Solid oxide fuel cell assembly

Abstract

A method for operating a fuel cell assembly, the fuel cell assembly including a fuel cell stack having a solid oxide fuel cell having an anode, a cathode, and an electrolyte, the method including determining a temperature set point for the fuel cell stack, an output product of the fuel cell stack, or both, and in response to the determined temperature set point, controlling a volume of oxidant provided to the anode to control a temperature of the fuel cell stack, a temperature of the output product of the fuel cell stack, or both.

Description

Technical Field

[0001] This disclosure relates to fuel cell components, and more specifically, to solid oxide fuel cell components that can be incorporated into aerospace propulsion systems. 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] Figure 1 This is a cross-sectional view of a gas turbine engine according to an exemplary aspect of this disclosure.

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

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

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

[0010] Figure 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] Figure 6 This is a flowchart of a method for starting a gas turbine engine according to an exemplary aspect of this disclosure.

[0012] Figure 7 is a flowchart of a method for starting a fuel cell assembly according to an example aspect of the present disclosure.

[0013] Figure 8 is a flowchart of a method for starting a fuel cell assembly according to another example aspect of the present disclosure.

[0014] Figure 9 is a flowchart of a method for starting a fuel cell assembly according to yet another example aspect of the present disclosure.

[0015] Figure 10 is a flowchart of a method for starting a fuel cell assembly according to still another example aspect of the present disclosure.

[0016] Figure 11 is a schematic diagram of a gas turbine engine including an integrated fuel cell and combustor assembly according to another example aspect of the present disclosure.

[0017] Figure 12 is a schematic diagram of a gas turbine engine including an integrated fuel cell and combustor assembly according to yet another example aspect of the present disclosure.

[0018] Figure 13 is a schematic diagram of a gas turbine engine including an integrated fuel cell and combustor assembly according to still another example aspect of the present disclosure.

[0019] Figure 14 is a flowchart of a method for performing a hot start of a fuel cell assembly according to still another example aspect of the present disclosure.

[0020] Figure 15 is a schematic diagram of a gas turbine engine including an integrated fuel cell and combustor assembly according to another example aspect of the present disclosure.

[0021] Figure 16 is Figure 15 is a close-up schematic of a fuel cell of an example integrated fuel cell and combustor assembly of

[0022] Figure 17 is a chart showing the open circuit operating voltage (OCV) percentage of a fuel cell stack having a nickel / yttria stabilized zirconia anode during a redox cycle.

[0023] Figure 18 is a chart showing the open circuit operating voltage (OCV) percentage of a fuel cell stack having a nickel / yttria stabilized zirconia anode during a redox cycle.

[0024] Figure 19is a graph showing the hydrogen stack output percentage of a fuel cell stack with a lanthanum strontium titanate / gadolinium oxide doped ceria anode during a redox cycle.

[0025] Figure 20 is a flowchart of a method for starting a fuel cell assembly according to another example aspect of the disclosure.

[0026] Figure 21 is a flowchart of a method for operating a gas turbine engine and a fuel cell assembly according to another example aspect of the disclosure.

[0027] Figure 22 is a flowchart of a method for shutting down a gas turbine engine and cooling a fuel cell assembly according to an example aspect of the disclosure.

[0028] Figure 23 is a schematic diagram of a control system according to the disclosure. DETAILED DESCRIPTION

[0029] Reference will now be made in detail to the current embodiments of the disclosure, one or more examples of which are illustrated in the drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the disclosure.

[0030] 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, unless otherwise indicated, the description herein is to be considered as illustrative only and not as restricting the scope of the disclosure.

[0031] For purposes of the description hereinafter, the terms "upper", "lower", "right", "left", "vertical", "horizontal", "top", "bottom", "lateral", "longitudinal", and derivatives thereof shall relate to the embodiments as they are oriented in the drawings. However, it is to be understood that the embodiments can assume various alternative orientations and, unless otherwise specified, the specific embodiments can be implemented in any orientation. It is also to be understood that the specific devices illustrated in the attached drawings, and described herein, are simply exemplary embodiments of the disclosure. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless otherwise indicated.

[0032] 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.

[0033] 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.

[0034] The terms "upstream" and "downstream" refer to the relative direction with respect to the flow of fluid in a fluid path. For example, "upstream" refers to the direction from which the fluid flows and "downstream" refers to the direction to which the fluid flows.

[0035] Unless otherwise specified herein, the terms "coupled," "fixed," "attached to," and the like, mean either directly coupled, fixed, or attached by one or more intermediate components or features.

[0036] The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0037] The term "at least one of' in the context of, for example, "at least one of A, B, and C" or "at least one of A, B, or C" means only A, only B, only C, or any combination of A, B, and C.

[0038] 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,” is 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.

[0039] 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, 2-9, 3-8, etc. Furthermore, such an interpretation applies regardless of the capabilities of a particular measurement instrument. For example, an instrument that measures to the nearest one-tenth of a unit can not be capable of discerning between 1.5 and 1.6 on a range from 1-10, even though the instrument is certainly capable of making the distinction between 1.5 and 1.6 on a range from 1.0-1.1. It is in such instances that the present disclosure will serve its most useful purpose by widening the range interpreted by the instrument to the full range covered by the combination of precision with which the individual values are quantified and the precision of the instrument.

[0040] "Third flow" as used herein refers to a non-primary gas flow that is capable of increasing 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). The 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).

[0041] In certain example embodiments, the operating temperature of the airflow through the third stream can be below a maximum compressor discharge temperature of the engine, and more specifically, can be below 350 degrees Fahrenheit (such as below 300 degrees Fahrenheit, such as below 250 degrees Fahrenheit, such as below 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 airflow through the third stream and the separate fluid stream. Further, in certain example embodiments, the airflow through the third stream 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.

[0042] Further, in certain example embodiments, aspects of the airflow through the third stream (e.g., airflow, mixing, or exhaust properties), and thus the above example percentages of total thrust contribution, can be passively adjusted during engine operation or purposefully modified through the use of engine control features (such as fuel flow, electric machine power, variable stators, variable inlet guide vanes, valves, variable exhaust geometry, or fluidic features) to adjust or optimize overall system performance across a wide range of potential operating conditions.

[0043] The term “turbomachine” or “turbomachinery” 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.

[0044] The term “gas turbine engine” refers to an engine having 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.

[0045] The terms “low” and “high,” or their respective comparative forms (e.g., more “low” and more “high,” as 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 of the engine.

[0046] 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 some 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, etc.

[0047] (i) Figure 1 Embodiments of the application

[0048] Reference is now made to the drawings, in which like reference numerals refer to like elements throughout the several views, Figure 1 A schematic cross-sectional view of an engine in accordance with example embodiments of the present disclosure is provided. The engine can be incorporated into a vehicle. For example, the engine can be an aeroengine incorporated into an aircraft. However, alternatively, the engine can be any other suitable type of engine for any other suitable vehicle.

[0049] For the depicted embodiment, the engine is configured as a high-bypass turbofan engine 100. As shown, the turbofan engine 100 defines an axial direction A (extending parallel to a centerline axis 101 provided for reference), a radial direction R, and a circumferential direction (extending about the axial direction A; not shown in the drawings). Generally, the turbofan engine 100 includes a fan section 102 and a turbine machine 104 disposed downstream of the fan section 102. Figure 1 Figure 1

[0050] ​​The depicted exemplary turbine engine 104 generally includes a substantially tubular outer casing 106 defining an annular inlet 108. The casing 106 encloses in serial flow relationship: a compressor section including a booster 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 ejection exhaust nozzle section 120. The compressor section, the combustion section 114, and the turbine section together at least partially define a core air flowpath 121 extending from the annular inlet 108 to the ejection 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.

[0051] For the depicted embodiment, the fan section 102 includes a fan 126 having a plurality of fan blades 128 coupled to a disk 130 in a spaced apart manner. The plurality of fan blades 128 and the disk 130 are rotatable together about the centerline axis 101 by the LP shaft 124. The disk 130 is covered by a rotatable forward hub 132 that is aerodynamically shaped to facilitate airflow through the plurality of fan blades 128. In addition, an annular fan casing or outer nacelle 134 is disposed circumferentially around the fan 126 and / or at least a portion of the turbine engine 104. The nacelle 134 is supported relative to the turbine engine 104 by a plurality of circumferentially spaced outlet guide vanes 136. A downstream section 138 of the nacelle 134 extends over an outer portion of the turbine engine 104 so as to define a bypass airflow passage 140 therebetween.

[0052] In this manner, it will be appreciated that the turbofan engine 100 generally includes a first flow (e.g., the core air flowpath 121) and a second flow (e.g., the bypass airflow passage 140) extending parallel to the first flow. In certain exemplary embodiments, the turbofan engine 100 can further define a third flow extending, for example, from the LP compressor 110 to the bypass airflow passage 140 or to the ambient. With this configuration, the LP compressor 110 can generally include a first compressor stage configured as a ducted inter-fan and a downstream compressor stage. An inlet of the third flow can be positioned between the first compressor stage and the downstream compressor stage.

[0053] Still referring to Figure 1, the turbofan engine 100 additionally includes an accessory gearbox 142 and a fuel delivery system 146. The fuel delivery system 146 can be an aircraft fuel supply, such as an aircraft fuel supply for a propulsion system of an aircraft. For the illustrated embodiment, the accessory gearbox 142 is located within the shroud / housing 106 of the turbine 104. Additionally, it will be appreciated that, for Figure 1 For the illustrative embodiment depicted in FIG. 1, the accessory gearbox 142 is mechanically coupled to and rotatable with one or more shafts or spools of the turbine 104. For example, in the depicted example embodiment, the accessory gearbox 142 is mechanically coupled to and rotatable with the HP shaft 122 by a suitable gear train 144. The accessory gearbox 142 can provide power to one or more suitable accessory systems of the turbofan engine 100 during at least certain operations, and can further provide power back to the turbofan engine 100 during other operations. For example, for the illustrated embodiment, the accessory gearbox 142 is coupled to a starter motor / generator 152. The starter motor / generator can be configured to extract power from the accessory gearbox 142 and the turbofan engine 100 during certain operations to generate electricity, and can provide power back to the accessory gearbox 142 and the turbofan engine 100 (e.g., to the HP shaft 122) during other operations to add mechanical work back to the turbofan engine 100 (e.g., for starting the turbofan engine 100).

[0054] Further, the fuel delivery system 146 generally includes a fuel source 148, such as a fuel tank, and one or more fuel delivery lines 150. The one or more fuel delivery lines 150 provide a 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 greater detail below, the combustion section 114 includes an integrated fuel cell and combustor assembly 200. For the described embodiment, the one or more fuel delivery lines 150 provide the fuel flow to the integrated fuel cell and combustor assembly 200.

[0055] However, it will be appreciated that, Figure 1 The example turbofan engine 100 depicted in FIG. 1 is provided by way of example only. In other example embodiments, any other suitable gas turbine engine can be used with aspects of the present disclosure. For example, in other embodiments, the turbofan engine can be any other suitable gas turbine engine, such as a turboshaft engine, a turboprop engine, a turbojet engine, etc. In this manner, it will be further appreciated that, in other embodiments, the gas turbine engine can have any other suitable configuration, such as any other suitable number or arrangement of shafts, compressors, turbines, fans, etc. Further, although Figure 1The exemplary gas turbine engine depicted herein is schematically shown as a direct-drive fixed-pitch turbofan engine, but in other embodiments, the gas turbine engine of this disclosure may be a geared gas turbine engine (i.e., including a gearbox between a fan 126 and a shaft (such as LP shaft 124) driving the fan), a variable-pitch gas turbine engine (i.e., including a fan 126 having a plurality of fan blades 128 capable of rotating about their respective pitch axes), etc. Furthermore, although the exemplary turbofan engine 100 includes a ducted fan 126, in other exemplary aspects, the turbofan engine 100 may include a non-ducted fan 126 (or an open rotor fan) without a nacelle 134. Moreover, although not depicted herein, in other embodiments, the gas turbine engine may be any other suitable type of gas turbine engine, such as a marine gas turbine engine.

[0056] (ii) Figure 2 Implementation examples

[0057] Now for reference Figure 2 The illustration schematically shows a portion of a combustion section 114 according to an embodiment of the present disclosure, which includes... Figure 1 Gas turbine engine 100 (above about Figure 1 Described as part of the integrated fuel cell and burner assembly 200 used in the turbofan engine 100.

[0058] It will be understood that the combustion section 114 includes a compressor diffuser nozzle 202 and extends generally along the axial direction A between an upstream end and a downstream end. The combustion section 114 is fluidly connected via the compressor diffuser nozzle 202 to the compressor section at the upstream end and to the turbine section at the downstream end.

[0059] The integrated fuel cell and burner assembly 200 generally includes fuel cell assembly 204. Figure 2 Only a partial description is provided; see also Figures 3 to 5 The 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.

[0060] The dome assembly 212 is disposed proximate an 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 a swirler assembly 216. The swirler assembly 216 also includes an opening for receiving and retaining a fuel flow line 218. The fuel flow line 218 is further coupled to the fuel source 148 (see Figure 1 ) disposed outside the outer casing 220 in the radial direction R, and is configured to receive fuel from the fuel source 148. In this manner, the fuel flow line 218 can be fluidically coupled to one or more fuel delivery lines 150 described above with reference to Figure 1 .

[0061] The swirler assembly 216 can include a plurality of swirlers (not shown) configured to swirl the compressed fluid prior to injection of the compressed fluid into the combustion chamber 228 to generate the combustion gas. 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.

[0062] During operation, the compressor diffuser nozzle 202 is configured to direct the compressed fluid 230 from the compressor section to the combustor 206, where the compressed fluid 230 is configured to mix with the fuel within the swirler assembly 216 and combust within the combustion chamber 228 to generate the combustion gas. The combustion gas is provided to the turbine section to drive one or more turbines (e.g., the high pressure turbine 116 and the low pressure turbine 118) of the turbine section.

[0063] During operation of the gas turbine engine 100 including the integrated fuel cell and combustor assembly 200, the 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 the 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 is configured to provide a portion of the fuel and air flow to the combustion chamber 228, the dedicated fuel cell igniter 233 is positioned downstream of at least a portion of the fuel cell, and in particular, downstream of at least a portion of the fuel cell stack (as described below). In this manner, the dedicated fuel cell igniter 233 can more effectively combust the output products of the fuel cell. Figure 2

[0064] As described above and Figure 2 ​As schematically depicted, the integrated fuel cell and combustor assembly 200 further includes a fuel cell assembly 204. The depicted example fuel cell assembly 204 includes a first fuel cell stack 232 and a second fuel cell stack 234. More specifically, the first fuel cell stack 232 is constructed with the outer liner 210, and the second fuel cell stack 234 is constructed with the inner liner 208. Still more specifically, the first fuel cell stack 232 is integrated with the outer liner 210, and the second fuel cell stack 234 is integrated with the inner liner 208. Operation of the fuel cell assembly 204, and more specifically, the fuel cell stacks (e.g., the first fuel cell stack 232 or the second fuel cell stack 234) of the fuel cell assembly 204, will be described in greater detail below.

[0065] For the described embodiment, the fuel cell assembly 204 is constructed as a solid oxide fuel cell (“SOFC”) assembly, with the first fuel cell stack 232 being constructed as a first SOFC fuel cell stack, and the second fuel cell stack 234 being constructed 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 the 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.

[0066] 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).

[0067] The first power converter 236 controls the 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 the 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).

[0068] 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 configured in the same manner as the fuel cell controller 240 described below with reference to Figure 5

[0069] (iii) Figure 3 and 4 embodiments.

[0070] 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 Figure 3 , a simplified cross-sectional view of an 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 Figure 3 , the second fuel cell stack 234 can be configured in a similar manner.

[0071] 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 Figure 3 the fuel cells 242 visible in Figure 2 may be a single ring of fuel cells 242, with the fuel cells 242 stacked together along the axial direction A (see ), to form the first fuel cell stack 232. In another example, a plurality of additional rings of fuel cells 242 can be placed on top of one another to form the first fuel cell stack 232 elongated along the centerline axis 101.

[0072] Figure 5 ​The fuel cells 242 in the first fuel cell stack 232 are positioned to receive exhaust air 244 from, for example, the compressor section and fuel 246 from the fuel delivery system 146. The fuel cells 242 use the air 244 and at least some of the fuel 246 to generate an electrical current and direct partially oxidized fuel 246 and unused portions of air 248 radially toward the centerline axis 101 into the combustion chamber 228. The integrated fuel cell and combustor assembly 200 combusts the partially oxidized fuel 246 and air 248 in the combustion chamber 228 into combustion gases that are directed downstream into the turbine section to drive or assist in driving one or more turbines therein.

[0073] Further, reference is now made to Figure 4 A perspective view of the first fuel cell stack 232 of the integrated fuel cell and combustor assembly 200 is provided as Figure 2 A perspective view of the first fuel cell stack 232 of the integrated fuel cell and combustor assembly 200 is provided as

[0074] The depicted first fuel cell stack 232 includes a housing 250 having a combustion outlet side 252 and a side 254 opposite the combustion outlet side 252, a fuel and air inlet side 256 and a side 588 opposite the fuel and air inlet side 256, and sides 260, 262. The side 260, the side 258, and the side 254 are not visible in the perspective view of Figure 4

[0075] 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., the side 258). It will thus be further appreciated that the combustion outlet side 252 includes a plurality of combustion outlets 264, each 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 combustion chamber 228 and, during operation, are combusted to generate combustion gases that are used to generate thrust for the gas turbine engine 100 (and a carrier / aircraft incorporating the gas turbine engine 100).

[0076] ​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 vessels of a fuel handling 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 handling 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.

[0077] In certain example embodiments, Figures 2 to 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 entire contents of which are incorporated herein by reference. It will be further understood that, Figure 2 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.

[0078] (iv) Figure 5 Embodiments of the present disclosure

[0079] Reference is now made to Figure 5 Operation of the integrated fuel cell and combustor assembly 200 according to example embodiments of the present disclosure will be described. More specifically, Figure 5 A schematic view 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 gas turbine engines and integrated fuel cell and combustor assemblies described in U.S. Patent Application Publication No. 2020 / 0194799 Al, filed December 17, 2018, the entire contents of which are incorporated herein by reference. Figures 1 to 4

[0080] It will thus be appreciated that the gas turbine engine 100 generally includes a fan section 102 having a fan 126, a LP compressor 110, a HP compressor 112, a combustion section 114, a HP turbine 116, and a LP turbine 118. The combustion section 114 generally includes an integrated fuel cell and combustor assembly 200 having a combustor 206 and a fuel cell assembly 204.

