in the figure). In certain example aspects, the fuel processing unit input parameters 610 can include an inlet temperature of the fuel provided to the fuel processing unit 602, an inlet pressure of the fuel provided to the fuel processing unit 602, a flow rate of the fuel provided to the fuel processing unit 602, a percentage of various components (e.g., sulfur) within the fuel provided to the fuel processing unit 602, an oxygen-to-carbon ratio (e.g., determined based on the percentage of oxygen within the fuel), a steam-to-carbon ratio (e.g., determined based on the percentage of H2O within the fuel), and the like.

[0153] Further, the flow provided from the fuel processing unit 602 to the fuel cell stack 604 defines a plurality of fuel cell stack (abbreviated as "FCS" in the figure) input parameters 612 that can affect the operation of the fuel cell stack 604. The fuel cell stack input parameters 612 generally include the gas composition of the flow provided from the fuel processing unit 602 to the fuel cell stack 604; the temperature, pressure, and / or flow rate of the flow provided from the fuel processing unit 602 to the fuel cell stack 604; and the like. FIG. 9

[0154] In addition, the output product flow provided from the fuel cell stack 604 to the combustor 606 further defines a plurality of output product parameters 614 that can affect the operation of the combustor 606. The output product parameters 614 can include the gas composition (e.g., percentage H2, indicative of the enthalpy of the output product) of the flow provided from the fuel cell stack 604 to the combustor 606; the temperature, pressure, and / or flow rate of the flow provided from the fuel cell stack 604 to the combustor 606; and the like.

[0155] Still further, the combustor 606 and the combustion gases from the combustor 606 define a plurality of engine parameters 616 that can affect the amount of power provided to the shaft-driven compressor 608. The engine parameters 616 generally include the temperature within the combustor 606, the turbine inlet temperature, the high pressure shaft speed, the low pressure shaft speed, and the like.

[0156] Finally, the shaft-driven compressor 608 and the gas flow through the shaft-driven compressor 608 define a plurality of compressor parameters 618 that can affect one or more flows provided to the fuel processing unit 602 and, optionally, to the fuel cell stack 604. The compressor parameters 618 can generally include the pressure of the gas flow through the shaft-driven compressor 608, the temperature of the gas flow through the shaft-driven compressor 608, the flow rate of the gas flow through the shaft-driven compressor 608, and the like.

[0157] ​In this manner, it will be appreciated that while various parameters 610, 612, 614, 616, 618 can be specific to one aspect of the fuel cell assembly and gas turbine engine, the parameters 610, 612, 614, 616, 618 can impact other components of the fuel cell assembly and gas turbine engine. Thus, by sensing gas composition data of the fluid flow into or to the turbine, the fuel cell assembly, or both, one or more of these parameters 610, 612, 614, 616, 618 can be sensed, allowing for a higher level of health monitoring, fuel cell assembly / gas turbine engine control, anomaly detection, and / or fault detection and diagnosis.

[0158] In particular, it will be appreciated that various ones of these parameters 610, 612, 614, 616, 618 can further be indicative of certain failure modes within the fuel cell assembly, the gas turbine engine, or both. For example, various ones of these parameters 610, 612, 614, 616, 618 can be indicative of certain failure modes of a particular component, or certain failure modes of a downstream or upstream component.

[0159] For example, the fuel processing unit 602 can be susceptible to failure modes including carbon deposition, catalyst poisoning, and catalyst oxidation. Carbon deposition can generally be driven by the temperature of the fuel provided to the fuel processing unit 602 and the oxygen-to-carbon ratio of the fuel provided to the fuel processing unit 602. Carbon deposition can cause one or more of catalyst deactivation within the fuel processing unit, blockage within the fuel processing unit, higher pressure loss across the fuel processing unit, and lower hydrogen production from the fuel processing unit (e.g., a reduction in the percentage of hydrogen provided to the fuel cell stack 604 from the flow of the fuel processing unit 602). Catalyst poisoning can generally be driven by the percentage of sulfur in the fuel provided to the fuel processing unit 602, and can have similar effects as carbon deposition. Further, catalyst oxidation can be driven by providing too much air in the flow provided to the fuel processing unit 602, and can further cause similar effects as carbon deposition.

[0160] Further, the fuel cell stack 604 can be susceptible to failure modes including cross-over leakage between the anode and cathode of the fuel cells of the fuel cell stack 604, off-gas leakage from the anode or cathode of the fuel cells of the fuel cell stack 604, anode oxidation, and carbon deposition. Cross-over leakage between the anode and cathode can generally be caused by cracks in the electrode layers positioned therebetween. Above with respect to the fuel processing unit 602, the fuel cell stack 604 can also be susceptible to catalyst poisoning and catalyst oxidation. FIG. 7 and FIG. 8The consequences of cross-leakage or external leakage are described. When anodizing occurs, this can lead to lower output voltage from fuel cell stack 604 and cracking of the anode. Carbon deposition in fuel cell stack 604 can be caused by a low vapor-to-carbon ratio in the stream supplied to fuel cell stack 604 and can lead to one or more of the following: catalyst deactivation, blockage within the catalyst (potentially causing hot spots), increased pressure loss across the catalyst, and reduced power output from fuel cell stack 604.

[0161] As should be understood, carbon deposition within fuel cell stack 604 may occur relatively quickly (e.g., within 30 minutes or less) and may further lead to carbon deposition within combustor 606, which may potentially flow into the turbine section of the gas turbine engine, potentially damaging the turbine rotor blades (e.g., causing the thermal barrier coating of one or more turbine rotor blades to peel off). As discussed below, including one or more gas sensors operating at a relatively fast temporal resolution to sense gas composition data including fuel cell stack input parameter 612, output product parameter 614, or both, can provide early notification of potential carbon deposition within fuel cell stack 604 (hereinafter referred to as “early anomaly”), allowing modifications to the operation of the gas turbine engine, fuel cell assembly, or both to minimize any damage.

[0162] Furthermore, combustor 606 may be susceptible to failure modes, including flameout, combustor kinetics, and carbon deposition / damage. Flameout within combustor 606 can generally be a result of the fuel-air ratio supplied to combustor 606, the temperature of the fuel supplied to combustor 606, the pressure of the fuel supplied to combustor, or a combination thereof. Output product parameter 614, engine parameter 616, or both can provide data indicating one or more of these combustor failure modes.

[0163] Now for reference FIG. 10 A flowchart of a method 700 for operating a propulsion system according to an exemplary aspect of this disclosure is provided. In particular, method 700 relates to a method for determining a health indicator of a gas turbine engine, a fuel cell assembly, or both, and further to a method for providing a maintenance response, a reporting response, a control response, or a combination thereof in response to the determined health indicator. Method 700 can be used with one or more of the exemplary propulsion systems described above, such as with one or more exemplary fuel cell assemblies and gas turbine engines described herein.

[0164] Method 700 generally includes, at (702), operating a propulsion system to generate thrust for a vehicle. The vehicle can be an aerial vehicle, such as an aircraft. The propulsion system can generally include a gas turbine engine and a fuel cell assembly. The fuel cell assembly may, for example, be integrated into the gas turbine engine in one or more manners described herein (see, e.g., FIG. 6) FIG. 2 In at least certain example aspects, operating the propulsion system at (702) to generate thrust for the vehicle can include operating the propulsion system under flight conditions, such as takeoff flight conditions, climb flight conditions, cruise flight conditions, descent flight conditions, and the like.

[0165] Method 700 further includes, at (704), collecting data. In particular, collecting data at (704) includes, at (706), receiving, from the multi-gas sensor, gas composition data of one or more fluid streams flowing into or toward the gas turbine engine, the fuel cell assembly, or both, while operating the propulsion system at (702). The gas composition data received at (706) can include one or more of the parameters 610, 612, 614, 616, 618 described above with reference to flowchart 600 FIG. 9 Additionally or alternatively, the gas composition data can be any other suitable gas composition data.

[0166] Notably, for the depicted example aspects, collecting data at (704) further includes, at (708), receiving data indicative of operating parameters of the propulsion system. The operating parameters of the propulsion system can include one or more of flight conditions of the propulsion system, environmental conditions (e.g., ambient temperature, pressure, flight speed, and the like), temperature data (e.g., temperature of the fuel cell assembly, compressor outlet temperature, turbine inlet temperature, and the like), pressure data (e.g., compressor pressure, fuel cell stack pressure drop), and the like.

[0167] Method 700 further includes, at (710), determining baseline data of the gas turbine engine, the fuel cell assembly, or both, in response to the data collected at (704), and more particularly, in response to the operating parameters received at (708). The baseline data of the gas turbine engine, the fuel cell assembly, or both, determined at (710) can include baseline information for the gas turbine engine, the fuel cell assembly, or both, for a given flight condition and / or for a given operating condition of the gas turbine engine, the fuel cell assembly, or both.

[0168] Still referring to FIG. 10The method 700 further includes determining, at (712), a health indicator for the gas turbine engine, the fuel cell assembly, or both, in response to the gas composition data received at (706). More specifically, for the depicted example aspect, determining the health indicator at (712) includes at least one of detecting an anomaly at (714), determining a system health parameter at (728), or detecting a component failure at (730).

[0169] As used herein, the term "anomaly" refers to a condition in which an affected component is considered to be operating outside of a nominal degradation state, but is still operable to provide a beneficial result for the propulsion system. The term "system health parameter" refers to degradation information (e.g., accumulated degradation information, a percentage of degradation from new, etc.). A system health parameter for a component can indicate that the component is operating in a manner less than nominal degradation, can indicate that the component experienced an anomaly condition, or can indicate that the component experienced a failure. The term "failure" refers to a condition in which a component is no longer able to provide a beneficial result for the propulsion system.

[0170] Detecting an anomaly at (714) more specifically includes detecting the anomaly with a fuel cell / engine anomaly detection module at (716), and detecting the anomaly with the fuel cell / engine anomaly detection module at (716) includes using one or more anomaly detection rules at (718). For example, in the depicted example aspect, detecting an anomaly at (714) can include comparing the gas composition data received at (706) to baseline data determined using data determined using the operational parameters received at (708). For example, detecting an anomaly at (714) can include detecting an anomalous level of a gas component of a fluid stream as compared to an expected level of the gas component in the fluid stream for an operational condition of the propulsion system. The anomalous level can refer to a level that is above or below a predetermined threshold for the gas component in the fluid stream for the given operational condition.

[0171] Still referring to the example method 700, FIG. 10 For the depicted example aspect, determining the health indicator at (712) further includes determining an anomaly type, determining an affected portion, or both, at (720). More specifically, for the depicted example aspect, determining the anomaly type, determining the affected portion, or both, at (720) includes operating a fuel cell / engine anomaly diagnostic module at (722). Operating the fuel cell / engine anomaly diagnostic module at (722) can include determining the affected portion using fuel cell / engine anomaly location rules at (724), and determining the anomaly type using fuel cell / engine anomaly root cause analysis rules at (726).

[0172] In certain example aspects, examples of the anomaly type and the anomaly location can be examples described above with reference to FIG. 9 the one or more example failure modes identified. Examples are described below with reference to FIG. 11 to FIG. 14 Example methods are described in greater detail, including more details regarding determining the anomaly type, determining the affected portion, or both, at (720).

[0173] Still referring to FIG. 10 the example method 700, as briefly mentioned above, determining the health indicator at (712) can further include, at (728), determining a system health parameter. The system health parameter can be indicative of a degree of degradation of one or more components of the gas turbine engine, the fuel cell assembly, or both. For example, the method 700 can determine the system health indicator at (728) based on a comparison of the gas composition data received at (706) to baseline gas composition data (e.g., determined using the operating parameters received at (708)).

[0174] Notably, the system health parameter determined at (728) can provide data related to degradation of the system component before the system component degrades to a point at which the method 700 would detect an anomaly during operation of the component. For example, the system health parameter determined at (728) can provide data related to a degree of degradation of the component while the component is operating within a normal operating range. More specifically, the system health parameter determined at (728) can provide data of incipient anomalies.

[0175] Further, as also briefly mentioned above, still referring to FIG. 10 the example method 700, determining the health indicator at (712) can further include, at (730), detecting a component failure. The component failure can be indicative of the component no longer being able to operate in a manner that is beneficial to the gas turbine engine, the fuel cell assembly, or both. The method 700 can detect the component failure at (730) by comparing the gas composition data received at (706) to baseline gas composition data (e.g., determined using the operating parameters received at (708)) and determining that the gas composition data is outside of a predetermined failure threshold of the baseline gas composition data. Thus, the failure threshold can be specific to an operating parameter of the gas turbine engine.

[0176] Although not depicted, the method 700 can perform one or more diagnostic steps to determine the affected component, a root cause of the component failure, or both, in response to detecting the component failure at (730).

[0177] Still referring to FIG. 10of the example method 700, it will be appreciated that the method 700 further includes performing a maintenance response, a reporting response, a control response, or a combination thereof, in response to the health indicator determined at (712).

[0178] In particular, the method 700 includes operating a maintenance module to provide a maintenance response in response to the health indicator determined at (712) at (732), operating a reporting module to provide a reporting response in response to the health indicator determined at (712) at (734), operating a control module to provide a control response in response to the health indicator determined at (712) at (736), or a combination thereof.

[0179] Referring first to the operation of the maintenance module at (732), operating the maintenance module at (732) can include receiving flight plan data for a current flight of a vehicle including the propulsion system at (738), and receiving maintenance schedule data for one or more components of the fuel cell assembly, the gas turbine engine, or both at (740).

[0180] Further, the operation of the maintenance module at (732) includes providing maintenance guidance in response to the health indicator determined at (712) at (742). For example, in certain example aspects, providing the maintenance guidance at (742) can include providing maintenance guidance in response to detecting the anomaly at (714), in response to determining the system health parameter at (728), or both. In this way, providing the maintenance guidance at (742) can include providing maintenance guidance for the components while the components are still able to provide beneficial operation for the gas turbine engine, the fuel cell assembly, or both.

[0181] The maintenance guidance provided at (742) can include providing an indicator to an operator or controller to perform a maintenance action on a component of the fuel cell assembly, the gas turbine engine, or both at, for example, the next regularly scheduled maintenance operation. Additionally or alternatively, the maintenance guidance provided at (742) can include a flight planning modification, a maintenance schedule modification, or a service guide (e.g., guidance as to which components need maintenance, what type of maintenance is needed, etc.). For example, in certain example aspects, in response to the health indicator determined at (712), the maintenance guidance can indicate that a change in flight plan is needed, for example, based on a type of detected anomaly or failure, a component affected by the detected anomaly or failure, or both.

[0182] Further, the operation of the reporting module at (734) generally includes providing reporting content at (744) in response to the health indicator determined at (712). In certain example aspects, the reporting content provided at (744) can be a diagnostic tree indicating the root cause of the anomaly detected at (714). Further, in other example aspects, the reporting content provided at (744) can include expected partial degradation information, inventory planning, replacement duration, inventory requirements, etc. Providing the reporting content at (744) can include providing the reporting content to a controller of the propulsion system, the vehicle, or both, can include providing the reporting content to a visual indicator viewable by an operator of the propulsion system, etc.

[0183] Still further, the operation of the control module at (736) generally can include modifying an engine operating parameter at (746) in response to the health indicator determined at (712), modifying a fuel cell assembly operating parameter at (748) in response to the health indicator determined at (712), or both.

[0184] In certain example aspects, the operating parameter of the gas turbine engine modified at (746) can include a combustor fuel flow rate, a combustor fuel air ratio, a fuel flow rate ratio between the combustor fuel flow and a fuel cell fuel flow, a variable bleed valve, a variable guide vane, a low pressure shaft speed, a high pressure shaft speed, a variable fan nozzle, an engine driven generator output, or a combination thereof. Further, in certain example aspects, the operating parameter modified at (748) can include a fuel flow rate to the fuel cell assembly, a fuel pressure, an equivalence ratio of a fuel processing unit of the fuel cell assembly, a steam to carbon ratio of the fuel processing unit of the fuel cell assembly, an air pressure, an air flow rate, an anode to cathode differential pressure, an anode inlet temperature, a cathode inlet temperature, a fuel cell stack temperature, a fuel cell current, a fuel cell utilization, a fuel cell air utilization, or a combination thereof.

[0185] Reference is now generally made to FIG. 11 to FIG. 13 A flowchart of a method 800 for determining a health indicator of a gas turbine engine, a fuel cell assembly, or both, and further providing a maintenance response, a reporting response, or both, in response to the health indicator, in accordance with example aspects of the present disclosure, is provided.

[0186] Reference is now generally made to FIG. 11 A flowchart of a method 800 for determining fuel cell leak diagnostic information, in accordance with example aspects of the present disclosure, is provided. The method 800 can be used in conjunction with the method 700 described above with reference to FIG. 1 to FIG. 8One or more of the exemplary fuel cells and fuel cell components described are used together. Thus, the method 800 can be used with a fuel cell assembly having a control system with a gas sensor configured to sense gas composition data from an output product stream of a cathode of a fuel cell (fuel cell stack), gas composition data from an output product stream of an anode of the fuel cell, gas composition data of a fluid surrounding the fuel cell, or a combination thereof.

[0187] The method 800 generally entails receiving, from the gas sensor, gas composition data from an output product stream of a cathode, gas composition data from an output product stream of an anode, gas composition data of a fluid surrounding the fuel cell, or a combination thereof; and in response to the received gas composition data, determining fuel cell leak diagnostic information.

[0188] More specifically, for the exemplary aspects of the described method 800, the method 800 includes, at (802), detecting a trigger. Detecting a trigger at (802) can include detecting an abnormality of the fuel cell assembly, such as detecting an uncommanded change in voltage from the fuel cell and / or fuel cell stack, resistance from the fuel cell and / or fuel cell stack, temperature of the fuel cell and / or fuel cell stack, pressure of one or more flows into or out of or within the fuel cell and / or fuel cell stack, etc.

[0189] The method 800 further includes, at (804), collecting gas composition data. In particular, for the depicted aspects, collecting gas composition data at (804) can be in response to the trigger detected at (802). Collecting gas composition data at (804) can include collecting gas composition data using one or more sensors, such as a gas sensor (such as a multi-gas sensor), a dedicated oxygen sensor, etc.

[0190] The method 800 additionally includes, at (808), initiating an off-board leak diagnosis, and at (810), initiating a cross-leak diagnosis. Aspects of the off-board leak diagnosis initiated at (808) are described in more detail below and with reference to FIG. 12 Aspects of the cross-leak diagnosis initiated at (810) are described in more detail below. FIG. 13 Aspects of the cross-leak diagnosis initiated at (810) are described in more detail below.

