Hydrogen fuel system

Abstract

A fuel system for a vehicle having an engine is provided. The fuel system includes: a fuel tank for holding hydrogen fuel in a liquid phase; a fuel delivery assembly extending from the fuel tank to the engine for supplying hydrogen fuel from the fuel tank to the engine; a vaporizer in communication with the fuel delivery assembly for heating the liquid-phase hydrogen fuel to a gas phase, a supercritical phase, or both; and a high-pressure pump in fluid communication with the fuel delivery assembly at a location downstream of the vaporizer for directing a hydrogen fuel stream through the fuel delivery assembly to the engine.

Description

[0001] Priority Information

[0002] This application claims priority to Italian Patent Application No. 102020000026590, filed on November 6, 2020. Technical Field

[0003] The present subject matter generally relates to hydrogen fuel systems for vehicles, such as hydrogen fuel systems for aircraft vehicles. Background Art

[0004] Conventional commercial aircraft typically include a fuselage, a pair of wings, and a propulsion system that provides thrust. The propulsion system generally includes one or more aircraft engines, such as turbofan jet engines. Turbofan jet engines can typically be mounted to a respective one of the wings of the aircraft, such as at a suspended location below the wing, using pylons attached to the wing.

[0005] The aircraft includes a fuel delivery assembly that generally includes a fuel tank and one or more fuel lines extending between the fuel tank and the aircraft engine. Conventional aircraft engines are powered by aviation turbine fuel, which is typically a combustible hydrocarbon liquid fuel having a desired number of carbon atoms, such as kerosene-type fuel. Aviation turbine fuel is a fuel with a relatively high power density, which is relatively easy to transport and remains in the liquid phase under most environmental operating conditions of the aircraft.

[0006] It has been argued that improvements in the emissions of conventional aircraft having aircraft engines powered by aviation turbine fuel can be achieved by using hydrogen fuel. Hydrogen fuel is not a fuel with a relatively high power density in its gaseous form, and has a relatively low boiling point and a relatively low freezing point. When in the gaseous form, hydrogen fuel further tends to permeate materials.

[0007] The inventors of the present disclosure have found that these and other problems may make it difficult to effectively use hydrogen fuel in aircraft engines. Thus, in view of these and other problems, technical improvements that facilitate the use of hydrogen fuel in aircraft engines would be welcome. Summary of the Invention

[0008] Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

[0009] In an exemplary embodiment of the present disclosure, a fuel system for a vehicle having an engine is provided. The fuel system includes: a fuel tank for holding hydrogen fuel in a liquid phase; a fuel delivery assembly extending from the fuel tank to the engine for supplying hydrogen fuel from the fuel tank to the engine; a vaporizer in communication with the fuel delivery assembly for heating the liquid-phase hydrogen fuel to a gaseous phase, a supercritical phase, or both; and a high-pressure pump fluidly connected to the fuel delivery assembly at a location downstream of the vaporizer for directing a flow of hydrogen fuel through the fuel delivery assembly to the engine.

[0010] These and other features, aspects, and advantages of the present invention will be better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] A complete and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth in the specification, which makes reference to the accompanying drawings, in which:

[0012] Figure 1 is a schematic view of an aircraft having a fuel system according to an exemplary embodiment of the present disclosure.

[0013] Figure 2 is a schematic cross-sectional view of a gas turbine engine according to an exemplary embodiment of the present disclosure.

[0014] Figure 3 is a schematic view of a fuel system according to an exemplary aspect of the present disclosure.

[0015] Figure 4 is a schematic view of a fuel system according to another exemplary aspect of the present disclosure.

[0016] Figure 5 is Figure 3 a close-up schematic view of an exemplary fuel system of

[0017] Figure 6 is a schematic view of a fuel system according to yet another exemplary aspect of the present disclosure.

[0018] Figure 7 is a schematic view of a fuel system according to yet another exemplary aspect of the present disclosure.

[0019] Figure 8 is a schematic view of a fuel system according to yet another exemplary aspect of the present disclosure.

[0020] Figure 9 is a schematic view of a controller according to an exemplary aspect of the present disclosure.

[0021] Figure 10 is a flowchart of a method for operating a fuel system according to an exemplary aspect of the present disclosure.

[0022] Figure 11 is a flowchart of a method for operating a fuel system according to another exemplary aspect of the present disclosure.

[0023] Figure 12 is a flowchart of a method for operating a fuel system according to yet another exemplary aspect of the present disclosure.

[0024] Figure 13 is a flowchart of a method for operating a fuel system according to yet another exemplary aspect of the present disclosure. Detailed Description

[0025] Reference will now be made in detail to the present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter names to refer to features in the drawings. The same or similar names have been used in the drawings and the description to refer to the same or similar parts of the invention.

[0026] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration". Any embodiment described herein as "exemplary" is not necessarily to be construed as superior or better than other embodiments. Further, unless otherwise specifically specified, all embodiments described herein shall be considered exemplary.

[0027] As used herein, the terms "first", "second", and "third" may be used interchangeably to distinguish one component from another, and are not intended to denote the position or importance of each component.

[0028] The terms "front" and "rear" 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, for a gas turbine engine, front refers to a position closer to the engine inlet, and rear refers to a position closer to the engine nozzle or exhaust port.

[0029] The terms "upstream" and "downstream" refer to the relative direction with respect to the flow in a path. For example, for fluid flow, "upstream" refers to the direction from which the fluid flows, and "downstream" refers to the direction towards which the fluid flows. However, the terms "upstream" and "downstream" as used herein may also refer to an electric current.

[0030] Unless the context clearly dictates otherwise, the singular forms "a", "an", and "the" include plural referents.

[0031] As used throughout this specification and the claims, approximating language is applied to modify any quantitative representation that can vary without resulting in a change in the basic function associated therewith. Thus, values modified by terms such as "about," "approximately," and "substantially" are not limited to the specified exact values. In at least some instances, the approximating language can correspond to the precision of the instrument used to measure the value, or the precision of the method or machine used to construct or manufacture the components and / or systems. In at least some instances, the approximating language can correspond to the precision of the instrument used to measure the value, or the precision of the method or machine used to construct or manufacture the components and / or systems. For example, the approximating language can refer to a margin of 1%, 2%, 4%, 5%, 10%, 15%, or 20% within a single value, a range of values, and / or the endpoints of a range defining values.

[0032] Herein and throughout the specification and claims, range limitations are combined and interchanged, and such ranges are identified and include all subranges subsumed therein unless the context or language indicates otherwise. For example, all ranges disclosed herein include the endpoints, and the endpoints can be combined independently of each other.

[0033] Vaporizer upstream of the HP pump in the hydrogen fuel system :

[0034] In certain exemplary aspects, a fuel system for a vehicle having an engine is provided. The engine is a hydrogen engine, and the fuel system is configured to supply hydrogen fuel to the engine. The fuel system generally includes: a fuel tank for holding hydrogen fuel in a liquid phase (e.g., at least partially within the liquid phase or substantially entirely within the liquid phase); a fuel delivery assembly extending from the fuel tank to the engine for supplying the hydrogen fuel from the fuel tank to the engine; a vaporizer in communication with the fuel delivery assembly for heating the liquid-phase hydrogen fuel to a gas phase, a supercritical phase, or both; and a high-pressure pump in fluid communication with the fuel delivery assembly at a location downstream of the vaporizer for directing the hydrogen fuel flow through the fuel delivery assembly to the engine.