[0081] ​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 also includes a fuel pump 272 and a flow splitter 274, and that 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 15C. The flow splitter 274 splits the flow of fuel 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 the 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 flow of fuel 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 151A associated with the first fuel delivery line 150A (e.g., for controlling the first fuel flow), a second fuel valve 151B associated with the second fuel delivery line 150B (e.g., for controlling the second fuel flow), and a third fuel valve 151C associated with the third fuel delivery line 150C (e.g., for controlling the third fuel flow).

[0082] The gas turbine engine 100 further includes a compressor discharge system and an airflow delivery system. More specifically, the compressor discharge 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.

[0083] 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 discharge system if the compressor air source is insufficient or unavailable.

[0084] The compressor discharge system (and air flow supply conduit 288) is in air flow communication with the air flow delivery system for providing compressed air flow to the fuel cell assembly 204, as will be explained in greater detail below.

[0085] Still referring to Figure 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.

[0086] 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.

[0087] The anode side 298 can support an electrochemical reaction that generates electricity. Fuel can be oxidized in the anode side 298 using oxygen ions received from the cathode side 296 via diffusion through the electrolyte 300. This reaction can produce heat, steam, 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 returned to the cathode side 296 from the energy consuming devices via oxygen reduction of a cathode oxidant.

[0088] The cathode side 296 can be coupled to a source of cathode oxidant, such as oxygen in the atmosphere. Cathode oxidant is defined as an oxidant supplied to the cathode side 296 that is used by the fuel cell system in generating electricity. The cathode side 296 can be permeable to oxygen ions received from the cathode oxidant.

[0089] The electrolyte 300 can be in communication with the anode side 298 and the cathode side 296. The electrolyte 300 can pass oxygen ions from the cathode side 296 to the anode side 298, and can have little or no electrical conductivity to prevent free electrons from passing from the cathode side 296 to the anode side 298.

[0090] The anode side of a solid oxide fuel cell, such as fuel cell stack 294, can be composed of nickel / yttria stabilized zirconia (Ni / YSZ) cermet. The 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.

[0091] Fuel cell stack 294 is disposed downstream of LP compressor 110, HP compressor 112, or both. Further, as will be understood from the description above regarding Figure 2 It will be understood from the description above regarding

[0092] As shown in FIG. 2, fuel cell stack 294 is disposed downstream of LP compressor 110, HP compressor 112, or both. Further, as will be understood from the description above regarding Figure 5 Fuel cell assembly 204 also includes a fuel processing unit 304 and an air processing unit 306, as shown in FIG. 3. Fuel processing unit 304 can be any suitable structure for generating a hydrogen-rich fuel stream. For example, fuel processing unit 304 can include a fuel reformer or catalytic partial oxidation converter (CPO x ) for producing a hydrogen-rich fuel stream for fuel cell stack 294. Air processing 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 processing unit includes a preburner system that operates based on a fuel stream through second fuel delivery line 150B, configured for raising the temperature of air through combustion, for example, during transient conditions such as start-up, shutdown, and abnormal situations.

[0093] In the depicted example embodiment, fuel processing unit 304 and air processing unit 306 are manifolded together within a housing 308 to provide conditioned air and fuel to fuel cell stack 294.

[0094] It will be understood, however, that fuel processing 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 processing unit 304 can also include a reformer integrated with fuel cell stack 294. Similarly, it will be understood that Figure 5The 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).

[0095] As noted 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 the 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 the fuel processing unit 304, a cathode air flow conduit 314 and associated cathode air flow valve 316 for providing air flow to the air handling unit 306, and a cathode bypass air conduit 318 and associated cathode bypass air valve 320 for providing air flow directly to the fuel cell stack 294 (or more precisely, to the cathode side 296 of the fuel cell). The fuel delivery system 146 is configured to provide a first fuel stream to the fuel processing unit 304 through the first fuel delivery line 150A, and to provide a second fuel stream (e.g., as fuel for a pre-combustor system, if provided) to the air handling unit 306 through the second fuel delivery line 150B.

[0096] The fuel cell stack 294 outputs electrical power generated as a fuel cell power output 322. In addition, the fuel cell stack 294 directs cathode air exhaust and anode fuel exhaust (both not labeled for clarity) into the combustion chamber 228 of the combustor 206.

[0097] In operation, the air handling unit 306 is configured to heat / cool a portion of the compressed air entering through the cathode air flow conduit 314 to generate treated air to be directed into the fuel cell stack 294 to facilitate the fuel cell stack 294 functioning. The air handling unit 306 receives the second fuel stream from the second fuel delivery line 150B, and can, for example, combust this 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 functioning. The air treated 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 treated 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.

[0098] In addition, as Figure 5As shown in the embodiment of FIG. 3, the first fuel flow through the first fuel delivery line 150A is directed to the fuel processing unit 304 for producing a hydrogen-rich fuel flow (e.g., optimizing the hydrogen content of the fuel flow) to also be fed into the fuel cell stack 294. It will be appreciated, and as discussed below, that the flow of air (process air and bypass air) to the fuel cell stack 294 (e.g., cathode side 296) and the fuel from the fuel processing unit 304 to the fuel cell stack 294 (e.g., anode side 298) can facilitate power generation.

[0099] As the inlet air to 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 to the fuel cell stack 294 that is discharged from the compressor section can be affected by the air temperature changes that occur during different flight phases. By way of illustrative example only, air within a particular location in the compressor section of the gas turbine engine 100 can operate 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.

[0100] Accordingly, by fluidly connecting the air processing unit 306 between the compressor section and the fuel cell stack 294, the air processing unit 306 can be used as a control device or system to maintain the air processed by the air processing 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 processing unit 306. By increasing the fuel flow to the air processing unit 306, the temperature of the air flow to the fuel cell stack 294 can be increased. By decreasing the fuel flow to the air processing unit 306, the temperature of the air flow to the fuel cell stack 294 can be decreased. Alternatively, no fuel can be delivered to the air processing unit 306 to prevent the air processing unit 306 from increasing and / or decreasing the temperature of the air discharged from the compressor section and directed into the air processing unit 306.

[0101] Further, as depicted in dashed lines, the fuel cell assembly 204 further includes an air flow bypass conduit 321 extending around the fuel cell to allow a portion or all of the air flow 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 enter the combustion chamber 228 directly. The air flow 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 reforming fuel from the fuel handling unit 304 to bypass the anode side 298 of the fuel cell and enter the combustion chamber 228 directly.

[0102] As briefly mentioned above, the fuel cell stack 294 converts the anode fuel flow from the fuel handling unit 304 and the air processed by the air handling unit 306 sent to the fuel cell stack 294 into electrical energy in the form of DC current, i.e., a fuel cell power output 322. This fuel cell power output 322 is directed to a 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.

[0103] Still referring to Figure 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.

[0104] Further, as Figure 5Further illustratively depicted, the propulsion system, the 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, combinations thereof, and the like.

[0105] The controller 240 is operably connected to various sensors, valves, and the like within at least one of the gas turbine engine 100 and the fuel delivery system 146. More particularly, 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 sensors 330 of the gas turbine engine 100 and fuel cell sensors 302. As will be appreciated 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 valves of the airflow delivery system that direct the airflow discharged from the compressor section, and the valves of the fuel delivery system 146 that direct the flow of fuel within the gas turbine engine 100).

[0106] 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.

[0107] 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., method 600) 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 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.

[0108] 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 interfaces.

[0109] The technology discussed herein makes reference to computer-based systems, actions taken by and information sent to and from computer-based systems. It is understood 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.

[0110] 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 hydrogen fuel, and the fuel delivery assembly 146 is configured to provide hydrogen fuel to the integrated fuel cell and combustor assembly 200, particularly to the fuel cell assembly 204, the fuel cell assembly 204 can not require a fuel processing unit 304.

[0111] (v) Introduction to ground starting

[0112] As will be appreciated from the description herein, ground starting of a gas turbine engine including an integrated fuel cell and combustor assembly, such as the one described above with reference to Figures 1 to 5 one or more example integrated fuel cell and combustor assemblies 200 described above, can need to be performed in a coordinated manner in order to address various issues associated with start-up times, environmental and safety standards, etc. As used herein, the term "ground starting" with respect to a gas turbine engine refers to accelerating the gas turbine engine from an off position (or a slow rotation position, e.g., less than about 50 revolutions per minute) to at least ground idle operation.

[0113] For example, as briefly mentioned above, in at least certain example embodiments, an anode of a solid oxide fuel cell (SOFC) can be composed of a porous cermet that includes nickel and yttria-stabilized zirconia. The nickel component can provide electrical conductivity, electrochemical capability, and fuel handling capability. The nickel component can also enhance certain mechanical properties of the fuel cell. However, nickel is a relatively unstable metal at high temperatures, and in particular, at temperatures above approximately 350 degrees Celsius ("°C") to 400°C, it is unstable in the presence of free oxygen. At normal operating temperatures of a fuel cell assembly, for example, 600°C to 1000°C, the anode can need to be subjected to a reducing atmosphere having an oxygen partial pressure below the nickel-nickel oxide equilibrium level. This can allow the nickel to remain in a reduced metallic state without oxidizing the nickel. Oxidation of the nickel can cause structural and operational problems in the SOFC start-up and shut-down cases. If the nickel anode oxidizes to form nickel oxide, a volume and weight increase can occur, introducing undesirable stresses in the anode structure. This can lead to physical failure of the anode, the electrolyte of the fuel cell, or both. Further, after conversion to nickel oxide, the fuel cell can be unable to efficiently convert chemical energy to electrical energy and can be considered a failed component. Thus, for a fuel cell having an anode made of nickel, a reducing gas can need to be maintained in the fuel cell anode when the fuel cell anode temperature is above approximately 350°C-400°C.

[0114] Additionally, if nickel (or nickel oxide) is contacted with carbon monoxide at temperatures below about 150°C to about 230°C, nickel carbonyl can form. The chemical reaction is: Ni + 4CO → Ni(CO)4. This reaction is undesirable for environmental and safety reasons.

[0115] Thus, during fuel cell assembly start-up and shut-down, it can be desirable to protect a nickel-containing anode from oxidation, and to prevent carbon monoxide-containing gas from contacting the anode at temperatures below about 230°C to ensure that nickel carbonyl does not form.

[0116] (vi) Embodiments Figure 6 ; Gas turbine engine start-up process

[0117] As mentioned above, it can be desirable to coordinate the start-up of a fuel cell assembly with the start-up of a gas turbine engine capable of operating with the fuel cell assembly. This coordination will be described in more detail below with reference to subsequent drawings.

[0118] However, first reference is made to Figure 6, a method 400 for starting a gas turbine engine is provided. In particular, the method 400 depicts a ground start sequence for a gas turbine engine that can be performed to accelerate the gas turbine engine from a shutdown condition (e.g., rotating at zero RPM, or less than about 50 RPM) to a ground idle operating condition. The method 400 can be used with any suitable gas turbine engine, such as one or more of the example gas turbine engines 100 described above, for example, with reference to Figure 1 and Figure 5 .

[0119] The method 400 includes, at (402), activating a starter of the gas turbine engine (e.g., opening a starter switch). The starter activated at (402) can be configured in a similar manner as the example starter motor-generator 152 of the example gas turbine engine 100 of Figure 1 . The starter activated at (402) can generate an initial rotation of the gas turbine engine.

[0120] The method 400 further includes, at (404), opening a fuel flow once the gas turbine engine reaches a first threshold rotational speed. In the example embodiment shown, the first threshold rotational speed can refer to a core speed between about 15% and 20% of a rated core speed. The core speed can generally refer to a rotational speed of a high pressure spool of the gas turbine engine, for example, capable of rotating with a high pressure compressor and a high pressure turbine (see, e.g., the HP compressor 112 and the HP turbine 116 of the example gas turbine engine 100 of Figure 1 .

[0121] Subsequently, the method 400 includes, at (406), igniting the gas turbine engine. The gas turbine engine can include, at (408), detecting a flame within a combustion section of the gas turbine engine via one or more sensors, such as a flame detector. The method 400 can use data from the flame detector at (408) to determine, at (410), whether a flame is present within the combustion section of the gas turbine engine, and more particularly, whether a flame is present within a combustion chamber of the gas turbine engine (see, e.g., the combustion chamber 228 of the example gas turbine engine 100 of Figure 2 . If no flame is detected, the method can continue to accelerate the gas turbine engine to a higher rotational speed using the starter at (412), and retry igniting at (406). In contrast, however, if a flame is detected at (410), the method 400 includes, at (414), continuing to accelerate the gas turbine engine. Accelerating the gas turbine engine at (414) can include providing a combination of electrical power from the starter motor-generator and energy input by fuel combustion.

[0122] It will be appreciated that, in response to detecting the flame at (410), the gas turbine engine can be considered to be in a “flame on condition.”

[0123] The method 400 includes, at (416), shutting down the starter. Shutting down the starter at (416) can include shutting down the starter in response to determining that the gas turbine engine is rotating at a predetermined self-sustaining speed. Once the starter is shut down at (416) and the gas turbine engine is rotating at a sufficient speed to sustain combustion within the combustion section (e.g., the predetermined self-sustaining speed), the gas turbine engine can be considered to be in a “sustained flame on condition.”

[0124] The method 400 further includes, at (418), accelerating the gas turbine engine to a desired idle speed, such as a ground idle speed. Once at the idle speed, the gas turbine engine can be considered to be in an “idle condition.” It will be appreciated that the term “idle speed” with respect to the gas turbine engine speed refers to a rotational speed of the gas turbine engine sufficient to sustain operation and, for example, power desired accessory systems of the gas turbine engine and, for example, an aircraft in which the gas turbine engine is installed.

[0125] It will be appreciated that the example method 400 for starting the gas turbine engine is provided by way of example only, and that any other suitable method for starting the gas turbine engine can be provided in other example embodiments.

[0126] (vii) Figure 7 Embodiments of the present disclosure; fuel cell assembly ground start without use of air handling unit

[0127] Reference is now made specifically to Figure 7 A method 500 for operating a propulsion system of an aircraft is provided, and more specifically, a method 500 for starting a fuel cell assembly and a gas turbine engine in accordance with example aspects of the present disclosure is provided. The fuel cell assembly can be constructed in a similar manner as one or more example fuel cell assemblies described herein (e.g., the fuel cell assembly 204 of Figures 2 to 5 , Figures 11 to 13 , Figures 15 to 16 and the gas turbine engine can be constructed in accordance with one or more example gas turbine engines described herein (e.g., the gas turbine engine 100 of Figure 1 , Figure 2 , Figure 5 and the gas turbine engine can be constructed in accordance with one or more example gas turbine engines described herein (e.g., the gas turbine engine 100 of

[0128] The method 500 can be generally referred to as a start-up sequence of the fuel cell assembly. From Figure 7It will be appreciated that the method 500 can be performed concurrently with or after the method 400 (see Figure 6 ) for starting a gas turbine engine. More specifically, it will be appreciated that for the exemplary aspects of Figure 7 , the method 500 can be performed concurrently with or after starting a start-up sequence of a gas turbine engine, such as starting the method 400 of Figure 6 ( e.g., turning on a starter at (402)). The benefits of this timing will be described in greater detail below.

[0129] Briefly, as will also be described in greater detail below and with other exemplary aspects of the present disclosure, more specifically, the method 500 can be performed concurrently with or after the gas turbine engine achieving a flame on condition; concurrently with or after achieving a sustained flame on condition for the gas turbine engine; or concurrently with or after achieving an idle condition of the gas turbine engine. The benefits of these timings will also be described in greater detail below.

[0130] Still referring to Figure 7 , the method 500 generally includes, at (502), operating in a purge state after starting a start-up sequence of a fuel cell assembly; at (504), operating in a first heating state before a temperature of a fuel cell stack reaches a first fuel cell temperature threshold; at (506), operating in a second heating state after the temperature of the fuel cell stack reaches the first fuel cell temperature threshold and before the temperature of the fuel cell stack reaches a second fuel cell temperature threshold; and at (508), operating in a power generation mode after the temperature of the fuel cell stack reaches the second fuel cell temperature threshold.

[0131] More specifically, referring first to operating in a purge state at (502), the method 500 includes, at (510), operating in a purge state to provide a flow of gas from a compressor section of a gas turbine engine to purge a fuel cell, and more specifically, to purge an anode and a cathode of the fuel cell. The flow of gas from the compressor section can be at a temperature of at least about 150 °C and up to about 225 °C. Purging the fuel cell during the purge state at (502) can also serve as an initial heating of the fuel cell. Notably, starting a start-up sequence of a fuel cell assembly concurrently with or after starting a start-up sequence of a gas turbine engine at (400) can allow pressurized air from a compressor of the gas turbine engine to perform such operations.

[0132] The method 500 further includes determining, at (516), whether a temperature of the fuel cell assembly, such as a temperature of a fuel cell stack of the fuel cell assembly, has reached a first fuel cell temperature threshold. For example, the method 500 can include receiving data indicating that a temperature of the fuel cell stack is greater than or equal to the first fuel cell temperature threshold, and in response, beginning operation in the second heating state at (506).

[0133] As will be appreciated from the above description, the first fuel cell temperature threshold can be a temperature threshold at which a risk of formation of undesirable gases is eliminated. When the temperature of the fuel cell stack is within a certain temperature range, undesirable gases can form within the anode of the fuel cell upon exposure to certain gases, such as carbon monoxide. The first fuel cell temperature threshold can be between about 150 °C and 400 °C, such as between about 200 °C and 300 °C, such as approximately 230 °C, to avoid such formation of undesirable gases.

[0134] For example, when nickel (or nickel oxide) in the fuel cell anode encounters carbon monoxide at a temperature below the first fuel cell temperature threshold, nickel carbonyl can form. The chemical reaction is: Ni + 4CO → Ni(CO)4. It is undesirable to form nickel carbonyl for a variety of reasons. Thus, during SOFC system start-up and shut-down, it can be desirable to protect the nickel-containing anode from oxidation and prevent carbon monoxide-containing gases from contacting the anode at temperatures below the first fuel cell temperature threshold to ensure that nickel carbonyl does not form. Based on this design consideration, step (504) in the method 500 avoids the passage of fuel processing unit exhaust (or reformate) through the fuel cell anode having nickel material.