[0191] Notably, as depicted by the dashed line, the method 800 can include determining, at (806), from the collected gas composition data, whether the percentage of oxygen within the enclosure portion at least partially surrounding the fuel cell and fuel cell stack is increasing. If the percentage of oxygen within the enclosure portion is increasing, as determined at (806), the method 800 can continue to initiate an off-board leak diagnosis at (808), and if not, the method 800 can rule out an off-board leak and continue to a cross-over leak diagnosis at (810). Notably, even if the percentage of oxygen within the enclosure portion is increasing, as determined at (806), the method can continue to the cross-over leak diagnosis at (810).

[0192] Referring to FIG. 12 In response to initiating the off-board leak diagnosis at (808), the method 800 further includes determining, at (812), from the collected gas composition data, whether the percentage of oxygen within the enclosure portion is greater than the percentage of oxygen within the output product stream from the cathode. If the percentage of oxygen within the enclosure portion is less than the percentage of oxygen within the output product stream from the cathode, as determined at (812), the method 800 determines, at (814), that the fuel cell is experiencing an anode off-board leak. In contrast, if the percentage of oxygen within the enclosure portion is greater than the percentage of oxygen within the output product stream from the cathode, as determined at (812), the method 800 determines, at (816), that the fuel cell is experiencing a cathode off-board leak.

[0193] Referring now to FIG. 13 In response to initiating the cross-over leak diagnosis at (810), the method includes determining, at (818), whether the percentage of nitrogen within the output product stream from the anode of the fuel cell is increasing or exceeds a threshold value. If the percentage of nitrogen within the output product stream from the anode is increasing or exceeds a threshold value, as determined at (818), the method 800 further includes determining, at (820), whether the percentage of carbon dioxide within the output product stream from the cathode is increasing or exceeds a threshold value, whether the percentage of H20 within the output product stream from the cathode is increasing or exceeds a threshold value, or both. If one or both of the percentage of carbon dioxide or H20 within the output product stream from the cathode is increasing or exceeds a threshold value, as determined at (820), the method 800 includes determining, at (822), that the fuel cell is experiencing an anode-to-cathode cross-over leak and a cathode-to-anode cross-over leak.

[0194] In particular, when nitrogen is not to be part of the fuel provided to the anode of the fuel cell during operation of the fuel cell assembly, an increased percentage of nitrogen within the output product stream from the anode, or the presence of nitrogen within the output product stream from the anode beyond some threshold, can be indicative of cross-over leakage from the cathode to the anode. Similarly, when carbon dioxide and H20 are not to be part of the gas stream provided to the cathode of the fuel cell during operation of the fuel cell assembly, an increased percentage of carbon dioxide or H20 within the output product stream from the cathode, or the presence of carbon dioxide or H20 within the output product stream from the cathode beyond some threshold, can be indicative of cross-over leakage from the anode to the cathode.

[0195] Still referring to the example aspects of the method 800 depicted in FIG. 13 With respect to the example aspects of the method 800 depicted in

[0196] Further, in the event that the percentage of nitrogen within the output product stream from the anode is not increasing or not exceeding the threshold at (818), the method 800 can still check for leakage from the cathode to the anode at (826) by determining whether the flow rate of the output product from the anode is increasing. If the flow rate of the output product from the anode is increasing as determined at (826), the method 800 can again determine at (824) that the fuel cell is experiencing cross-over leakage from the cathode to the anode.

[0197] Following the determination at (826), whether the determination is "yes" or "no", the method includes determining at (828) whether the flow rate of the output product from the cathode is increasing. If the flow rate of the output product from the cathode is increasing as determined at (828), the method includes determining at (830) that the fuel cell is experiencing cross-over leakage from the anode to the cathode.

[0198] In the event that the flow rate of the output product from the cathode is not increasing at (828), the method 800 includes determining at (832) whether the percentage of H20, carbon dioxide, or both, within the output product stream from the cathode is increasing (similar to the determination at (820)). If the percentage of H20, carbon dioxide, or both, is increasing as determined at (832), the method again includes determining at (830) that the fuel cell is experiencing cross-over leakage from the anode to the cathode.

[0199] However, if it is determined at (832) that the percentage of H2O, carbon dioxide, or both, within the output product stream from the cathode has not increased, the method determines at (834) that the fuel cell is not experiencing cross-leakage.

[0200] It will be appreciated that the example method 800 described above with reference to FIG. 11 to FIG. 13 The example method 800 described above is provided by way of example only. In other example aspects of the disclosure, the method 800 can not include each of the steps outlined above, and can further include the inquiries outlined above in any other suitable order. For example, in other example aspects in which the method 800 is operable with a fuel cell assembly that is not capable of sensing gas composition data from the output product stream of the cathode, the method 800 can not include one or more of (820), (828), (832), etc. Similarly, in other example aspects in which the method 800 is operable with a fuel cell assembly that is not capable of sensing gas composition data from the output product stream of the anode, the method 800 can not include one or more of (818), (826). Further, in other example aspects in which the method 800 is operable with a fuel cell assembly that is not capable of sensing gas composition data of the fluid surrounding the fuel cell, the method can not include (808) or FIG. 13 other aspects of the method 800 depicted in FIG. 8.

[0201] Similarly, as described above, in other example aspects, the method 800 can include the inquiries outlined above in any other suitable order. For example, in other example aspects, one or more of (818), (820), and (832), (826), and (828) can be performed in parallel.

[0202] Further, as will be further appreciated from the description below, the method 800 can occur in real-time. For example, in certain example aspects, receiving the gas composition data (or collecting the gas composition data at (804)) can include receiving the data at a resolution of 1 minute or less. For example, in certain example aspects, receiving the gas composition data (or collecting the gas composition data at (804)) can more particularly include receiving the data at a resolution of 30 seconds or less, such as 15 seconds or less, or 5 seconds or less.

[0203] In this way, the method is able to make control decisions based on data collected 1 minute or faster in advance.

[0204] Referring now to FIG. 14 a flowchart of a method 900 for determining a health indicator of a gas turbine engine, a fuel cell assembly, or both, and further for providing a maintenance response, a reporting response, or both, in response to the health indicator, in accordance with another example aspect of the disclosure is provided. In particular, forFIG. 14 In exemplary aspects of the method 900, the health indicator relates to carbon deposition within a fuel processing unit of the fuel cell assembly, carbon deposition within anodes of fuel cells of a fuel cell stack of the fuel cell assembly, or both.

[0205] The method 900 includes, at (902), determining a baseline condition of the fuel cell assembly. Determining the baseline condition can include determining the baseline condition in response to one or more operating conditions or operating parameters of the fuel cell assembly, the gas turbine engine, or both.

[0206] The method 900 further includes, at (904), receiving gas composition data from one or more gas sensors at various locations within the fuel cell assembly. In particular, the gas composition data includes gas composition data from a first gas sensor located downstream of a fuel processing unit and upstream of a fuel cell stack, and gas composition data from a second gas sensor located downstream of the fuel cell stack and upstream of a combustor of the gas turbine engine.

[0207] At (906), the method 900 determines whether the gas composition data from the first gas sensor located downstream of the fuel processing unit (abbreviated as “FPU” in FIG. 14 ) and upstream of the fuel cell stack indicates carbon deposition within the fuel processing unit. If, as determined at (906), the gas composition data indicates carbon deposition within the fuel processing unit, then the method 900 further determines, at (908), whether the gas composition data from the second gas sensor located downstream of the fuel cell stack and upstream of the combustor indicates carbon deposition within anodes of fuel cells of the fuel cell stack. If, as determined at (908), the gas composition data indicates carbon deposition within anodes of fuel cells of the fuel cell stack, then the method 900 further determines, at (910), that both the fuel processing unit and the fuel cell include carbon deposition. In contrast, if, as determined at (908), the gas composition data indicates no carbon deposition within anodes of the fuel cell stack, then the method 900 determines, at (912), that the fuel processing unit includes carbon deposition.

[0208] Referring back to the inquiry at (906), if the method 900 determines at (906) that, based on gas composition data from a first gas sensor located downstream of the fuel processing unit and upstream of the fuel cell stack, there is no indication of carbon deposition within the fuel processing unit, the method proceeds to the inquiry at (914) to determine whether gas composition data from a second gas sensor located downstream of the fuel cell stack and upstream of the combustor indicates carbon deposition within the anode of a fuel cell of the fuel cell stack. If, as determined at (914), the gas composition data indicates carbon deposition within the anode of a fuel cell of the fuel cell stack, the method 900 further determines at (916) that the fuel cell includes carbon deposition. In contrast, if, as determined at (914), the gas composition data does not indicate carbon deposition within the anode of the fuel cell stack, the method 900 determines at (918) that neither the fuel cell nor the fuel processing unit includes carbon deposition.

[0209] If it is determined at (910), (912), or (916) that the fuel cell, the fuel processing unit, or both include carbon deposition, the method 900 can further include recommending at (920) a maintenance response related to cleaning or inspecting the combustor, the turbine section, or both to ensure that any carbon from the fuel processing unit, the fuel cell, or both has not traveled to the combustor or turbine section and potential damage aspects of the turbine section (e.g., spallation of a thermal barrier coating of a turbine nozzle or turbine rotor blade).

[0210] Referring now to FIG. 15A , one example of a reporting module 734 in accordance with example aspects of the present disclosure is provided. In particular, the reporting module 734 can be constructed in substantially the same manner as the reporting module 734 described above with reference to FIG. 10 .

[0211] FIG. 15A The reporting content is depicted more particularly, and the report 750, which can be a part of the reporting content, is depicted even more particularly. The report 750 provides system health parameter information for the fuel cell assembly and various components of the gas turbine engine as determined at (712) in the method 700 of, for example, FIG. 10 . The report 750 includes a first column 752 providing a name of a fuel cell assembly or component in the gas turbine engine, a second column 754 representing a health status of the corresponding component (e.g., a system health parameter of the component), and a third column 756 representing more particular details of the health status of the corresponding component (e.g., cumulative degradation information of the system health parameter, such as a percent of lifetime, where a shorter bar means an early stage of life and a longer bar means close to the end of life).

[0212] As described above with reference to FIG. 10As described, gas composition data from the gas sensor, along with a component life degradation model, can generate life consumption data based on an aging indicator, such as a carbon deposition thickness, a catalyst deactivation state of the fuel processing unit and / or fuel cell, etc. This information can be communicated to a flight database, such that a fleet management team can schedule corresponding inventory preparation and maintenance. FIG. 15B representing inventory management and maintenance plans 758 generated based on the information reported. FIG. 15A representing inventory management and maintenance plans 758 generated based on the information reported.

[0213] Referring now to FIG. 16 A flowchart of a method 1000 for operating a propulsion system according to another example aspect of the present disclosure is provided. In particular, the method 1000 relates to a method of operating a propulsion system having a gas turbine engine and a fuel cell assembly. The method 1000 can be used with one or more example propulsion systems described herein, such as with one or more example fuel cell assemblies and gas turbine engines described herein.

[0214] The method 1000 includes, at (1002), operating the propulsion system during flight operations. Operating the propulsion system during flight operations at (1002) can include operating the propulsion system during normal flight operations, such as during takeoff operating conditions, climb operating conditions, cruise operating conditions, descent operating conditions, etc.

[0215] Further, FIG. 16 The example method 1000 includes, at (1004), receiving gas composition data of an output product from a fuel cell of a fuel cell stack of the fuel cell assembly. Receiving the gas composition data at (1004) can include receiving the gas composition data from a gas sensor positioned downstream of the fuel cell and upstream of a combustor of the gas turbine engine. The gas sensor can be positioned in-line with the output product stream, or alternatively, can be separated from the output product stream by a gap of less than 100 millimeters (e.g., less than about 50 mm, such as less than about 20 mm, such as less than about 5 mm). In this manner, the gas sensor can be configured to sense the gas composition data directly from the output product stream, or can be configured to sample the output product stream.

[0216] Further, for FIG. 16 For the example aspects of the method 1000 depicted in FIG. 10, receiving the gas composition data of the output product from the fuel cell at (1004) further includes, at (1006), receiving the gas composition data of the output product from the fuel cell while operating the propulsion system during flight operations at (1002).

[0217] As will be appreciated from the description herein, the gas sensor used to determine the gas composition data can be capable of sensing the gas composition data at a relatively fast time resolution. In this manner, it will be appreciated that the gas composition data can be provided to a controller configured to make control decisions in response to the gas composition data in a relatively short time after the initial measurement is made. FIG. 16 In one example aspect of the method 1000 depicted in FIG. 10, receiving the gas composition data at (1004) can further include sensing the gas composition data from the output product of the fuel cell at a time resolution of 10 minutes or less at (1008), or sensing the gas composition data from the output product of the fuel cell at a time resolution of one minute or less at (1010). As used herein, the term "time resolution" in the context of sensing the gas composition data refers to the time between when the initial measurement is made and when the gas composition data is available to be provided to, for example, a controller configured to make control decisions in response to the gas composition data. In certain example aspects, the time resolution at which the gas sensor senses the gas composition data from the output product of the fuel cell can be less than about 30 seconds, such as less than about 15 seconds, such as less than about 5 seconds, such as less than about 2 seconds. In this manner, the gas sensor can be configured to sense the gas composition data in real time.

[0218] Still referring to the example aspect of the method 1000 depicted in FIG. 10, FIG. 16 In one example aspect of the method 1000 depicted in FIG. 10, receiving the gas composition data at (1004) can further include sensing the gas composition data from the output product of the fuel cell at a time resolution of 10 minutes or less at (1008), or sensing the gas composition data from the output product of the fuel cell at a time resolution of one minute or less at (1010). As used herein, the term "time resolution" in the context of sensing the gas composition data refers to the time between when the initial measurement is made and when the gas composition data is available to be provided to, for example, a controller configured to make control decisions in response to the gas composition data. In certain example aspects, the time resolution at which the gas sensor senses the gas composition data from the output product of the fuel cell can be less than about 30 seconds, such as less than about 15 seconds, such as less than about 5 seconds, such as less than about 2 seconds. In this manner, the gas sensor can be configured to sense the gas composition data in real time.

[0219] More specifically, in one example aspect of the method 1000 depicted in FIG. 10, controlling the operation of the fuel cell assembly, the gas turbine engine, or both at (1012) includes controlling the operation of the fuel cell assembly at (1014) in response to the received gas composition data from the output product of the fuel cell. FIG. 16 More specifically, in one example aspect of the method 1000 depicted in FIG. 10, controlling the operation of the fuel cell assembly, the gas turbine engine, or both at (1012) includes controlling the operation of the fuel cell assembly at (1014) in response to the received gas composition data from the output product of the fuel cell.

[0220] Further, in one example aspect of the method 1000 depicted in FIG. 10, controlling the operation of the fuel cell assembly at (1014) can include modifying an operating parameter of the fuel cell assembly at (1016) in response to the received gas composition data from the output product of the fuel cell. In certain example aspects, the operating parameter modified at (1016) can include a fuel flow rate to the fuel cell assembly, a fuel pressure, an equivalence ratio of a fuel processing unit of the fuel cell assembly, a steam-to-carbon ratio of the fuel processing unit of the fuel cell assembly, an air pressure, an air flow rate, an anode-to-cathode differential pressure, an anode inlet temperature, a cathode inlet temperature, a fuel cell stack temperature, a fuel cell current, a fuel cell utilization, a fuel cell air utilization, or a combination thereof.FIG. 16 In another example aspect of the method 1000 depicted, controlling operation of the fuel cell assembly, the gas turbine engine, or both at (1012) includes, at (1018), controlling operation of the gas turbine engine. Controlling operation of the gas turbine engine can include, at (1020), modifying an operating parameter of the gas turbine engine in response to the received gas composition data from the output product of the fuel cell. In certain example aspects, the operating parameter of the gas turbine engine can include: combustor fuel flow rate, combustor fuel air ratio, fuel flow rate ratio between combustor fuel flow and fuel cell fuel flow, variable bleed valve, variable guide vane, low pressure shaft speed, high pressure shaft speed, variable fan nozzle, engine drive generator output, or combinations thereof.

[0221] As will be appreciated, the gas composition data received from the output product of the fuel cell at (1004) can include data indicative of a percentage of hydrogen within the output product. The percentage of hydrogen within the output product can allow for determinations to be made regarding the heat value of the output product provided to the combustor of the combustion section of the gas turbine engine. Such information can impact the amount of energy provided to the turbine section of the gas turbine engine, as well as other operational aspects of the gas turbine engine, such as combustor dynamics, emissions, etc.

[0222] In this manner, it will be appreciated that the method 1000 can control the gas turbine engine directly in response to the gas composition data received at (1004) to, for example, provide a desired amount of energy to the turbine section, modify combustor dynamics and / or emissions, etc. Additionally or alternatively, the method 1000 can modify operation of the fuel cell assembly in response to the gas composition data received at (1004) to, for example, change the amount of hydrogen provided to the combustor, which in turn changes the amount of energy provided to the turbine section, modifies combustor dynamics and / or emissions, etc.

[0223] As an example, it will be appreciated that, in at least certain example aspects, controlling operation of the fuel cell assembly, the gas turbine engine, or both, at (1011) includes, at (1022), controlling operation of the fuel cell assembly, the gas turbine engine, or both, using model-based control. With this example aspect, it will be appreciated that controlling operation of the fuel cell assembly, the gas turbine engine, or both, at (1011) more specifically includes, at (1024), controlling operation of the fuel cell assembly, the gas turbine engine, or both, based on the gas composition data of the output product from the fuel cell received at (1004), and using the model-based control. Controlling operation of the fuel cell assembly, the gas turbine engine, or both, at (1024) includes, at (1026), controlling operation of the fuel cell assembly, the gas turbine engine, or both, using a fusion filter configured to receive the gas composition data of the output product from the fuel cell received at (1004) and configured to receive data from one or more models of the model-based control.

[0224] Notably, with this example aspect, the method 1000 further includes, at (1028), updating one or more models of the model-based control in response to the received gas composition data of the output product from the fuel cell. For example, the received gas composition data of the output product from the fuel cell can be used to calibrate one or more models of the model-based control.

[0225] It will be appreciated that controlling operation of the fuel cell assembly, the gas turbine engine, or both, in accordance with one or more of these example aspects can allow for redundancy in the control scheme by updating and / or calibrating one or more models of the model-based control with gas composition data sensed at a relatively fast time resolution, and further by determining whether one or more gas sensors are to be used because the gas composition data has failed with data output from one or more models of the model-based control. Notably, the method 900 can determine that one or more gas sensors are to be used because the gas composition data has failed in response to determining that the provided gas composition data is outside of a predetermined range of data output from one or more models of the model-based control.