[0035] The vaporizer is positioned upstream of the high-pressure pump to facilitate certain functions of the vaporizer, provide a more compact configuration, etc. For example, the vaporizer can be positioned close to the fuel tank, such as within the same structure as the fuel tank (e.g., in the wing of an aircraft having a fuel tank). As part of a priming operation of the fuel system, the vaporizer is capable of heating at least a portion of the liquid hydrogen fuel to a gas phase during, for example, pre-start operating conditions of the engine. In particular, the vaporizer can supply the heated / gaseous hydrogen fuel to the fuel delivery assembly during such pre-start operating conditions such that when the hydrogen fuel is subsequently supplied through the fuel delivery assembly to the engine for combustion, such a hydrogen fuel flow does not freeze the fluid within the fuel delivery assembly.

[0036] Priming the hydrogen fuel system with air

[0037] In addition, in some exemplary aspects, a method of operating a fuel system for a vehicle having an engine is provided such that a primer fluid is provided through a portion of the fuel system prior to starting the engine and thereby freezing an initial fluid within the portion of the fuel system. The method may include priming a fuel delivery assembly of the fuel system with a primer fluid that defines a phase change point of the primer fluid, and providing a hydrogen fuel stream from a fuel tank of the fuel system to the engine through the fuel delivery assembly. The hydrogen fuel within the fuel tank may be at least partially in a liquid phase. For such exemplary aspects, providing a hydrogen fuel stream from the fuel tank may include providing the hydrogen fuel stream from the fuel tank at a temperature equal to or higher than the phase change point of the primer fluid.

[0038] In some exemplary aspects, the primer fluid may be a fluid having a freezing point lower than that of the hydrogen fuel, such as helium. In other aspects, priming the fuel delivery assembly may include providing a pre-priming fluid having a freezing point (or boiling point) higher than that of the hydrogen fuel, followed by a primer fluid, which may be heated hydrogen fuel. More specifically, for such aspects, the primer fluid may be hydrogen fuel heated from a liquid phase to a gas phase, for example, by a primer vaporizer.

[0039] Such exemplary aspects may ensure that providing a hydrogen fuel stream through the fuel delivery assembly to operate the engine does not freeze any remaining fluid in the fuel delivery assembly.

[0040] Purging air through the hydrogen fuel system

[0041] In addition, in some exemplary aspects, a method of operating a fuel system for a vehicle having an engine is provided such that a remaining volume of hydrogen fuel in the fuel system is purged after the engine is shut down. The method may include: providing a hydrogen fuel stream from a fuel tank of the fuel system to the engine through a fuel delivery assembly during operation of the engine; terminating the hydrogen fuel stream from the fuel tank to the engine through the fuel delivery assembly; and discharging the remaining volume of hydrogen fuel from the fuel delivery assembly.

[0042] In some exemplary aspects, discharging the remaining volume of hydrogen fuel from the fuel delivery assembly may include providing a purge fluid through the fuel delivery assembly after the engine is shut down. The purge fluid may define a freezing temperature lower than the freezing temperature of the hydrogen fuel, in which case, the purge fluid may be provided immediately after the engine is shut down. Alternatively, the purge fluid may define a freezing temperature greater than the freezing temperature of the hydrogen fuel, in which case, the purge fluid may be provided after a boiling period after the engine is shut down.

[0043] In addition, in some exemplary aspects, discharging the remaining volume of hydrogen fuel may include one or more of burning at least some of the remaining portion of the hydrogen fuel, discharging at least some of the remaining portion of the hydrogen fuel to the atmosphere, recapturing at least some of the remaining portion of the hydrogen fuel, and the like.

[0044] By discharging the remaining portion of the hydrogen fuel from the fuel delivery assembly of the fuel system after the engine is shut down, the risk that the hydrogen fuel penetrates the fuel delivery assembly and accumulates, for example, in an undesired location can be reduced.

[0045] Hydrogen fuel system having multiple vaporizers

[0046] In addition, in some exemplary aspects, a hydrogen fuel system for a vehicle is provided such that the fuel system includes at least two separate vaporizers for heating the hydrogen fuel during at least two different operating conditions of the engine to ensure that the hydrogen fuel can be provided to the engine within a desired operating range with a desired overall efficiency. For example, an exemplary fuel system may include a first vaporizer in communication with the fuel delivery assembly for heating the liquid-phase hydrogen fuel to the gas phase, supercritical phase, or both when the engine is in a first operating condition. The fuel system may also include a second vaporizer in communication with the fuel delivery assembly for heating the liquid-phase hydrogen fuel to the gas phase, supercritical phase, or both when the engine is in a second operating condition.

[0047] For example, the first operating condition may be an engine operating condition in which the engine has not yet reached a thermally stable mode. For such exemplary aspects, the first vaporizer may be configured to receive heat from a heat source external to the engine such that the first vaporizer does not rely on receiving heat from the engine. In contrast, the second operating condition may be an engine operating condition in which the engine has reached a thermally stable mode. In such exemplary aspects, the second vaporizer may be configured to receive heat from the engine such that the second vaporizer can operate effectively by utilizing, for example, waste heat from the engine.

[0048] Drawings

[0049] Now referring to Figure 1 , a perspective view of a vehicle of the present disclosure is provided. Specifically, for an exemplary embodiment of Figure 1 , the vehicle is configured as an aerial vehicle or aircraft 10. The exemplary aircraft 10 has a fuselage 12, wings 14 attached to the fuselage 12, and a tail 16.

[0050] The exemplary aircraft 10 further includes a fuel system 20 having a fuel tank 22. In the exemplary aircraft 10 shown in Figure 1 , at least a portion of the fuel tank 22 is located in the wings 14 of the aircraft 10. However, in some embodiments, the fuel tank 22 may be located at other suitable locations in the fuselage 12 or wings 14.

[0051] The aircraft 10 further includes a propulsion system 24 that generates the propulsion thrust required to propel the aircraft 10 during flight, taxi operations, etc. Although in Figure 1 the propulsion system 24 is shown attached to the wing 14, in other embodiments it may additionally or alternatively include one or more aspects coupled to other parts of the aircraft 10 (such as the tail fin 16, the fuselage 12, or both).

[0052] For the depicted exemplary aspect, the propulsion system 24 includes engines, and more specifically includes a pair of engines. More specifically, each engine of the pair of engines is configured as a gas turbine engine 26, which is mounted to one of the respective wings 14 of the aircraft 10 in an under-wing configuration via a respective pylon 28. Each gas turbine engine 26 is capable of selectively generating propulsion thrust for the aircraft 10. The amount of propulsion thrust can be controlled at least in part based on the volume of fuel provided to the gas turbine engine 26 via the fuel system 20. In at least some of the exemplary embodiments described herein, the fuel is a cryogenic fuel stored at extremely low temperatures, and more specifically is hydrogen fuel stored substantially in a liquid phase. In this way, it should be understood that the hydrogen fuel is stored in the fuel tank 22 at low temperatures. For example, the hydrogen fuel can be stored in the fuel tank 22 at a temperature of approximately -253 degrees Celsius or lower at atmospheric pressure, or at other temperatures and pressures to keep the hydrogen fuel substantially in a liquid phase. The fuel tank 22 can be made of known materials (such as titanium, Inconel, aluminum, or composite materials).