[0135] Still referring to Figure 7 As mentioned, the method 500 further includes operating, at (504), in a first heating state prior to the temperature of the fuel cell stack reaching the first fuel cell temperature threshold. Operating in the first heating state at (504) includes, at (512), beginning operation of a fuel processing unit and providing a heated gas stream from the fuel processing unit to the cathode of the fuel cell. In particular, for the depicted example aspect, providing the heated gas stream from the fuel processing unit to the cathode of the fuel cell can include providing exhaust gas from the fuel processing unit to the cathode of the fuel cell along with an additional gas stream. The fuel processing unit can be configured in a similar manner to one or more of the fuel processing units described herein (see, e.g., the fuel processing unit 304 of FIG. 3), including but not limited to a catalytic partial oxidizer, an autothermal reformer, and a steam reformer. The exhaust gas from the fuel processing unit can include reformed fuel from the fuel processing unit. Figure 5

[0136] ​Operating in a first heated state at (504) further includes continuing to heat the fuel cell at (514), for example, using a fuel processing unit. It will be understood that continuing to heat the fuel cell at (514) may further include using an additional heat source, such as a resistance heater. Furthermore, continuing to heat the fuel cell at (514) may include supplying heated air from the fuel processing unit, hydrogen from the fuel processing unit, or both to the anode of the fuel cell. The flow from the fuel processing unit to the anode at (514) may be free of carbon monoxide or substantially completely free of carbon monoxide (e.g., less than 1% carbon monoxide by volume).

[0137] It is worth noting that, in at least some exemplary aspects of this disclosure, operation at (504) in a first heating state may further include a burner to the combustion section (see, for example...). Figure 2 The combustor 206 provides output products from the fuel cell while the gas turbine engine operates at flame-opening conditions or faster (i.e., faster than when flame-opening conditions are met), and more specifically, to the combustion chamber (e.g., Figure 2 The combustion chamber 228 provides output products from the fuel cell. The output products may be, for example, exhaust gas from the fuel treatment unit passing through the cathode of the fuel cell. Additionally or alternatively, in one or more exemplary aspects of this disclosure, operating at (504) in a first heated state may include supplying exhaust gas from the fuel treatment unit to the combustor of the combustion section of the gas turbine engine around (i.e., bypassing) the anode of the fuel cell, and particularly may include supplying exhaust gas from the fuel treatment unit to the combustor of the combustion section around the anode of the fuel cell while the gas turbine engine operates more rapidly in flame-open conditions. In this way, the exhaust gas may bypass the anode of the fuel cell. In one or more of these exemplary aspects, the output products and / or exhaust gas may include hydrogen. When a flame is present within the gas turbine engine in these exemplary aspects, hydrogen can be used to help stabilize combustion in the gas turbine engine and improve combustion efficiency.

[0138] As mentioned above, method 500 further includes, at (516), determining whether the temperature of the fuel cell assembly (such as the temperature of the fuel cell stack of the fuel cell assembly) has reached a first fuel cell temperature threshold.

[0139] As mentioned, once the temperature of the fuel cell assembly, and more specifically, the temperature of the fuel cell stack, has reached the first fuel cell temperature threshold, as determined at (516), the method 500 begins operating in the second heating state at (506). The anode of a solid oxide fuel cell (SOFC) is typically composed of a porous metal ceramic made of nickel and yttria stabilized zirconia. The nickel component provides electrical conductivity, electrochemical capability, and fuel handling capability. The nickel component also enhances the mechanical properties of the cell. Nickel is a relatively unstable metal at high temperatures, and in particular, at temperatures above approximately 350-400°C (high end of the first temperature threshold), it is unstable in the presence of free oxygen. At normal SOFC operating temperatures of 600°C to 1000°C, the anode must be subjected to a reducing atmosphere with an oxygen partial pressure below the nickel-nickel oxide equilibrium level. This allows the nickel to remain in a reduced metallic state. The tendency of the nickel to oxidize can cause structural and operational problems in the case of SOFC start-up and shut-down. If the nickel anode oxidizes to form nickel oxide, there will be an increase in volume and weight, introducing large stresses in the anode structure. This can lead to physical failure of the anode, electrolyte, or both. Further, after conversion to nickel oxide, the cell is unable to efficiently convert chemical energy to electrical energy and is considered a failed component. Thus, when the fuel cell anode temperature is above the first temperature threshold as shown later at step (506), it is necessary to maintain a reducing gas in the fuel cell anode.

[0140] When operating in the second heating state at (506), the method can include providing, at (518), the exhaust gas (reducing or reduced gas) from the fuel processing unit to the anode of the fuel cell. This process can be in response to receiving data indicating that the temperature of the fuel cell stack is greater than or equal to the first fuel cell temperature threshold. Providing the exhaust gas from the fuel processing unit to the anode of the fuel cell can help protect the anode of the fuel cell from anode oxidation, as the reduced gas from the fuel processing unit can be free of oxygen or substantially free of oxygen.

[0141] Further, it will be understood that for Figure 7 For the example aspects of the method 500 depicted in FIG. 5, providing the exhaust gas from the fuel processing unit to the anode of the fuel cell at (518) can further include, for example, providing the exhaust gas from the fuel processing unit to the cathode of the fuel cell, also in response to receiving data indicating that the temperature of the fuel cell stack is greater than or equal to the first fuel cell temperature threshold. In this way, the method 500 can simultaneously heat both the anode and the cathode of the fuel cell while operating in the second heating state at (506).

[0142] It will be further appreciated that in certain example aspects of the present disclosure, operating in the second heated state at (506) can further include setting the pressure within the anode to be higher than the pressure within the cathode to prevent gas (e.g., oxygen-containing gas) from within the cathode from permeating into the anode through the electrolyte layer positioned therebetween.

[0143] Still referring to Figure 7 The method 500 includes determining, at (520), whether the temperature of the fuel cell assembly has exceeded a second fuel cell temperature threshold, or more specifically, whether the temperature of the fuel cell stack of the fuel cell assembly has exceeded a second fuel cell temperature threshold. In at least certain example aspects, the determination at (520) can include receiving data indicating that the temperature of the fuel cell stack is greater than or equal to the second fuel cell temperature threshold. In response, the method 500 can transition to operating in a power generation mode at (508). For example, the method 500 can include starting operation of the fuel cell assembly in the power generation mode at (522), e.g., in response to determining that the temperature of the fuel cell assembly has exceeded the second fuel cell temperature threshold, or more specifically, in response to the temperature of the fuel cell stack of the fuel cell assembly having exceeded the second fuel cell temperature threshold.

[0144] The second fuel cell temperature threshold can be a temperature threshold at which the fuel cell assembly can operate to generate power with a desired efficiency. In certain example aspects, the second fuel cell temperature threshold can be greater than the first fuel cell temperature threshold, and between about 400°C and 800°C, such as at least about 500°C, such as at least about 600°C, such as at least about 700°C, such as up to 750°C. The second fuel cell temperature threshold can be driven by various seals and other structures within the fuel cell assembly, such as within the fuel cell stack.

[0145] Following execution of the start-up sequence of the fuel cell assembly, the fuel cell can operate in a fuel cell power generation mode at (524). As will be appreciated, operating the fuel cell assembly in the power generation mode at (508) can include operating the fuel cell assembly to provide an output product to the combustion section of the gas turbine engine at (526).

[0146] As described above, the example method 500 generally includes starting a start-up sequence of a fuel cell assembly at or after a start-up sequence of a gas turbine engine at (400). One or more example aspects of the example method 500 can facilitate certain efficiencies, such as allowing air flow from a compressor of the gas turbine engine to be used for start-up operations (e.g., providing a purge air flow during (502), providing an air flow to a fuel processing unit during (504) and / or during (506), etc.). Further, exhaust gas from the fuel processing unit containing hydrogen can improve combustion within a combustion chamber of the gas turbine engine. Further efficiencies can be realized because heating the fuel cell assembly can require less fuel combustion because preheated air from the engine can be used for start-up operations of the fuel cell assembly, and radiant heat from the combustor can also assist in heating the fuel cell stack during the start-up sequence of the fuel cell assembly. This benefit can be unique to the integrated combustor and fuel cell assembly configurations disclosed herein (see, e.g., Figure 2

[0147] Further, while the start-up sequence of the fuel cell assembly is started at or after the start-up sequence of the gas turbine engine, further benefits can be realized by starting the start-up sequence of the fuel cell assembly at or after achieving a flame on condition of the gas turbine engine, achieving a sustainable flame on condition of the gas turbine engine, or achieving an idle condition of the gas turbine engine. In particular, the higher the rotational speed of the gas turbine engine and the hotter the flame, the more of the one or more efficiency benefits described above can be realized, and combustion within the combustion chamber can use any hydrogen in the output product and / or exhaust gas provided thereto at, e.g., (504), (506). Another benefit from the example method 500 is enhanced reliability and reduced weight when it is applied to a system without a pre-combustor, or enhanced flexibility and availability when the pre-combustor has partial or complete failure for a fuel cell system with a pre-combustor.

[0148] (i) Figure 8 Embodiments of the application; fuel cell assembly ground start using an air processing unit

[0149] As will be appreciated, Figure 7 The example method 500 operates independent of an air processing unit, such as the example air processing unit 306 described above with reference to, e.g., the example method 500 described above with reference to Figure 5 Figure 8 ​​, a flowchart of a method 600 for operating a propulsion system of an aircraft according to another example aspect of the present disclosure is provided. More specifically, a flowchart of an example method 600 for starting a fuel cell assembly including an air handling unit and a gas turbine engine is depicted. The fuel cell assembly can be configured in a similar manner to one or more of the example fuel cell assemblies described herein (e.g., Figures 2 to 5 , Figures 11 to 13 , Figures 15 to 16 , etc.), and the gas turbine engine can be configured according to one or more of the example gas turbine engines described herein (e.g., Figure 1 , Figure 2 , Figure 5 , etc.).

[0150] The example method 600 can generally operate in a similar manner to the example method 500 of Figure 7 , and similar reference numbers can refer to similar processes (e.g., Figure 8 (602) corresponds to (502) of Figure 7 , unless otherwise noted herein).

[0151] Accordingly, it will be appreciated that the example method 600 generally includes operating in a purge state after starting a start-up sequence of the fuel cell assembly at (602); operating in a first heating state until a temperature of the fuel cell stack reaches a first fuel cell temperature threshold at (604); operating in a second heating state after the temperature of the fuel cell stack reaches the first fuel cell temperature threshold and until the temperature of the fuel cell stack reaches a second fuel cell temperature threshold at (606); and operating in a power generation state after the temperature of the fuel cell stack reaches the second fuel cell temperature threshold at (608).

[0152] However, as mentioned, the example method 600 can be used with a fuel cell assembly that includes an air handling unit, or specifically, a fuel cell assembly that includes a preburner that generates fully oxidized gas (no H2and CO). In this way, the method 600 can include additional or alternative steps when operating, for example, in the first heating state and / or in the second heating state. In particular, for the depicted example embodiment, when operating in the first heating state at (604), the method 600 generally includes operating the air handling unit to provide oxidized exhaust gas to the anode of the fuel cell, the cathode of the fuel cell, or both at (612). In particular, in at least certain example aspects, the air handling unit can be operated at (612) to provide oxidized exhaust gas to both the anode and the cathode of the fuel cell. Similarly, operating in the first heating state at (604) can further include continuing to heat the fuel cell, e.g., the cathode and the anode, in accordance with a temperature control schedule using the air handling unit at (614).

[0153] Further, still referring to Figure 8 For the depicted example aspects, operating in the second heating state at (606) includes using both the air handling unit and the fuel handling unit to heat the fuel cell stack to the second fuel cell temperature threshold. More specifically, the method 600 includes providing exhaust gas from the fuel handling unit to the anode of the fuel cell and providing exhaust gas from the air handling unit to the cathode of the fuel cell to simultaneously heat the anode and the cathode at (618). As with Figure 8 the example method 500, providing exhaust gas from the fuel handling unit to the anode and providing exhaust gas from the air handling unit to the cathode at (618) can include setting the pressure within the anode to be higher than the pressure within the cathode to prevent the oxygen-containing gas within the cathode from permeating through the electrolyte layer to the anode.

[0154] Reference is made herein to Figure 8 other aspects of the method 600 that are not described can be similar to the corresponding aspects of the method 500 described above with reference to Figure 7 the example method 500.

[0155] Although not reflected in the example flowchart of Figure 8 the example method 600, it will be appreciated that aspects of the method 600 can be combined with aspects of the method 500 in at least certain example aspects. For example, in certain example aspects, operating in the first heating state at (604) can additionally include operating the fuel handling unit to provide exhaust gas to the cathode to aid in heating the fuel cell and / or to provide exhaust gas to the combustor of the gas turbine engine to aid in combustion operation of the gas turbine engine.

[0156] The example method 600 has similar benefits as the example method 500. One additional benefit in the example method 600 is a potentially faster start-up process. This is because the preburner is utilized to simultaneously heat the cathode and the anode prior to reaching the first temperature threshold, enhancing heat transfer from the heating gas to the fuel cell solids.

[0157] (ii) Figure 9 and Figure 10 Embodiments; Fuel Cell Assembly Ground Start Prior to Gas Turbine Engine Start-Up

[0158] Reference is now made to Figure 9 and Figure 10 depicting flowcharts of two additional methods and systems for an aircraft. In particular, Figure 9 is a flowchart of a method 700 for starting a fuel cell assembly according to a first additional example embodiment of the present disclosure, and Figure 10 is a flowchart of a method 800 for starting a fuel cell assembly according to a second additional example embodiment of the present disclosure.

[0159] Figure 9 The example method 700 of Figure 7 can be constructed in substantially the same manner as the example method 500 of Figure 9 (e.g., (702) of Figure 7 corresponds to (502) of Figure 9 Thus, it will be understood that the example method 700 of

[0160] Similarly, Figure 10 The example method 800 of Figure 8 can be constructed in substantially the same manner as the example method 600 of Figure 10 (e.g., (802) of Figure 8 corresponds to (602) of Figure 10 Thus, it will be understood that the example method 800 of

[0161] However, in contrast to the example methods 500, 600 of Figure 7 and Figure 8 the example methods 700, 800 of Figure 9 and Figure 10 define different timing relationships than the start of the start-up sequence 400 (see Figure 6 ) of the gas turbine engine. In particular, Figure 9 and Figure 10 A first start-up sequence 400A, a second start-up sequence 400B, and a third start-up sequence 400C are depicted.

[0162] In particular, the methods 700, 800 each include starting a start-up sequence of the fuel cell assembly (generally 700, 800), and further include starting a start-up sequence of the gas turbine engine after starting the start-up sequence of the fuel cell assembly at (402A), (402B), (402C). As a result, the methods 700, 800 can vary with respect to the methods 500, 600 discussed above. For example, when operating in a purge operating mode (702), (802), the method can receive a purge airflow from an air source external to the gas turbine engine (e.g., a ground air supply cart, an auxiliary power unit, etc.). Similarly, the airflow used in the operation of the air handling unit (if included) and the fuel handling unit can also come from an air source external to the gas turbine engine, at least until the engine start-up procedure / sequence 400A, 400B, 400C is started.

[0163] (1) Procedure 1

[0164] Referring first to the first engine start-up sequence 400A, with such a configuration, starting the start-up sequence of the gas turbine engine after starting the start-up sequence of the fuel cell assembly at (402A) includes starting the start-up sequence of the gas turbine engine after the temperature of the fuel cell stack has reached the second fuel cell temperature threshold (as determined at (720), (820)). In particular, for Figure 9 With the example aspects depicted in FIGS. 7 and 8, starting the first engine start-up sequence 400A is started concurrently with or after starting the operation of the fuel cell assembly in power generation mode at (722), (822).

[0165] It will be appreciated that using the first engine start-up sequence 400A can result in a more efficient start-up of the gas turbine engine, as with such a configuration, the fuel cell, and more particularly, the fuel cell stack, will heat up one or more of the liners of the combustor of the gas turbine engine, resulting in higher combustion efficiency. Further, with such a configuration, the output products of the fuel cell can be used to help achieve combustion stability more quickly due to the relatively high hydrogen content within the output products. Still further, with such a configuration, the electrical power generated by the fuel cell assembly can be used to help start the gas turbine engine.

[0166] (2) Procedure 2

[0167] Referring now to the second engine start sequence 400B, with this configuration, starting the start-up sequence of the gas turbine engine after starting the start-up sequence of the fuel cell assembly can include starting the start-up sequence of the gas turbine engine after the temperature of the fuel cell stack has reached the first fuel cell temperature threshold (as determined at (716), (816)) and before the temperature of the fuel cell stack reaches the second fuel cell temperature threshold (as determined at (720), (820)).

[0168] It will be appreciated that, similar to using the first engine start sequence 400A, using the second engine start sequence 400B can result in a more efficient start-up of the gas turbine engine, as the fuel cell stack will heat one or more of the liners of the combustor of the gas turbine engine, resulting in higher combustion efficiency during start-up. Further, the output products of the fuel cell can again help to achieve combustion stability more quickly due to the relatively high hydrogen content within the output products. Notably, however, compared to the first engine start sequence 400A, less fuel and air can be required to achieve start-up of the fuel cell assembly by using the second engine start procedure 400B, as heat from the gas turbine engine can help to heat the fuel cell during the second heating state (706), (806) and air can be extracted from, for example, the compressor of the gas turbine engine.

[0169] (3) Procedure 3

[0170] Further, referring now to the third engine start sequence 400C, with this configuration, starting the start-up sequence of the gas turbine engine after starting the start-up sequence of the fuel cell assembly includes starting the start-up sequence of the gas turbine engine before the temperature of the fuel cell stack reaches the first fuel cell temperature threshold. For the illustrated embodiment, for the third engine start sequence 400C, starting the start-up sequence of the gas turbine engine occurs before operating the fuel cell assembly in the first heating state (704), (804), or more specifically, before starting operation of the air handling unit of the fuel cell assembly, operation of the fuel handling unit of the fuel cell assembly, or both.