[0226] It will be appreciated that, for example aspects of the method 1000 of FIG. 16 The method 100 uses gas composition data of an output product of a fuel cell / fuel cell stack as a basis for control of a gas turbine engine, a fuel cell assembly, or both. This can allow for control based on an amount of energy provided from the fuel cell assembly to a combustor, which provides a number of benefits as described herein.

[0227] However, in other exemplary embodiments, method 1000 may additionally or alternatively be based on control of the gas turbine engine, fuel cell assembly, or both based on gas composition data received from multiple gas sensors of one or more other flows into, towards, or through the gas turbine engine, fuel cell assembly, or both (e.g., at (1011), (1012), (1014), (1016), (1018), (1020), (1022), (1024), (1026), (1028)). In this way, method 1000 can... FIG. 10 The method at (736) in 700 is executed by the control module.

[0228] Now for reference FIG. 17 Flowcharts of exemplary model-based control systems and methods for fuel cell components and gas turbine engines, based on exemplary aspects of this disclosure, are provided. FIG. 17 The exemplary model-based control systems and methods described herein can be used with one or more exemplary gas turbine engine and fuel cell components. Furthermore, FIG. 17 The exemplary model-based control systems and methods described herein can be incorporated into one or more other methods (such as...) FIG. 16 The model-based control method introduced in Method 1000.

[0229] refer to FIG. 17 The exemplary model-based control system and method are more specifically described as a coordinated control system 1100 for a propulsion system. As shown, the coordinated control system 1100 includes a fuel cell system 1102 and a burner 1104. The burner 1104 can be configured in accordance with the above reference, for example... FIG. 2 The combustor 206 discussed is constructed in a similar manner to that of the combustor 1104, such that the combustor 1104 may include a swirler assembly 216 configured to deliver an aviation fuel stream 1105 to the combustor 1104. The fuel cell system 1102 may be configured as described herein, for example, with reference to... FIG. 2 to FIG. 5 Any of the fuel cell components 204 discussed are constructed in a similar manner. That is, the fuel cell system 1102 may be fluidly coupled to the burner 1104 and configured to deliver output product 1106 to the burner 1104. In addition to output product 1106, the fuel cell system 1102 may also generate power output 1118 (such as electrical output) that can be used, for example, in one or more motors in a propulsion system.

[0230] As shown in the figure, the coordination control system 1100 may include a controller 240, which may be the controller mentioned above. FIG. 5The controller 240 discussed may be a different controller. Controller 240 may be configured to receive data from one or more sub-controllers or sensors of a coordinated control system 1100 that communicates with fuel cell system 1102 and / or burner 1104. Additionally, controller 240 may be configured to send data, control commands, or other operations on sub-controllers, fuel cell system 1102, and / or burner 1104.

[0231] In many embodiments, the coordinated control system 1100 may include a fuel cell controller 1108 operably in communication with the controller 240. The fuel cell controller 1108 may be configured to communicate with... FIG. 5 The controller 240 shown is constructed in a similar manner (e.g., having one or more processors and a memory), or alternatively, the fuel cell controller 1108 may be constructed as part of the controller 240. The fuel cell controller 1108 may be operable to modify one or more operating parameters of the fuel cell system 1102, such as the fuel flow rate or amount supplied to the fuel cell system 1102, the equivalence ratio (such as the air / fuel ratio supplied to the fuel cell system 1102), fuel utilization (e.g., the amount of fuel converted into electrical energy), the current generated by the fuel cell system 1102, and / or temperature (e.g., fuel and / or air inlet temperature). In particular, the fuel cell controller 1108 may be configured to modify the amount of output product 1106 introduced into the burner 1104 and the composition of the output product 1106 introduced into the burner 1104 (e.g., H2% within the output product 1106). In an exemplary embodiment of the fuel cell controller 1108, the fuel cell controller 1108 may include a power controller 1110 and a fuel utilization rate controller 1112. The power controller 1110 and the fuel utilization rate controller 1112 may be configured as part of the fuel cell controller 1108 or may be independent controllers.

[0232] In various embodiments, the coordinated control system 1100 may include a burner fuel flow rate controller 1114 operably in communication with the controller 240. The burner fuel flow rate controller 1114 may be configured to communicate with... FIG. 5The controller 240 shown is constructed in a similar manner (e.g., having one or more processors and memory), or alternatively, the burner fuel flow rate controller 1114 may be constructed as part of the controller 240. The burner fuel flow rate controller 1114 may be operable to modify and / or monitor one or more operating parameters of the burner 1104. Additionally, the burner fuel flow rate controller 1114 may be operable to transmit data indicating the aviation fuel flow (or flow rate) 1105 supplied to the burner 1104. In particular, the burner fuel flow rate controller 1114 may be configured to modify (e.g., increase or decrease) the aviation fuel flow 1105 supplied to the burner 1104.

[0233] like FIG. 17 As shown, combustor 1104 can receive combustible products from at least two separate sources (e.g., aviation fuel stream 1105 and output product stream 1106), each of which will generate a certain amount of heat or enthalpy within combustor 1104. Aviation fuel stream 1105 and output product stream 1106 will co-combust within combustor 1104 to generate enthalpy output 1116 at the outlet of combustor 1104. It will be understood that regulating the enthalpy output 1116 from combustor 1104 is important for meeting thrust requirements and minimizing thrust disturbances during operation of the propulsion system.

[0234] like FIG. 17 As shown, controller 240 can provide power setpoint 1120 to power controller 1110, which is also referred to as power offtake demand from the aircraft computer or pilot. In response to receiving power setpoint 1120, power controller 1110 can modify the operating conditions of fuel cell system 1102 such that the power output 1118 of fuel cell system 1102 is equal to power setpoint 1120. Similarly, controller 240 can provide requested enthalpy 1122 to combustor fuel flow rate controller 1114 (e.g., based at least in part on the desired thrust of the propulsion system). This requested enthalpy 1122 can be derived from thrust demand from the aircraft computer or pilot. In response to receiving requested enthalpy 1122, combustor fuel flow rate controller 1114 can modify the aviation fuel flow 1105 to combustor 1104 such that enthalpy output 1116 is equal to requested enthalpy 1122.

[0235] The power exhaust demand, or power setpoint 1120, reflects the electrical load requirements of the aircraft, while the requested enthalpy 1122 reflects the aircraft thrust demand, which can be independent of the power setpoint 1120. The coordinated control system 1100 needs to handle both the power setpoint 1120 and the requested enthalpy 1122 in a systematic manner. However, it has been found that fuel cell operation can cause significant coupling effects from the combustor due to variations in fuel cell exhaust composition / enthalpy; on the other hand, variations in combustor and engine operating conditions can, in turn, affect fuel cell operation. Therefore, a coordinated fuel cell and combustor control system is proposed to mitigate the inherent coupling effects.

[0236] In an exemplary embodiment, the coordinated control system 1100 may be configured to determine, at least in part, data indicative of at least one of the enthalpy or composition of the output products 1106 from the fuel cell system 1102, based on a modified fuel cell model 1126. The modified fuel cell model 1126 may utilize memory stored in either controller (such as...). FIG. 5 One or more models are stored in the memory 332B of the controller 240 shown, and can be processed by a processor (such as...) FIG. 5 The processor 332A shown executes this. Generally, the modified fuel cell model 1126 can provide one or more inputs 1124, and based at least in part on the one or more inputs 1124, the modified fuel cell model 1126 can generate one or more fuel cell model outputs 1128. For example, the fuel cell controller 1108 can provide fuel cell component operating parameters as inputs 1124 to the modified fuel cell model 1126, and based at least in part on the fuel cell component operating parameters, the modified fuel cell model 1126 can generate data (e.g., gas composition data) indicating at least one of the enthalpy or composition of the output product 1106 as the fuel cell model output 1128. (Refer to below...) FIG. 18 The operation of the modified fuel cell model 1126 is described in more detail.

[0237] like FIG. 17 As shown, based at least in part on the fuel cell model output 1128, the controller 240 can generate or determine an enthalpy trimming 1130. The enthalpy trimming 1130 can be used to adjust and / or modify the value of the requested enthalpy 1122 transmitted to the burner fuel flow rate controller 1114. For example, the enthalpy trimming 1130 can adjust the requested enthalpy 1122 based on the amount of enthalpy added to the burner 1104 via the output product 1106.

[0238] The enthalpy trim 1130 can be based on a transfer function that accounts for the steady state and dynamic relationship between the fuel cell model output 1128 and the combustor enthalpy. The enthalpy trim 1130 can include an "inverse model" to calculate an expected combustor enthalpy change that can compensate for potential changes in SOFC exhaust composition or enthalpy. For example, if the fuel cell model output 1128 indicates that the fuel cell exhaust enthalpy entering the combustor will increase, the enthalpy trim 1130 can calculate the amount of combustor enthalpy that should be trimmed to mitigate the potential disturbance caused by the fuel cell exhaust enthalpy entering the combustor. As a non-limiting example, the enthalpy trim 1130 can be a first order transfer function, a second order transfer function, or a higher order transfer function that captures the transient time from a change in fuel cell operation to the time at which the fuel cell exhaust affects the combustor enthalpy.

[0239] In this manner, the controller 240 can account for the enthalpy added to the combustor 704 via the output product 1106 by adjusting the aviation fuel flow 1105 based at least in part on the enthalpy trim 1130. This feature advantageously allows the fuel cell system 1102 to be operated independently of the combustor 1104 without causing any thrust disturbances.

[0240] In some embodiments, the coordinated control system 1100 can determine data indicative of the combustor exit enthalpy based at least in part on combustor operating parameters and data indicative of at least one of the enthalpy or composition of the output product. In various embodiments, the combustor operating parameters can include at least one of a fuel / air ratio to the combustor 1104, a combustor pressure, or a combustor temperature. The combustor operating parameters can be received via one or more sensors disposed in operable communication with the combustor 1104. At other times, the combustor operating parameters can be received via a calculation from one or more sensors not disposed in operable communication with the combustor 1104. For example, the coordinated control system 1100 can include a combustor enthalpy model 1132. The combustor enthalpy model 1132 can be stored within the memory (such as the memory 332B of the controller 240 shown) of any one of the controllers and can be executed by a processor (such as the processor 332A of the controller 240 shown). FIG. 5 The memory 332B of the controller 240 shown). The combustor enthalpy model 1132 can be executed by a processor (such as the processor 332A of the controller 240 shown). FIG. 5The processor 332A shown executes this. Specifically, the burner enthalpy model 1132 can be a first-principles-based model, a data-driven model such as a neural network, fuzzy logic, a lookup table, or any combination thereof. Generally, the burner enthalpy model 1132 can be provided with one or more inputs 1129, 1131, and based at least in part on one or more inputs 1129, 1131, the burner enthalpy model 1132 can generate one or more outputs 1133. For example, the burner enthalpy model 732 can receive the enthalpy of the output product 706 from the modified fuel cell model 1126 as a first input 1129, and can receive burner operating parameters as a second input 1131. Based at least in part on the first input 1129 and the second input 1131, the controller 240 can use the burner enthalpy model 1132 to generate data indicating the burner outlet enthalpy and temperature as output 1133.

[0241] The estimated output 1133 from the combustor enthalpy model 1132 can be used (e.g., via controller 240) to calculate the compressor exhaust flow rate for both fuel cell and combustor control, as well as for combustor performance evaluation and thrust calculation. In aircraft engine operation, the combustor outlet work affects the turbine work, which in turn affects the compressor outlet air conditions via the shaft. This compressor outlet air supplies both the fuel cell and the combustor. Therefore, the compressor outlet air conditions have a direct impact on the operation of both the fuel cell and the combustor. In some applications, the air flow rate at the outlet of compressor 112 can be calculated based on flight and engine conditions. The combustor outlet enthalpy model 1132 described herein takes into account not only the primary aviation fuel effects but also the fuel cell exhaust effects, significantly improving the accuracy of compressor exhaust flow rate calculations, which in turn improves the quality of stoichiometric control of the fuel cell reformer and the air-fuel ratio of the combustor.

[0242] Now for reference FIG. 18 This will be described in more detail. FIG. 17 The modified fuel cell model 1126 operates as described above. The modified fuel cell model 1126 receives fuel cell operating parameters as input 1124. In many embodiments, the fuel cell assembly operating parameter input 1124 may be at least one of the following: fuel and / or air flow rate, equivalence ratio (e.g., air / fuel ratio provided to fuel cell system 1102), fuel utilization rate (such as the percentage of fuel used by fuel cell system 1102), current (such as the power output 1118 generated by fuel cell system 1102), pressure, or temperature.

[0243] The modified fuel cell model 1126 further includes a fuel cell model 1136, which is configured to receive fuel cell operating parameter input 1124. The fuel cell model 1136 can be a first-principles-based model, a data-driven model such as a neural network, fuzzy logic, a lookup table, or any combination thereof. The fuel cell model 1136 can generally be configured to determine estimated gas composition data 1138 in response to the fuel cell operating parameter input 1124.

[0244] However, in the illustrated embodiment, the modified fuel cell model 1126 is further configured to receive sensed gas composition data 1140 from the gas sensor 1141. The sensed gas composition data 1140 may include the same gas composition data as the estimated gas composition data 1138.

[0245] The modified fuel cell model 1126 further includes a fusion filter 1142, configured to receive estimated gas composition data 1138 and further configured to receive sensed gas composition data 1140. Through one or more control algorithms, rules, etc., the fusion filter 1142 can determine the actual gas composition data to be provided as the fuel cell model output 1128. For example, the fuel cell model output 1128 may include fuel cell exhaust components, including volume percentages of one or more of H2, CO, CO2, H2, N2, O2, etc. An alternative to the fuel cell model output 1128 could be exhaust enthalpy (or the low calorific value of fuel cell exhaust).

[0246] Furthermore, for FIG. 18 An exemplary aspect of the modified fuel cell model 1126 depicted herein further includes a calibration module 1144 configured to calibrate the fuel cell model 1136 at least in part based on sensed gas composition data 1140. More specifically, the calibration module 1144 is configured to receive actual gas composition data provided as fuel cell model output 1128 and estimated gas composition data 1138 generated by the fuel cell model 1136. Calibrating the fuel cell model 1136 may include updating one or more multipliers of the fuel cell model 1136, assumptions of the fuel cell model 1136, etc.

[0247] Further, the example modified fuel cell model 1126 further includes a fault detection module 1146. The fault detection module 1146 is structured to receive the actual gas composition data provided as the fuel cell model output 1128 and the sensed gas composition data 1140. The fault detection module 1146 can include one or more algorithms, rules, etc. for comparing the actual gas composition data to the sensed gas composition data 1140 to determine potential faults in the gas sensor 1141.

[0248] It will be appreciated, however, that in other example embodiments, the fault detection module 1146 can be structured to receive the estimated gas composition data 1138 directly from the fuel cell model 1136.

[0249] Further, although the fault detection module 1146 and the calibration module 1144 are described as being separate from, for example, the fusion filter 1142, in other embodiments, one or more of the fault detection module 1146, the calibration module 1144, and the fusion filter 1142 can be integrated.

[0250] Briefly returning to FIG. 17 It will be appreciated that the example combustor enthalpy model 1132 can be a modified combustor enthalpy model structured in a similar manner as the example modified fuel cell model 1126 described above with reference to FIG. 18 For example, the combustor enthalpy model 1132 can receive a first input 1129 from the modified fuel cell model 1126 (which can include enthalpy data from the output product of the fuel cell), and further can receive sensed gas composition data from a gas sensor indicative of the enthalpy of the output product of the fuel cell. The combustor enthalpy model 1132 can further include a fusion filter for receiving the first input 1129 and the sensed gas composition data, and determining actual enthalpy data from the output product of the fuel cell. Similar calibration and fault detection modules can also be included.

[0251] Reference is now made to FIG. 19 , a gas turbine engine 100 and a fuel cell assembly 204 according to another example aspect of the present disclosure are provided, which can operate according to the example method 1000 discussed above with reference to FIG. 16 .

[0252] For the depicted example aspect, the gas turbine engine 100 and the fuel cell assembly 204 can operate in a similar manner as the example gas turbine engine 100 and the example fuel cell assembly 204 discussed above with reference to FIG. 2The exemplary gas turbine engine 100 and fuel cell assembly 204 are constructed in substantially the same manner. Accordingly, like or similar numbers can refer to like or similar parts. Thus, it will be understood that the fuel cell assembly 204 generally includes a fuel cell stack 294 having one or more fuel cells, and further includes a fuel inlet line 150 and an air inlet line 315. In addition, the fuel cell assembly 204 includes a fuel valve 151 for controlling operation of fuel flow through the fuel inlet line 150 to the fuel cell stack 294, and an air valve 317 for controlling air flow through the air inlet line 315. Although the fuel valve 151 and the air valve 317 are depicted as being aligned with the fuel inlet line 150 and the air inlet line 315 at a location just upstream of the fuel cell stack 294, in other embodiments, the fuel valve 151, the air valve 317, or both, can be located more upstream, e.g., upstream of the fuel processing unit 304, the air processing unit 306, or both (see FIG. 4). Each of the fuel valve 151 and the air valve 317 is operably connected to the controller 240. FIG. 5

[0253] In addition, it will be understood that for the exemplary embodiment depicted in FIG. 4, the control system of the propulsion system, including the controller 240, can include a safety management control system for the fuel cell assembly 204 and the gas turbine engine 100. In particular, the fuel cell assembly 204 further includes a fuel cell safety gas line 380 and a fuel cell safety gas valve 382. The fuel cell safety gas line 380 is in fluid communication with the fuel inlet line 150, and more particularly, at a location downstream of the fuel valve 151. FIG. 19

[0254] The fuel cell assembly 204, the gas turbine engine 100, or both, further include a gas sensor 350. The gas sensor 350 can be positioned to sense gas composition data of the fluid 362 surrounding the fuel cell stack 294. For example, the gas sensor 350 can be configured to sense gas composition data including a percentage of oxygen within the fluid 362 surrounding the fuel cell stack 294, a percentage of hydrogen within the fluid 362 surrounding the fuel cell stack 294, a percentage of flammable gas within the fluid 362 surrounding the fuel cell stack 294, and the like. In this manner, the gas sensor 350 can be configured as a low explosive level (LEL) sensor.