[0053] Now referring to Figure 2 , a schematic cross-sectional view of a gas turbine engine according to an exemplary embodiment of the present disclosure is provided. For example, Figure 2 the exemplary gas turbine engine of Figure 1 can be incorporated as one of the gas turbine engines 26 into the propulsion system 24 described above with reference to

[0054] For the depicted embodiment, the engine is configured as a high-bypass turbofan engine 100. As Figure 1 shown, the turbofan engine 100 defines an axial direction A (extending parallel to the longitudinal centerline 101 provided for reference), a radial direction R, and a circumferential direction (extending around the axial direction A; Figure 2 not depicted in

[0055] The exemplary turbine 104 depicted generally includes a substantially tubular housing 106 that defines an annular inlet 108. The housing 106 surrounds in serial flow relationship: a compressor section that includes a booster or low pressure (LP) compressor 110 and a high pressure (HP) compressor 112; a combustion section 114; a turbine section that includes a high pressure (HP) turbine 116 and a low pressure (LP) turbine 118; and an exhaust nozzle section 120. The compressor section, combustion section 114, and turbine section together at least partially define a core air flow path 121 that extends from the annular inlet 108 to the exhaust nozzle section 120. The turbofan engine also includes one or more drive shafts. More specifically, the turbofan engine includes a high pressure (HP) shaft or spool 122 that drivingly connects the HP turbine 116 to the HP compressor 112, and a low pressure (LP) shaft or spool 124 that drivingly connects the LP turbine 118 to the LP compressor 110.

[0056] For the depicted embodiment, the fan section 102 includes a fan 126 that has a plurality of fan blades 128 coupled to a disk 130 in a spaced-apart manner. The fan blades 128 and the disk 130 are rotatable together about a longitudinal axis 201 via the LP shaft 124. The disk 130 is covered by a rotatable front hub 132 that is aerodynamically shaped to facilitate air flow through the plurality of fan blades 128. Additionally, an annular fan casing or nacelle 134 is provided that circumferentially surrounds the fan 126 and / or at least a portion of the turbine 104. The nacelle 134 is supported relative to the turbine 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 104 to define a bypass air flow path 140 therebetween.

[0057] Still referring to Figure 2 , the turbofan engine 100 may be operated in conjunction with a fuel system 146 for receiving a fuel flow from the fuel system 146. The fuel system 146 may be similarly configured to the Figure 1 fuel system 20. Thus, the fuel system 146 generally includes a fuel tank 148 and a fuel delivery assembly 150. The fuel delivery assembly 150 supplies a fuel flow from the fuel tank 148 to the engine 100 and, more specifically, to a fuel manifold (not labeled) of the combustion section 114 of the turbine 104 of the turbofan engine 100.

[0058] In addition, as schematically depicted, the exemplary turbofan engine 100 also includes various accessory systems to assist in the operation of the turbofan engine 100 and / or an aircraft including the turbofan engine 100. For example, the exemplary turbofan engine 100 also includes a main lubrication system 152 that is configured to supply lubricant to various bearings and gear meshes in, for example, the compressor section, the turbine section, the HP spool 122, the LP spool 124, and the like. The lubricant provided by the main lubrication system 152 can increase the service life of these components and can remove a certain amount of heat from these components. In addition, the turbofan engine 100 includes a compressor cooling air (CCA) system 154 for supplying air from one or both of the HP compressor 112 or the LP compressor 110 to one or both of the HP turbine 116 or the LP turbine 118. In addition, the exemplary turbofan engine 100 includes an active clearance control (ACC) system 156 for cooling the casing of the turbine section to maintain the clearance between various turbine rotor blades and the turbine casing within a desired range under various engine operating conditions. In addition, the exemplary turbofan engine 100 includes a generator lubrication system 158 for lubricating an electrical generator (not shown) and for providing cooling / heat dissipation for the electrical generator. The electrical generator can supply power to, for example, a starting motor of the turbofan engine 100, and / or various other electrical components of the turbofan engine 100 and / or an aircraft including the turbofan engine 100.

[0059] Heat from these accessory systems 152, 154, 156, 158 and other accessory systems can be provided as waste heat from the turbofan engine 100 to various radiators (e.g., provided to various vaporizers, as described below) during operation. In addition, although not depicted, the turbofan engine 100 can include, for example, one or more heat exchangers within the turbine section or the exhaust section 120 for extracting waste heat from the airflow passing therethrough such that the waste heat can be used to add heat as waste heat to various radiators (e.g., added to various vaporizers, as described below) during operation.

[0060] However, it should be understood that Figure 1 the exemplary turbofan engine 100 depicted in Figure 1The exemplary gas turbine engine depicted schematically shows a direct drive, fixed pitch turbofan engine 100, but in other embodiments, the gas turbine engines of the present disclosure can be geared gas turbine engines (i.e., including a gearbox between a fan 126 and a shaft (such as LP shaft 124) driving the fan), can be variable pitch gas turbine engines (i.e., including a fan 126 having a plurality of fan blades 128 that can rotate about their respective pitch axes), etc. Additionally, still in alternative embodiments, aspects of the present disclosure can be incorporated into any other type of engine (such as a reciprocating engine) or otherwise used in conjunction with any other type of engine. Further, in other exemplary embodiments, the exemplary turbofan engine 100 can include or be operably connected to any other suitable accessory system. Additionally or alternatively, the exemplary turbofan engine 100 can not include or not be operably connected to one or more of the accessory systems 152, 154, 156, 158 described above.

[0061] Now referring to Figure 3 , there is provided a schematic diagram of a fuel system 200 for a vehicle 202 having an engine 204 according to an exemplary embodiment of the present disclosure. More specifically, for Figure 3 's exemplary embodiment, the vehicle 202 can be an aerial vehicle (such as Figure 1 's exemplary aircraft 10), and the engine 204 can be an aero gas turbine engine (such as Figure 1 's exemplary engine 26 and / or Figure 2 's exemplary turbofan engine 100). Thus, as shown, the vehicle 202 includes wings 206, where the engine 204 is mounted to the wings 206 in an underwing configuration via pylons 208.

[0062] However, it should be understood that in other embodiments, the vehicle can be any other suitable land or aerial vehicle, and the engine can be any other suitable engine mounted to or within the vehicle in any suitable manner.

[0063] The depicted exemplary fuel system 200 is generally a hydrogen fuel system that is configured to store hydrogen fuel in a liquid phase and supply hydrogen fuel in a gaseous or supercritical phase to the engine 204.

[0064] For the illustrated embodiment, fuel system 200 generally includes a fuel tank 210 for containing hydrogen fuel and a fuel delivery assembly 212 extending from the fuel tank 210 to the engine 204 for supplying hydrogen fuel from the fuel tank 210 to the engine 204. The fuel tank 210 may be configured to hold the hydrogen fuel at least partially in the liquid phase and may be configured to supply the fuel system 200 with hydrogen fuel that is substantially entirely in the liquid phase (e.g., entirely in the liquid phase). For example, the fuel tank 210 may define a fixed volume such that as the fuel tank 210 supplies the fuel system 200 with hydrogen fuel that is substantially entirely in the liquid phase, the volume of liquid hydrogen fuel in the fuel tank 210 decreases and the volume consists of, for example, gaseous hydrogen. The fuel tank 210 and the fuel system 200 may include a variety of support structures to facilitate storing hydrogen fuel in this manner.

[0065] It should be understood that as used herein, the term "substantially entirely" when used to describe the phase of hydrogen fuel means that at least 99% of the mass of the described portion of the hydrogen fuel is in the described phase, e.g., at least 97.5%, e.g., at least 95%, e.g., at least 92.5%, e.g., at least 90%, e.g., at least 85%, e.g., at least 75% of the mass of the described portion of the hydrogen fuel is in the described phase.