[0171] Notably, however, in other example embodiments of the present disclosure, for the third engine start sequence 400C, starting the start-up sequence of the gas turbine engine can occur concurrently with or after operating the fuel cell assembly in the first heating state (704), (804), and more specifically, concurrently with or after starting operation of the air handling unit of the fuel cell assembly, operation of the fuel handling unit of the fuel cell assembly, or both.

[0172] It will be appreciated that, similar to the use of the first engine start sequence 400A and the second engine start sequence 400B, the use of the third engine start sequence 400C can result in a more efficient gas turbine engine start-up, as the fuel cell stack will heat one or more of the combustor liners of the gas turbine engine, resulting in higher combustion efficiency during start-up. Further, similar to the use of the second engine start procedure 400B, by using the third engine start sequence 400C, less fuel and air can be required to achieve start-up of the fuel cell assembly, as heat from the gas turbine engine can assist in heating the fuel cell during the second heating state (706), (806), and air can be extracted from, for example, the compressor of the gas turbine engine. Further, with the third engine start sequence 400C, any combustible gas provided from the fuel cell assembly to the combustor of the gas turbine engine during start-up of the fuel cell assembly can be combusted by a flame within the combustion section.

[0173] (iii) Figures 11 to 13 Embodiments of recycling

[0174] As will be appreciated, in accordance with one or more example aspects described herein above with reference to, for example, Figure 9 and Figure 10 , when starting up a fuel cell assembly and a gas turbine engine, output products of the fuel cells of the fuel cell assembly can be provided to the combustion chamber of the combustor of the gas turbine engine prior to the gas turbine engine achieving a flame-on condition, a sustained flame-on condition, or an idle condition. The output products can include, for example, hydrogen gas, which can be undesirable to accumulate within the combustion chamber and / or flow through the uncombusted gas turbine engine.

[0175] Accordingly, now briefly referring to Figures 11 to 13 , a simplified schematic of a fuel cell assembly and a gas turbine engine in accordance with various example embodiments of the present disclosure, and more particularly, a simplified schematic of a gas turbine engine having an integrated fuel cell and combustor assembly, which can address the above problems, is provided. Figures 11 to 13 The example gas turbine engine and integrated fuel cell and combustor assembly of Figure 5 may be constructed in substantially the same manner as the example gas turbine engine 100 and integrated fuel cell and combustor assembly 200 described above with reference to Figures 11 to 13 . Accordingly, the same or similar reference numerals can refer to the same or similar parts. For example, Figure 5 the fuel cell controller 240 of the embodiment depicted in may be constructed in a similar manner as the example fuel cell controller 240 of

[0176] For example, with each of these configurations, the integrated fuel cell and combustor assembly 200 generally includes a fuel cell assembly 204 having an air processing unit 306, a fuel processing unit 304, and a fuel cell stack 294, the fuel cell stack 294 including a fuel cell (and is depicted as a single fuel cell) having a cathode 296, an anode 298, and an electrolyte layer 300 positioned between the cathode 296 and the anode 298. As will be understood from the description herein, in certain example aspects of the fuel cell assembly 204, the air processing unit 306 can be configured to additionally or alternatively provide a first stream to the anode 298, and the fuel processing unit 304 can be configured to additionally or alternatively provide a second stream to the cathode 296. The first stream can generally be a flow of air heated by the air processing unit 306. The second stream can generally be a reformate stream containing hydrogen. Figures 11 to 13 As schematically depicted in FIG. 3, the air processing unit 306 can provide a first stream (not labeled for clarity) to the cathode 296, and the fuel processing unit 304 can provide a second stream (not labeled for clarity) to the anode 298. As will be understood from the description herein, in certain example aspects of the fuel cell assembly 204, the air processing unit 306 can be configured to additionally or alternatively provide the first stream to the anode 298, and the fuel processing unit 304 can be configured to additionally or alternatively provide the second stream to the cathode 296. The first stream can generally be a flow of air heated by the air processing unit 306. The second stream can generally be a reformate stream containing hydrogen.

[0177] Further, for each of these configurations, the fuel cell is configured to provide an output product to the combustor 206, or more specifically, to the combustion chamber 228 of the combustor 206. In particular, for the illustrated embodiment, the fuel cell assembly 204 includes a cathode path 350 and an anode path 354. The cathode path 350 provides fluid communication between the cathode 296 and the combustion chamber 228, and the anode path 354 provides fluid communication between the anode 298 and the combustion chamber 228.

[0178] As mentioned, during certain example aspects of the present disclosure, during start-up of the fuel cell assembly 204, the output product from the fuel cell can include hydrogen, and it can be undesirable to provide hydrogen to the combustion chamber 206 prior to having achieved certain operating conditions of the gas turbine engine. Similarly, it can be desirable to provide one or more streams to, for example, the anode 298 during certain operations to avoid undesirable results. For example, it can be desirable to provide a gas stream containing little or no oxygen to the anode 298 during start-up operations of the fuel cell assembly 204, for example, to avoid oxidation of the anode 298.

[0179] (1) Embodiment A, Figure 11

[0180] Accordingly, particular reference is made to Figure 11In an exemplary embodiment, for the depicted exemplary fuel cell assembly 204, the fuel cell assembly 204 further defines a cathode recirculation path 352 and a first anode recirculation path 356. The cathode recirculation path 352 fluidly connects the cathode path 350 back to the air handling unit 306, and the first anode recirculation path 356 similarly fluidly connects the anode path 354 back to the air handling unit 306. In this way, the air handling unit 306 can be configured to further utilize any fuel (e.g., hydrogen) from the fuel cell's output products, causing combustion of the fuel cell's output products. This prevents the supply of fuel from the anode 298 and / or cathode 296's output products to the combustion chamber 228 before, for example, sufficient airflow has been achieved through the combustion chamber 228 and / or the gas turbine engine 100 has achieved flame-opening conditions (such as stable flame conditions). Further, the airflow further combusted by the air handling unit 306 can then be supplied to the cathode 296 for heating the cathode 296, and to the anode 298 for heating the anode 298, or both. This flow is indicated by the dashed line 358. Additionally or alternatively, the flow provided back to the air treatment unit 306 to the recirculation paths 352, 356 can be completely converted from unused fuel into carbon dioxide and steam through the air treatment unit 306. This can mitigate or eliminate the emission impact of unused fuel on downstream equipment when the SOFC is started before the burner is started.

[0181] (2) Example B Figure 12

[0182] Now for specific reference Figure 12 In an exemplary embodiment, the fuel cell assembly 204 again includes a cathode path 350 and an anode path 354. However, for Figure 12 In an exemplary aspect, the fuel cell assembly 204 further includes a second anode recirculation path 360, which fluidly connects the anode path 354 back to the fuel processing unit 304. Figure 11 Similar embodiments include a second anode recirculation path 360 that allows all or part of the output products from anode 298 to be transferred back to fuel treatment unit 304 during one or more start-up operations to prevent or minimize the amount of fuel (e.g., hydrogen) supplied to combustion chamber 228 of the gas turbine engine. The fuel within the output products recirculated back via the second anode recirculation path 360 can be used for fuel treatment, which can reduce overall fuel consumption during the sequential execution of the start-up sequence of fuel cell assembly 204, while also reducing any emission impact from unused fuel supplied to combustor 206 of gas turbine engine 100. When there is no air treatment unit (e.g., pre-combustion unit) in the system or when the air treatment unit (e.g., pre-combustion unit) fails, Figure 12This embodiment B in the Summary provides valuable alternatives.

[0183] (3) Embodiment C, Figure 13

[0184] Referring now particularly to the exemplary aspects of Figure 13 , the exemplary fuel cell assembly 204 includes Figure 11 and Figure 12 aspects of the two exemplary fuel cell assemblies 204. In particular, Figure 13 the exemplary fuel cell assembly 204 includes a cathode recycle path 352, a first anode recycle path 356, and a second anode recycle path 360. The functions of these respective paths are described above with reference to Figure 11 and Figure 12 .

[0185] In this manner, it will be appreciated that, in accordance with one or more exemplary aspects of the present disclosure (e.g., the method 700 of Figure 9 , the method 800 of Figure 10 ), during execution of a start-up sequence of the fuel cell assembly 204, the fuel cell assembly 204 can be configured to use one or more of these recycle paths. In one example, the system can include a cathode exhaust gas recycle path 352 to an air processing unit 306 (e.g., a preburner), and an anode exhaust gas recycle path 360 to a fuel processing unit 304 (e.g., a CPO x ). In another example, the system can include a cathode exhaust gas recycle path 352 to an air processing unit 306 (e.g., a preburner), while anode exhaust gas is recycled to a fuel processing unit (e.g., a CPO x ) via flow path 360 and to an air processing unit (e.g., a preburner) via first anode recycle path 356. Actively actuated control valves can be used with the system controller (referred to herein as a fuel cell controller 240) to achieve the desired recycle flow distribution between flow paths 356 and 360.

[0186] (4) Recycle’s impact on start-up sequence

[0187] Referring briefly back to Figure 9 and Figure 10 , in certain exemplary aspects, the methods 700, 800 can include directing one or more streams of output products from the fuel cell to the air processing unit through one or more recycle paths prior to completion of a start-up sequence of the fuel cell assembly. For example, the one or more streams can include a cathode stream, such that the methods 700, 800 include directing the cathode stream through a recycle path (such as the cathode recycle path 352; Figure 11 , 13) directing output products from the cathode to the air processing unit can include an anode stream, such that the method 700, 800 includes directing one or more streams of output products from the fuel cell to the fuel processing unit through one or more recirculation paths (such as the first cathode recirculation path 356; Figure 11 、 13 ) directing output products from the anode to the air processing unit, or both.

[0188] Still briefly referring to Figure 9 and Figure 10 , in certain example aspects, the method 700, 800 can further include directing one or more streams of output products from the fuel cell to the fuel processing unit through one or more recirculation paths prior to completing a start-up sequence of the fuel cell assembly. For example, the one or more streams can include a cathode stream, such that the method 700, 800 includes directing output products from the cathode to the fuel processing unit through a recirculation path (such as the first cathode recirculation path 356; Figures 11 to 13 not depicted in FIG. 8) can include an anode stream, such that the method 700, 800 includes directing one or more streams of output products from the fuel cell to the fuel processing unit through one or more recirculation paths (such as the second anode recirculation path 360; Figure 12 、 13 ) directing output products from the anode to the fuel processing unit, or both.

[0189] (iv) Figure 14 Embodiments of FIG. 8; warm standby mode

[0190] In certain example aspects, the fuel cell assembly can be maintained in a warm state to facilitate, for example, a faster start-up sequence of the fuel cell assembly, power generation of the fuel cell assembly, etc. Referring now to Figure 14 , a flow diagram of a method 900 is provided that illustrates a warm ground start operation of a gas turbine engine and a fuel cell assembly in accordance with one or more example aspects of the present disclosure. The fuel cell assembly can be configured in a similar manner as one or more example fuel cell assemblies described herein (e.g., the fuel cell assembly 204 of FIGS. 1-7), and the gas turbine engine can be configured in accordance with one or more example gas turbine engines described herein (e.g., the gas turbine engine 100 of FIGS. 1-7). Figures 2 to 5 、 Figures 11 to 13 、 Figures 15 to 16 , Figure 1 、 Figure 2 、 Figure 5 ,

[0191] The example method 900 can be similar to one or more other methods described herein for starting a fuel cell assembly.

[0192] However, in contrast to the previously described methods, Figure 14The example method 900 includes, at (912), maintaining a fuel cell stack of the fuel cell assembly in a warm standby state (or warm standby mode). Maintaining the fuel cell stack of the fuel cell assembly in the warm standby state at (912) can include maintaining the fuel cell stack in the warm standby state during, for example, aircraft turnaround, aircraft refueling, engine shutdown state (e.g., where the gas turbine engine is in a shutdown mode), etc. During the warm standby state, there can be no electrical power output drawn from the fuel cell stack, or alternatively, there can be a relatively small amount of electrical power output drawn from the fuel cell stack (e.g., less than about 10% of a maximum power output, such as less than about 5% of a maximum power output) for thermal self-sustainability. It will be appreciated that when the gas turbine engine is not in a flame on operating condition, the gas turbine engine can not be able to effectively process hydrogen gas within the output products from the fuel cells of the fuel cell stack, so not operating the fuel cell assembly to extract electrical power can prevent hydrogen gas from flowing into, for example, a combustion section of the gas turbine engine.

[0193] As used herein, the term “warm standby state” can refer to a condition where the fuel cell assembly, or more specifically the fuel cell stack, is at a temperature equal to at least about 40% of a maximum operating temperature (i.e., a maximum design temperature for intended operation), such as at least about 60% of a maximum operating temperature, such as at least about 70% of a maximum operating temperature, and up to about 90% of a maximum operating temperature. In this way, when maintained in the warm standby state, the fuel cell assembly is able to transition to a power generation mode within about five minutes or less. If no electrical power is extracted, the fuel cell stack can be maintained in the warm standby mode using, for example, a source of heated air external to the gas turbine engine, an electrical resistance heater, a gas turbine engine hot bus, etc.

[0194] While optional, for the example aspects of the depicted method 900, the method further includes, at (914), switching the fuel cell assembly to a ground idle power output mode (also referred to as a “ground idle power generation mode”) in order to provide electrical power to, for example, an aircraft. Operating in the ground power output mode at (914) includes, at (915), operating the fuel cell assembly to achieve a highest level of fuel utilization and fuel efficiency. For example, the fuel cell assembly can be operated within 10% of a maximum fuel utilization for a given level of electrical power output. This can minimize the amount of hydrogen gas provided to a combustion chamber of the gas turbine engine, and can further reduce fuel usage and loading on, for example, an air handling unit, a fuel handling unit, or both.

[0195] Additionally, for aspects of the depicted method 900, operating in the ground power output mode at (914) includes, at (916), operating the fuel cell assembly to recirculate output products of the fuel cells of the fuel cell stack to thereby minimize the amount of hydrogen provided to the combustion chamber of the gas turbine engine. In this manner, unused fuel in the output products of the fuel cells of the fuel cell stack produced at (914) (and, for example, (912)) can be recirculated to, for example, the fuel processing unit in order to eliminate the need for an additional afterburner to combust the unused fuel from the anode of the fuel cell. Output products originating from the cathode of the fuel cell can similarly be recirculated to the air processing unit, potentially reducing the air flow required by the fuel cell assembly. This can reduce the auxiliary power usage of a separate air supply unit, potentially reducing the size and weight of such an air supply unit.

[0196] The method 900 further includes, at (918), receiving an engine start command to start the gas turbine engine. Receiving the engine start command at (918) can trigger execution of an engine start procedure, such as the method 400 described above with reference to Figure 6 The method 400 or any other suitable engine start procedure). Notably, by operating the fuel cell assembly in the warm standby mode at (912) and using the method 900 described herein, the start of the gas turbine engine can be aided by maintaining the temperature of, for example, one or more liners of the combustor of the gas turbine engine at an elevated temperature, which can result in more quickly achieving sustainable combustion therein.

[0197] For the depicted example aspects, once the engine start sequence (e.g., the method 400) is complete, the method 900 includes, at (920), switching to a normal power generation mode of the fuel cell assembly. Switching to the normal power generation mode of the fuel cell assembly can be in response to completion of the engine start sequence, or alternatively, or can be in response to determining that the temperature of the fuel cell stack has reached a second fuel cell assembly reference temperature (not shown).

[0198] (v) Figures 15 to 16 Embodiments of a redox stable anode system

[0199] As discussed above, the solid oxide fuel cell assembly can generally include a fuel cell stack 294 having a solid oxide fuel cell (or more precisely, a plurality of solid oxide fuel cells 294 arranged in series, for example). The solid oxide fuel cell generally includes a cathode 296 and an electrolyte layer 300, and an anode 298 positioned opposite the electrolyte layer 300 from the cathode 296. With certain constructions, the anode 298 includes a metal ceramic having a relatively high concentration of nickel. For example, the metal ceramic can be a nickel / yttria stabilized zirconia (Ni / YSZ) metal ceramic. While such constructions provide certain benefits to the solid oxide fuel cell in the form of, for example, electrical conductivity, there are certain operational limitations when the solid oxide fuel cell is used in, for example, an aviation duty. To address one or more of these operational limitations, the inventors of the present disclosure have proposed an aviation assembly having a more stable solid oxide fuel cell that can address one or more of the operational limitations.

[0200] For example, referring now to Figure 15 depicts a gas turbine engine and fuel cell assembly according to another example embodiment of the present disclosure. Figure 15 The example gas turbine engine and fuel cell assembly depicted in Figure 5 may be constructed in substantially the same manner as the example gas turbine engine and fuel cell assembly described above with reference to

[0201] For example, the fuel cell assembly generally includes an air delivery assembly, an air handling unit 306, and a fuel cell stack 294 having a fuel cell. For the illustrated embodiment, the fuel cell is a solid oxide fuel cell. The air delivery assembly is configured to receive an airflow from a compressor section of the gas turbine engine and / or an additional airflow supply 290. The air delivery assembly is further configured to provide such airflow directly to the cathode 296, or alternatively to the air handling unit 306, which can then provide, for example, heated air to the cathode 296.

[0202] However, the anode 298 of the fuel cell is configured as an operatively stable anode 298, as will be described below with reference to, for example Figure 16as described in greater detail below. In particular, the anode 298 can be capable of internal fuel reforming operations, and can be further configured to accommodate oxygen-containing gas across a wider temperature range. Thus, it will be appreciated that for the illustrated embodiment, the fuel cell assembly does not include a separate fuel processing unit configured to convert a hydrocarbon-based fuel to a hydrogen fuel. In particular, the fuel supply of the aircraft including the depicted system can be a hydrocarbon fuel supply, and the fuel cell assembly can be configured to provide the anode 298 with a hydrocarbon fuel from the hydrocarbon fuel supply. The hydrocarbon fuel supply can be a fuel supply without a fuel reformer (providing a hydrocarbon fuel that has not been processed by, for example, an onboard fuel reformer). More specifically, for the illustrated embodiment, the fuel cell assembly includes a fuel line in fluid communication with the first fuel delivery line 150A of the fuel supply for receiving a hydrocarbon fuel and providing the hydrocarbon fuel to the anode 298 of the fuel cell.