[0255] ​​The gas sensor 350 is operably connected to the controller 240 for providing gas composition data to the controller 240. Notably, when configured as an LEL sensor, the gas composition data from the gas sensor 350 can be a Boolean response indicating, for example, whether the percentage of flammable gas within the fluid 362 surrounding the fuel cell stack 294 exceeds a lower explosive level threshold.

[0256] In response to receiving data from the gas sensor 350 indicating that the percentage of flammable gas within the fluid 362 surrounding the fuel cell stack 294 exceeds a lower explosive level threshold, the controller 240 can be configured to actuate the fuel valve 151 to shut off the flow of fuel to the fuel cell stack 294 and further actuate the fuel cell safety gas valve 382 to provide a flow of safety gas to the fuel cell stack 294. More particularly, actuating the fuel cell safety gas valve 382 can provide a flow of safety gas to the fuel inlet line 150 through the fuel cell safety gas line 380 and to the fuel cell stack 294 through the fuel inlet line 150. The safety gas can be, for example, carbon dioxide (e.g., supercritical carbon dioxide), nitrogen, a gas having less than about 10% flammable gas volume (such as less than about 5% flammable gas volume), air, etc.

[0257] Briefly, it will also be appreciated that, for the depicted example aspects, the gas turbine engine 100 includes a fire detection sensor 384 that can be operably connected to the controller 240 to provide data indicating the presence of a fire in the area surrounding the fuel cell stack 294. The controller 240 can similarly be configured to provide safety gas to the fuel inlet line 150 and the fuel cell stack 294 through the fuel cell safety gas line 380 in response to receiving data from the fire detection sensor 384 indicating the presence of a fire in the area surrounding the fuel cell stack 294.

[0258] Referring now to FIG. 20 , a propulsion system is depicted in accordance with another example aspect of the present disclosure that can be used with one or more example control systems and methods described herein. In particular, the propulsion system includes a gas turbine engine 100 and a fuel cell assembly 204. Although only the combustor 206 of the gas turbine engine 100 is depicted for illustrative purposes, the gas turbine engine 100 can be configured in a similar manner as one or more example gas turbine engines 100 described above. Similarly, the fuel cell assembly 204 can be configured in a similar manner as one or more example fuel cell assemblies 204 described above.

[0259] For example, with respect to the gas turbine engine 100, the gas turbine engine 100 generally includes a combustion section 114 that includes the combustor 206. Further, for the depicted embodiment, the fuel cell assembly 204 generally includes a fuel processing unit in a fuel cell stack 294. The fuel cell stack 294 can include fuel cells that define an outlet configured to provide an output product from the fuel cells to the combustor 206.

[0260] However, for the depicted embodiment, the fuel cell assembly 204 is more specifically configured as a modular fuel cell assembly 1200. In particular, FIG. 5 The modular fuel cell assembly 1200 generally includes a first fuel cell string 1202, a second fuel cell string 1204, and, for the depicted embodiment, a third fuel cell string 1206 and a fourth fuel cell string 1208.

[0261] The first fuel cell string 1202 includes a first processing unit 1210 and a first fuel cell stack 1212, where the first fuel cell stack 1212 includes first fuel cells that define an outlet configured to provide an output product 1214 from the first fuel cells to the combustor 206. Similarly, the second fuel cell string 1204 includes a second processing unit 1216 and a second fuel cell stack 1218. The second fuel cell stack 1218 includes second fuel cells that define an outlet configured to provide an output product 1220 from the second fuel cells to the combustor 206.

[0262] In this manner, it will be appreciated that the first fuel cell string 1202 and the second fuel cell string 1204 include dedicated processing units 1210, 1216. More specifically, for the depicted embodiment, the first processing unit 1210 can be configured as a first fuel processing unit, and the second processing unit 1216 can be configured as a second fuel processing unit. The first fuel processing unit is dedicated to the first fuel cell string 1202 for providing a first fuel flow 1222 to the first fuel cell stack 1212. The second fuel processing unit is dedicated to the second fuel cell string 1204 for providing a second fuel flow 1224 to the second fuel cell stack 1218. The first fuel processing unit and the second fuel processing unit can be configured in a similar manner as the example fuel processing unit 304 described above, for example, with reference to FIG. 3. FIG. 5

[0263] Although not depicted, each of the first fuel cell string 1202 and the second fuel cell string 1204 can further include an air processing unit (similar to the air processing unit 306 described above, for example, with reference to FIG. 3) that can be dedicated to the respective fuel cell string 1202, 1204. FIG. 20

[0264] ​​Further, for the example aspects described, the propulsion system further includes a control system having one or more sensors configured to sense gas composition data of a first flow through the first fuel cell string 1202 and gas composition data of a second flow through the second fuel cell string. The first flow can include, for example, a first fuel stream 1222 from the first fuel processing unit to the first fuel cell stack 1212, an output product stream 1214 from the first fuel cell stack 1212 to the combustor 206, and a first air stream (not shown) from the first air processing unit to the first fuel cell stack 1212. Similarly, the second flow can include, for example, a second fuel stream 1224 from the second fuel processing unit to the second fuel cell stack 1218, an output product stream 1220 from the second fuel cell stack 1218 to the combustor 206, and a second air stream (not shown) from the second air processing unit to the second fuel cell stack 1218.

[0265] More particularly, for the illustrated embodiment, the one or more sensors include gas sensors, and still more particularly, multi-gas sensors. The gas sensors can be configured in a similar manner as the example gas sensor 350 described above. Still more particularly, for the illustrated embodiment, the one or more sensors include a first fuel stream gas sensor 1226A configured to sense gas composition data of a first fluid flow (e.g., the first fuel stream 1222) through the first fuel cell string 1202 at a location downstream of the first processing unit 1210 and upstream of the first fuel cell stack 1212, and a first output product gas sensor 1228A configured to sense gas composition data of the first fluid flow (e.g., the output product 1214) through the first fuel cell string 1202 at a location downstream of the first fuel cell stack 1212. Similarly, for the illustrated embodiment, the one or more sensors include a second fuel stream gas sensor 1226B configured to sense gas composition data of a second fluid flow (e.g., the second fuel stream 1224) through the second fuel cell string 1204 at a location downstream of the second processing unit 1216 and upstream of the second fuel cell stack 1218, and a second output product gas sensor 1228B configured to sense gas composition data of the second fluid flow (e.g., the output product 1220) through the first fuel cell string 1202 at a location downstream of the second fuel cell stack 1218.

[0266] Notably, for the depicted embodiment, the third fuel cell string 1206 and the fourth fuel cell string 1208 are configured in a similar manner as the first fuel cell string 1202 and the second fuel cell string 1204 (e.g., having third processing units 1230 and third fuel cell stacks 1232, and fourth processing units 1234 and fourth fuel cell stacks 1236, respectively). Similarly, the control system further includes a third fuel stream gas sensor 1226C, a third output product gas sensor 1228C, a fourth fuel stream gas sensor 1226D, and a fourth output product gas sensor 1228D.

[0267] It will be appreciated that, although the depicted modular fuel cell assembly 1200 includes four fuel cell strings, in other example embodiments, any other suitable number of fuel cell strings can be provided (e.g., 2, 3, 5, between 2 and 20, etc.). It will also be appreciated that, although the depicted embodiment includes two gas sensors for each fuel cell string, in other example embodiments, the control system can include only fuel stream gas sensors, such as fuel stream gas sensors 1226A-D, or alternatively, can include only output product gas sensors, such as output product gas sensors 1228A-D. FIG. 21

[0268] It will also be appreciated that, in at least certain example embodiments, the first fuel cell string 1202 and the second fuel cell string 1204 are independently connected within the gas turbine engine 100. In this manner, the first fuel cell string 1202 or the second fuel cell string 1204 can be individually disconnected and connected from the gas turbine engine 100 in the event of failure, repair, or maintenance of the respective fuel cell string. This can allow one of the fuel cell strings to be removed and replaced without removing the remaining fuel cell string.

[0269] Furthermore, it will be appreciated that, for the depicted example embodiment, the one or more sensors include a first sensor (e.g., 1226A, 1228A) positioned in alignment with the first fuel cell string 1202 and a second sensor (e.g., 1226B, 1228B) positioned in alignment with the second fuel cell string 1204. More specifically, for the depicted embodiment, each of the first fuel stream gas sensor 1226A and the first output product gas sensor 1228A are positioned in alignment with the first fuel cell string 1202, and each of the second fuel stream gas sensor 1226B and the second output product gas sensor 1228B are positioned in alignment with the second fuel cell string 1204.

[0270] ​It will be appreciated, however, that in other example embodiments, the control system can have one or more sensors of any other suitable configuration to sense the desired gas composition data of the first fluid flow through the first fuel cell string 1202 and the desired gas composition data of the second flow through the second fuel cell string 1204. For example, reference will now be made to FIG. 21 A schematic view of a modular fuel cell assembly 1200 is provided in accordance with another example aspect of the present disclosure. FIG. 20 The example modular fuel cell assembly 1200 can be constructed in substantially the same manner as the example modular fuel cell assembly 1200 of FIG. 21 The example modular fuel cell assembly 1200 can be constructed in substantially the same manner as the example modular fuel cell assembly 1200 of

[0271] It will be appreciated, however, that in the example aspect of FIG. 21 the control system includes one or more gas sensors, and more particularly, one or more multi-gas sensors configured to sample the first fluid flow through the first fuel cell string 1202 and to sample the second fluid flow through the second fuel cell string 1204. In particular, for the example embodiment of FIG. 20 the one or more multi-gas sensors are spaced apart from the first fluid flow and the second fluid flow and are configured to sense the gas composition data from these spaced apart locations. In particular, for the depicted embodiment, the control system includes a fuel stream gas sensor 1226 and a fuel stream sampling conduit 1238. The fuel stream sampling conduit 1238 is configured to provide a sample stream from the fuel cell strings 1202, 1204, 1206, 1208 (e.g., from a location downstream of the respective processing units and upstream of the respective fuel cell stacks) to the fuel stream gas sensor 1226. Similarly, for the depicted embodiment, the control system includes an output product gas sensor 1228 and an output product sampling conduit 1240. The output product sampling conduit 1240 is configured to provide a sample stream from the fuel cell strings 1202, 1203, 1206, 1208 (e.g., from a location downstream of the respective fuel cell stacks) to the output product gas sensor 1228. In this manner, it will be appreciated that the first multi-gas sensor (fuel stream gas sensor 1226) and the second multi-gas sensor (output product gas sensor 1228) of the control system can be configured to sample the first fluid flow through the first fuel cell string 1202, the second fluid flow through the second fuel cell string 1204, the third fluid flow through the third fuel cell string 1206, and the fourth fluid flow through the fourth fuel cell string 1208.

[0272] Reference will now be made back to the example embodiment of FIG. 5 It will be appreciated that the example control system further includes a controller 240. The controller 240 can be configured in substantially the same manner as the controller 240 described above, for example, with reference to FIG. 22One or more example controllers 240 are configured in a similar manner as described. The controller 240 is operably connected to one or more sensors (1226A-D, 1228A-D), and further, for example embodiments, the controller 240 is operably connected to each of the fuel cell strings 1202, 1204, 1206, 1208 for independent control of each fuel cell string. For example, in the depicted embodiment, the first fuel cell string 1202 is independently controllable relative to the second fuel cell string 1204 (as well as the third fuel cell string 1206 and the fourth fuel cell string 1208). More specifically, for the depicted example embodiment, a first fluid flow through the first fuel cell string 1202 is independently controllable relative to a second fluid flow through the second fuel cell string 1204. In particular, for the depicted embodiment, the modular fuel cell assembly includes a first fuel flow valve 1242 operable to control one or more aspects of the first fluid flow through the first fuel cell string 1202, a second fuel flow valve 1244 operable to control one or more aspects of the second fluid flow through the second fuel cell string 1204, a third fuel flow valve 1246 operable to control one or more aspects of a third fluid flow through the third fuel cell string 1206, and a fourth fuel flow valve 1248 operable to control one or more aspects of a fourth fluid flow through the fourth fuel cell string 1208.

[0273] The first fuel flow valve 1242 of the first fuel cell string 1202, the second fuel flow valve 1244 of the second fuel cell string 1204, the third fuel flow valve 1246 of the third fuel cell string 1206, and the fourth fuel flow valve 1248 of the fourth fuel cell string 1208 are each operably connected to the controller 240 and are independently controllable by the controller 240.

[0274] In this manner, it will be appreciated that the controller 240 of the control system can be configured to receive gas composition data of the first fluid flow through the first fuel cell string 1202 and gas composition data of the second fluid flow through the second fuel cell string 1204, and can be further configured to modify an operating parameter of the first fuel cell string 1202, the second fuel cell string 1204, or both, in response to the received gas composition data.

[0275] Notably, for the depicted embodiment, the controller 240 is further configured to receive operational data from the flight database 1250, e.g., of the modular fuel cell assembly 1200, the gas turbine engine 100, the aircraft comprising the modular fuel cell assembly 1200 and the gas turbine engine 100, or combinations thereof. The controller 240 can be further configured to make control decisions in response to the received operational data and the sensed gas composition data of one or more of the fuel cell strings 1202, 1204, 1206, 1208. Further, the controller 240 can be configured to provide data to an engine controller 1252, such as a full authority digital engine control controller (“FADEC”), of the gas turbine engine 100 to assist in controlling the gas turbine engine 100, and can further provide one or more notifications to an operator, such as a pilot cockpit at 1254.

[0276] Referring now to FIG. 20 , a flowchart of a method 1300 of operating a propulsion system in accordance with example aspects of the present disclosure is provided. The example method 1300 can be used to control a propulsion system comprising a modular fuel cell assembly and a gas turbine engine configured in a similar manner as the example modular fuel cell assembly 1200 and gas turbine engine 100 of FIG. 21 and FIG. 22 .

[0277] The method 1300 includes, at (1302), providing output products from first fuel cells of a first fuel cell string of a modular fuel cell assembly and output products from second fuel cells of a second fuel cell string of the modular fuel cell assembly to a combustor of a combustion section of a gas turbine engine. Providing the output products at (1302) can occur while the propulsion system is being operated during flight operations.

[0278] The method 1300 further includes, at (1304), receiving gas composition data of a first fluid flow through the first fuel cell string and gas composition data of a second fluid flow through the second fuel cell string. Receiving the gas composition data at (1304) can include receiving the gas composition data from one or more sensors, such as from one or more gas sensors, such as from one or more multi-gas sensors.

[0279] Further, for the depicted example aspects, the method 1300 includes, at (1306), modifying an operating parameter of the first fuel cell string, the second fuel cell string, or both. More particularly, modifying the operating parameter at (1306) includes, at (1308), modifying the operating parameter of the first fuel cell string, the second fuel cell string, or both, in response to the gas composition data received at (1304).

[0280] More specifically, for the depicted example aspect, the method 1300 is structured to further utilize operational data to control the modular fuel cell assembly. For example, the method 1300 further includes, at (1310), receiving operational data of the fuel cell assembly, the gas turbine engine, the aircraft including the fuel cell assembly and the gas turbine engine, or a combination thereof. The operational data received at (1310) can be a health indicator of the fuel cell assembly, the gas turbine engine, or both. For example, the operational data received at (1310) can include a system health indicator such as accumulated health data or a degree of degradation of one or more aspects of the modular fuel cell assembly. For example, the operational data received at (1310) can include a percent to end-of-life of one or more of the fuel processing unit, the fuel cell stack (and fuel cells), etc., of the modular fuel cell assembly. Similar data can be received for various components of the gas turbine engine. The operational data received at (1310) related to the aircraft can include a flight plan of the aircraft, a maintenance plan of the aircraft, etc.

[0281] Still referring to FIG. 23 the example aspect of the method 1300, modifying the operational parameter of the first fuel cell string, the second fuel cell string, or both (1306) further includes, at (1312), modifying the operational parameter of the first fuel cell string, the second fuel cell string, or both in response to the gas composition data received at (1304) and in response to the operational data received at (1310).

[0282] For example, modifying the operational parameter at (1312) includes, at (1314), determining that a component of the first fuel cell string exceeds a health threshold. The health threshold can be a percent to end-of-life threshold or other accumulated health data threshold. Determining that the component of the first fuel cell string exceeds the health threshold at (1314) can include determining that the component of the first fuel cell string is unlikely to proceed in an expected manner (e.g., fail) to a next planned maintenance of the aircraft. In response to determining that the component of the first fuel cell string exceeds the health threshold at (1314), modifying the operational parameter at (1312) further includes, at (1316), increasing a power output of the first fuel cell string. Increasing the power output of the first fuel cell string at (1316) can include increasing a flow of fuel to the first fuel cell stack relative to a flow of fuel to the second fuel cell stack.

[0283] In this way, the method 1300 can accelerate the useful life of the first fuel cell string such that it can be replaced during the next planned maintenance of the aircraft rather than failing during a subsequent flight mission.

[0284] In alternative example aspects of the method 1300, modifying the operational parameter at (1312) includes, at (1318), detecting an anomaly within the fuel cell assembly. Detecting the anomaly within the fuel cell assembly can include detecting an anomaly within the first fuel cell string. The anomaly can indicate that the affected component can continue to provide a desired output, but that the component has degraded beyond a nominal level. In response to detecting the anomaly at (1318), modifying the operational parameter at (1312) further includes, at (1320), reducing a power output of the first fuel cell string. Reducing the power output of the first fuel cell string at (1320) can include reducing a flow of fuel to the first fuel cell stack relative to a flow of fuel to the second fuel cell stack. In certain example aspects, reducing the power output of the first fuel cell string at (1320) can further include increasing a flow of fuel to the second fuel cell stack, or alternatively, can include increasing a power draw from a separate power source of the gas turbine engine, the fuel cell assembly, or the aircraft (e.g., an electric motor driven by the gas turbine engine).

[0285] In this way, the method 1300 can spare components of the first fuel cell string from failure until the first fuel cell string can receive maintenance to address the detected anomaly.

[0286] It will be appreciated that the gas sensor described herein above can be any suitable gas sensor for detecting gas composition data of a fluid flow into, toward, or through the gas turbine engine, the fuel cell assembly, or both.

[0287] In particular, in certain example embodiments, the gas sensor can be configured to sense gas composition data of a single component of a fluid (e.g., a percentage of nitrogen within an output product stream from the anode). This can allow for a simpler and cost-effective detection, maintenance, reporting, and / or control system while still providing gas composition data.

[0288] Alternatively, the gas sensor can be configured to sense gas composition data of multiple components of a single fluid (e.g., a percentage of CO2 and a percentage of H2O within an output product stream from the cathode). Such a configuration can provide a more versatile detection, maintenance, reporting, and / or control system, providing valuable gas composition data.