[0066] In addition, as will be explained in more detail below, the exemplary fuel system 200 includes: a vaporizer in communication with the fuel delivery assembly 212 for heating the hydrogen fuel in the liquid phase to the gas phase, the supercritical phase, or both; and a high-pressure pump 214 in fluid communication with the fuel delivery assembly 212 at a location downstream of the vaporizer for directing the flow of hydrogen fuel through the fuel delivery assembly 212 to the engine 204.

[0067] The high-pressure pump 214 may generally be the primary source of pressure elevation in the fuel delivery assembly 212 between the fuel tank 210 and the engine 204. The high-pressure pump 214 may be configured to increase the pressure in the fuel delivery assembly 212 to a pressure greater than the pressure in the combustion chamber of the engine 204. For example, the high-pressure pump 214 may be configured to increase the pressure in the fuel delivery assembly 212 to at least 400 pounds per square inch ("psi"), e.g., at least 500 psi, e.g., at least 600 psi, e.g., at least 700 psi, e.g., at least 750 psi, e.g., up to 2000 psi.

[0068] Especially for Figure 3 the embodiment, both the fuel tank 210 and the vaporizer are positioned within the fuselage of the carrier 202 ( Figure 3 not shown in, see for example Figure 1within the fuselage 12), the wings 206 of the carrier 202, or both. More specifically, for the illustrated embodiment, the vaporizer is the starting vaporizer 216. As will be appreciated, hydrogen fuel defines a relatively low boiling point such that if hydrogen fuel is provided in the liquid phase through the fuel delivery assembly 212, the hydrogen fuel can freeze the gas within the fuel delivery assembly 212. Accordingly, the starting vaporizer 216 is provided to receive a liquid-phase hydrogen fuel stream and heat the hydrogen fuel from the liquid phase to the gas phase or supercritical phase such that the heated hydrogen fuel does not freeze the gas within the fuel delivery assembly 212. Operation of the starting vaporizer 216 can occur, for example, prior to starting of the engine 204, where non-hydrogen gas is positioned within the fuel delivery assembly 212 at a location between the fuel tank and the engine 204.

[0069] Pre-start operations will be described in more detail below. However, briefly, it should be understood that the fuel system also includes a purge / priming assembly 218 that can be configured to provide a starting fluid stream or a pre-start fluid stream to the fuel delivery assembly 212 in conjunction with operation of the starting vaporizer 216 during pre-start operations to introduce a gas into the fuel delivery assembly 212 that can contact the hydrogen fuel during subsequent operations without freezing. For example, the purge / priming assembly 218 can be configured to provide a helium gas stream (which has a lower freezing point than hydrogen fuel) through the fuel delivery assembly 212. Alternatively, the purge / priming assembly 218 can provide a gas having a higher freezing point through the fuel delivery assembly as a pre-start fluid, and the fuel system 200 can subsequently operate the starting vaporizer 216 to introduce gaseous hydrogen fuel at a temperature above the freezing point of the pre-start fluid, thereby introducing the hydrogen fuel into the fuel delivery assembly 212 without freezing the gas within the fuel delivery assembly. The pre-start fluid can be, for example, nitrogen.

[0070] In some exemplary embodiments, the purge / priming assembly 218 can include a fluid tank for providing a pre-start fluid stream during use. Additionally or alternatively, the purge / priming assembly 218 can include an on-board generation system, such as an on-board nitrogen generation system.

[0071] Still referring to Figure 3, as noted, the starting vaporizer 216 is in communication with the fuel delivery assembly 212, and the fuel delivery assembly 212 may include one or more pipelines, conduits, etc. capable of carrying hydrogen fuel between fuel tanks 210 in the engine 204. The starting vaporizer 216 is more specifically in thermal communication with the hydrogen fuel in one or more pipelines, conduits, etc. of the fuel delivery assembly 212. For example, the starting vaporizer 216 may be in fluid communication with the fuel delivery assembly 212 for receiving a hydrogen fuel stream and positioning such hydrogen fuel stream in thermal communication with the heat provided to it. Alternatively, the starting vaporizer 216 may be in thermal communication with the hydrogen fuel stream in the fuel delivery assembly 212 in any other suitable manner (e.g., the starting vaporizer 216 may include a coil or other structure in contact with the fuel delivery assembly 212 to add heat to the hydrogen fuel stream passing therethrough).

[0072] The heat provided to the starting vaporizer 216 may be provided by a heat source 220, where the starting vaporizer 216 is in thermal communication with the heat source 220. For the depicted exemplary embodiment, the heat source 220 is external to the engine 204. For example, the heat source providing heat to the starting vaporizer 216 may include a power source (in which case the starting vaporizer 216 may include one or more resistance heaters, etc.), a catalytic heater or burner, a bleed air stream from an auxiliary power unit, etc. In this way, the heat source 220 can provide heat to the starting vaporizer 216 regardless of whether the engine 204 is running (which typically will not be running).

[0073] As will be described in more detail below, the starting vaporizer 216 can operate prior to starting the engine 204 to provide an initial volume of gas / fluid in the fuel delivery assembly that is capable of contacting the hydrogen fuel without freezing. In this way, it should be understood that the starting vaporizer 216 can be configured to heat a relatively small amount of the liquid-phase hydrogen fuel stream and provide such heated hydrogen fuel to the fuel delivery assembly 212 in a substantially fully gaseous phase or a substantially fully supercritical phase.

[0074] Still referring to Figure 3 , it should be understood that the depicted exemplary fuel system 200 also includes a second vaporizer or main vaporizer 222 in communication with the fuel delivery assembly 212 for heating the hydrogen fuel flowing through the fuel delivery assembly 212. Notably, for the depicted exemplary aspect, the main vaporizer 222 is positioned external to the fuselage and wing 206 of the carrier 202 and alternatively is at least partially positioned within the pylon 208, the engine 204, or both. More specifically, for the illustrated embodiment, the main vaporizer 222 is at least partially positioned within the engine 204.

[0075] The main vaporizer 222 is configured to operate once the engine 204 is in a thermally stable state. More specifically, for the illustrated exemplary embodiment, the main vaporizer 222 is in thermal communication with a heat source 224 of the engine 204. In this way, it should be understood that the main vaporizer 222 can be configured to operate once the engine 204 is able to provide sufficient heat via the heat source 224 to the main vaporizer 222 to facilitate the operation of the main vaporizer 222 as described herein.

[0076] The heat source 224 of the engine 204 can be one of the exemplary heat sources described above with reference to Figure 2 or, alternatively, the heat source 224 of the engine 204 can include a plurality of exemplary heat sources described above with reference to Figure 2 that can operate together as a heat bus. Additionally or alternatively, any other suitable heat source of the engine 204 can be used as the heat source 224 for the main vaporizer 222. For example, in other exemplary embodiments, the heat source 224 of the main vaporizer can be a heat source external to the engine (e.g., a dedicated burner or other catalytic heater, a resistive heater, an air stream from an auxiliary power unit, etc.).

[0077] As described above, the main vaporizer 222 is in communication with the hydrogen fuel stream passing through the fuel delivery assembly 212. The main vaporizer 222 can be in communication with the hydrogen fuel stream passing through the fuel delivery assembly 212 in any suitable manner (e.g., in the same manner as described above with reference to the starting vaporizer 216, or in any other suitable manner). The main vaporizer 222 can be configured to heat the fuel stream from substantially completely in the liquid phase to substantially completely in the gas phase or substantially completely in the supercritical phase.