[0203] Further, it will be appreciated that the air delivery assembly is further configured to provide an oxygen-containing gas stream to the anode 298. In particular, for the illustrated embodiment, the cathode gas flow duct of the fuel cell assembly is instead configured as a cathode and anode gas flow duct 314' configured to further provide the oxygen-containing gas stream to the anode 298 through the anode supply duct 319. In the illustrated embodiment, the heat exchanger 317 is thermally coupled to the air processing unit 306 for increasing the temperature of the gas stream through the anode supply duct 319. In this manner, it will be appreciated that the fuel cell assembly is configured to provide both a hydrocarbon fuel stream and an oxygen-containing gas to the anode 298 to facilitate internal fuel reforming operations within the anode 298, for example, during operation of the fuel cell assembly. Figure 15

[0204] As will be further appreciated from the description herein, the internal fuel reforming operations can generate relatively high heat within the fuel cell. In this manner, the fuel cell assembly can be configured to control the oxygen-containing gas stream to the anode 298, the hydrocarbon fuel stream to the anode 298, or both. Such control can be responsive to one or more thermal demands on or for the fuel cell assembly (e.g., a temperature of the fuel cell stack 294), one or more thermal demands on or for the gas turbine engine (e.g., a thermal energy demand within a combustor of a combustion section of the gas turbine engine, combustion dynamics within a combustor of a combustion section of the gas turbine engine), and the like.

[0205] Thus, Figure 15 The example gas turbine engine and fuel cell assembly depicted in FIG. 1 includes one or more features for controlling the oxygen-containing gas to the anode 298 of the fuel cell and the hydrocarbon fuel to the anode 298 of the fuel cell, as well as more features for sensing data to facilitate certain control decisions by the controller 240, as described in greater detail below.​

[0206] In particular, for the illustrated embodiment, the fuel cell assembly includes an anode gas flow valve 312 in gas flow communication with the anode gas flow conduit 318 for controlling gas flow through the anode gas flow conduit 318. The anode gas flow valve 312 is depicted as being in wireless operable communication with the controller 240. Similarly, the fuel cell assembly includes a hydrocarbon fuel flow valve 151 A in fluid communication with the fuel line 150A of the fuel cell assembly for controlling fuel flow through the fuel line 150A to the anode 298. The hydrocarbon fuel flow valve 151 A is depicted as being in wireless operable communication with the controller 240.

[0207] Further, the fuel cell assembly, the gas turbine engine, or both include one or more sensors configured to sense data indicative of one or more operating conditions of the gas turbine engine or both. For example, the fuel cell assembly 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 the fuel cell), a pressure within the fuel cell stack 294 (e.g., within the cathode side 296 or the anode side 298 of the fuel cell), and / or a composition (e.g., a chemical composition) of an output product from the fuel cell assembly 204. Also by way of example, the depicted example gas turbine engine includes a sensor 330. The sensor 330 can be, for example, a temperature sensor configured to sense data indicative of an exit 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. The sensors 302, 330 are depicted as being in wireless operable communication with the controller.

[0208] It will be appreciated that, although Figure 15 the example fuel cell assembly of FIG. 1 does not include a separate fuel processing unit (see, e.g., the fuel processing unit 304 of FIG. 3), in other example embodiments, an example fuel cell assembly can be provided having both an operatively stable anode 298 and a fuel processing unit. Figure 5

[0209] Referring now to Figure 16 , a close-up schematic view of a fuel cell stack 294 having an operatively stable solid oxide fuel cell that can be incorporated into one or more fuel cell assemblies of the present disclosure, such as the example fuel cell assembly of FIG. 1, is depicted. The fuel cell stack 294 is schematically depicted in FIG. 1 as having a single solid oxide fuel cell. Figure 15 Figure 16 ​​​

[0210] Figure 16 The operatively stable fuel cell assembly generally includes a cathode 296 and an electrolyte layer 300, and an anode 298 positioned opposite the electrolyte layer from the cathode 296.

[0211] The cathode 296 defines an inlet 362 configured to receive a first gas stream 364 from an air delivery assembly of the fuel cell assembly. The anode 298 defines a second inlet 366 for receiving a second gas stream 368 from the air delivery assembly and a third inlet 370 for receiving a hydrocarbon fuel 372. In this way, the fuel cell can be incorporated into a fuel cell assembly without a fuel processing unit.

[0212] However, as depicted in dashed lines, the anode 298 of the fuel cell can further define a fourth inlet 374 configured to receive a reformed fuel 376 from the fuel processing unit 304. In this way, the fuel cell can be further incorporated into a fuel cell assembly with a fuel processing unit.

[0213] As will be appreciated, the anode 298 generally includes a composite material including an operatively stable ceramic phase and a metallic phase (i.e., a cermet). The metallic phase can be finely dispersed within a ceramic matrix of the ceramic phase. As used herein, the term “operatively stable” means that the presence of an oxidizing gas (e.g., oxygen) at the anode 298 at normal operating temperatures of the fuel cell assembly, e.g., 600°C to 1000°C, does not result in significant oxidation of the metallic phase of the cermet in the anode 298. For example, the oxygen content of the oxidizing gas on the anode 298 can be greater than about 0.1 mass%, such as greater than about 2 mass%, such as greater than about 5 mass% (and, for example, up to 100% oxygen). In embodiments, the anode 298 of the operatively stable fuel cell can have substantially no nickel content. In another embodiment, the anode 298 of the operatively stable fuel cell can have a nickel content of less than or equal to about 25% volume percent (nickel volume divided by total volume, or vol / vol), such as less than or equal to about 10% vol / vol, such as less than or equal to about 5% vol / vol, such as less than or equal to about 1% vol / vol, or such as less than or equal to about 0.5% vol / vol.

[0214] The ceramic phase of the anode 298 can include any suitable ionically conductive ceramic material, such as doped ceria and / or doped zirconia. For example, the ceramic phase can include, but is not limited to, yttria-stabilized zirconia (YSZ), gadolinia-doped ceria (GDC), samaria-doped ceria (SDC), ytterbia-doped ceria (YDC), scandia-stabilized zirconia (SSZ), ytterbia-ceria-scandia-stabilized zirconia (YCSSZ), and the like.

[0215] The metal phase of the anode 298 can include a perovskite-based catalyst and a p- or n-type semiconductor. Perovskite-based catalysts have a crystal structure similar to that of the mineral perovskite, which consists of calcium titanium oxide (CaTi03). The general chemical formula for perovskite-based catalysts is ABX3. A and B are two different cations. X is an anion, typically an oxide. The anion bonds the two cations. Perovskite-based catalysts can also have a double perovskite structure (i.e., A2B2O6).

[0216] Examples of suitable perovskite-based catalysts include titanate-based materials such as lanthanum strontium titanate (LaSrTi03), strontium titanate (SrTi03), niobium titanate (niobium-doped SrTi03), calcium titanate (CaTi03), lead titanate (PbTi03), and the like. Other examples of suitable perovskite-based catalysts include lanthanum strontium iron molybdenum oxide (LaSrFeMo06), bismuth ferrite (BiFe03), lanthanum ytterbium oxide (LaYb03), silicate perovskite (MsSi03), lanthanum manganite (LaMn03), yttrium aluminum perovskite (YAl03), and the like. Examples of suitable p-type or n-type semiconductors include boron-doped silicon, aluminum-doped silicon, boron-doped germanium, arsenic-doped silicon, phosphorus-doped silicon, arsenic-doped germanium, phosphorus-doped germanium, and the like. Alternatively or additionally, the metal phase of the anode 298 can include any suitable metal catalyst that operates as an electronic conductor, such as nickel (Ni), cobalt (Co), copper (Cu), alloys thereof, and the like.

[0217] In embodiments, the operatively stable fuel cell can also have an internal fuel reforming capability, i.e., the fuel cell can be capable of catalytic partial oxidation (CPOx) fuel reforming. Thus, in embodiments, a separate fuel processing unit (see, e.g., fuel processing unit 304 of FIG. 1) can be optional. However, even in embodiments having an internal fuel reforming capability, the operatively stable fuel cell assembly can be effectively operated with reformate (e.g., using a separate fuel processing unit). Figure 5

[0218] In embodiments, the internal fuel reforming capability is provided by the cermet material of the anode 298. In embodiments, the internal fuel reforming capability can be enhanced and / or provided by introducing a noble metal (e.g., platinum, ruthenium, palladium, etc.) or other ceramic material (such as doped ceria, including gadolinia-doped ceria (GDC), samaria-doped ceria (SDC), etc.) on the surface of the anode or on any surface of the fuel within the fuel cell assembly upstream of the anode 298.

[0219] ​The operational stability of the solid oxide fuel cell 294 produces advantages over prior solid oxide fuel cells 294. The anode 298 is less susceptible to oxidation due to the conditions in which the oxidizing gas is present on the anode 298 at operating temperatures or otherwise elevated temperatures (e.g., above 230 °F). Examples of such conditions include an abnormal shut down or the flow of oxidizing gas from the combustor prior to fuel cell cooling. As a result, the anode 298 has increased volumetric stability during redox and / or thermal cycling, and thus is less susceptible to structural damage associated with volumetric changes in the anode 298. Further, in embodiments of the operationally stable fuel cell 294 having an anode 298 with substantially no nickel content or an anode 298 with a nickel content less than or equal to about 25% vol / vol, such as less than or equal to about 10% vol / vol, such as less than or equal to about 5% vol / vol, such as less than or equal to about 1% vol / vol, or such as less than or equal to about 0.5% vol / vol, this can eliminate or reduce the threat of the production of the toxic gas nickel carbonyl due to oxidation of nickel in the anode 298.

[0220] The advantages of the operationally stable fuel cell assemblies discussed herein can produce savings in the manufacture and operation of an aircraft. The operational stability of the fuel cell assemblies allows for reduced shut down and start up times, more flexibility in the shut down and start up procedures, and a reduced need for external controls to ensure safety and reliability. In addition, the internal fuel reforming capability provides flexibility and redundancy in the operation of the fuel cell assembly, and when not including a separate fuel processing unit (see, e.g., the fuel processing unit 304 of Figure 5 The advantages of the operationally stable fuel cell assemblies discussed herein can produce savings in the manufacture and operation of an aircraft. The operational stability of the fuel cell assemblies allows for reduced shut down and start up times, more flexibility in the shut down and start up procedures, and a reduced need for external controls to ensure safety and reliability. In addition, the internal fuel reforming capability provides flexibility and redundancy in the operation of the fuel cell assembly, and when not including a separate fuel processing unit (see, e.g., the fuel processing unit 304 of

[0221] Further explanation and benefits will be understood from the following examples:

[0222] Example 1, Redox Stress Test: Comparison of Nickel / Yttria-Stabilized Zirconia (Ni / YSZ) Metal Ceramic Anode Fuel Cell Stacks

[0223] 2-Cell 100 cm 2 The fuel cell stacks were subjected to a redox stress test as described below. The fuel cell stacks were placed at operating temperature (about 800 °C), and fuel and air flow was initiated. The open circuit operating voltage was measured to obtain a baseline (Cycle 0). The fuel cell stacks were shut down using normal conditions, and the fuel cell stacks were cooled (i.e., cooled with a protective hydrogen flow).

[0224] The fuel cell stack is placed at operating temperature and the fuel and air flows are started for the second time. The open circuit operating voltage is measured and compared to the baseline to determine if damage has occurred in the previous shutdown (Cycle 1). The fuel cell stack is shut down using normal conditions and the fuel cell stack is cooled for the second time (i.e., cooled using a protective hydrogen flow).

[0225] The fuel cell stack is placed at operating temperature and the fuel and air flows are started for the third time. The open circuit operating voltage is measured and compared to the baseline to determine if damage has occurred in the previous shutdown (Cycle 2). Using redox stress conditions (e.g., conditions that allow for anode oxidation), the fuel cell stack is shut down. Specifically, the fuel and air flows are stopped at operating temperature. For safety, the anode gas line is purged with nitrogen for five minutes. The fuel cell stack is allowed to cool while air is allowed to diffuse into the fuel line. Cooling is performed at about 1.5 °C / min over a total time of 12 hours (some stacks were only cooled to 90-100 °C).

[0226] The fuel cell stack is placed at operating temperature and the fuel and air flows are started for the last time. The open circuit operating voltage is measured and compared to the baseline to determine if damage has occurred in the previous shutdown (Cycle 3).

[0227] Figure 17 Results are shown in FIG. 2, where the x-axis represents the cycle number and the y-axis represents the open circuit voltage (“OCV”) for the cycle relative to the baseline OCV. The point on the y-axis represents the baseline OCV (Cycle 0). The first two vertical lines (i.e., the vertical lines immediately to the right of the y-axis) represent thermal cooling with a protective hydrogen flow. The third vertical line represents thermal cooling under redox stress conditions. The subsequent OCVs when cooled with a protective hydrogen flow were 100% of the baseline (Cycles 1 and 2). However, cooling under redox stress conditions caused irreversible damage to the fuel cell stack, as shown by the OCV of Cycle 3, which was about 75% of the baseline OCV. Furthermore, at the stack outlet, no hydrogen was detected at the OCV after the redox stress cooling cycle, indicating that the volume change associated with oxidation of the nickel caused irreversible structural damage to the electrolyte layer and resulted in the combustion of nearly all of the hydrogen in the stack.

[0228] Example 2: Operationally stable lanthanum strontium titanate / gadolinium oxide doped ceria (LST / GDC) cermet anode fuel cell stack

[0229] Two two-cell fuel cell stacks, fabricated using standard or modified surfaces and doped with lanthanum strontium titanate / gadolinium oxide anodes, were subjected to redox stress testing as described below under hydrogen plasma conditions. The fuel cell stacks were placed at operating temperature (approximately 800°C) and fuel and air flow were initiated. The open-circuit operating voltage was measured to obtain a baseline (cycle 1). The fuel cell stacks were then shut down under normal conditions and cooled (i.e., cooled using a protective hydrogen flow).

[0230] The fuel cell stack is brought to operating temperature, and fuel and air flow are initiated for the second time. The open-circuit operating voltage and stack outlet hydrogen percentage are measured and compared to a baseline to determine if damage has occurred during the previous shutdown (cycle 2).

[0231] When used under redox stress conditions (e.g., conditions that allow for anodic oxidation), the fuel cell stack is repeatedly shut down. Specifically, fuel and air flows are stopped at the operating temperature. For safety, the anode gas lines are purged with nitrogen for five minutes. The fuel cell stack is allowed to cool while air is allowed to diffuse into the fuel lines. Cooling is performed at approximately 1.5°C / min over a total of 12 hours (some stacks are cooled only to 90-100°C). After each shutdown, the open-circuit operating voltage is measured and compared to a baseline to determine if any damage has occurred during the previous shutdown (cycles 3-5). In cycles 3 and 4, the stack outlet hydrogen percentage is measured and compared to a baseline to determine if any damage has occurred during the previous shutdown.

[0232] Figure 18 and 19 The results are displayed, where the x-axis represents the number of cycles and the y-axis represents the open-circuit voltage of the cycle relative to the baseline OCV. Figure 18 ) or the amount of hydrogen at the outlet ( Figure 19 The first vertical line to the right of the y-axis represents thermal cooling using a protective hydrogen flow. Subsequent vertical lines represent thermal cooling under redox stress conditions. (Special Reference) Figure 18 When cooled using a protective hydrogen stream, the subsequent OCV is 100% of the baseline (cycle 1). Under redox stress cooling, the subsequent OCV is approximately 100% of the baseline. Furthermore, specific references are made. Figure 19 The reactor outlet showed that the percentage of hydrogen at the OCV after the redox stress cooling cycle did not decrease compared to the percentage of hydrogen at the OCV after thermal cooling using a protective hydrogen flow.

[0233] In this manner, it will be appreciated that these examples show that a benefit of an operatively stable fuel cell (e.g., an operatively stable fuel cell stack) is that the fuel cell can withstand redox stress conditions without experiencing a failure, or a significant drop in OCV of the hydrogen content at the outlet of the fuel cell. As described herein, further benefits can be realized based on this operational stability when the fuel cell (and fuel cell stacks and fuel cell assemblies) are incorporated into an aeroengine.

[0234] (vi) Figure 20 Embodiments of a redox stable anode system; start-up

[0235] As will be appreciated from the description herein, a fuel cell including an operatively stable anode can further facilitate changes to certain operations of a fuel cell assembly having such a fuel cell.

[0236] For example, referring now to Figure 20 A flowchart of a method 1100 for starting a gas turbine engine and a fuel cell assembly according to another example embodiment of the present disclosure is provided. The example method 1100 can be used with one or more example gas turbine engines of the present disclosure (e.g., the gas turbine engine 100 of Figure 1 , Figure 2 , Figure 5 and so forth), and one or more example fuel cell assemblies of the present disclosure having a fuel cell with an operatively stable anode (e.g., the fuel cell assembly 204 of Figures 15 to 18 ). Alternatively, the method 1100 can be used with any other suitable gas turbine engine and fuel cell assembly.

[0237] The example method 1100 includes performing a start-up sequence of the fuel cell assembly. In particular, performing the start-up sequence of the fuel cell assembly includes purging, at (1102), the anode and cathode of the fuel cell within the air source.

[0238] Further, the method 1100 includes, at (1104), heating the fuel cell assembly, and in particular, heating the fuel cell stack of the fuel cell assembly including the fuel cell. Heating the fuel cell assembly at (1104) can generally include, at (1105), heating the fuel cell assembly from a cold start temperature to a second fuel cell reference temperature. The cold start temperature can be less than 100°C, such as less than about 80°C, and at least about equal to an ambient temperature.

[0239] Further, for Figure 20An exemplary aspect of the method 1100 described herein includes, at (1104), heating the fuel cell assembly, further comprising, at (1106), using an air treatment unit to heat the fuel cell assembly. Heating the fuel cell assembly using the air treatment unit at (1106) includes, at (1108) activating the pre-combustion unit of the air treatment unit, and at (1110) supplying exhaust gas from the pre-combustion unit to the anode and cathode of the fuel cell to simultaneously heat both the anode and cathode. In this manner, heating the fuel cell assembly using the air treatment unit at (1106) generally includes, by arranging the air treatment unit at a heating rate, heating the fuel cell assembly to a desired temperature, such as a second fuel cell reference temperature.