[0289] Yet alternatively, the gas sensor can be configured to sense gas composition data of one or more components of multiple fluids (e.g., a percentage of CO2 and / or a percentage of H2O within an output product stream from the cathode, a percentage of nitrogen within an output product stream from the anode, and / or a percentage of oxygen within a fluid surrounding the fuel cell). Such a configuration can provide a more versatile detection, maintenance, reporting, and / or control system, providing valuable gas composition data.

[0290] In this manner, it will be appreciated that the gas sensor can be a multi-gas sensor having a plurality of sensing nodes configured to sense a plurality of unique responses (e.g., a plurality of unique electrical responses, vibrational responses, etc.), etc.

[0291] For example, in one example embodiment, the gas sensor can use Raman spectroscopy, which is an optical analysis technique that relies on measurements of the vibrational and rotational properties of molecules. Raman spectroscopy produces a unique spectral fingerprint of data that can identify the chemical composition and molecular structure of a fluid. Raman spectroscopy can use a laser directed at the fluid. A spectrometer collects and measures the Raman scattered photons, creating a unique spectral fingerprint. Raman measurements are non-destructive and can be collected in seconds (e.g., less than 10 seconds, less than 5 seconds, or less than 3 seconds, depending on the laser power and the required detection resolution). Raman signals are easy to interpret: the distribution of spectral peaks describes the composition of the molecule, while the signal intensity is linearly related to the concentration. Known data analysis techniques can be used to resolve overlapping Raman peaks.

[0292] In certain example aspects, a gas sensor configured to sense the percentage of nitrogen (either a multi-gas sensor or a single gas sensor) can use Raman spectroscopy, as this technique can be well suited to determine the concentration of nitrogen at relatively low levels disclosed herein.

[0293] In another embodiment, a gas sensor configured as a multi-gas sensor can be a multi-response sensor, also known as a multi-variable sensor, also known as a multi-output sensor, also known as a multi-parameter sensor. Such a sensor has one or more variable control parameters that predictably affect the multi-gas sensing capabilities of the sensor. Non-limiting examples of such variable control parameters include the operating frequency of the sensor, the operating wavelength of the sensor, the operating temperature of the sensor, the energy source applied to the sensor, such as the optical illumination of the sensor at different wavelengths and light intensities, the acoustic excitation of the sensor at different frequencies. Alternatively, the multi-variable gas sensor can be a sensor array.

[0294] Non-limiting examples of multi-gas sensors are impedance sensors, optical sensors, thermal conductivity sensors, electromechanical sensors, field effect transistor sensors.

[0295] Additionally or alternatively, in other example embodiments, the gas sensor can use any other suitable technique. For example, referring now to FIG. 23 , a gas sensor is provided in accordance with another example aspect of the present disclosure. FIG. 1 to FIG. 22 The gas sensor of FIG. 23 may be incorporated into one or more example systems and methods described above with reference to

[0296] In particular, FIG. 24 One embodiment of a gas sensor configured as a multi-gas sensing system 1400 (i.e., a multi-gas sensor) is shown. The multi-gas sensing system 1400 interrogates a fluid in contact with the multi-gas sensing system 1400. The fluid can be a gas, a liquid, a gas-liquid mixture, a solid, a particulate or particulate matter, etc., containing one or more analyte gases therein to determine gas composition data.

[0297] The multi-gas sensing system 1400 can represent one or more different versions of the sensing systems described herein. The multi-gas sensing system 1400 includes a sensing circuit 1500, a modifier assembly 1422, and a management circuit 1410, which can control the operation of the modifier assembly 1422 and the sensing circuit 1500. In one or more embodiments, the sensing circuit 1500 can be a resistor-capacitor (RC) circuit that includes one or more resistor R and capacitor C components that can change due to the presence of one or more analyte gases of interest. For example, the management circuit 1410 can change the resistance and / or capacitance of the sensing circuit 1500. In one or more embodiments, the circuitry of the multi-gas sensing system 1400 is capable of making impedance measurements of the multi-gas sensing system 1400 to determine an impedance response to one or more analyte gases of interest. The impedance measurements can be made at one or more different frequencies or one or more different RC configurations of the sensing circuit 1500. For example, the sensing circuit 1500 of the multi-gas sensing system 1400 can measure the impedance response of the multi-gas sensing system 1400 at different frequencies, at different resistances of the RC circuit, at different capacitances of the RC circuit, or at any combination of two or more thereof.

[0298] The term impedance used herein can be a non-limiting term for any electrical response of a sensing system to an alternating current applied to the sensing system. Such a response can be measured as different electrical properties. Non-limiting examples of these different electrical responses commonly measured by a sensing system to an alternating current include impedance, admittance, reactance, susceptance, etc. In this specification, an example of the response is given as impedance, however, other electrical responses of a sensing system to an alternating current can equally be produced.

[0299] In one embodiment, the electrical response of the sensing system can be monitored at a gas-modulated pre-shoulder of a dielectric relaxation peak of the sensing material.

[0300] Measurements of the impedance of the multi-gas sensing system 1400 can be made by an impedance analyzer or impedance analyzer circuit, which can be part of or coupled to the management circuit 1410 and / or the system controller 1420, and in conductive communication with the sensing circuit 1500, at a single frequency, at discrete frequencies, or at a plurality of swept frequencies. Optionally, the management circuit 1410 of the multi-gas sensing system 1400 can also or instead be referred to as a spectrum analyzer, an analyzer, an alternating current response analyzer, etc.

[0301] In one or more embodiments, the impedance analyzer can be part of the management circuit 1410 and can measure the electrical response of at least two sensing elements of the multi-gas sensing system, where the two sensing elements are based on different detection principles. A non-limiting example of a first sensing element can be a pair of electrodes coated with a sensing material and positioned on a substrate. The impedance analyzer can measure the gas response of this first sensing element at a frequency or a single frequency near the dielectric relaxation peak of the sensing material. A non-limiting example of a second sensing element can be a mechanical resonator coated with a sensing material, such as a tuning fork resonator, a thickness shear mode resonator, or a surface acoustic wave resonator. The impedance analyzer can measure the resonant peak frequency position of this resonant second sensing element.

[0302] The multi-gas sensing system 1400 can include a system controller 1420. The system controller 1420 can include one or more devices, such as but not limited to a power source 1430, a data analysis unit 1432, an output device 1434 (e.g., such as a safety alarm), and a communication system 1436. One or more components of the system controller 1420 can include one or more processors, including one or more microprocessors, field programmable gate arrays, and / or integrated circuits. In one or more embodiments, the multi-gas sensing system 1400 can be a battery-operated device, and / or can be powered using energy available from a host control system or by harvesting energy from environmental sources (e.g., light, vibration, heat, electromagnetic energy, etc.). In one or more embodiments, the management circuit 1410 and / or the modifier assembly 1422 can be part of the system controller 1420. For example, one or more processors of the system controller 1420 can operate in a similar manner as the management circuit 1410 and / or the modifier assembly 1422.

[0303] The data analysis unit 1432 can be in the form of an integrated circuit controller positioned on the same board as the sensing elements. As one example, the multi-gas sensing system 1400 can operate with a power requirement of about 30 milliamps or less per hour of substantially continuous operation. The data analysis unit 1432 can receive data directly from one or more of the sensing elements 1402A-C, or via the management circuit 1410 from other sensing elements positioned on the same board, such as temperature and / or ambient humidity sensing elements. The data analysis unit 1432 can receive data wirelessly directly from one or more of the sensing elements 1402A-C, or via the management circuit 1410 from one or more of the sensing elements 1402A-C, or from other sensing elements positioned at different locations in or around the multi-gas sensing system 1400, etc.

[0304] The data can be stored in short and / or long term memory storage devices, such as an archival communication system, which can be located within or remote from the multi-gas sensing system 1400, and / or reconstructed and displayed for an operator, such as at an operator workstation, via an output device of the multi-gas sensing system 1400, etc. The data analysis unit 1432 can include one or more processors for analyzing data received from the management circuit 1410. For example, the one or more processors can be one or more computer processors, controllers (e.g., microcontrollers), or other logic-based devices that operate based on one or more sets of instructions (e.g., software). The instructions that the one or more processors operate on can be stored on a tangible and non-transitory computer readable storage medium, such as a memory device. The memory device can include a hard disk drive, a flash drive, RAM, ROM, EEPROM, etc. Alternatively, the one or more sets of instructions that direct the operation of the one or more processors can be hardwired into the logic of the one or more processors, such as by being hardwired logic that is formed and / or stored in the hardware of the one or more processors.

[0305] FIG. 23 It is shown FIG. 24FIG. 1 illustrates one embodiment of a multi-gas sensing system 1400. The multi-gas sensing system 1400 includes a sensing circuit 1500. The sensing circuit 1500 includes one or more sensing elements 1402A-C. Each of the sensing elements 1402A-C is operable to be in contact with a fluid in which one or more analyte gases can be contained. The sensing elements 1402A-C include a common material for their respective substrates 1502, such as a dielectric material. Notably, in other embodiments, a single substrate 1502 for two or more of the sensing elements 1402A-C can be included. Suitable materials for the substrate 1502 can include aluminum oxide, ceramic, and the like. Each of the sensing elements 1402A-C also includes a sensing film or sensing material 1508 coupled to the substrate 1502, and sensing electrodes 1510, 1512. Suitable examples of the sensing material or sensing film include metal oxide materials, composite materials, semiconductor materials, n-type semiconductor materials, p-type semiconductor materials, combinations of n-type and p-type semiconductor materials, nanocomposite materials, inorganic materials, any known sensing material capable of operating up to 900 °C, and the like. Non-limiting examples of sensing materials that operate around 900 °C include gallium oxide and silicon carbide. Suitable electrodes can be formed using metal etching, screen printing, inkjet printing, and mask-based metal deposition techniques. The thickness of the electrodes fabricated on the substrate 1502 can range from about 10 nanometers to about 1000 micrometers. The materials for the substrate 1502, sensing layer 1508, and sensing electrode 1510, 1512 formation methods can be selected based at least in part on application-specific parameters.

[0306] The sensing material 1508 is exposed to, contacts, indirectly contacts at least one analyte gas, and the like. One or several heating elements 1504, such as high resistance bodies, are coupled to different sides of the substrate 1502 relative to the sensing material 1508. The heating elements 1504 receive current from a heater controller 1506, which represents a hardware circuit that conducts heater current or voltage to the heating elements 1504 to heat the substrate 1502, and the sensing film or sensing material 1508 coupled to the other side of the substrate 1502. For example, in one or more embodiments of the inventive subject matter described herein, the sensing material 1508 uses a metal oxide sensing film. The management circuit 1410 can manage the temperature of each of the sensing elements 1402A-C by controlling the operation of the heater controller 1506 to control each of the heating elements 1504. The sensing material 1508 can include one or more materials deposited onto the substrate 1502 to perform a function that predictably and repeatably affects the impedance sensor response when interacting with the environment. For example, metal oxides such as gallium oxide and silicon carbide, or any other material can be deposited as the sensing material 1508.

[0307] In one or more embodiments, one or more filters (not shown) can be disposed over the one or more sensing elements 1402A-C. For example, the one or more filters can be a barrier or alternative protective mechanism or device that can prevent or reduce the amount of gaseous, liquid, and / or solid particles that can come into contact with the sensing material 1508, the sensing electrodes 1510, 1512, etc. As one example, a single filter can be disposed over the one or more sensing elements, or alternatively, each sensing element can include an individual filter disposed over the top of each sensing element. The one or more filters can be a gas permeable membrane filter such that the filter can enable a gas of interest to pass from one side of the filter to the other side, and can prevent or reduce the amount of interfering gases or solid particles that can pass from one side of the filter to the other side. In one or more embodiments, the gas permeable membrane filter can include a fluoropolymer or a fluoropolymer coating. Optionally, the filter can include an alternative coating, such as a flame retardant.

[0308] In the illustrated embodiment, the sensing electrodes 1510, 1512 of each sensing element 1402A-C are coupled with and / or disposed in the sensing material 1508, and are connected with the substrate 1502. The sensing electrodes 1510, 1512 are conductive bodies that are conductively coupled with one or more of the modifier assembly 1422, the transducers 1524A-C, and the management circuit 1410. In one or more embodiments, the transducers 1524A-C are electrode structures connected to an impedance detector system, and the sensor is a transducer coated with a sensing material. The management circuit 1410 can include an impedance detector system or a resistance detector system. Each of the modifier assembly 1422, the transducers 1524A-C, and the management circuit 1410 can have one or more processors including one or more microprocessors, field programmable gate arrays, and / or integrated circuits.

[0309] In FIG. 25 In the illustrated embodiment, each sensing element 1402A-C is operably coupled with a transducer 1524A-C, respectively. Alternatively, the sensing circuit 1500 can include a single transducer that is conductively coupled with each sensing element 1402, which can receive the electrical response from each sensing element 1402A-C and convert changes in the electrical response into a physical quantity.

[0310] In one or more embodiments, the sensing electrodes 1510, 1512 can be coated with a sensing material responsive to one or more analyte gases of interest. The one or more processors of the management circuit 1410 can direct the sensing electrodes 1510, 1512 to apply electrical stimulation at a frequency, such as an electrical excitation frequency or a single excitation frequency. For example, the management circuit 1410 can excite the sensing elements 1402A-C with alternating current at at least one predetermined frequency, at a predetermined range of frequencies, and the like.

[0311] The one or more processors of the management circuit 1410 can receive electrical signals from the sensing electrodes 1510, 1512 of each sensing element 1402A-C, the electrical signals representative of an electrical impedance or impedance response of the sensing elements 1402A-C during exposure of the sensing material 1508 to the fluid sample. For example, the one or more processors of the management circuit 1410 can measure one or more electrical responses of the sensing elements 1402A-C in response to exciting the sensing electrodes 1510, 1512 with alternating current at at least one frequency or range of frequencies.

[0312] The management circuit 1410 can determine one or more characteristics of the sensing circuit 1500 based on the electrical responses from each different sensing element 1402A-C. The characteristics of the sensing circuit 1500 can include a temperature of one or more sensing elements, a temperature variation between two or more sensing elements, a state of the sensing circuit 1500 based on a configuration of the sensing elements 1402, one or more environmental conditions (e.g., ambient temperature, humidity, and the like) within a predetermined area proximate to the sensing circuit 1500, and the like. In one or more embodiments, the management circuit 1410 can manage a configuration of each of the one or more sensing elements 1402A-C such that the management circuit 1410 can manage a resistor-capacitor configuration of at least one sensing element. The management circuit 1410 can determine a state of the sensing circuit 1500 based on the resistor-capacitor configuration of each sensing element of the sensing circuit. Alternatively, the state of the sensing circuit 1500 can be based on another configuration of the sensing circuit 1500.

[0313] In one or more embodiments, the management circuit 1410 can be referred to as a frequency impedance source and detector system. The management circuit 1410 interrogates the electrical impedance of the sensing elements 1402A-C in order to determine the presence and / or amount (e.g., concentration) of one or more analyte gases in the environment to which the sensing material 1508 of each sensing element 1402A-C is exposed, as described herein. The management circuit 1410 can provide a scanning capability to measure sensor impedance responses at a single or multiple discrete frequencies. Alternatively, the system controller 1420 can provide a capability to measure sensor impedance responses across a range of frequencies.

[0314] The sensing circuit 1500 can be operably coupled with a modifier assembly 1422, which can include a multiplexer. The multiplexer can be a single multi-frequency scanning signal analyzer that can operate at a power demand that is less than 10 milliwatts (mW), less than 5 mW, or in more preferred embodiments, less than 1 mW. In one or more embodiments, each sensing element 1402A-C can be conductively coupled with the modifier assembly 1422. The system controller 1420 and / or the management circuit 1410 can direct one or more sensing elements 1402A-C to change an impedance of an electrical stimulus applied to the corresponding sensing material 1508 without changing an excitation frequency. As one example, the modifier assembly 1422 can include a set of circuits with multiple circuits (not shown) to change the impedance of each sensing element 1402A-C based on which circuits are electrically coupled or decoupled with the management circuit. Alternatively, the modifier assembly 1422 can include a single circuit, which can be a variable circuit or a variable device, that can change the impedance of each sensing element 1402A-C. In alternative embodiments, the modifier assembly can include a multiplexer with any alternative configuration, one or more circuits, or any combination therein.

[0315] The management circuit 1410 and / or the system controller 1420 can control the modifier assembly 1422 to apply the electrical stimulus to each sensing element 1402A-C at a single or discrete impedance, or at a predetermined range of varying impedances, for interrogating the sensing material 1508 of each respective sensing element 1402A-C, and at what interrogation times, in order to measure the sensor response at each frequency. For example, the multiplexer of the modifier assembly can electrically connect and / or decouple one or more different sensing elements 1402A-C with the management circuit 1410 and the corresponding sensing electrode 1510, 1512 to change which sensing element 1402A-C of the sensing circuit 1500 is electrically coupled and decoupled with the modifier assembly 1422 and the management circuit 1410. For example, the modifier assembly 1422 can change the impedance of each sensing element 1402A-C without changing an electrical excitation frequency of the electrical stimulus applied to the sensing electrode 1510, 1512.

[0316] The multiplexer of the modifier assembly 1422 can combine the plurality of electrical response signals received from each sensing element 1402A-C into a single output that is directed to the management circuit 1410. The management circuit 1410 receives the electrical response signals and determines one or more characteristics of the sensing circuit 1500 in response to exciting the sensing electrodes 1510, 1512 with an alternating current at at least one predetermined frequency. The management circuit 1410 can transmit or otherwise communicate the electrical response signals and the determined characteristics of the sensing circuit 1500 to one or more processors of the system controller 1420. The concentration of at least one gas analyte can be determined based on the electrical response of the sensing elements 1402A-C and the characteristics of the sensing circuit 1500. For example, the data analysis unit 1432 of the system controller 1420 can convert the sensor response into analytically useful gas composition data, such as detecting the concentration of a gas. Additionally, the data analysis unit 1432 can determine the concentration of at least one gas analyte based on one or more temperatures of each sensing element 1402A-C, environmental conditions proximate to the sensing circuit 1500 (e.g., within a predetermined proximity or area of the sensing circuit, such as within 1 meter, 5 meters, 10 meters, 100 meters, etc.), and the like.

[0317] As one example, the system controller 1420 can determine the concentration of at least one analyte gas based on the electrical response from two or more different sensing elements (e.g., sensing elements 1402A, 1402B). The first sensing element 1402A can operate at a first substantially constant temperature, and the second sensing element 1402B can operate at a different second substantially constant temperature. For example, the management circuit 1410 can control the heating element 1504 such that the first sensing element 1402A can operate at a first temperature, and the second sensing element 1402B can operate at a different temperature that can be greater than or less than the first temperature.