[0078] In addition, for Figure 3 the exemplary embodiment, the fuel system 200 further includes a third vaporizer, or more specifically, a supplementary vaporizer 226. The supplementary vaporizer 226 is also in communication with the fuel delivery assembly 212 for heating the hydrogen fuel flowing through the fuel delivery assembly 212. The supplementary vaporizer 226 includes or is in thermal communication with a heat source 228 external to the engine 204. As used herein, the term "heat source external to the engine 204" refers to a heat source that does not rely on the heat generated by the operation of the engine 204. For example, the supplementary vaporizer 226 can include, for example, one or more resistive heaters, catalytic heaters or burners, bleed air streams from an auxiliary power unit, etc. or be in thermal communication therewith.

[0079] Figure 3 The exemplary supplementary vaporizer 226 depicted in Figure 3 is positioned external to the fuselage and wing 206 of the vehicle 202. For example, Figure 3 the supplementary vaporizer 226 depicted in is at least partially positioned in the pylon 208 or the engine 204, and more specifically, for the depicted exemplary aspect, at least partially positioned within the engine 204.

[0080] Still referring to Figure 3 , as briefly mentioned above, the fuel system 200 further includes a high-pressure pump 214 at a location downstream of the carburetor (and more specifically, downstream of the starting carburetor 216). For the illustrated exemplary embodiment, the high-pressure pump 214 is positioned external to the fuselage and wings 206 of the vehicle 202, and more specifically, at least partially within the pylon 208 of the vehicle 202, or at least partially within the engine 204 of the vehicle 202. Even more specifically, Figure 3 the exemplary high-pressure pump 214 is at least partially positioned within the engine 204.

[0081] The high-pressure pump 214 can be configured to direct a hydrogen fuel stream from the tank to the engine 204 via the fuel delivery assembly 212 during operation of the engine 204. The high-pressure pump 214 can operate optimally when it receives a substantially fully single-phase stream. For the depicted exemplary embodiment, the high-pressure pump 214 is located downstream of the main carburetor 222 and downstream of the supplementary carburetor 226. In this manner, it should be understood that the high-pressure pump 214 is configured to receive a hydrogen fuel stream that is substantially fully in the gaseous phase or the supercritical phase. This can facilitate more precise operation of the high-pressure pump 214, more efficient operation of the high-pressure pump 214, or both.

[0082] However, it should be understood that in other exemplary embodiments, the high-pressure pump 214 can be positioned at any other suitable location. For example, now briefly referring to Figure 4 , a schematic diagram of a fuel system 200 for a vehicle 202 according to another exemplary embodiment of the present disclosure is provided. Figure 4 The exemplary fuel system 200 of Figure 3 is constructed in substantially the same manner as the exemplary fuel system 200 of Figure 4 However, for the exemplary embodiment of Figure 4 , the high-pressure pump 214 is located upstream of the main carburetor 222 and upstream of the supplementary carburetor 226. In this way, the high-pressure pump 214 can be configured to receive a hydrogen fuel stream through the fuel delivery assembly 212 in substantially fully liquid phase during operation of the engine 204. It is noteworthy that for the exemplary embodiment of

[0083] Now returning to refer to Figure 3, it should be understood that the fuel system 200 further includes a fuel metering unit 230, which is in fluid communication with a fuel delivery assembly 212 downstream of the vaporizer and the high-pressure pump 214 (and more specifically, downstream of the starting vaporizer 216, downstream of the main vaporizer 222, downstream of the supplementary vaporizer 226, and downstream of the high-pressure pump 214). In this way, the fuel system 200 is configured to provide the fuel metering unit 230, and the fuel metering unit 230 is configured to receive hydrogen fuel in a substantially fully gaseous phase or a substantially fully supercritical phase.

[0084] The fuel metering unit 230 of the fuel system 200 is also configured to supply a fuel flow to the engine 204 in a desired manner. More specifically, as Figure 3 schematically depicted, the fuel metering unit 230 is configured to supply a desired volume of hydrogen fuel to the fuel manifold 232 of the engine 204 at a desired flow rate, for example. The fuel manifold 232 may be configured to supply the received hydrogen fuel to a plurality of fuel nozzles within the combustion section of the engine 204 to facilitate the mixing of the hydrogen fuel and the compressed air and to combust the mixture of the hydrogen fuel and the compressed air to generate combustion gases that drive the engine 204.

[0085] Now also referring to Figure 5 , a close-up schematic view of a portion of the exemplary fuel system 200 described above with reference to Figure 3 is depicted. It should be understood that in some exemplary aspects, the engine 204 may operate under transient conditions that require a change in the fuel flow to the engine 204. To accommodate one or more of these changes, the fuel system 200 may include features for redirecting or absorbing excess fuel flow within the fuel delivery assembly 212.

[0086] For example, as Figure 5 shown, in some exemplary embodiments, the fuel system 200 may include a recirculation flow path 234 for redirecting excess fuel flow within the fuel delivery assembly 212. In some exemplary embodiments, the recirculation flow path 234 may be in fluid communication with the fuel delivery assembly 212 at a location downstream of the high-pressure pump 214 and at a location upstream of the high-pressure pump 214. More specifically, the fuel delivery assembly 212 may include a recirculation overflow valve 236 that fluidly connects the recirculation flow path 234 to the fuel delivery assembly 212 at a location downstream of the high-pressure pump 214 and upstream of the fuel metering unit 230 for supplying a fuel flow in excess of the desired amount to the recirculation flow path 234. The recirculation flow path 234 may supply the received excess fuel flow back to the fuel delivery assembly 212 at a location upstream of the high-pressure pump 214 and downstream of the main vaporizer 222 and the supplementary vaporizer 226.

[0087] In addition, for Figure 5In the exemplary embodiment shown, the fuel system 200 further includes an accumulator 238 in fluid communication with the fuel delivery assembly 212 for receiving overflow hydrogen fuel from the fuel delivery assembly 212. For Figure 5 the embodiment shown, the accumulator 238 is in fluid communication with the fuel delivery assembly 212 at a location downstream of the high-pressure pump 214 and upstream of the fuel metering unit 230. More specifically, for the embodiment shown, the fuel delivery assembly 212 includes an accumulator overflow valve 240 for providing an excess fuel flow from the fuel delivery assembly 212 to the accumulator 238. The accumulator overflow valve 240 can be a pressure-actuated valve, an electrically actuated valve (operated in response to, for example, a sensed pressure value), etc. Additionally, the accumulator 238 can provide a fuel flow back to the fuel delivery assembly 212 under certain conditions (e.g., transient conditions where a higher fuel flow is required).

[0088] However, it should be understood that in other exemplary embodiments, any other suitable configuration can be provided. For example, in other embodiments, the fuel system 200 may not include both the recirculation flow path 234 and the accumulator 238, but may include only one of the recirculation flow path 234 or the accumulator 238. Alternatively, in other embodiments, the fuel system 200 may not include either the recirculation flow path 234 or the accumulator 238, or may include one or both of these features at any other suitable location with any other suitable configuration.

[0089] Now returning to reference Figure 3 , the fuel system 200 further includes one or more features for discharging any remaining hydrogen fuel within the fuel delivery assembly 212 during or after shutdown of the engine 204. More specifically, Figure 3 the exemplary fuel system 200 includes a purge / priming assembly 218 in fluid communication with the fuel delivery assembly 212 as briefly mentioned above. During or after shutdown of the engine 204, the purge / priming assembly 218 can provide a purge fluid flow through the fuel delivery assembly 212. The purge fluid can be a gas that is substantially free of oxygen. For example, the purge fluid can be nitrogen, helium, etc.