[0240] However, for the exemplary aspect described, heating the fuel cell assembly at (1104) further includes heating the fuel cell at (1112) using a fuel processing unit. Specifically, for Figure 20 An exemplary aspect of the method 1100 described herein includes heating the fuel cell using a fuel treatment unit at (1112) and further including starting operation of the fuel treatment unit at (1114) and supplying exhaust gas from the fuel treatment unit to the anode of the fuel cell at (1116).

[0241] Generally speaking, it will be understood that including an operationally stable anode in a fuel cell can provide greater flexibility in ground-start operations by heating the fuel cell stack.

[0242] Specifically, still refer to Figure 20 It will be understood that the startup sequence of the fuel cell assembly, and more specifically, heating the fuel cell assembly at (1104) generally includes, at (1118) providing a flow containing oxygen to the anode of the fuel cell when the temperature of the fuel cell stack is less than or equal to a first fuel cell temperature threshold. The oxygen content can be greater than about 0.1% by mass, such as greater than about 2% by mass, such as greater than about 5% by mass. The first fuel cell temperature threshold can be between about 230°C and about 400°C. The oxygen-containing gas (i.e., the flow containing oxygen) provided to the anode of the fuel cell at (1114) can be a heated gas flow from an air handling unit, or any other suitable heated gas flow source. With this configuration, an operationally stable fuel cell can include an anode that is substantially nickel-free.

[0243] Furthermore, for Figure 20In exemplary aspects of the method 1100 depicted, performing a start-up sequence of a fuel cell assembly, and more particularly, heating the fuel cell assembly at (1104) further includes providing a flow having an oxygen content to an anode of the fuel cell at (1120) when a temperature of the fuel cell stack is less than or equal to a second fuel cell temperature threshold (e.g., prior to the temperature of the fuel cell stack being greater than or equal to the second fuel cell temperature threshold during the start-up sequence). For example, providing the flow to the anode of the fuel cell at (1120) can include providing the flow having the oxygen content to the anode of the fuel cell when the temperature of the fuel cell stack is between the first fuel cell temperature threshold and the second fuel cell temperature threshold. The oxygen content can be greater than about 0.1 mass%, such as greater than about 2 mass%, such as greater than about 5 mass%. The second fuel cell temperature threshold can be greater than the first fuel cell temperature threshold, for example between about 400 °C and about 750 °C. With this configuration, the operatively stable fuel cell can include an anode having a nickel content less than or equal to about 25%, such as less than or equal to about 10%.

[0244] Further, a fuel cell including an operatively stable anode and a noble metal or ceramic material that catalyzes partial oxidation of, for example, catalytic aviation fuel, can allow for internal fuel reforming action at the anode of the fuel cell assembly. The internal fuel reforming action can generate relatively high heat, which can aid in heating the fuel cell stack during a start-up sequence of the fuel cell assembly.

[0245] In particular, for Figure 20 In exemplary aspects of the method 1100 depicted, performing a start-up sequence of a fuel cell assembly, and more particularly, heating the fuel cell assembly at (1104) further includes performing a fuel reforming action at an anode of a fuel cell of the fuel cell assembly at (1122). For the exemplary aspects described, performing the fuel reforming action at the anode of the fuel cell at (1122) includes providing a hydrocarbon fuel flow to the anode of the fuel cell at (1124) and providing an oxygen-containing gas flow to the anode of the fuel cell at (1126). In this manner, the method 1100 can heat the fuel cell stack more quickly, resulting in a faster start-up time of the fuel cell assembly. Notably, it will be appreciated that the fuel reforming action at the anode of the fuel cell at (1122) can include providing a limited or controlled amount of oxygen in order to prevent complete combustion of the provided hydrocarbon fuel. As will be appreciated, since the anode is an operatively stable anode, the oxygen content of the fuel will not result in oxidation of the anode.

[0246] Still referring to Figure 20In the example method 1100 depicted, the method 1100 further includes, at (1128), determining that the fuel cell stack temperature is greater than or equal to a second fuel cell temperature threshold, and, at (1130), switching to a power generation mode of the fuel cell assembly.

[0247] Further, as will be appreciated, Figure 20 The example startup sequence depicted can be performed in conjunction with a gas turbine engine startup sequence, such as according to the example gas turbine engine startup sequence of the method 400 described above with reference to Figure 6 The example gas turbine engine startup sequence according to the method 400 can be initiated prior to beginning execution of the startup sequence of the fuel cell assembly (e.g., prior to (1102)), or, alternatively, can be initiated at any other suitable time during heating of the fuel cell stack at (1104). Alternatively, the gas turbine engine startup sequence can still not be initiated until the fuel cell stack temperature is determined to be greater than or equal to the second fuel cell temperature threshold at (1128) and the fuel cell assembly is switched to the power generation mode (1130).

[0248] (vii) Figure 21 Thermal management of fuel cell assemblies having redox stable anodes

[0249] Reference is now made to Figure 21 It will be further appreciated that, in certain example aspects of the present disclosure, including a fuel cell having an operationally stable anode in a fuel cell stack of a fuel cell assembly can allow for thermal management of the fuel cell, thermal management of a gas turbine engine comprising the fuel cell assembly, or both.

[0250] In particular, Figure 21 A flowchart of a method 1200 for operating a fuel cell assembly according to example aspects of the present disclosure is provided. The example method 1200 can be used with one or more example fuel cell assemblies described herein (e.g., one or more fuel cell assemblies 204 described above with reference to Figures 15 to 19 The example method 1200 can be used with one or more example gas turbine engines described herein (e.g., the gas turbine engine 100 described above with reference to Figure 1 and Figure 5 In this manner, it will be appreciated that the method 1200 can be used with a fuel cell assembly having a fuel cell stack with a solid oxide fuel cell. The solid oxide fuel cell can include an anode, a cathode, and an electrolyte layer positioned therebetween. The anode and the cathode can be configured to provide an output product through an outlet of the fuel cell during operation of the fuel cell assembly.

[0251] The method 1200 includes determining, at (1202), a temperature setpoint for the fuel cell stack, an output product of the fuel cell stack, or both, and controlling, at (1204), a volume of oxidant provided to the anode in response to the temperature setpoint determined at (1202) to control a temperature of the fuel cell stack, a temperature of the output product of the fuel cell stack, or both.

[0252] In particular, for the example aspect of the method 1200 depicted in Figure 21 For the example aspect of the method 1200 depicted in

[0253] As described in detail above, performing the fuel reforming action at the anode can generate relatively large amounts of heat, which can allow the fuel cell stack to reach (or more quickly reach) a temperature setpoint, can allow an output product of the fuel cell to reach a setpoint, or both.

[0254] Further, as noted above, the oxygen-containing gas can be an ambient airflow, or alternatively, the oxygen-containing gas can be an airflow from a compressor section of a gas turbine engine.

[0255] Still referring to the example aspect of the method 1200 depicted in Figure 21 For the example aspect of the method 1200 depicted in

[0256] Further, with such example aspects, controlling the volume of oxidant provided to the anode at (1204) further includes providing an oxygen-containing gas to the anode prior to the temperature of the fuel cell stack exceeding the first fuel cell temperature threshold at (1218). This can be due at least in part to including an operatively stable anode.

[0257] In this way, the method 1200 can be used to achieve, or more quickly achieve, a desired operating temperature of the fuel cell assembly.

[0258] Still further, with respect to Figure 21 With respect to the example aspects of the method 1200 depicted in FIG. 12, the method 1200 includes operating the fuel cell assembly in a power generation mode at (1220). Operating the fuel cell assembly in a power generation mode can generally include providing power from the fuel cell stack to a power bus, one or more accessory systems, or both. With such a configuration, determining the temperature setpoint at (1202) can include determining the temperature setpoint in response to a gas turbine engine operating condition at (1221). The gas turbine engine operating condition can generally refer to a gas turbine engine operating condition indicative of an emissions parameter, a combustion dynamics parameter, a power output parameter, or a combination thereof. As will be appreciated from the description herein, adding heat to the combustion chamber of the combustor of the gas turbine engine generally impacts the emissions of the gas turbine engine (e.g., NOxand CO emissions), the combustion dynamics within the combustor of the gas turbine engine, the amount of power that can be extracted through the turbine section of the gas turbine engine, etc. In this way, it will be appreciated that the temperature setpoint determined at (1202), (1221) can be determined to, for example, reduce gas turbine engine emissions, reduce combustion dynamics within the combustor of the gas turbine engine, increase the amount of power that can be extracted to the turbine section of the gas turbine engine, etc.

[0259] Still referring to Figure 21 It will be further appreciated that controlling the volume of oxidant provided to the anode at (1204) can more specifically include controlling the volume of oxidant provided to the anode at (1222) while operating the fuel cell assembly in a power generation mode at (1220), and more specifically, in response to the temperature setpoint determined at (1220), (1221).

[0260] (viii) Figure 22 Cooling procedure for redox stable anode system

[0261] Referring now to Figure 22 It will be further appreciated that, in certain example aspects of the present disclosure, including a fuel cell having an operatively stable anode in the fuel cell stack of the fuel cell assembly can allow for improvements to the cooling and shutdown procedures of the fuel cell assembly.

[0262] In particular, Figure 22 A propulsion system for operating an aircraft is provided, and in particular, a method 1300 for coordinating the cooling or shutdown of a fuel cell assembly in conjunction with the shutdown of a gas turbine engine incorporating the fuel cell assembly. The fuel cell assembly and the gas turbine engine can be constructed in a manner similar to one or more exemplary fuel cell assemblies and gas turbine engines described herein. For example, the fuel cell assembly may generally comprise a fuel cell stack of a solid oxide fuel cell with a defined outlet positioned to remove output products from the solid oxide fuel cell during operation.

[0263] Method 1300 includes, at (1302), operating a fuel cell assembly to provide output products to a combustor (e.g., the combustion chamber of the combustor) in the combustion section of a gas turbine engine. Operating the fuel cell assembly at (1302) to provide output products may include, at (1303), operating the fuel cell assembly, the gas turbine engine, or both, in steady-state flight operation (e.g., cruise operating conditions and / or power generation mode).

[0264] Method 1300 further includes, at (1315), operating the fuel cell assembly, the gas turbine engine, or both, such that while operating the gas turbine engine, the pressure within the anode of the solid oxide fuel cell is less than the pressure within the cathode of the solid oxide fuel cell, less than the pressure within the combustion chamber of the gas turbine engine, or both.

[0265] For example, as will be understood from the description herein, operating the fuel cell assembly, gas turbine engine, or both at (1315) may generally include operating the fuel cell assembly at (1316) such that, while operating the gas turbine engine, the pressure within the anode of the solid oxide fuel cell is less than the pressure within the cathode of the solid oxide fuel cell. This may, for example, occur while the fuel cell assembly is shut down. Utilizing this exemplary aspect, operating the fuel cell assembly at (1316) such that, while operating the gas turbine engine, the pressure within the anode of the solid oxide fuel cell is less than the pressure within the cathode of the solid oxide fuel cell includes, at (1318), reducing the fuel flow to the anode of the solid oxide fuel cell.

[0266] Furthermore, in certain exemplary aspects, such as in Figure 22In the depicted example aspects, operating the fuel cell assembly, at (1316), such that the pressure within the anode of the solid oxide fuel cell is less than the pressure within the cathode of the solid oxide fuel cell while the gas turbine engine is being operated further includes flowing an oxidant into the anode when the temperature of the solid oxide fuel cell is between about 230 degrees Celsius and 700 degrees Celsius, at (1320). As noted, this can be accommodated by including a fuel cell that is operatively stable.

[0267] Still referring to Figure 22 Operating the fuel cell assembly, the gas turbine engine, or both, at (1315) can additionally or alternatively include operating the fuel cell assembly, the gas turbine engine, or both, such that the pressure within the anode of the solid oxide fuel cell is less than the pressure within the combustion chamber of the gas turbine engine or both while the gas turbine engine is being operated. More particularly, for the depicted example aspects, operating the fuel cell assembly, the gas turbine engine, or both, at (1315) includes executing a shutdown sequence of the gas turbine engine, at (1304), and executing a cooling sequence of the fuel cell assembly while the shutdown sequence of the gas turbine engine is being executed at (1304), at (1306). Figure 20 More particularly, for the depicted example aspects, executing the shutdown sequence of the gas turbine engine, at (1304), can include executing the shutdown sequence of the gas turbine engine after operating the fuel cell assembly, at (1302), at (1305). Further, for the depicted example, executing the shutdown sequence of the gas turbine engine, at (1304), includes decelerating the gas turbine engine to a shutdown condition, at (1308), and, more particularly, includes decelerating the gas turbine engine from at least a ground idle operating condition to the shutdown condition.

[0268] "cooling" as used in this context refers to any reduction in temperature of, for example, the fuel cell stack, and does not necessarily require shutdown of the fuel cell assembly. In certain example aspects, the cooling sequence can refer to allowing the fuel cell assembly to cool down without any active cooling of the fuel cell assembly. For example, executing the cooling sequence can include allowing the fuel cell assembly, or more particularly the fuel cell stack, to cool at a rate of less than 0.75 °C per minute, such as less than about 0.70 °C per minute, such as less than about 0.65 °C per minute, such as less than about 0.60 °C per minute, such as less than about 0.50 °C per minute.

[0269] More particularly, for the depicted example aspects, executing the shutdown sequence of the gas turbine engine, at (1304), can include executing the shutdown sequence of the gas turbine engine after operating the fuel cell assembly, at (1302), at (1305). Further, for the depicted example, executing the shutdown sequence of the gas turbine engine, at (1304), includes decelerating the gas turbine engine to a shutdown condition, at (1308), and, more particularly, includes decelerating the gas turbine engine from at least a ground idle operating condition to the shutdown condition.

[0270] Further, still referring to Figure 22In the exemplary aspect described, performing the shutdown sequence of the gas turbine engine at (1306) while simultaneously performing the cooling sequence of the fuel cell assembly more specifically includes (1310) operating the fuel cell assembly to limit the pressure in the anode of the solid oxide fuel cell to be less than the pressure in the combustion chamber of the combustor of the gas turbine engine. (See references herein) Figure 22 In the exemplary aspects of method 1300 described herein, the term "pressure" may refer to static pressure.

[0271] It is noteworthy that, when performing the cooling sequence of the gas turbine engine at (1306), method 1300 includes, at (1312), reducing the pressure of the fuel flow to the anode of the solid oxide fuel cell, reducing the pressure of the gas flow to the cathode of the solid oxide fuel cell, or both. Specifically, for the illustrated embodiment, performing the cooling sequence of the fuel cell assembly at (1306) more specifically includes reducing the pressure of the fuel flow to the anode of the solid oxide fuel cell as part of (1312).

[0272] More specifically, for an exemplary aspect of the depicted method 1300, performing the cooling sequence of the fuel cell assembly at (1306) includes cutting off the fuel flow to the anode of the solid oxide fuel cell, the gas flow to the cathode of the solid oxide fuel cell, or both, at (1313). In particular, for the illustrated embodiment, performing the cooling sequence of the fuel cell assembly at (1306) more specifically includes cutting off the fuel flow to the anode of the solid oxide fuel cell. In some exemplary aspects, cutting off the fuel flow to the anode of the solid oxide fuel cell may occur when the temperature of the fuel cell stack is between about 230°C and about 700°C, and when the gas turbine engine is operating at a speed of at least 100 revolutions per minute.

[0273] In this way, it will be understood that while performing the shutdown sequence of the gas turbine engine at (1306), the gas in the combustion chamber of the gas turbine engine can travel to the anode of the solid oxide fuel cell (e.g., through the outlet of the solid oxide fuel cell). More specifically, it will be understood that, for the exemplary aspects described, performing the cooling sequence of the fuel cell assembly at (1306) includes, at (1314), providing an airflow from the combustion chamber to the anode of the solid oxide fuel cell. The airflow may include oxygen-containing gas and may be at a temperature between about 230°C and about 700°C.

[0274] It will be understood that, in some exemplary aspects, performing the cooling sequence of the fuel cell assembly at (1306) may further include transitioning to a warm standby state, as referenced above. Figure 14and the method 900 describes a warm standby state (e.g., can include maintaining the fuel cell stack of the fuel cell assembly in a warm standby state at (912)).

[0275] In this manner, it will be appreciated that operating a fuel cell assembly according to one or more example aspects of the present disclosure can allow for more efficient operation of the fuel cell assembly and the gas turbine engine incorporating the fuel cell assembly. For example, during a shutdown operation of the gas turbine engine, operating a fuel cell assembly, a gas turbine engine, or both, according to the present disclosure with an operatively stable fuel cell can allow the fuel flow to the fuel cell assembly to terminate before the flame in the combustion chamber of the gas turbine engine is extinguished, allowing all of the hydrogen in the output product to be combusted. Further, such example aspects can allow for more efficient operation by allowing the pressure within the cathode of the fuel cell to exceed the pressure within the anode of the fuel cell without concern for anode oxidation, thereby saving fuel and air flow.

[0276] Further, operating a fuel cell assembly, a gas turbine engine, or both, according to the present disclosure with an operatively stable fuel cell can allow the fuel cell to be maintained at a lower baseline pressure as it is tolerant of surge conditions within the combustor, such that the gases within the combustion chamber can flow into the anode of the fuel cell.

[0277] (ix) Figure 23 Embodiments of a control system diagram

[0278] Reference is now made to Figure 23 , Figure 23 A schematic diagram showing a diagram of a control system 1400 that can be used in one or more example systems and methods described herein, such as one or more example fuel cell assemblies 204 described herein above; ground start methods 500, 600, 700, 800, 1100, 1200; example warm standby method 900; and example cooling method 1300.

[0279] Referring to Figure 23 , the control system 1400 includes a hybrid controller 1410 (which can be constructed in a similar manner as the example fuel cell controller 240 described above with reference to Figure 5 , a human machine interface (HMI) 1412, a memory device 1414, and a processor 1416. The human machine interface (HMI) 1412 can be used to input data and interact with the hybrid controller 1410. The processor 1416 can be constructed in a similar manner as the processor 332A described above with reference to Figure 5 , and the memory device 1414 can be constructed in a similar manner as the memory device 332B described above with reference to Figure 5 .