[0318] As another example, the system controller 1420 can determine a concentration of one or more gas analytes based on electrical responses from two or more different sensing elements, such as sensing elements 1402A and 1402B. The management circuit 1410 can control operation of the heating element 1504 to operate the first sensing element 1402A at a periodically varying temperature, and can operate the second sensing element 1402B at a different periodically varying temperature. For example, the heating element 1504 can vary the temperature of the first sensing element 1402A (e.g., such as over a temperature range) that increases and / or decreases the temperature to a predetermined value at a predetermined time, over a predetermined duration, or any combination thereof. Additionally, the heating element 1504 can vary the temperature of the second sensing element 1402B (e.g., over a different or the same temperature range) that increases and / or decreases the temperature to a different predetermined value at a different predetermined time, over a different predetermined duration, or any combination thereof. Optionally, the first sensing element 1402A and the second sensing element 1402B can operate over similar temperature ranges for different durations, can operate over similar durations but different temperature ranges, can operate over similar temperatures and durations but different times, etc.

[0319] The sensing elements 1402A-C including the sensing material 1508 and the substrate 1502, the heating element 1504, the heater controller 1506, the modifier assembly 1422, and the transducers 1524A-C are disposed within a housing 1514. The housing 1514 can be operably coupled with the substrate or circuit board 1404 of the multi-gas system 1400. Optionally, one or more of the sensing elements 1402A-C can be disposed in individual housings to separate each sensing element from the other sensing elements. Optionally, one or more of the modifier assembly 1422, the heater controller 1506, the one or more transducers 1524, or the management circuit 1410 can be operably coupled with the circuit board 1404 of the multi-gas sensing system 1400 and can be disposed outside of or separate from the housing 1514. Optionally, one or more components of the multi-gas sensing system 1400 can be disposed or contained within a housing with or separate from any other components of the multi-gas sensing system 1400.

[0320] FIG. 26A system layout of a multi-gas sensing system 1600 is shown in accordance with one embodiment. The components and devices of the multi-gas sensing system 1600 are disposed on a substrate or circuit board 1404. In one or more embodiments, one or more components or devices of the multi-gas sensing system 1600 can be disposed on one or both sides of the circuit board 1404. The multi-gas sensing system 1600 can include one or more power devices or components, such as a power source 1430 or power switch, a power regulator 1630, a non-volatile memory or other memory or storage device 1606, a charging source 1608, such as a micro-USB, or a charger or charging device 1610. In one or more embodiments, the power source 1430 can be or include a battery source or any alternative untethered power source. The multi-gas sensing system 1600 can include processing components, such as a management circuit 1410, a system controller 1420, and a modifier component 1422. The management circuit 1410 can include one or more processors, including one or more microprocessors, field programmable gate arrays, and / or integrated circuits, which can operate or function as an impedance analyzer, a resistor detector system, or the like. The system controller 1420 can include one or more processors, which can operate as a data analysis unit, a memory system (e.g., memory 1606), or the like. The modifier component 1422 is shown separate from the system controller 1420 and the management circuit 1410, but alternatively can be included with one or both of the management circuit 1410 or the system controller 1420.

[0321] The multi-gas sensing system 1600 includes two different sensing elements 1402A, 1402B. In one or more embodiments, the sensing elements 1402A, 1402B can each be designed to sense or otherwise detect the presence of one or more of nitrogen (N2), oxygen (O2), carbon dioxide (CO2), water (H2O), methane (CH4), carbon monoxide (CO), etc. Alternatively, different sensing elements can be designed to sense or otherwise detect different gases. The multi-gas sensing system 1600 includes a sensing element 1602 that can be designed to sense or otherwise detect environmental conditions, such as ambient temperature, ambient humidity, ambient pressure, etc. For example, the sensing elements 1402A, 1402B can be excited by the management circuit with an alternating current at at least one predetermined frequency in response to the management circuit, communicate an electrical response to the management circuit 1410. The management circuit 1410 can measure the electrical response from the sensing elements 1402A, 1402B to determine one or more characteristics of the sensing circuit. Additionally, the sensing element 1602 can detect environmental conditions of an area proximate to the multi-gas sensing system 1400, and the management circuit 1410 can determine characteristics of the multi-gas sensing system 1400 based on the environmental conditions detected by the sensing element 1602. One or more processors of the system controller 1420 can receive the electrical response and the characteristics of the sensing circuit, and determine a concentration of at least one gas analyte, such as a gas analyte of interest, based on the electrical response and the characteristics of the sensing circuit.

[0322] In one or more embodiments, the multi-gas sensing system 1600 can include an output device 1604. As one example, the output device 1604 can be illustrated as an LED light. For example, the LED light can illuminate based on the electrical response of the sensing elements, based on the characteristics of the sensing circuit, etc. Alternatively, the output device 1604 can be any alternative safety device that can illuminate, sound an alarm, vibrate, or otherwise communicate with an operator of the multi-gas sensing system 1400 if the system controller 1420 determines that a gas of interest exceeds a predetermined threshold.

[0323] FIG. 23 A flow diagram illustrating one embodiment of a method 1700 for sensing a plurality of different gas analytes using a multi-gas sensing system is shown, in accordance with one embodiment. The multi-gas sensing system can be FIG. 22the system shown in FIG. 17. At (1702A-C), each of the sensing elements 1402A-C can be operated. For example, the management circuit can energize each sensing element with an alternating current at at least one predetermined frequency. The management circuit can energize the sensing element 1402A at a first predetermined frequency, and can energize the sensing elements 1402B, 1402C at different, unique, or common frequencies relative to each other and the sensing element 1402A. Alternatively, one or more of the sensing elements 1402A-C can be energized at a range of predetermined frequencies. In FIG. 23 and FIG. 27 In the illustrated embodiment of FIG. 17, the system includes three sensing elements. Alternatively, the system can include fewer than three or more than three sensing elements. Alternatively, the system can include only one sensing element.

[0324] In one or more embodiments, the management circuit can manage the temperature of the one or more sensing elements by controlling the heating element. For example, the management circuit can control operation of the heating element such that the one or more sensing elements operate at a predetermined temperature, operate at a predetermined range of temperatures, such that different sensing elements operate at different temperatures or at different ranges of temperatures, etc. In one embodiment, the management circuit can control the heating element to periodically vary the temperature of the first sensing element 1402A and to substantially maintain the temperature of the second sensing element 1402B and the third sensing element 1402C. For example, the management circuit can control the heating element such that the first sensing element 1402A operates at a first constant or first variable temperature and the second sensing element 1402B operates at a different second constant temperature or second variable temperature. As another example, the management circuit can control the heating element such that the first sensing element 1402A operates at a periodic variable temperature and the second sensing element 1402B operates at a different periodic variable temperature. The different periodic temperature of the second sensing element can be substantially the same temperature, but heated at a different periodic time than the first sensing element. Alternatively, the first and second sensing elements can be heated at substantially the same or common periodic time, but the first sensing element can be heated to a different temperature than the temperature of the second sensing element.

[0325] The management circuit can synchronize the temperature of the one or more sensing elements with the excitation of the one or more sensing elements. For example, the management circuit can synchronously control the heating element to control the temperature of the one or more sensing elements to a predetermined value at substantially the same time or within a predetermined window of time as the one or more sensing elements are excited with an alternating current at a predetermined frequency. For example, the management circuit can control the heating element and excite the one or more sensing elements at substantially the same time, within a window of time, etc. Alternatively, the management circuit can synchronize the change in temperature of the one or more sensing elements with the duration of the excitation of the sensing elements. Alternatively, the management circuit can substantially synchronize the maintenance of a temperature range of the one or more sensing elements while variably exciting the sensing elements at a predetermined frequency or range of frequencies. Alternatively, the management circuit can otherwise synchronize the temperature of the sensing elements with the excitation of the sensing elements in any alternative configuration or based on one or more predetermined rules.

[0326] At (1704), the one or more processors of the management circuit and / or the system controller can analyze an electrical response from the sensing elements in response to the excitation of the sensing electrodes of the sensing elements. The electrical response can be represented as a signal output from each of the one or more sensing elements. The alternating current can be applied to each of the one or more sensing elements at one or more different frequencies or at one or more different resistor-capacitor configurations for each sensing element. For example, a first sensing element can have a first resistor-capacitor configuration and a first frequency can be applied to the sensing electrode of the first sensing element to excite the first sensing element. Alternatively, a second sensing element can have a second, different, resistor-capacitor configuration and a second, different, frequency can be applied to the sensing electrode of the second sensing element. Alternatively, the one or more sensing elements can have a common resistor-capacitor configuration or a common frequency can be applied to excite the one or more sensing elements.

[0327] FIG. 26 A plot of the electrical response of various sensing elements of a multi-gas sensing system is shown in accordance with one embodiment. Graph A represents the electrical response from a first sensing element, which can be designed to detect the presence of methane (CH4). Graph B represents the electrical response from a second sensing element, which can be designed to detect the presence of carbon monoxide (CO). Alternatively, the electrical response can be received from a single sensing element, which can be configured to operate to detect the presence of CH4, CO, and any other gas. Graphs A and B are illustrated with a common horizontal axis 1802 representing time and vertical axes 1804, 1806 representing the impedance of the sensing circuit 1500, respectively.

[0328] Measurements of one or more of the real part Z’ or the imaginary part Z” of the impedance of the sensing circuit 1500 can be performed within a dielectric relaxation region of the sensing circuit 1500. The dielectric relaxation region of the multi-gas sensing system 1400 can be a range of frequencies within a specified threshold of the measured impedance of the sensing circuit 1500 at which a relaxation peak occurs, and / or a relaxation point frequency or inflection point frequency range of the imaginary part Z” of the impedance. For example, a relaxation peak (also referred to as a relaxation frequency) can be identified as a location along the imaginary part of the impedance spectrum at which the impedance response changes from concave to convex, or from convex to concave. An inflection point frequency is the frequency or range of frequencies at which an inflection point occurs. Alternatively, an inflection point can be determined by examining the real part of the measured impedance of the sensing material 1508 to locate a location at which the curvature of the real part of the impedance changes from concave to convex or from convex to concave. In one or more embodiments, the electrical response of the sensing system is monitored at a gas-modulated front shoulder of a dielectric relaxation peak of a semiconducting sensing material. For n-type semiconducting sensing materials, the front shoulder can be a high frequency region of the relaxation peak. For p-type semiconducting sensing materials, the front shoulder can be a low frequency region of the relaxation peak.

[0329] As one example, the sensing circuit can be exposed to about 11.36% by volume CH4and 1090 parts per million (ppm) of CO. As shown in graphs A and B, the second sensing element (e.g., CO sensor) detects an increase in impedance when CO is present as shown in the first segment 1810, but the first sensing element (e.g., CH4sensor) only indicates a minimal increase in impedance when CO is present. Similarly, the second sensing element detects an increase when CO is present as shown in the third segment 1814, but the first sensing element only has a minimal increase. Alternatively, the first sensing element detects an increase in impedance when CH4is present as shown in the second segment 1812, but the second sensing element only has a minimal increase. Graphs A and B show the discrimination between CH4and CO by the first and second sensing elements of the sensing circuit.

[0330] Returning to FIG. 28At (1706), the electrical responses received from the one or more sensing elements at the plurality of frequencies are converted into analytically useful concentrations of the detected analyte gases. For example, the management circuit and / or data analysis unit of the multi-gas sensing system 1400 can analyze the electrical responses received from the sensing elements to determine one or more concentrations of one or more of the sensed analyte gases. The analysis can be based on one or more of the electrical responses of the sensing elements; characteristics of the sensing circuit, such as but not limited to the temperature of the sensing elements, the state of the sensing circuit based on the configuration of the sensing elements, environmental conditions proximate to the sensing circuit, etc.; or any combination of two or more thereof. In one or more embodiments, the analysis can be based on one or more of the sensing elements operating at a periodically variable temperature, one or more of the sensing elements operating at a common or unique substantially constant temperature, different discrete frequencies or frequency ranges used to excite the sensing elements, etc.

[0331] For example, FIG. 27 A plot showing results of analysis of the electrical responses of two sensing elements of the multi-gas sensing system shown in FIG. 1 1 A is shown. FIG. 27

[0332] The electrical responses can be evaluated using one or more different statistical analysis tools, for example, such as by performing a principal component analysis (PCA) on the electrical responses and other characteristics obtained by the system controller. Alternatively, the concentrations of one or more of the gases can be calculated from a multivariate transfer function that can be constructed based on the electrical responses of the alternating current to the management system, the temperature of the sensing elements, the state of the resistor-capacitor configuration of the sensing elements, information from the sensing circuit or other sensors about environmental conditions proximate to the multi-gas sensing system, etc. Alternatively, alternative statistical analyses can be used to evaluate the data obtained by the system controller.

[0333] Chart A represents results of analysis of the combined electrical responses using PCA and expressed as the fraction of principal component #1 as a function of experimental time.

[0334] Chart B represents results of analysis of the combined electrical responses using PCA and expressed as the fraction of principal component #2 as a function of experimental time.

[0335] Charts A and B are shown with a common horizontal axis 1902 representing experimental time and vertical axes 1904, 1906 representing linear scales of principal component #1 and principal component #2, respectively, of the developed PCA classification, respectively.

[0336] As shown in Chart A, first and third sections 1910, 1914 indicate increasing concentrations of CO, and a second section 1912 indicates increasing concentrations of CH4. For example, the first and third sections indicate a response to a change in the concentration of CO from 0.1 ppm to 0.2 ppm and from 0.2 ppm to 0.3 ppm, respectively, and the second section indicates a response to a change in the concentration of CH4from 0.1 ppm to 0.2 ppm. FIG. 27 ​PCA principal component #1 response to CO gas (e.g., segments 1810, 1814 of chart B), and the second segment indicates a PCA principal component #1 response to CH4 gas (e.g., segment 1812 of chart A). FIG. 27 PCA principal component #1 response to CH4 gas (e.g., segment 1812 of chart A).

[0337] As shown in chart B, the first and third segments 1910, 1914 indicate increasing CO concentrations, and the second segment 1912 indicates increasing CH4concentrations. For example, the first and third segments 1910, 1914 indicate a PCA principal component #2 response to CO gas (e.g., segments 1810, 1814 of chart B), and the second segment 1912 indicates a PCA principal component #2 response to CH4 gas (e.g., segment 1812 of chart A). FIG. 27 PCA principal component #2 response to CH4 gas (e.g., segment 1812 of chart A). FIG. 26

[0338] In one or more embodiments, one or more processors of the system controller can provide for baseline correction of the sensing elements. Baseline correction can be performed periodically, at scheduled intervals (e.g., after so many minutes, hours, days, years, etc. of operation), etc. Baseline correction can also be referred to as calibration of the sensing elements. The amount of correction or the method of correcting or verifying the baseline can be based on the electrical response received from the sensing elements, the temperature of the sensing elements, the state of the resistor-capacitor configuration of the sensing elements, information about environmental conditions (e.g., ambient temperature, humidity, pressure, etc.) surrounding or proximate to the multi-gas sensing system, information received from other sensors or sensing devices, information wirelessly transmitted to the multi-gas sensing system (e.g., such as from a workstation separate from the multi-gas sensing system), information or protocols stored within the multi-gas sensing system, etc.

[0339] ​Optionally, the one or more processors can change the selectivity, sensitivity, or linearity of the electrical response of the multi-gas sensing system 1400 to allow the system to be more sensitive to one analyte gas than another analyte gas at different times or under different operating conditions. In one or more embodiments, the one or more processors can dynamically change the selectivity, sensitivity, or linearity such that the one or more processors can change one or more of the selectivity, sensitivity, or linearity while the sensing system is operating. Optionally, the one or more processors can change one or more of the selectivity, sensitivity, or linearity of the electrical response of the sensing system while the system is not sensing. For example, the one or more processors can determine a relaxation region of the impedance response of the sensing circuit. Both the real part of the impedance and the imaginary part of the impedance have a relaxation region. As one example, the relaxation region can be determined by examining the real part of the measured impedance of the sensing material 1508 as a function of frequency to locate where the real part of the impedance goes from a high impedance value having a substantially zero slope at low frequencies to a decreasing impedance value having a relatively high slope at a higher frequency and a decreasing impedance value having a relatively low slope at an even higher frequency, and where the impedance value approaches zero at the highest frequency.

[0340] The one or more processors can determine the location of the relaxation peak of the relaxation region of the imaginary part of the sensor impedance by identifying the inflection point frequency of the sensing circuit 1500. The inflection point frequency can be determined as the frequency of the current associated with the inflection point.

[0341] The one or more processors can determine a frequency range of sensor operation that is below and above the relaxation peak of the imaginary part of the sensor impedance and at or near (e.g., within 11%, within 3%, within 5%, or within 110% in different embodiments) the relaxation peak of the imaginary part of the sensor impedance. Current can be applied to the sensing material 1508 via the sensing electrodes 1510, 1512 of the one or more sensing elements only at frequencies greater than the inflection point frequency and / or at frequencies within a frequency range greater than the inflection point frequency. Operating the sensing circuit 1500 at these frequencies can improve the selective sensing (e.g., the sensitivity of the sensing circuit 1500) of one or more analytes of interest in a second sample by the sensing circuit 1500 relative to one or more other analytes (and relative to operating the sensing circuit 1500 at one or more frequencies at or below the inflection point frequency). The sensitivity of the sensing circuit 1500 includes the measured sensor response signal per analyte concentration unit.

[0342] As another example, the one or more processors can selectively sense at least one analyte of interest with improved interference rejection effects. The resistive and capacitive properties of the sensing circuit 1500 are measured during exposure of the sensing circuit 1500 to a first gas sample and during exposure of the sensing circuit 1500 to a second gas sample. The one or more processors determine a capacitance value or a range of capacitance values of one or more passive electrical components (e.g., a capacitive element) to change the capacitance of one or more sensing elements of the sensing circuit 1500 to match a frequency range or a discrete frequency response of the system controller within a dielectric relaxation region of the sensing circuit 1500. Changing the capacitance of the sensing circuit 1500 coupled with the system controller allows the system controller to selectively sense an analyte of interest (e.g., methane, ethane, another hydrocarbon, hydrogen, carbon monoxide, etc.) with interference rejection effects.