[0090] For the embodiment shown, the purge / priming assembly 218 is located near the fuel tank 210 relative to the fuel manifold 232. More specifically, for the embodiment shown, the purge / priming assembly 218 is positioned within the wing 206 and is in airflow communication with the fuel delivery assembly 212 at a location just downstream of the starting carburetor 216 and upstream of the main carburetor 222 and the high-pressure pump 214.

[0091] In this manner, the hydrogen fuel within the fuel delivery assembly 212 and the hydrogen fuel within the fuel manifold 232 and the fuel nozzles of the engine 204 can be removed during or after an engine shutdown of the engine 204. In certain exemplary embodiments, the hydrogen fuel can be vented to the atmosphere or alternatively can be recaptured during operation of the purge / priming assembly 218. It should be understood that if the hydrogen fuel remains within the fuel delivery assembly 212, the hydrogen fuel may be capable of permeating any fuel lines or conduits of the fuel delivery assembly 212. Thus, purging the hydrogen fuel from the fuel delivery assembly 212 can prevent such leakage of the hydrogen fuel and, for example, the accumulation of the hydrogen fuel at undesired locations.

[0092] Although the depicted exemplary embodiment includes a purge / priming assembly 218 having the functions described herein, in other exemplary embodiments, the purge / priming assembly 218 can be configured as two separate configurations or can be configured to perform only one of the purge function or the priming function.

[0093] However, it should be understood that in other exemplary embodiments, the fuel system 200 can have any other suitable configuration.

[0094] For example, with brief reference to Figure 6 , a fuel system 200 according to another exemplary embodiment of the present disclosure is provided. Figure 6 The exemplary fuel system 200 of Figure 3 can be configured in a manner substantially similar to the exemplary fuel system 200 described above with reference to Figure 6 . For example,

[0095] However, for the depicted exemplary embodiment, the fuel system 200 does not include a separate starting carburetor 216, a main carburetor 222, and a supplementary carburetor 226. Instead, for Figure 6 the exemplary embodiment shown, the fuel system 200 includes a dual-function carburetor. The dual-function carburetor can be configured to operate as a starting carburetor under pre-start operating conditions and as a main carburetor under thermally stable operating conditions. Additionally or alternatively, the dual-function carburetor can be configured to operate as a starting carburetor under pre-start operating conditions and as a main carburetor under thermally stable operating conditions.

[0096] More specifically, for Figure 6In the depicted exemplary embodiment, the fuel system 200 includes only the primary vaporizer 242. As described above, the primary vaporizer 242 is upstream of the high-pressure pump 214 and is located external to the engine 204. More specifically, Figure 6 the primary vaporizer 242 is located external to the engine 204 and external to the pylon 208. More specifically, still for Figure 6 the exemplary embodiment, the primary vaporizer 242 is at least partially located within the fuselage of the aircraft or within the wing 206 of the aircraft, such as at least partially within the wing 206 of the aircraft. Figure 6 the primary vaporizer 242 is configured to perform the same functions as the starting vaporizer 216 and the supplementary vaporizer 226 described above with reference to Figure 3 . In this way, it will be understood that the primary vaporizer 242 includes a heat source 244 that is different from the waste heat source of the engine 204 or is in thermal communication with the heat source 244. For example, in some exemplary embodiments, the primary vaporizer 242 incorporates or utilizes a burner, a catalytic heater, bleed air flow from an auxiliary power unit, or a resistance heater or is in thermal communication therewith. This can facilitate the operation of the primary vaporizer 242 before the engine 204 operates under thermally stable operating conditions.

[0097] It is noted that, as schematically depicted, the primary vaporizer 242 may further include a plurality of heat sources 244 or be in thermal communication with a plurality of heat sources 244. At least one of the plurality of heat sources 244 may be an engine heat source, such as one or more of the exemplary sources described above with reference to Figure 2 . In this way, it should be understood that before the engine 204 operates under thermally stable operating conditions, the primary vaporizer 242 may be in thermal communication with a heat source 244 that is different from the waste heat source of the engine 204, and further once the engine 204 operates under thermally stable operating conditions, the primary vaporizer 242 may be in thermal communication with the waste heat source of the engine 204. This can facilitate more efficient operation of the fuel system 200.

[0098] It is noted that although Figure 6 only one vaporizer (i.e., the primary vaporizer 242) is depicted, in other embodiments, the primary vaporizer 242 may alternatively perform only the functions of the starting vaporizer 216 and the supplementary vaporizer 226 (each using a heat source external to the engine 204), and the fuel system may further include a separate main vaporizer 222.

[0099] In addition, it should be understood that in some exemplary embodiments, the fuel system 200 may also include aspects for assisting fuel flow through the fuel delivery assembly 212. For example, in some exemplary embodiments, the fuel tank 210 may be a pressurized fuel tank 210 configured to maintain an absolute pressure greater than 50 pounds per square inch absolute pressure ("psia") during operation of the vehicle 202 and the engine 204, such as at least 70 psia, such as up to 500 psia. Additionally or alternatively, in other exemplary embodiments, the fuel system 200 may also include an auxiliary pump. For example, now briefly referring to Figure 7 , a schematic diagram of a fuel system 200 according to another exemplary embodiment of the present disclosure is provided. Figure 7 The exemplary fuel system 200 of Figure 3 may be constructed in substantially the same manner as the exemplary fuel system 200 of Figure 7 . However, for the exemplary embodiment of Figure 7 , the fuel system 200 further includes a low-pressure pump 246. For the illustrated embodiment, the low-pressure pump 246 is located upstream of the vaporizer, and more specifically, upstream of the starting vaporizer 216. The low-pressure pump 246 may be configured to provide an initial pressurization to cause a flow of hydrogen fuel through the fuel delivery assembly 212. It should be understood that the low-pressure pump 246 may be configured to provide a smaller pressure increase within the fuel delivery assembly 212 than the high-pressure pump 214. For example, in some exemplary embodiments, the low-pressure pump 246 may be configured to provide a pressure increase between 20 psi and 300 psi (such as between 50 psi and 200 psi), while the high-pressure pump 214 may be configured to provide a pressure increase between 200 psi and 2000 psi (such as at least 500 psi, such as at least 750 psi). In such a manner, it should be understood that the low-pressure pump 246 may be configured to provide less than 80% of the pressure increase of the high-pressure pump 214, such as less than 70% of the pressure increase of the high-pressure pump 214, such as less than 60%, such as less than 50%, such as less than 40%, such as less than 30%, such as less than 20%, such as at least 5%.

[0100] In addition, still in other exemplary embodiments, other suitable configurations may be provided for the fuel system 200. For example, now referring to Figure 8 , a schematic diagram of a fuel system 200 according to another exemplary embodiment of the present disclosure is provided. Figure 8 The exemplary fuel system 200 of Figure 3 may be constructed in a manner similar to the exemplary fuel system 200 of Figure 8 . For example, the exemplary fuel system 200 of Figure 8 generally includes a fuel tank 210, a fuel delivery assembly 212, a vaporizer, and a high-pressure pump 214. However, for Figure 8In an exemplary embodiment, the high-pressure pump 214 of the fuel system 200 is located upstream of the carburetor. It is noted that with such a configuration, the high-pressure pump 214 can be configured to receive the fuel flow from the fuel tank 210 in a known phase. For the depicted exemplary embodiment, the high-pressure pump 214 is located outside the engine 204, and more specifically, outside the pylon 208 and the engine 204, and more specifically, at least partially within the fuselage or wing 206 of the aircraft, and even more specifically, at least partially positioned within the wing 206 of the aircraft.