[0280] The control system 1400 includes a fuel cell subsystem 1420 that controls parameters and conditions related to a fuel cell stack of a fuel cell assembly during, for example, ground start, warm-up, or cool-down processes. The control system 1400 further includes an engine subsystem 1430 that controls parameters and conditions related to a gas turbine engine system, such as a gas turbine engine system incorporating a fuel cell assembly, during, for example, ground start, warm-up, or cool-down processes.

[0281] The fuel cell subsystem 1420 includes a fuel cell temperature sensor 1422 that senses data indicative of a temperature of the high temperature fuel cell stack and a fuel cell pressure sensor 1424 that senses data indicative of a pressure of the high temperature fuel cell stack. The fuel cell subsystem 1420 also includes a fuel cell fuel flow sensor 1426 that senses data indicative of a fuel flow associated with the high temperature fuel cell stack and a fuel cell air flow sensor 1428 that senses data indicative of an air fuel flow associated with the high temperature fuel cell stack. The fuel cell subsystem 1420 further includes a fuel cell fuel flow valve 1442 that controls a fuel flow stream to the high temperature fuel cell stack and a fuel cell air flow valve 1444 that controls an air stream to the high temperature fuel cell stack. The fuel cell subsystem 1420 also includes a fuel cell stack exhaust igniter 1446 that ignites fuel cell effluent within a combustor. In this manner, it will be understood that the fuel cell subsystem 1420 includes both data inputs (e.g., sensors) and control outputs (e.g., controls for valves, igniters, etc. that control operation of the fuel cell assembly) of the fuel cell assembly.

[0282] The engine subsystem 1430 includes an engine speed sensor 1432 that senses data indicative of an operating speed of the gas turbine engine, an engine fuel flow sensor 1434 that senses data indicative of a fuel flow of the gas turbine engine, and an engine temperature sensor 1436 that senses data indicative of a temperature of the gas turbine engine. The engine subsystem 1430 also includes an engine starter 1452 that starts the gas turbine engine and a combustor igniter 1454 that ignites a combustion mixture of fuel and air within the combustor. The engine subsystem 1430 also includes an engine fuel flow valve 1456 that controls a flow of fuel to the combustor. In this manner, it will be appreciated that the engine subsystem 1430 includes both data inputs (e.g., sensors) and control outputs (e.g., controls for valves, igniters, etc. that control operation of the gas turbine engine) of the fuel cell assembly.

[0283] As noted above, a gas turbine engine having a fuel cell assembly, such as a SOFC fuel cell assembly, can be used in a hybrid aircraft system. Certain operations of the hybrid aircraft can require coordination of the gas turbine engine, the fuel cell, the fuel processing unit, and other components. For example, as the hybrid aircraft is started on the ground, the start timing of these components needs to be coordinated. With certain example embodiments, the heating process of the fuel cell can take the longest, such as about twenty to thirty minutes. The start process of the fuel processing unit, such as CPOx, can take about one to two minutes. The engine can take about one to two minutes to reach a predetermined idle speed from a start speed.

[0284] Further, environmental and safety standards during ground start require compliance with emission limits related to H2 / CO emissions to human / airport personnel, maintaining fuel cell materials within the chemical, thermal, and mechanical limits of integrity. The control system 1400 including the present disclosure can more efficiently allow coordination of the fuel cell assembly and the gas turbine engine, for example, by directly receiving data indicative of the fuel cell assembly via the fuel cell subsystem 1420, directly receiving data indicative of the gas turbine engine via the engine subsystem 1430, and directly implementing control decisions to the gas turbine engine and the fuel cell assembly via the engine subsystem 1430 and the fuel cell subsystem 1420, respectively. In this manner, control of the gas turbine engine and the fuel cell assembly can be more efficiently implemented, including performing one or more example methods disclosed herein.

[0285] 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.

[0286] Further aspects are provided by the subject matter of the following clauses:

[0287] A method for operating a propulsion system of an aircraft, the propulsion system including a gas turbine engine and a fuel cell assembly, the fuel cell assembly including a fuel cell stack having fuel cells defining an outlet positioned to remove output products from the fuel cells during operation, the method comprising: performing a start-up sequence of the gas turbine engine, wherein performing the start-up sequence includes initiating the start-up sequence of the gas turbine engine; performing a start-up sequence of the fuel cell assembly simultaneously with or after initiating the start-up sequence of the gas turbine engine; and operating the fuel cell assembly to provide output products to a combustion section of the gas turbine engine.

[0288] The method according to one or more of these clauses, wherein performing the start-up sequence of the gas turbine engine includes achieving a flame on condition of the gas turbine engine, and wherein performing the start-up sequence of the fuel cell assembly includes performing a start-up sequence of the fuel cell assembly simultaneously with or after achieving the flame on condition of the gas turbine engine.

[0289] The method according to one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly includes operating in a purge state after initiating the start-up sequence of the fuel cell assembly; operating in a first heating state before a temperature of the fuel cell stack reaches a first fuel cell temperature threshold; operating in a second heating state after the temperature of the fuel cell stack reaches the first fuel cell temperature threshold and before the temperature of the fuel cell stack reaches a second fuel cell temperature threshold; and operating in a power generation state after the temperature of the fuel cell stack reaches the second fuel cell temperature threshold.

[0290] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly comprises operating in a purge state to provide a gas stream from a compressor section of the gas turbine engine to purge an anode and a cathode of the fuel cell.

[0291] The method of one or more of these clauses, wherein the gas stream from the compressor section is at a temperature of at least about 200 degrees Celsius.

[0292] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly further comprises providing an output product from the fuel cell to a combustor of the combustion section while the gas turbine engine is operating in a flame on condition or faster, wherein the output product comprises hydrogen.

[0293] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly comprises initiating operation of a fuel processing unit and providing exhaust gas of the fuel processing unit to a combustor of a combustion section of the gas turbine engine around an anode of the fuel cell.

[0294] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly further comprises providing a heated gas stream from the fuel processing unit to a cathode of the fuel cell.

[0295] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly further comprises receiving data indicating that a temperature of the fuel cell stack is greater than or equal to a first fuel cell temperature threshold; and in response to receiving data indicating that the temperature of the fuel cell stack is greater than or equal to a first fuel cell temperature threshold, providing exhaust gas of the fuel processing unit to an anode of the fuel cell.

[0296] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly further comprises in response to receiving data indicating that a temperature of the fuel cell stack is greater than or equal to a first fuel cell temperature threshold, providing exhaust gas of the fuel processing unit to a cathode of the fuel cell.

[0297] The method of one or more of these clauses, wherein providing the exhaust gas of the fuel processing unit to the cathode of the fuel cell comprises providing the exhaust gas of the fuel processing unit to the cathode of the fuel cell at a pressure that is less than a pressure of the exhaust gas of the fuel processing unit provided to the anode of the fuel cell.

[0298] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly further comprises: receiving data indicating that a temperature of the fuel cell stack is greater than or equal to a second fuel cell temperature threshold; and beginning operation of the fuel cell assembly in a power generation mode.

[0299] The method of one or more of these clauses, wherein the second fuel cell temperature threshold is at least about 400 degrees Celsius.

[0300] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly comprises: operating an air handling unit; and providing exhaust gas of the air handling unit to a cathode of the fuel cell, an anode of the fuel cell, or both.

[0301] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly further comprises receiving data indicating that a temperature of the fuel cell stack is greater than or equal to a first fuel cell temperature threshold; operating a fuel handling unit; in response to receiving data indicating that the temperature of the fuel cell stack is greater than or equal to a first fuel cell temperature threshold, providing exhaust gas of the fuel handling unit to the anode of the fuel cell; in response to receiving data indicating that the temperature of the fuel cell stack is greater than or equal to a first fuel cell temperature threshold, providing exhaust gas of the air handling unit to a cathode of the fuel cell.

[0302] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly comprises: providing a flow having an oxygen content to an anode of the fuel cell before a temperature of the fuel cell stack is greater than or equal to a first fuel cell temperature threshold.

[0303] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly comprises: providing a flow having an oxygen content to an anode of the fuel cell before a temperature of the fuel cell stack is greater than or equal to a second fuel cell temperature threshold.

[0304] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly comprises: performing a fuel reforming action at an anode of the fuel cell.

[0305] The method of one or more of these clauses, wherein performing a fuel reforming action at an anode of the fuel cell assembly comprises: providing a flow of a hydrocarbon fuel to the anode, and providing a flow of an oxygen-containing gas to the anode.

[0306] A propulsion system for an aircraft having a gas turbine engine, the aircraft including an aircraft fuel supply, the propulsion system comprising: a fuel cell assembly including a fuel cell stack having fuel cells, the fuel cells defining an outlet positioned to remove an output product from the fuel cells; a turbomachine including, in serial flow order, a compressor section, a combustion section, and a turbine section, the combustion section being configured to receive a flow of aviation fuel from the aircraft fuel supply, and further configured to receive the output product from the fuel cell; and a controller including a memory and one or more processors, the memory storing instructions that, when executed by the one or more processors, cause the propulsion system to perform operations including executing a start-up sequence of the gas turbine engine, wherein executing the start-up sequence includes initiating the start-up sequence of the gas turbine engine; concurrently with or after initiating the start-up sequence of the gas turbine engine, executing a start-up sequence of the fuel cell assembly; and operating the fuel cell assembly to provide an output product to a combustion section of the gas turbine engine.

[0307] A method for operating a propulsion system of an aircraft, the propulsion system including a gas turbine engine and a fuel cell assembly, the fuel cell assembly including a fuel cell stack having fuel cells defining an outlet positioned to remove an output product from the fuel cells during operation, the method comprising: executing a start-up sequence of the fuel cell assembly, wherein executing the start-up sequence of the fuel cell assembly includes initiating the start-up sequence of the fuel cell assembly; executing a start-up sequence of the gas turbine engine, wherein executing the start-up sequence of the gas turbine engine includes initiating the start-up sequence of the gas turbine engine after initiating the start-up sequence of the fuel cell assembly; and operating the fuel cell assembly to provide an output product to a combustion section of the gas turbine engine.

[0308] The method according to one or more of these clauses, wherein executing the start-up sequence of the fuel cell assembly includes: operating in a purge state after initiating the start-up sequence of the fuel cell assembly; operating in a first heating state before a temperature of the fuel cell stack reaches a first fuel cell temperature threshold; operating in a second heating state after the temperature of the fuel cell stack reaches the first fuel cell temperature threshold and before the temperature of the fuel cell stack reaches a second fuel cell temperature threshold; and operating in a power generation state after the temperature of the fuel cell stack reaches the second fuel cell temperature threshold.

[0309] The method of one or more of these clauses, wherein starting the start-up sequence of the gas turbine engine after starting the start-up sequence of the fuel cell assembly comprises starting the start-up sequence of the gas turbine engine before a temperature of the fuel cell stack reaches a first fuel cell temperature threshold.

[0310] The method of one or more of these clauses, wherein the first fuel cell temperature threshold is at least about 230 degrees Celsius.

[0311] The method of one or more of these clauses, wherein starting the start-up sequence of the gas turbine engine after starting the start-up sequence of the fuel cell assembly comprises starting the start-up sequence of the gas turbine engine after a temperature of the fuel cell stack has reached a first fuel cell temperature threshold and before the temperature of the fuel cell stack reaches a second fuel cell temperature threshold.

[0312] The method of one or more of these clauses, wherein the first fuel cell temperature threshold is between about 230 degrees Celsius and about 400 degrees Celsius, wherein the second fuel cell temperature threshold is between about 400 degrees Celsius and about 750 degrees Celsius, and wherein the second fuel cell temperature threshold is greater than the first fuel cell temperature threshold.

[0313] The method of one or more of these clauses, wherein starting the start-up sequence of the gas turbine engine after starting the start-up sequence of the fuel cell assembly comprises starting the start-up sequence of the gas turbine engine after a temperature of the fuel cell stack has reached a second fuel cell temperature threshold.

[0314] The method of one or more of these clauses, wherein the second fuel cell temperature threshold is between about 400 degrees Celsius and about 750 degrees Celsius.

[0315] The method of one or more of these clauses, wherein the fuel cell assembly comprises an air handling unit, and wherein performing the start-up sequence of the fuel cell assembly further comprises completing the start-up sequence of the fuel cell assembly and directing one or more streams of the output product from the fuel cell to the air handling unit before completing the start-up sequence of the fuel cell assembly.

[0316] The method of one or more of these clauses, wherein the one or more streams of the output product from the fuel cell comprise an anode stream, a cathode stream, or both.

[0317] The method of one or more of these clauses, wherein the fuel cell assembly includes a fuel processing unit, and wherein performing the start-up sequence of the fuel cell assembly further comprises: completing the start-up sequence of the fuel cell assembly, and directing one or more streams of the output product from the fuel cell to the fuel processing unit prior to completing the start-up sequence of the fuel cell assembly.

[0318] The method of one or more of these clauses, wherein the one or more streams of the output product from the fuel cell include an anode stream, a cathode stream, or both.

[0319] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly includes: operating the fuel cell assembly in a warm standby state; operating the fuel cell assembly in a ground idle power generation mode; and operating the fuel cell assembly in a normal power generation mode.

[0320] The method of one or more of these clauses, wherein operating the fuel cell assembly in the ground idle power generation mode includes: operating the fuel cell assembly at a fuel utilization that is within about 10% of a maximum fuel utilization.

[0321] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly includes: initiating operation of a fuel processing unit, and providing exhaust gas of the fuel processing unit to a combustor of a combustion section of the gas turbine engine, an air processing unit of the fuel cell assembly, or both around an anode of the fuel cell.

[0322] The method of one or more of these clauses, wherein the fuel cell assembly includes an air processing unit and a fuel processing unit, wherein performing the start-up sequence of the fuel cell assembly includes: providing exhaust gas from the air processing unit to a cathode of the fuel cell and providing exhaust gas from the fuel processing unit to an anode of the fuel cell.

[0323] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly includes: providing a flow having an oxygen content to an anode of the fuel cell prior to a temperature of the fuel cell stack being greater than or equal to a first fuel cell temperature threshold.

[0324] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly includes: providing a flow having an oxygen content to an anode of the fuel cell prior to a temperature of the fuel cell stack being greater than or equal to a second fuel cell temperature threshold.

[0325] The method of one or more of these clauses, wherein performing the start-up sequence of the fuel cell assembly includes performing a fuel reforming action at an anode of the fuel cell assembly.

[0326] The method of one or more of these clauses, wherein performing a fuel reforming action at an anode of the fuel cell assembly includes providing a flow of a hydrocarbon fuel to the anode and providing a flow of an oxygen-containing gas to the anode.

[0327] A propulsion system for an aircraft having a gas turbine engine, the aircraft including an aircraft fuel supply, the propulsion system including: a fuel cell assembly including a fuel cell stack having a fuel cell, the fuel cell defining an outlet positioned to remove an output product from the fuel cell; a turbomachine including a compressor section, a combustion section, and a turbine section arranged in serial flow order, the combustion section configured to receive a flow of aviation fuel from the aircraft fuel supply and further configured to receive the output product from the fuel cell; and a controller including a memory and one or more processors, the memory storing instructions that, when executed by the one or more processors, cause the propulsion system to perform operations including: performing a start-up sequence of the fuel cell assembly, wherein performing the start-up sequence of the fuel cell assembly includes starting the start-up sequence of the fuel cell assembly; performing a start-up sequence of the gas turbine engine, wherein performing the start-up sequence of the gas turbine engine includes starting the start-up sequence of the gas turbine engine after starting the start-up sequence of the fuel cell assembly; and operating the fuel cell assembly to provide an output product to a combustion section of the gas turbine engine.

[0328] A propulsion system for an aircraft, the aircraft including an aircraft fuel supply, the propulsion system including: a turbomachine including a compressor section, a combustion section, and a turbine section arranged in serial flow order, the combustion section configured to receive a flow of aviation fuel from the aircraft fuel supply; and a fuel cell assembly including a fuel cell stack having a solid oxide fuel cell, the solid oxide fuel cell defining an outlet positioned to remove an output product from the solid oxide fuel cell and provide the output product to the combustion section, the solid oxide fuel cell including a cathode; an electrolyte layer; and an anode positioned opposite the electrolyte layer from the cathode, the anode including a metal ceramic including less than 25 vol% nickel.

[0329] The propulsion system according to one or more of these clauses, wherein the cermet comprises less than 10 volume percent nickel.

[0330] The propulsion system according to one or more of these clauses, wherein the cermet comprises less than 0.01 volume percent nickel.

[0331] The propulsion system according to one or more of these clauses, wherein the aircraft fuel supply is a hydrocarbon fuel supply, and wherein the fuel cell assembly is configured to provide a hydrocarbon fuel from the hydrocarbon fuel supply to the anode.

[0332] The propulsion system according to one or more of these clauses, wherein the fuel cell assembly comprises a gas stream delivery system in communication with the anode gas stream for providing an oxygen-containing gas to the anode.

[0333] The propulsion system according to one or more of these clauses, wherein the gas stream delivery system is configured to receive the oxygen-containing gas from the compressor section of the turbine, from an ambient location, or both.

[0334] The propulsion system according to one or more of these clauses, wherein the cermet catalyzes catalytic partial oxidation of an aviation fuel.

[0335] The propulsion system according to one or more of these clauses, wherein the anode comprises a noble metal or a ceramic material that catalyzes catalytic partial oxidation of an aviation fuel.

[0336] The propulsion system according to one or more of these clauses, wherein the cermet catalyzes catalytic partial oxidation of an aviation fuel, and wherein the anode further comprises a noble metal or a ceramic material that catalyzes catalytic partial oxidation of an aviation fuel.

[0337] The propulsion system according to one or more of these clauses, wherein a noble metal or a ceramic material that catalyzes catalytic partial oxidation of an aviation fuel is adhered to at least a portion of a surface of the fuel cell assembly upstream of the anode.

[0338] The propulsion system according to one or more of these clauses, wherein the fuel cell assembly comprises an air handling unit configured to provide a gas stream to the cathode.

[0339] The propulsion system according to one or more of these clauses, wherein the fuel cell stack defines a fuel cell stack temperature, and the fuel cell assembly is configured to provide an oxygen-containing gas to the anode when the fuel cell stack temperature is less than 450 degrees Celsius.