[0343] The selective sensing of one or more analytes of interest is performed using the sensing circuit 1500 operating within a dielectric relaxation region of the sensing circuit to match a discrete frequency response or a range of frequency responses of the system controller 1420. For example, the sensing material 1508 of each sensing element of the sensing circuit 1500 can be exposed to a gas sample having potentially one or more analytes of interest therein. The system controller 1420 can transmit a control signal to the management circuit 1410 to direct the management circuit 1410 to apply, via the sensing electrodes 1510, 1512, an alternating current to the sensing material 1508 at a specified frequency response range or a specified discrete frequency of the system controller 1420 within a dielectric relaxation region of the sensing circuit 1500. Operating the sensing circuit 1500 at these frequencies can increase the selective sensing (e.g., sensing sensitivity of the multi-gas sensing system 1400) of one or more analytes of interest in a sample relative to one or more other analytes (and relative to operating the sensing circuit 1500 at different frequencies or different frequency ranges of the system controller 1420) by the multi-gas sensing system 1400. Sensitivity of the sensing circuit 1500 includes a measured sensor response signal per analyte concentration unit.

[0344] Returning to FIG. 29 , a determination is made as to whether the resistor-capacitor configuration of one of the sensing elements needs to be changed. If the configuration does need to be changed, the flow of the method proceeds to (1712) where the management circuit changes the resistor-capacitor configuration of one or more of the sensing elements. The flow of the method returns to (1702A-C) where the method begins again. Alternatively, if no resistor-capacitor configuration of the sensing elements needs to be changed, the flow of the method moves to (1714).

[0345] At (1714), a determination is made as to whether the amount of at least one gas exceeds a predetermined threshold. For example, the system controller can determine, based on the analysis performed in steps (1704) through (1708), that there is an amount of gas that exceeds a predetermined threshold and that the concentration of that gas can be dangerous to an operator or user of the multi-gas sensing system. Alternatively, the concentration of the gas can be dangerous for the operator to perform a particular task, such as but not limited to driving or operating a motorized device, using inflammatory equipment, remaining in the environment without wearing appropriate safety equipment, etc. In one or more embodiments, a determination can be made as to whether there is any amount of a particular gas. For example, any trace or minimal amount of a particular gas can be dangerous for the operator to continue operating or remaining in the environment.

[0346] In one or more embodiments, the one or more processors of the system controller can determine a responsive action of the asset based on the electrical response of the multi-gas sensing system. For example, the system controller can determine at (1714) whether the concentration of at least one gas analyte exceeds a predetermined threshold.

[0347] If the amount or concentration of the gas analyte does not exceed the predetermined threshold, the flow of the method returns to (1702) and the method repeats for a predetermined amount of time while the operator is in the environment, until the operator disables the multi-gas sensing system, etc. Alternatively, if the amount or concentration of the gas exceeds the predetermined threshold, the flow of the method proceeds to (1716). At (1716), a notification is communicated to at least a controller or other system that incorporates the multi-gas sensing system.

[0348] FIG. 29 A plot of the response of a metal oxide sensing element to a gas of interest, such as methane, is shown according to one experiment. In this experiment, the sensing element is an integrated heater formed on a silicon substrate using microelectromechanical systems (MEMS) technology and a layer of metal oxide semiconductor material formed on the sensing chip as a surface mount ceramic package structure. The sensing element requires only about 15 mW of heater power consumption. In this experiment, methane was presented to the sensing element at concentrations of 1087 parts per million (ppm), 2174 ppm, 3261 ppm, 4348 ppm, 5435 ppm, 6522 ppm, 7609 ppm, and 8696 ppm.

[0349] Graphs A, B, and C are shown with a common horizontal axis 2002 representing time of the experiment. Graph A is shown with a vertical axis 2004 representing resistance, and graphs B and C are shown with vertical axes 2006, 2008 representing impedance, respectively. FIG. 30Graph A depicts the electrical response of the sensing element measured by conventional resistance measurements. The sensing element has a non-linear response of the resistance response to the methane concentration. Additionally, the sensitivity decreases with increasing methane gas concentration. Graphs B and C show the electrical response of the sensing element measured by the dielectric excitation method. The results shown in graph B were obtained by using a benchtop impedance analyzer. The results shown in graph C were obtained using an integrated circuit impedance analyzer. The very similar response linearity and noise levels in graphs B and C indicate that the quality of sensing methane using the integrated circuit impedance analyzer is approximately the same as the quality of sensing methane using the benchtop impedance analyzer.

[0350] The developed sensor system can measure the electrical response of the sensing element in response to an alternating current applied to the sensing element at one or more different frequencies and / or one or more different resistor-capacitor configurations. To quantify the gas of interest within its wide concentration range with a linear sensor response and its expected resolution, the dielectric excitation method can be applied at several frequencies. FIG. 31 Graphs showing three measured sensor responses at three frequencies ranging from relatively high to medium and to relatively low frequencies are shown (graphs A, B, and C). Graphs A, B, and C are shown with a common horizontal axis 2102 representing the time of the experiment and vertical axes 2104, 2106, 2108 representing the impedance.

[0351] While the response can be measured at all three frequencies of the measurement system, to determine the gas concentration, the calibration curve can start at the highest frequency. If the sensor response is above the approximate bottom 20% of the sensor response at that frequency (e.g., sensor response #1), a linear calibration curve at that frequency can be noted and can be related to the gas concentration (graph A). If the sensor response is below the bottom 20% of the sensor response at that frequency (e.g., sensor responses #2 and #3), the detection can be switched to ten times lower gas concentration by using a linear calibration curve at a lower frequency and relating the sensor response to the gas concentration (e.g., sensor response #2, as shown in graph B). If sensor response 3 is below the approximate 10% of the sensor response at that frequency, the detection can be further switched to ten times lower gas concentration and a corresponding calibration curve can be used (e.g., graph C). Thus, these sensor responses at different frequencies can allow high resolution determination of the gas concentration within a wide gas concentration range with a linear response.

[0352] Another experiment shows that variable air humidity affects the response of conventional chemical resistance sensors based on metal oxide sensing materials by changing their baseline and gas sensitivity. For example, FIG. 32The effects of water vapor in the range of 0–80% relative humidity (RH) on the resistivity and impedance (dielectric response) of ethanol (as model vapor) at concentrations of 4, 8, 12, 16, and 20 ppm are shown. Graphs A and B are shown with a common horizontal axis 2202 representing the experimental time. Graph A is shown with a vertical axis 2204 representing resistance, and Graph B is shown with a vertical axis 2206 representing impedance.

[0353] With increasing RH, the resistance response exhibits a known significant baseline decrease and a reduction in gas sensitivity (Figure A). Meanwhile, dielectric excitation and impedance measurement offer three advantages over resistance measurement (shown in Figure B). First, the response baseline is less affected by humidity variations. Second, sensor sensitivity can increase with increasing RH. Third, response linearity can be improved in the presence of water vapor.

[0354] In another experiment, the response of the multi-gas monitor to methane gas was measured outdoors under dynamic field conditions. FIG. 33 Graphical results of monitoring a dynamic methane plume outdoors using a developed multi-gas monitor are shown. Time is on the horizontal axis 2302, and impedance is on the vertical axis 2304. Uncontrolled wind conditions can produce response patterns for the monitor that can be affected by variable wind direction and speed. Therefore, the detected gas concentration can be the result of a convolution between variable wind direction and speed. Thus, this result can provide knowledge about the maximum gas concentration reaching the detector at a given time.

[0355] In another experiment, the responses of a multi-gas sensor were measured to monitor the responses of H2 and CH4. FIG. 33 The graphical results of these measurements are shown. In particular, FIG. 34 The response speeds for H2 and CH4 detection using a multi-gas sensor according to one or more exemplary aspects of this disclosure are depicted. In the top graph (Graph A), H2 sensor data is collected every 15 seconds, and one or two data points are required to achieve a 90% sensor-balanced response for H2. In the bottom graph (Graph B), CH4 sensor data is collected every 5 seconds, and one data point is required to achieve a 90% sensor-balanced response for CH4.

[0356] In tests using H2, sensor data was collected every 15 seconds (Figure A), and it was observed that the multi-gas sensor required only one or two data points to achieve its 90% equilibrium response to increased H2 concentration. However, the response to CH4 was even faster. Sensor data for CH4 was collected every 5 seconds (Figure B), and it was observed that the multi-gas sensor required only one data point to achieve its 90% equilibrium response to increased CH4 concentration.

[0357] FIG. 34 The detection results of the three gases H2, CH4 and CO, which are relevant to SOFC monitoring at their relevant high concentrations, are depicted in FIGS. 1-3. In particular, reference is made to FIG. 34 An excitation parameter (also referred to as a variable control parameter) is identified from the multi-gas sensor to detect and quantify the H2, CO and CH4 gases with a single multi-gas sensor. FIG. 34 Quantitative results of the H2, CO and CH4 gases with a single multi-gas sensor are shown in FIGS. 4-6. ​ FIGS. A, B and C in FIG. 1 depict the three steady-state responses of a single multi-gas sensor to the three gases recorded at different excitation frequencies (also referred to as variable control parameters). The dotted horizontal lines highlight the different response patterns to the three gases at the three frequencies. In addition, machine learning tools, such as support vector machines (SVM), are also applied to cross-validate the quantification of the H2, CO and CH4 gases using the multi-gas sensor, shown in FIGS. D, E and F.

[0358] In one or more embodiments of the subject matter described herein, a multi-gas sensing system includes a sensing circuit including one or more sensing elements. Each of the one or more sensing elements includes a sensing material configured to detect at least one gas analyte. A management circuit is configured to excite the one or more sensing elements with an alternating current at at least one predetermined frequency. The management circuit measures one or more electrical responses of the one or more sensing elements in response to exciting the one or more sensing elements with the alternating current at the at least one predetermined frequency. The management circuit determines one or more characteristics of the sensing circuit. One or more processors receive the one or more electrical responses of the one or more sensing elements and the one or more characteristics of the sensing circuit. The one or more processors determine a concentration of the at least one gas analyte based on the one or more electrical responses of the one or more sensing elements and the one or more characteristics of the sensing circuit.

[0359] This written description uses examples to disclose the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and can include other examples that occur to those skilled in the art. Such other examples are intended to fall within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

[0360] Further aspects are provided by the subject matter of the following clauses:

[0361] A propulsion system comprising: a propulsor; a turbine operable to drive the propulsor to generate thrust during operation; a fuel cell assembly configured to add power to the propulsor, the turbine, or both; and a multi-gas sensor operable with the turbine, the fuel cell assembly, or both, for sensing gas composition data of a fluid flow into or to the turbine, the fuel cell assembly, or both, the gas composition data including data indicative of at least two gases and their concentrations.

[0362] The propulsion system of any of the preceding clauses, wherein the turbine comprises a combustion section having a combustor, wherein the fuel cell assembly comprises a fuel cell stack having fuel cells, the fuel cells defining an outlet positioned to remove an output product from the fuel cells and provide the output product to the combustor.

[0363] The propulsion system of any of the preceding clauses, wherein the fluid flow is an output product flow from the fuel cell.

[0364] The propulsion system of any of the preceding clauses, wherein the fuel cell assembly comprises a fuel processing unit, and wherein the fluid flow is a fuel processing unit flow from the fuel processing unit.

[0365] The propulsion system of any of the preceding clauses, wherein the fuel cell assembly further comprises a fuel cell stack having fuel cells, wherein the fuel processing unit flow is provided to the fuel cells.

[0366] The propulsion system of any of the preceding clauses, wherein the fuel cell assembly comprises a fuel cell stack and an enclosure at least partially surrounding the fuel cell stack, wherein the fluid flow is air within the enclosure.

[0367] The propulsion system of any of the preceding clauses, further comprising: a fuel delivery assembly, wherein the turbine comprises a combustion section having a combustor, wherein the fuel delivery assembly is configured to provide a fuel flow to the combustion section, and wherein the fluid flow is the fuel flow provided to the combustor.

[0368] The propulsion system of any of the preceding clauses, wherein the propulsion system is an aerospace propulsion system, and wherein the multi-gas sensor is configured to sense the gas composition data of the fluid flow into or to the turbine, the fuel cell assembly, or both, during flight operation of the propulsion system.

[0369] The propulsion system of any of the preceding clauses, wherein the multi-gas sensor is positioned within an environment within the turbine, the fuel cell assembly, or both, having a temperature of at least 400 degrees Celsius and up to 1000 degrees Celsius during normal operating conditions of the propulsion system.

[0370] The propulsion system of any of the preceding clauses, wherein the at least two gases and concentrations thereof include two or more of: H2, CO, CO2, CH4, H2O, N2, NH3, non-volatile particulate matter, and volatile particulate matter.

[0371] The propulsion system of any of the preceding clauses, wherein the multi-gas sensor has a weight of less than about 50 grams and has a size of less than about 20 mm in length by less than about 20 mm in width by less than about 20 mm in thickness.

[0372] The propulsion system of any of the preceding clauses, wherein the propulsion system includes a fluid line through which a fluid flow into or to the turbine, the fuel cell assembly, or both, is provided, and wherein the multi-gas sensor is positioned in alignment with the fluid line.

[0373] The propulsion system of any of the preceding clauses, wherein the turbine includes a housing, wherein the multi-gas sensor is positioned within the housing of the turbine.

[0374] The propulsion system of any of the preceding clauses, wherein the multi-gas sensor is positioned within an environment within the turbine, the fuel cell assembly, or both, having a temperature of at least 200 degrees Celsius during normal operating conditions of the propulsion system.

[0375] The propulsion system of any of the preceding clauses, wherein the propulsion system further includes a fluid line through which the fluid flow into or to the turbine, the fuel cell assembly, or both, is provided, and wherein the multi-gas sensor is not separate from the fluid line.

[0376] The propulsion system of any of the preceding clauses, wherein the multi-gas sensor comprises: a sensing circuit comprising one or more sensing elements; a management circuit configured to excite the one or more sensing elements with an alternating current at a frequency, the management circuit configured to measure one or more electrical responses of the one or more sensing elements in response to exciting the sensing elements with the alternating current at the frequency, the management circuit configured to determine one or more characteristics of the sensing circuit; and one or more processors configured to receive the one or more electrical responses of the one or more sensing elements and the one or more characteristics of the sensing circuit, wherein the one or more processors are further configured to determine the gas composition data based on the one or more electrical responses of the one or more sensing elements and the one or more characteristics of the sensing circuit.

[0377] The propulsion system of any of the preceding clauses, wherein the gas composition data is a type of gas and a concentration of gas.

[0378] The propulsion system of any of the preceding clauses, wherein the gas composition data is provided in real-time during operation of the propulsion system according to one or more of the clauses.

[0379] The propulsion system of any of the preceding clauses, wherein the multi-gas sensor comprises: a sensing circuit comprising one or more sensing elements; a management circuit configured to excite the one or more sensing elements with a variable control parameter, the management circuit configured to measure one or more electrical responses of the one or more sensing elements in response to exciting the sensing elements with the variable control parameter, the management circuit configured to determine one or more characteristics of the sensing circuit; and one or more processors configured to receive the one or more electrical responses of the one or more sensing elements and the one or more characteristics of the sensing circuit, wherein the one or more processors are further configured to determine the gas composition data based on the one or more electrical responses of the one or more sensing elements and the one or more characteristics of the sensing circuit.

[0380] A method of operating a propulsion system, the method comprising: receiving, from a multi-gas sensor, gas composition data of a fluid stream flowing into or toward a turbine of the propulsion system, a fuel cell assembly of the propulsion system, or both, the gas composition data comprising data indicative of at least two gas compositions; and controlling operation of the fuel cell assembly, a gas turbine engine comprising the turbine, or both, in response to the gas composition data received from the multi-gas sensor.

[0381] A method for operating a propulsion system, the propulsion system including a gas turbine engine and a fuel cell assembly, the method including operating the propulsion system to generate thrust for a vehicle; while operating the propulsion system, receiving gas composition data from a multi-gas sensor of one or more fluid streams flowing into or toward the gas turbine engine, the fuel cell assembly, or both; and in response to the received gas composition data, determining a health indicator of the gas turbine engine, the fuel cell assembly, or both.

[0382] The method of any of the preceding clauses, further comprising: receiving data indicative of an operating parameter of the propulsion system; wherein determining the health indicator includes detecting an anomaly, wherein detecting the anomaly includes comparing the received gas composition data to the received operating parameter.

[0383] The method of any of the preceding clauses, wherein detecting the anomaly includes detecting an incipient anomaly, wherein receiving gas composition data from a multi-gas sensor of one or more fluid streams flowing into or toward the gas turbine engine, the fuel cell assembly, or both includes receiving gas composition data from the multi-gas sensor of one or more fluid streams flowing into or toward the gas turbine engine, the fuel cell assembly, or both at a time resolution of one minute or less, and wherein the method further comprises: in response to the gas composition data of the one or more fluid streams, modifying operation of the gas turbine engine, the fuel cell assembly, or both to mitigate effects of the incipient anomaly.

[0384] The method of any of the preceding clauses, wherein determining the health indicator further includes determining an anomaly type, determining an affected component, or both.

[0385] The method of any of the preceding clauses, wherein the anomaly type is carbon deposition in a fuel processing unit of the fuel cell assembly, catalyst poisoning within the fuel processing unit, catalyst oxidation within the fuel processing unit, carbon deposition in a fuel cell of the fuel cell assembly, carbon deposition within a combustor of the gas turbine engine, fuel cell leakage, anode oxidation, or a combination thereof.

[0386] The method of any of the preceding clauses, wherein determining the health indicator of the gas turbine engine, the fuel cell assembly, or both includes determining a system health parameter.

[0387] The method of any of the preceding clauses, further comprising: based on the system health parameter, providing maintenance guidance.

[0388] The method according to one or more of these clauses, wherein determining the health indicator comprises detecting a component failure.

[0389] The method according to any of the preceding clauses, wherein determining the health indicator of the gas turbine engine, the fuel cell assembly, or both comprises determining a system health parameter, and wherein the method further comprises modifying an operating parameter of the gas turbine engine, the fuel cell assembly, or both in response to the system health parameter.

[0390] The method according to any of the preceding clauses, wherein determining the health indicator comprises detecting a component failure, and wherein the method further comprises controlling operation of the fuel cell assembly, the gas turbine engine, or both in response to detecting the component failure.