[0101] As with the embodiment referenced above Figure 3 and Figure 5 described, Figure 8 the exemplary fuel system 200 may include an accumulator 248 in fluid communication with the fuel delivery assembly 212 for receiving fuel overflows. It is noted that for the illustrated embodiment, the accumulator 248 is located upstream of the carburetor, and more specifically, upstream of the starting carburetor 216, the main carburetor 222, and the supplementary carburetor 226. This can help to receive overflow fuel in the fuel delivery assembly 212 due to, for example, engine transients to low power modes and the vaporization of liquid fuel already in the fuel delivery assembly 212.

[0102] Now returning to reference Figure 3 , it should be understood that the fuel system 200 also includes a controller 250. The controller 250 can be a controller dedicated to the exemplary fuel system 200, or alternatively can be incorporated or configured as part of a controller for the engine 204 (e.g., a full-authority digital engine control, "FADEC", for the engine 204), a controller for the vehicle 202, etc.

[0103] The controller 250 is operatively communicable with various aspects of the fuel system 200. For example, for the illustrated embodiment, the controller 250 is operatively communicable with the starting carburetor 218, the main carburetor 222, the supplementary carburetor 226, the high-pressure pump 214, the fuel metering unit 230, and the purge / priming assembly 218. The controller 250 can also be operatively communicable with, for example, the fuel tank 210, the heat source 224 of the main carburetor 222, the heat source 228 of the supplementary carburetor 226, the heat source 220 of the starting carburetor 216, or one or more sensors 252 configured due to data indicating various operating conditions (e.g., temperature, pressure, etc.) of the fuel delivery assembly 212.

[0104] In this manner, it should be understood that the controller 250 can be configured to control various operations of the fuel system 200 in accordance with, for example, the operating conditions of the engine 204, the vehicle 202, or both. For example, from the description herein, it can be understood that the controller 250 can be configured to operate the starting carburetor 216 when the engine 204 is in a first operating condition, can be configured to operate the supplementary carburetor 226 when the engine 204 is in a second operating condition, and can further be configured to operate the main carburetor 222 when the engine 204 is in a third operating condition.

[0105] For example, the controller 250 can be configured to operate the starting carburetor 216 when the engine 204 is in a pre-start operating condition. The pre-start operating condition can be an operating condition before the engine 204 starts, such as an operating condition before any fuel within the combustion engine 204 is burned. When operating the starting carburetor 216 under the pre-start operating condition, the controller 250 can be configured to remove non-hydrogen fluids from the various pipelines and conduits of the fuel delivery assembly 212 such that when hydrogen fuel is subsequently supplied to the fuel delivery assembly 212, it does not freeze the non-hydrogen fluids within the fuel delivery assembly 212. In this manner, the controller 250 can be configured to operate the starting carburetor 216 to heat the hydrogen fuel from the liquid phase to the gas phase or the supercritical phase, and more specifically, can be configured to heat the hydrogen fuel to a temperature above the freezing point of the ambient air, the purge fluid, or both. Additionally or alternatively, the controller 250 can be configured to provide a pre-start fluid flow from the purge / priming assembly 218 through the fuel delivery assembly 212 before introducing the hydrogen fuel heated by the starting carburetor 216. The pre-start fluid can define a relatively low freezing point, even if it is greater than the freezing point of the hydrogen fuel.

[0106] Furthermore, the controller 250 can be configured to operate the supplementary carburetor 226 when the engine 204 is in a start operating condition before the engine 204 operates under a thermally stable operating condition. In such a manner, the controller 250 can be configured to utilize the supplementary carburetor 226 before the engine 204 is in a condition where there is sufficient waste heat to increase the temperature of the hydrogen fuel to a point where it is in a substantially fully gaseous phase or a substantially fully supercritical phase.

[0107] Subsequently, the controller 250 can be configured to operate the main carburetor 222 once the engine 204 is in a thermally stable operating condition such that it can provide a sufficient amount of heat to increase the temperature of the hydrogen fuel to a point where it is in a substantially fully gaseous phase or a substantially fully supercritical phase.

[0108] Notably, the controller 250 can be configured to operate only one of the start vaporizer 216, the supplementary vaporizer 226, or the main vaporizer 222 at a time, or alternatively, can be configured to overlap the operation of two of these vaporizers when transitioning between the first and second operating conditions, or between the second and third operating conditions.

[0109] The controller 250 can also be configured to operate the fuel system 200 during a shutdown mode. When the engine 204 is shut down, the controller 250 can be configured to shut down the operation of the high-pressure pump 214 (and other pumps within the fuel system 200) to allow the engine 204 to burn any high-pressure hydrogen fuel in the fuel manifold 232 and shut down.

[0110] Additionally or alternatively, the controller 250 can be configured to operate the purge / priming assembly 218 to inject a purge fluid into the fuel delivery assembly 212 during shutdown, before shutting down, for example, the high-pressure pump 214 or the low-pressure pump 246 (if provided). In this way, the purge fluid can force any remaining hydrogen gas within the fuel delivery assembly 212 into the engine 204 to be burned off before the engine 204 shuts down.

[0111] Additionally or alternatively, the controller 250 can be configured to operate the purge / priming assembly 218 to inject a purge fluid into the fuel delivery assembly 212 after shutdown. In this way, the hydrogen fuel within the fuel delivery assembly 212 can be vented to the atmosphere or recaptured, for example, using a dedicated tank.

[0112] In some exemplary aspects, when the purge fluid defines a freezing point above the boiling point of hydrogen, the controller 250 can wait for the temperature of the hydrogen gas within the fuel delivery assembly 212 to exceed the boiling point of the purge fluid before injecting the purge fluid into the fuel delivery assembly 212. For example, when the purge fluid is, for example, nitrogen, the controller 250 can wait for the temperature of the hydrogen fuel within the fuel delivery assembly 212 to exceed the boiling point of nitrogen before injecting nitrogen to purge the fuel delivery assembly 212.

[0113] However, it is notable that in other exemplary aspects, the purge fluid can be, for example, helium, in which case the controller 250 may not need to wait for the temperature of the hydrogen fuel to increase before injecting helium to purge the fuel delivery assembly 212.

[0114] Now referring to Figure 9 provided that can be incorporated into Figure 3Exemplary embodiments of the controller 250 in the exemplary fuel system 200. The controller 250 may include one or more computing devices 252. The computing device 252 may include one or more processors 252A and one or more memory devices 252B. The one or more processors 252A may include any suitable processing device, such as a microprocessor, a microcontroller 250, an integrated circuit, a logic device, and / or other suitable processing devices. The one or more memory devices 252B may include one or more computer-readable media, including but not limited to non-transitory computer-readable media, RAM, ROM, hard disk drives, flash drives, and / or other memory devices.

[0115] The one or more memory devices 252B may store information accessible by the one or more processors 252A, including computer-readable instructions 252C executable by the one or more processors 252A. The instructions 252C may be any set of instructions that, when executed by the one or more processors 252A, cause the one or more processors 252A to operate. In some embodiments, the instructions 252C may be executed by the one or more processors 252A to cause the one or more processors 252A to operate, such as any operations and functions for which the controller 250 and / or the computing device 252 are configured, operations for operating the fuel system 200 as described herein (e.g., methods 300, 400, 500), and / or any other operations or functions of the one or more computing devices 252. The instructions 252C may be software written in any suitable programming language or may be implemented in hardware. Additionally and / or alternatively, the instructions 252C may be executed in logically and / or virtually separated threads on the processor 252A. The memory device 252B may also store data 252D accessible by the processor 252A.