[0340] The propulsion system according to one or more of these clauses, wherein the fuel cell stack defines a fuel cell stack temperature, and the fuel cell assembly is configured to provide the oxygen-containing gas to the anode when the fuel cell stack temperature is greater than 80 degrees Celsius and less than 250 degrees Celsius.

[0341] The propulsion system according to one or more of these clauses, wherein the fuel cell stack defines a fuel cell stack temperature, and the fuel cell assembly is configured to provide the oxygen-containing gas to the anode when the fuel cell stack temperature is greater than 450 degrees Celsius and less than 750 degrees Celsius.

[0342] The propulsion system according to one or more of these clauses, wherein the aircraft fuel supply is a hydrocarbon fuel supply, wherein the fuel cell assembly includes a fuel processing unit, and wherein the fuel cell assembly is configured to selectively provide a hydrocarbon fuel from the hydrocarbon fuel supply to the anode and to provide hydrogen fuel from the fuel processing unit to the anode.

[0343] A fuel cell assembly for a propulsion system of an aircraft, the propulsion system including a gas turbine engine having a combustion section, the fuel cell assembly comprising: a fuel cell stack having a solid oxide fuel cell defining an outlet positioned to remove an output product from the solid oxide fuel cell when the fuel cell assembly is installed with the gas turbine engine and to provide the output product to the combustion section, the solid oxide fuel cell including a cathode; an electrolyte layer; and an anode positioned opposite the cathode from the electrolyte layer, the anode including a metal ceramic, the metal ceramic including less than 25 volume percent nickel.

[0344] The fuel cell assembly according to one or more of these clauses, wherein the metal ceramic includes less than 10 volume percent nickel.

[0345] The fuel cell assembly according to one or more of these clauses, wherein the metal ceramic includes less than 0.01 volume percent nickel.

[0346] The fuel cell assembly according to one or more of these clauses, wherein the anode includes a metal ceramic that catalyzes catalytic partial oxidation of an aviation fuel.

[0347] The fuel cell assembly according to one or more of these clauses, wherein the anode includes a noble metal or a ceramic material that catalyzes catalytic partial oxidation of an aviation fuel.

[0348] A method for operating a fuel cell assembly, the fuel cell assembly including a fuel cell stack having a solid oxide fuel cell having an anode, a cathode, and an electrolyte, the method including: determining a temperature setpoint for the fuel cell stack, an output product of the fuel cell stack, or both; and in response to the determined temperature setpoint, controlling a volume of oxidant provided to the anode to control a temperature of the fuel cell stack, a temperature of the output product of the fuel cell stack, or both.

[0349] The method according to one or more of these clauses, further comprising: performing a fuel reforming action at the anode.

[0350] The method according to one or more of these clauses, wherein performing the fuel reforming action at the anode includes: receiving a hydrocarbon-based fuel at the anode; and receiving an oxygen-containing gas at the anode.

[0351] The method according to one or more of these clauses, wherein the oxygen-containing gas is ambient air.

[0352] The method according to one or more of these clauses, wherein the fuel cell assembly is integrated into a gas turbine engine, and wherein the oxygen-containing gas is compressed air from a compressor section of the gas turbine engine.

[0353] The method according to one or more of these clauses, wherein the anode includes less than 25 vol% nickel.

[0354] The method according to one or more of these clauses, wherein the anode is substantially free of nickel.

[0355] The method according to one or more of these clauses, wherein the fuel cell assembly is integrated into a gas turbine engine, wherein the gas turbine engine includes a combustion section having a combustor, wherein the solid oxide fuel cell defines an outlet positioned to remove an output product from the solid oxide fuel cell, and wherein the method further includes: providing the output product from the solid oxide fuel cell to the combustor.

[0356] The method according to one or more of these clauses, further comprising: performing a start-up operation of the fuel cell assembly, and wherein controlling the volume of oxidant provided to the anode includes: controlling the volume of oxidant provided to the anode while performing the start-up operation of the fuel cell assembly.

[0357] The method of one or more of these clauses, further comprising performing a start-up operation of the fuel cell assembly, and wherein determining the temperature setpoint comprises determining the temperature setpoint while performing the start-up operation of the fuel cell assembly.

[0358] The method of one or more of these clauses, wherein controlling the volume of oxidant provided to the anode comprises providing a flow of oxygen-containing gas at the anode prior to a temperature of the fuel cell stack exceeding a first fuel cell temperature threshold.

[0359] The method of one or more of these clauses, further comprising operating the fuel cell assembly in a power generation mode, and wherein controlling the volume of oxidant provided to the anode comprises controlling the volume of oxidant provided to the anode while operating the fuel cell assembly in the power generation mode.

[0360] The method of one or more of these clauses, wherein the fuel cell assembly is integrated into a gas turbine engine, the gas turbine engine defining a gas turbine engine operating condition, and wherein determining the temperature setpoint comprises determining the temperature setpoint in response to the gas turbine engine operating condition.

[0361] The method of one or more of these clauses, wherein the gas turbine engine operating condition is indicative of an emissions parameter, a combustion dynamics parameter, a power output parameter, or a combination thereof.

[0362] A propulsion system for an aircraft, the aircraft comprising an aircraft fuel supply, the propulsion system comprising: a fuel cell assembly, the fuel cell assembly comprising a fuel cell stack having fuel cells, the fuel cells defining an outlet positioned to remove an output product from the fuel cells; a turbomachine comprising, in serial flow order, a compressor section, a combustion section, and a turbine section, the combustion section being configured to receive a flow of aviation fuel from the aircraft fuel supply, and further configured to receive the output product from the fuel cell; and a controller comprising a memory and one or more processors, the memory storing instructions that, when executed by the one or more processors, cause the propulsion system to perform operations comprising determining a temperature setpoint of the fuel cell stack, the output product of the fuel cell stack, or both; and in response to the determined temperature setpoint, controlling a volume of oxidant provided to an anode to control a temperature of the fuel cell stack, a temperature of the output product of the fuel cell stack, or both.

[0363] The propulsion system according to one or more of these clauses, wherein the aircraft fuel supply is a hydrocarbon fuel supply, wherein the fuel cell assembly includes a fuel processing unit, and wherein the fuel cell assembly is configured to selectively provide a hydrocarbon fuel from the hydrocarbon fuel supply to the anode and to provide hydrogen fuel from the fuel processing unit to the anode.

[0364] The propulsion system according to one or more of these clauses, wherein the instructions further include performing a fuel reforming action at the anode.

[0365] The propulsion system according to one or more of these clauses, wherein performing the fuel reforming action at the anode includes receiving a hydrocarbon-based fuel at the anode; and receiving an oxygen-containing gas at the anode.

[0366] The propulsion system according to one or more of these clauses, wherein the fuel cell assembly is integrated into a gas turbine engine, and wherein the oxygen-containing gas is compressed air from a compressor section of the gas turbine engine.

[0367] The propulsion system according to one or more of these clauses, wherein the anode includes less than 25 vol% nickel.

[0368] A method for operating a propulsion system for an aircraft, the propulsion system including a gas turbine engine and a fuel cell assembly, the fuel cell assembly including a fuel cell stack having solid oxide fuel cells, the solid oxide fuel cells defining an outlet positioned to remove output products from the solid oxide fuel cells during operation, the method comprising:

[0369] operating the fuel cell assembly to provide output products to a combustor of a combustion section of the gas turbine engine; and

[0370] operating the fuel cell assembly, the gas turbine engine, or both, such that a pressure within an anode of the solid oxide fuel cells is less than a pressure within a cathode of the solid oxide fuel cells, less than a pressure within a combustion chamber of the gas turbine engine, or both, while operating the gas turbine engine.

[0371] The method according to one or more of these clauses, wherein operating the fuel cell assembly, the gas turbine engine, or both, includes:

[0372] performing a shut down sequence of the gas turbine engine, wherein performing the shut down sequence includes causing the gas turbine engine to decelerate to a shut down condition; and

[0373] while executing the shutdown sequence of the gas turbine engine, executing a cool down sequence of the fuel cell assembly, wherein executing the cool down sequence of the fuel cell assembly includes operating the fuel cell assembly to define a pressure in the anode of the solid oxide fuel cell that is less than a pressure within the combustion chamber of the combustor of the gas turbine engine.

[0374] The method of one or more of these clauses, wherein executing the shutdown sequence includes decelerating the gas turbine engine from a ground idle operating condition to the shutdown condition.

[0375] The method of one or more of these clauses, wherein executing the cool down sequence of the fuel cell assembly while executing the shutdown sequence of the gas turbine engine includes providing a flow of gas from the combustion chamber into the anode of the solid oxide fuel cell.

[0376] The method of one or more of these clauses, wherein providing a flow of gas from the combustion chamber into the anode of the solid oxide fuel cell includes providing a flow of gas from the combustion chamber into the anode of the solid oxide fuel cell when a temperature of the solid oxide fuel cell is between about 230 degrees Celsius and 700 degrees Celsius.

[0377] The method of one or more of these clauses, wherein the flow of gas provided from the combustion chamber into the anode of the solid oxide fuel cell is an oxygen-containing flow of gas.

[0378] The method of one or more of these clauses, wherein executing a cool down sequence of the fuel cell assembly includes reducing a pressure of a flow of fuel to the anode of the solid oxide fuel cell, a pressure of a flow of gas to a cathode of the solid oxide fuel cell, or both.

[0379] The method of one or more of these clauses, wherein executing a cool down sequence of the fuel cell assembly includes shutting off a flow of fuel to the anode of the solid oxide fuel cell, a flow of gas to a cathode of the solid oxide fuel cell, or both.

[0380] The method of one or more of these clauses, wherein executing the cool down sequence includes maintaining the fuel cell assembly in a warm standby state.

[0381] The method of one or more of these clauses, wherein maintaining the fuel cell assembly in the warm standby state includes drawing less than about 10% of a maximum power output of the fuel cell assembly from the fuel cell assembly.

[0382] The method of one or more of these clauses, wherein performing the cooling sequence comprises operating the fuel cell assembly in a ground idle power output mode.

[0383] The method of one or more of these clauses, wherein operating the fuel cell assembly in the ground idle power output mode comprises recirculating output products from the solid oxide fuel cell to a location upstream of the fuel cell.

[0384] The method of one or more of these clauses, wherein performing the cooling sequence comprises maintaining the fuel cell assembly in a warm standby state, operating in a ground idle power output mode, or both, while the gas turbine engine is in the shut down condition.

[0385] The method of one or more of these clauses, wherein the anode comprises less than 25 volume percent nickel.

[0386] The method of one or more of these clauses, wherein the anode is substantially free of nickel.

[0387] The method of one or more of these clauses, wherein operating the fuel cell assembly, the gas turbine engine, or both, comprises operating the fuel cell assembly such that the pressure within the anode of the solid oxide fuel cell is less than the pressure within the cathode of the solid oxide fuel cell while operating the gas turbine engine.

[0388] The method of one or more of these clauses, wherein operating the fuel cell assembly such that the pressure within the anode of the solid oxide fuel cell is less than the pressure within the cathode of the solid oxide fuel cell while operating the gas turbine engine comprises flowing oxidant into the anode when the temperature of the solid oxide fuel cell is between about 230 degrees Celsius and 700 degrees Celsius.

[0389] The method of one or more of these clauses, wherein operating the fuel cell assembly such that the pressure within the anode of the solid oxide fuel cell is less than the pressure within the cathode of the solid oxide fuel cell while operating the gas turbine engine comprises reducing fuel flow to the anode of the solid oxide fuel cell.

[0390] A propulsion system for an aircraft having a gas turbine engine, the aircraft including an aircraft fuel supply, the propulsion system comprising: a fuel cell assembly including a fuel cell stack having a solid oxide fuel cell, the solid oxide fuel cell defining an outlet positioned to remove an output product from the solid oxide fuel cell; a turbomachine including, in serial flow order, a compressor section, a combustion section, and a turbine section, the combustion section configured to receive a flow of aviation fuel from the aircraft fuel supply, and further configured to receive the output product from the solid oxide fuel cell; and a controller including one or more processors and a memory, the memory storing instructions that, when executed by the one or more processors, cause the propulsion system to perform operations including: operating the fuel cell assembly, the gas turbine engine, or both, such that, while operating the gas turbine engine, a pressure within an anode of the solid oxide fuel cell is less than a pressure within a cathode of the solid oxide fuel cell, less than a pressure within a combustion chamber of the gas turbine engine, or both.

[0391] The propulsion system according to one or more of the clauses, wherein operating the fuel cell assembly, the gas turbine engine, or both, includes: performing a shut down sequence of the gas turbine engine, wherein performing the shut down sequence includes causing the gas turbine engine to slow down to a shut down condition; and, while performing the shut down sequence of the gas turbine engine, performing a cool down sequence of the fuel cell assembly, wherein performing the cool down sequence of the fuel cell assembly includes: operating the fuel cell assembly to define a pressure in an anode of the solid oxide fuel cell that is less than a pressure within a combustion chamber of the combustion section of the turbomachine.

Claims

1. A method for operating a fuel cell assembly integrated into a gas turbine engine, the fuel cell assembly comprising a fuel cell stack having a solid oxide fuel cell and a plurality of combustion outlets, the solid oxide fuel cell having an anode, a cathode, and an electrolyte, characterized in that, The method includes: Fuel is supplied from the fuel source of the gas turbine engine to the air handling unit and the fuel handling unit; A hydrogen-rich fuel stream is output from the fuel processing unit to the anode; Determine the temperature setpoint of the fuel cell stack, the output products of the fuel cell stack, or both. In response to the determined temperature setpoint, the volume of oxidant supplied to the anode is controlled to control the temperature of the fuel cell stack, the temperature of the output products of the fuel cell stack, or both. A first portion of the output product from the cathode of the solid oxide fuel cell is directed to the air treatment unit for combustion with the fuel in the air treatment unit; and A second portion of the output product from the solid oxide fuel cell is provided to the gas turbine engine.

2. The method according to claim 1, characterized in that, Further includes: Fuel reforming is performed at the anode.

3. The method according to claim 2, characterized in that, The fuel reforming process performed at the anode includes: Hydrocarbon-based fuel is received at the anode; and Oxygen-containing gas is received at the anode.

4. The method according to claim 3, characterized in that, The oxygen-containing gas mentioned above is ambient air.

5. The method according to claim 3, characterized in that, The oxygen-containing gas is compressed air from the compressor section of the gas turbine engine.

6. The method according to claim 1, characterized in that, The anode comprises less than 25% by volume of nickel.

7. The method according to claim 1, characterized in that, The anode therein is essentially nickel-free.

8. The method according to claim 1, characterized in that, The gas turbine engine includes a combustion section with a combustor, the combustor including a combustion chamber, and the method further includes: The second portion of the output product from the solid oxide fuel cell is supplied to the combustion chamber via the plurality of combustion outlets of the fuel cell stack.

9. The method according to claim 1, characterized in that, Further includes: Performing a start-up operation on the fuel cell assembly, wherein controlling the volume of oxidant supplied to the anode includes: controlling the volume of oxidant supplied to the anode while performing the start-up operation on the fuel cell assembly.

10. The method according to claim 1, characterized in that, Further includes: Performing the start-up operation of the fuel cell assembly, wherein determining the temperature setpoint includes: determining the temperature setpoint while performing the start-up operation of the fuel cell assembly.

11. The method according to claim 1, characterized in that, Controlling the volume of oxidant supplied to the anode includes providing an oxygen-containing gas flow at the anode before the temperature of the fuel cell stack exceeds a first fuel cell temperature threshold.

12. The method according to claim 1, characterized in that, Further includes: The fuel cell assembly is operated in a power generation mode, wherein controlling the volume of oxidant supplied to the anode includes controlling the volume of oxidant supplied to the anode while operating the fuel cell assembly in the power generation mode.

13. The method according to claim 1, characterized in that, The gas turbine engine defines gas turbine engine operating conditions, and determining the temperature setpoint includes: determining the temperature setpoint in response to the gas turbine engine operating conditions.

14. The method according to claim 13, characterized in that, The gas turbine engine operating conditions refer to emission parameters, combustion dynamics parameters, power output parameters, or combinations thereof.

15. A propulsion system for an aircraft, the aircraft including an aircraft fuel supply unit, characterized in that, The propulsion system includes: A fuel cell assembly, comprising a fuel cell stack having a fuel cell and multiple combustion outlets, the fuel cell having an anode, a cathode and an electrolyte; A turbine comprising a compressor section, a combustion section, and a turbine section arranged in a sequential flow order, the combustion section being configured to receive an aviation fuel flow from the aircraft fuel supply unit and further configured to receive output products from the fuel cell, wherein the fuel cell assembly is integrated into the turbine; and A controller, comprising a memory and one or more processors, the memory storing instructions that, when executed by the one or more processors, cause the propulsion system to perform operations, including... Fuel is supplied from the aircraft's fuel supply unit to the air processing unit and the fuel processing unit; A hydrogen-rich fuel stream is output from the fuel processing unit to the anode; Determine the temperature setpoint of the fuel cell stack, the output products of the fuel cell stack, or both. In response to the determined temperature setpoint, the volume of oxidant supplied to the anode is controlled to control the temperature of the fuel cell stack, the temperature of the output products of the fuel cell stack, or both. A first portion of the output product from the cathode of the fuel cell is directed to the air treatment unit for combustion with the fuel in the air treatment unit; and A second portion of the output product from the fuel cell is provided to the turbine.

16. The propulsion system according to claim 15, characterized in that, The aircraft fuel supply unit is a hydrocarbon fuel supply unit, the fuel cell assembly includes the fuel processing unit, and the fuel cell assembly is configured to selectively supply hydrocarbon fuel from the hydrocarbon fuel supply unit to the anode and hydrogen fuel from the fuel processing unit to the anode.

17. The propulsion system according to claim 15, characterized in that, The instructions further include: Fuel reforming is performed at the anode.

18. The propulsion system according to claim 17, characterized in that, The fuel reforming process performed at the anode includes: Hydrocarbon-based fuel is received at the anode; and Oxygen-containing gas is received at the anode.

19. The propulsion system according to claim 18, characterized in that, The fuel cell assembly is integrated into the gas turbine engine, and the oxygen-containing gas is compressed air from the compressor section of the gas turbine engine.

20. The propulsion system according to claim 15, characterized in that, The anode comprises less than 25% by volume of nickel.

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