[0391] The method according to any of the preceding clauses, wherein the multi-gas sensor comprises: a sensing circuit comprising one or more sensing elements; a management circuit configured to excite the one or more sensing elements with an alternating current at a frequency, the management circuit configured to measure one or more electrical responses of the one or more sensing elements in response to exciting the sensing elements with the alternating current at the frequency, the management circuit configured to determine one or more characteristics of the sensing circuit; and one or more processors configured to receive the one or more electrical responses of the one or more sensing elements and the one or more characteristics of the sensing circuit, wherein the one or more processors are further configured to determine data of one or more fluid flows based on the one or more electrical responses of the one or more sensing elements and the one or more characteristics of the sensing circuit.

[0392] A control system for a propulsion system having a gas turbine engine and a fuel cell assembly, the control system comprising: a multi-gas sensor; and a controller comprising one or more processors and a memory, the memory storing instructions that, when executed by the one or more processors, are configured to control one or more operations of the propulsion system, the memory comprising: a data collection module configured to receive data indicative of gas composition data of one or more fluid flows flowing into or toward the gas turbine engine, the fuel cell assembly, or both during operation of the propulsion system; and an inference module configured to determine a health indicator of the gas turbine engine, the fuel cell assembly, or both in response to the gas composition data received from the data collection module.

[0393] The control system of any of the preceding clauses, wherein the memory further comprises: a reporting module configured to provide reporting information in response to the determined health indicator.

[0394] The control system of any of the preceding clauses, wherein the memory further comprises: a maintenance service module configured to provide maintenance guidance in response to the determined health indicator.

[0395] The control system of any of the preceding clauses, wherein the memory further comprises: a control module configured to modify an operating parameter of the fuel cell assembly, the gas turbine engine, or both in response to the determined health indicator.

[0396] A propulsion system comprising: a gas turbine engine comprising a combustion section having a combustor; and a modular fuel cell assembly comprising a first fuel cell string comprising a first processing unit and a first fuel cell stack comprising first fuel cells defining an outlet configured to provide output products from the first fuel cells to the combustor; and a second fuel cell string comprising a second processing unit and a second fuel cell stack comprising second fuel cells defining an outlet configured to provide output products from the second fuel cells to the combustor.

[0397] The propulsion system of any of the preceding clauses, further comprising: a control system comprising one or more sensors configured to sense gas composition data of a first fluid flow through the first fuel cell string and gas composition data of a second fluid flow through the second fuel cell string.

[0398] The propulsion system of any of the preceding clauses, wherein the control system further comprises a controller, wherein the controller is configured to receive the gas composition data of the first fluid flow through the first fuel cell string and the gas composition data of the second fluid flow through the second fuel cell string; and modify an operating parameter of the first fuel cell string, the second fuel cell string, or both in response to the received gas composition data.

[0399] The propulsion system of any of the preceding clauses, wherein the one or more sensors comprise a first sensor positioned in alignment with the first fuel cell string and a second sensor positioned in alignment with the second fuel cell string.

[0400] The propulsion system of any of the preceding clauses, wherein the one or more sensors comprise one or more multi-gas sensors.

[0401] The propulsion system of any of the preceding clauses, wherein the one or more sensors comprise a multi-gas sensor configured to sample the first fluid stream through the first fuel cell string and the second fluid stream through the second fuel cell string.

[0402] The propulsion system of any of the preceding clauses, wherein the one or more sensors are configured to sense the gas composition data of the first fluid stream through the first fuel cell string at a location downstream of the first processing unit and upstream of the first fuel cell stack, and the gas composition data of the second fluid stream through the second fuel cell string at a location downstream of the second processing unit and upstream of the second fuel cell stack.

[0403] The propulsion system of any of the preceding clauses, wherein the one or more sensors are configured to sense the gas composition data of the first fluid stream through the first fuel cell string at a location downstream of the first fuel cell stack, and the gas composition data of the second fluid stream through the second fuel cell string at a location downstream of the second fuel cell stack.

[0404] The propulsion system of any of the preceding clauses, wherein the modular fuel cell assembly further comprises a third fuel cell string.

[0405] The propulsion system of any of the preceding clauses, wherein the first fuel cell string is independently controllable relative to the second fuel cell string.

[0406] The propulsion system of any of the preceding clauses, wherein a first fluid stream through the first fuel cell string is independently controllable relative to a second fluid stream through the second fuel cell string.

[0407] The propulsion system of any of the preceding clauses, wherein the first fuel cell string and the second fuel cell string are independently connected within the gas turbine engine.

[0408] A method of operating a propulsion system, the propulsion system comprising a modular fuel cell assembly and a gas turbine engine, the method comprising: providing output products from a first fuel cell of a first fuel cell string of the modular fuel cell assembly and output products from a second fuel cell of a second fuel cell string of the modular fuel cell assembly to a combustor of a combustion section of the gas turbine engine; receiving gas composition data of a first fluid flow through the first fuel cell string and gas composition data of a second fluid flow through the second fuel cell string; and modifying an operating parameter of the first fuel cell string, the second fuel cell string, or both, in response to the received gas composition data.

[0409] The method of any of the preceding clauses, further comprising: receiving operating data of the modular fuel cell assembly, the gas turbine engine, an aircraft comprising the modular fuel cell assembly and the gas turbine engine, or a combination thereof, and wherein modifying the operating parameter comprises modifying the operating parameter of the first fuel cell string, the second fuel cell string, or both, in response to the received gas composition data and the received operating data.

[0410] The method of any of the preceding clauses, wherein the operating data comprises: a health indicator of the fuel cell assembly, the gas turbine engine, or both; a flight plan of an aircraft comprising the fuel cell assembly and the gas turbine engine; a maintenance plan of the aircraft; or a combination thereof.

[0411] The method of any of the preceding clauses, wherein the health indicator of the fuel cell assembly, the gas turbine engine, or both, comprises accumulated health information.

[0412] The method of any of the preceding clauses, wherein modifying the operating parameter comprises determining that a component of the first fuel cell string exceeds a health threshold; and increasing a power output of the first fuel cell string in response to determining that the component of the first fuel cell string exceeds the health threshold.

[0413] The method of any of the preceding clauses, wherein modifying the operating parameter comprises detecting an anomaly within the fuel cell assembly; and decreasing a power output of the first fuel cell string in response to detecting the anomaly within the fuel cell assembly.

[0414] The method of any of the preceding clauses, wherein detecting the anomaly within the fuel cell assembly comprises detecting the anomaly within the first fuel cell string.

[0415] The method of any of the preceding clauses, wherein receiving the gas composition data of the first fluid stream through the first fuel cell string and the gas composition data of the second fluid stream through the second fuel cell string comprises receiving the gas composition data from one or more gas sensors.

[0416] The method of any of the preceding clauses, wherein the one or more gas sensors comprise one or more multi-gas sensors.

[0417] A method of operating a propulsion system having a gas turbine engine and a fuel cell assembly, the fuel cell assembly comprising a fuel cell, the method comprising: receiving gas composition data of an output product from the fuel cell; and in response to the received gas composition data of the output product from the fuel cell, controlling operation of the fuel cell assembly, the gas turbine engine, or both.

[0418] The method of any of the preceding clauses, further comprising: operating the propulsion system during a flight operation; wherein receiving gas composition data of an output product from the fuel cell comprises receiving gas composition data of an output product from the fuel cell while operating the propulsion system during the flight operation.

[0419] The method of any of the preceding clauses, wherein receiving gas composition data of an output product from the fuel cell further comprises sensing composition data of an output product from the fuel cell at a time resolution of ten minutes or less.

[0420] The method of any of the preceding clauses, wherein receiving gas composition data of an output product from the fuel cell further comprises sensing composition data of an output product from the fuel cell at a time resolution of one minute or less.

[0421] The method of any of the preceding clauses, wherein controlling operation of the fuel cell assembly, the gas turbine engine, or both comprises controlling operation of the fuel cell assembly.

[0422] The method of any of the preceding clauses, wherein controlling operation of the fuel cell assembly comprises modifying an operating parameter of the fuel cell assembly in response to the received gas composition data of the output product from the fuel cell.

[0423] The method of any of the preceding clauses, wherein the operating parameters include a fuel flow rate to the fuel cell assembly, a fuel pressure, an equivalence ratio of a fuel processing unit of the fuel cell assembly, a steam-to-carbon ratio of the fuel processing unit of the fuel cell assembly, an air pressure, an air flow rate, an anode-to-cathode differential pressure, an anode inlet temperature, a cathode inlet temperature, a fuel cell stack temperature, a fuel cell current, a fuel cell utilization, a fuel cell air utilization, or a combination thereof.

[0424] The method of any of the preceding clauses, wherein controlling operation of the fuel cell assembly, the gas turbine engine, or both includes controlling the gas turbine engine.

[0425] The method of any of the preceding clauses, wherein controlling operation of the gas turbine engine includes modifying an operating parameter of the gas turbine engine in response to the received gas composition data from the output product of the fuel cell.

[0426] The method of any of the preceding clauses, wherein the operating parameters of the gas turbine engine include a combustor fuel flow rate, a combustor fuel air ratio, a fuel flow rate ratio between a combustor fuel flow and a fuel cell fuel flow, a variable bleed valve, a variable guide vane, a low pressure shaft speed, a high pressure shaft speed, a variable fan nozzle, an engine driven generator output, or a combination thereof.

[0427] The method of any of the preceding clauses, wherein receiving the gas composition data includes receiving the gas composition data from a gas sensor, and wherein controlling operation of the fuel cell assembly, the gas turbine engine, or both in response to the received composition data includes controlling operation of the fuel cell assembly, the gas turbine engine, or both using model-based control, and wherein using the model-based control includes determining estimated gas composition data using a model, and determining actual gas composition data based on the determined estimated gas composition data and the received gas composition data using a fusion filter.

[0428] The method of any of the preceding clauses, further comprising calibrating the model in response to the received gas composition data.

[0429] The method of any of the preceding clauses, further comprising detecting a fault of the gas sensor based on the determined estimated gas composition data.

[0430] The method of any of the preceding clauses, wherein the gas composition data of an output product includes a percentage of hydrogen within the output product.

[0431] A propulsion system comprising: a gas turbine engine including a combustion section having a combustor; a fuel cell assembly including a fuel cell stack having a fuel cell, the fuel cell defining an outlet configured to provide an output product from the fuel cell to the combustor; and a control system including a gas sensor positioned to determine gas composition data of the output product at a location downstream of the fuel cell and upstream of the combustor, the control system configured to control operation of the fuel cell assembly, the gas turbine engine, or both, in response to the determined gas composition data of the output product from the fuel cell.

[0432] The propulsion system of any of the preceding clauses, wherein the control system is further configured to determine the gas composition data of an output product from the fuel cell while operating the propulsion system during flight operations.

[0433] The propulsion system of any of the preceding clauses, wherein the control system is configured to determine the gas composition data of an output product from the fuel cell at a time resolution of one minute or less.

[0434] The propulsion system of any of the preceding clauses, wherein the control system is configured to control operation of the fuel cell assembly by modifying an operating parameter of the fuel cell assembly, and wherein the operating parameter includes: a fuel flow rate to the fuel cell assembly, a fuel pressure, an equivalence ratio of a fuel processing unit of the fuel cell assembly, a steam-to-carbon ratio of the fuel processing unit of the fuel cell assembly, an air pressure, an air flow rate, an anode-to-cathode differential pressure, an anode inlet temperature, a cathode inlet temperature, a fuel cell stack temperature, a fuel cell current, a fuel cell utilization, a fuel cell air utilization, or a combination thereof.

[0435] The propulsion system of any of the preceding clauses, wherein the control system is configured to control operation of the gas turbine engine by modifying an operating parameter of the gas turbine engine, and wherein the operating parameter includes: a combustor fuel flow rate, a combustor fuel-to-air ratio, a fuel flow rate ratio between a combustor fuel flow and a fuel cell fuel flow, a variable bleed valve, a variable guide vane, a low pressure shaft speed, a high pressure shaft speed, a variable fan nozzle, an engine driven generator output, or a combination thereof.

[0436] The propulsion system of any of the preceding clauses, wherein the gas composition data includes a percentage of hydrogen within the output product.

[0437] The method of any of the preceding clauses, wherein receiving gas composition data from output products of the fuel cell further comprises sensing composition data from output products of the fuel cell at a time resolution of one second or less.

[0438] The method of any of the preceding clauses, wherein receiving gas composition data from output products of the fuel cell further comprises sensing composition data from output products of the fuel cell with a multi-gas sensor operated with variable control parameters.

[0439] The propulsion system of any of the preceding clauses, wherein the one or more multi-gas sensors are positioned within an environment having a temperature of at least 600 degrees Celsius and up to 1000 degrees Celsius during normal operating conditions of the propulsion system.

[0440] The propulsion system of any of the preceding clauses, wherein the one or more multi-gas sensors are configured to sense gas composition data of at least two types of gases and their concentrations.

[0441] The propulsion system of any of the preceding clauses, wherein the one or more sensors comprise one or more multi-gas sensors configured to sense the gas composition data in real time and operated with variable control parameters.

Claims

1. A propulsion system, characterized in that, include: A gas turbine engine, the gas turbine engine including a combustion section with a burner; Modular fuel cell assembly, the modular fuel cell assembly including A first fuel cell string, the first fuel cell string including a first processing unit and a first fuel cell stack, the first fuel cell stack including a first fuel cell, the first fuel cell defining an outlet, the outlet being configured to provide output products from the first fuel cell to the burner; A second fuel cell string, the second fuel cell string including a second processing unit and a second fuel cell stack, the second fuel cell stack including a second fuel cell, the second fuel cell defining an outlet configured to provide output products from the second fuel cell to the burner; as well as A control system comprising one or more sensors configured to sense gas composition data of a first fluid flow through the first fuel cell string and gas composition data of a second fluid flow through the second fuel cell string; The control system is configured as follows: Detecting anomalies within the fuel cell assembly; the anomalies are used to indicate that the component has deteriorated beyond its nominal level. In response to the anomaly, the power output of the first fuel cell string is reduced; reducing the power output of the first fuel cell string includes at least one of the following: The fuel flow to the second fuel cell string is reduced to the fuel flow to the first fuel cell string; Increase the fuel flow to the second fuel cell string; or Increase power extraction from separate power sources such as gas turbine engines, fuel cell components, or aircraft.

2. The propulsion system according to claim 1, characterized in that, The control system further includes a controller, wherein the controller is configured to Receive the gas composition data of the first fluid flow through the first fuel cell string and the gas composition data of the second fluid flow through the second fuel cell string; and In response to the received gas composition data, the operating parameters of the first fuel cell string, the second fuel cell string, or both are modified.

3. The propulsion system according to claim 1, characterized in that, The one or more sensors include a first sensor and a second sensor, the first sensor being positioned to align with the first fuel cell string and the second sensor being positioned to align with the second fuel cell string.

4. The propulsion system according to claim 1, characterized in that, The one or more sensors include one or more multi-gas sensors configured to sense the gas composition data in real time and operated using variable control parameters.

5. The propulsion system according to claim 4, characterized in that, The one or more multi-gas sensors are located in an environment with a temperature of at least 600 degrees Celsius and up to 1000 degrees Celsius during normal operating conditions of the propulsion system.

6. The propulsion system according to claim 4, characterized in that, The one or more multi-gas sensors are configured to sense gas composition data of at least two types of gases and their concentrations.

7. The propulsion system according to claim 1, characterized in that, The one or more sensors include a multi-gas sensor configured to sample the first fluid flow through the first fuel cell string and the second fluid flow through the second fuel cell string.

8. The propulsion system according to claim 1, characterized in that, The one or more sensors are configured to sense the gas composition data of the first fluid flow through the first fuel cell string at a location downstream of the first processing unit and upstream of the first fuel cell stack, and the gas composition data of the second fluid flow through the second fuel cell string at a location downstream of the second processing unit and upstream of the second fuel cell stack.

9. The propulsion system according to claim 1, characterized in that, The one or more sensors are configured to sense the gas composition data of the first fluid flow through the first fuel cell string at a location downstream of the first fuel cell stack, and the gas composition data of the second fluid flow through the second fuel cell string at a location downstream of the second fuel cell stack.

10. The propulsion system according to claim 1, characterized in that, The modular fuel cell assembly further includes a third fuel cell string.

11. The propulsion system according to claim 1, characterized in that, The first fuel cell string is independently controllable relative to the second fuel cell string.

12. The propulsion system according to claim 11, characterized in that, The first fluid flow through the first fuel cell string is independently controllable relative to the second fluid flow through the second fuel cell string.

13. The propulsion system according to claim 1, characterized in that, The first fuel cell string and the second fuel cell string are independently connected within the gas turbine engine.

14. A method of operating a propulsion system, said propulsion system comprising a modular fuel cell assembly and a gas turbine engine, characterized in that, The method includes: The combustor of the combustion section of the gas turbine engine is supplied with the output products of the first fuel cell from the first fuel cell string of the modular fuel cell assembly and the output products of the second fuel cell from the second fuel cell string of the modular fuel cell assembly; Receive gas composition data of a first fluid flow through the first fuel cell string and gas composition data of a second fluid flow through the second fuel cell string; and In response to the received gas composition data, modify the operating parameters of the first fuel cell string, the second fuel cell string, or both; The step of modifying the operating parameters of the first fuel cell string, the second fuel cell string, or both includes: Detecting anomalies within the fuel cell assembly; the anomalies are used to indicate that the component has deteriorated beyond its nominal level. In response to the anomaly, the power output of the first fuel cell string is reduced; Reducing the power output of the first fuel cell string includes at least one of the following: The fuel flow to the second fuel cell string is reduced to the fuel flow to the first fuel cell string; Increase the fuel flow to the second fuel cell string; or Increase power extraction from separate power sources such as gas turbine engines, fuel cell components, or aircraft.

15. The method according to claim 14, characterized in that, Further includes: The system receives operational data of the modular fuel cell assembly, the gas turbine engine, an aircraft including the modular fuel cell assembly and the gas turbine engine, or a combination thereof, and wherein modifying the operational parameters includes modifying the operational parameters of the first fuel cell string, the second fuel cell string, or both in response to received gas composition data and the received operational data.

16. The method according to claim 15, characterized in that, The operational data mentioned therein includes: health indicators of the fuel cell assembly, the gas turbine engine, or both; flight plans of the aircraft including the fuel cell assembly and the gas turbine engine; maintenance plans of the aircraft; or combinations thereof.

17. The method according to claim 16, characterized in that, The health indicator of the fuel cell assembly, the gas turbine engine, or both includes accumulated health information.

18. The method according to claim 14, characterized in that, Modifying the operating parameters includes It was determined that a component of the first fuel cell string exceeded a health threshold; and In response to determining that a component of the first fuel cell string exceeds the health threshold, the power output of the first fuel cell string is increased.

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