[0116] The computing device 252 may also include a network interface 252E for communicating, for example, with other components of the system 500 (e.g., via a network). The network interface 252E may include any suitable components for interfacing with one or more networks, including, for example, a transmitter, a receiver, a port, a controller 250, an antenna, and / or other suitable components. One or more external display devices (not depicted) may be configured to receive one or more commands from the computing device 252. For example, as Figure 3 shown by the dashed lines in, the controller 250 may communicate operably with various components of the fuel system 200 via a wireless communication network.

[0117] The techniques discussed herein refer to computer-based systems, actions taken by computer-based systems, information sent to computer-based systems, and information from computer-based systems. One of ordinary skill in the art will recognize that the inherent flexibility of computer-based systems allows for a variety of possible configurations, combinations, and divisions of tasks and functions among and within components. For example, the processes discussed herein may be implemented using a single computing device or multiple computing devices working in combination. Databases, memories, instructions, and applications may be implemented on a single system or distributed across multiple systems. Distributed components may operate sequentially or in parallel.

[0118] Now referring to Figure 10 , a flowchart of a method 300 for operating a fuel system of a vehicle having an engine is provided. Figure 10 Exemplary aspects of the method 300 depicted in Figures 1 to 9 may be used to operate one or more of the exemplary fuel systems described above with reference to

[0119] Method 300 includes priming a fuel delivery assembly of the fuel system with a priming fluid that defines a priming fluid phase change point at (302), and providing a flow of hydrogen fuel from a fuel tank of the fuel system to the engine through the fuel delivery assembly at (304). The hydrogen fuel within the fuel tank is at least partially in a liquid phase, and the fuel system is configured to provide hydrogen fuel that is substantially entirely in a liquid phase from the fuel tank. Additionally, for Figure 10 exemplary aspects of the method 300 depicted in Figure 10 providing a flow of hydrogen fuel from the fuel tank at (304) includes providing the flow of hydrogen fuel from the fuel tank at a temperature equal to or higher than the priming fluid phase change point of the priming fluid. For

[0120] However, alternatively, the priming fluid phase change point may be the priming fluid boiling point. This can prevent the priming fluid from transitioning to a liquid and having a negative impact on the flow of the priming fluid through the fuel system.

[0121] In this manner, it should be understood that method 300 may prime the fuel delivery assembly with a priming fluid to minimize freezing of the priming fluid within the fuel delivery assembly during an initial operating phase of the engine.

[0122] More specifically, still referring to Figure 10Exemplary aspects of method 300 depicted in [description] may include, at (302), priming a fuel delivery assembly of a fuel system by providing a priming fluid flow at (308), where the priming fluid has a freezing point lower than that of the hydrogen fuel. For example, the priming fluid may be a helium fluid. In this manner, it should be understood that providing the priming fluid flow at (308) through the fuel delivery assembly may include providing the priming fluid through the fuel delivery assembly at a temperature above the freezing point of the fluid (e.g., air) within the fuel delivery assembly.

[0123] However, it should be understood that in other exemplary aspects, method 300 may utilize other priming fluids. For example, still referring to Figure 10 , in other exemplary aspects, priming the fuel delivery assembly of the fuel system at (302) may include providing a priming fluid flow at (310), where the priming fluid has a freezing point greater than or equal to that of the hydrogen fuel. For example, the priming fluid may be hydrogen fuel.

[0124] For such exemplary aspects, priming the fuel delivery assembly at (302) may further include pre-priming the fuel delivery assembly at (312) with a pre-priming fluid that defines a pre-priming fluid freezing temperature. The pre-priming fluid freezing temperature may be within 150 °C of the freezing temperature of the hydrogen fuel, e.g., within 100 °C of the freezing temperature of the hydrogen fuel, e.g., within 75 °C of the freezing point of the hydrogen fuel. For example, the pre-priming fluid may be nitrogen.

[0125] Furthermore, through such exemplary aspects, priming the fuel delivery assembly of the fuel system at (302) may further include gradually providing the priming fluid at (314) to minimize freezing of the pre-priming fluid within the fuel delivery system. For example, in certain exemplary aspects, gradually providing the priming fluid at (314) may include providing the priming fluid at (316) at a rate less than the fuel flow rate to the engine during idle operation of the engine (e.g., at a rate equal to between 5% and 90% of the fuel flow rate to the engine during idle operation of the engine). Additionally, gradually providing the priming fluid at (314) may include providing the priming fluid in a gaseous phase.

[0126] Still referring to Figure 10, Through such an exemplary aspect, the fuel delivery assembly of the fuel system at (302) may further include heating the hydrogen fuel stream from the fuel tank at (318) to convert the hydrogen fuel stream from the liquid phase to the gas phase, and providing the hydrogen fuel stream heated to the gas phase through the fuel delivery assembly as a starting fluid at (320). For example, in some exemplary aspects, heating the hydrogen fuel stream from the fuel tank at (318) may include heating the hydrogen fuel stream at (322) to a temperature higher than the freezing point of the fluid in the fuel delivery assembly. For example, when using a pre-starting fluid, heating the hydrogen fuel stream at (322) may include heating the hydrogen fuel stream to a temperature higher than the pre-starting freezing point. Alternatively, when not using a pre-starting fluid, heating the hydrogen fuel stream at (322) may include heating the hydrogen fuel stream to a temperature higher than the freezing point of air.

[0127] In addition, for the exemplary aspects of the described method 300, it should be understood that providing the hydrogen fuel stream from the fuel tank of the fuel system to the engine via the fuel delivery assembly at (304) further includes metering the hydrogen fuel stream at (324) with a flow metering unit. The fuel may be provided from the flow metering unit to, for example, the fuel manifold of the engine and subsequently to one or more fuel nozzles of the engine.

[0128] A fuel system operating in accordance with the exemplary method 300 described herein may allow the utilization of hydrogen fuel as a fuel source for the engine, and more specifically, may allow the storage of hydrogen fuel in the liquid phase while providing hydrogen fuel in the gas phase to the engine for combustion. In this way, it should be understood that providing the hydrogen fuel stream from the fuel tank of the fuel system to the engine at (304) further includes providing a hydrogen fuel stream that is substantially entirely in the liquid phase through the outlet of the fuel tank at (326), and providing a hydrogen fuel stream that is substantially entirely in the gas phase or substantially entirely in the supercritical phase to the flow metering unit at (328). More specifically, providing a hydrogen fuel stream that is substantially entirely in the gas phase or substantially entirely in the supercritical phase to the flow metering unit at (328) includes, in at least some exemplary aspects, providing a hydrogen fuel stream that is substantially entirely in the gas phase to the flow metering unit.

[0129] It should be understood that the exemplary method 300 can be used to prevent the fluid in the fuel delivery assembly from freezing during operation. More specifically, by priming the fuel delivery assembly according to one or more of the exemplary aspects described herein before operating the engine, or rather, before providing the hydrogen fuel stream to the engine for combustion, the fuel delivery assembly can be prepared to receive relatively cold hydrogen fuel from the fuel tank without experiencing an undesirable delay and / or damage due to the freezing of the fluid in the fuel delivery assembly.

[0130] Now refer to Figure 11 , which depicts another exemplary aspect of the present disclosure. More specifically,Figure 11 A flowchart of a method 400 for operating a fuel system in accordance with another example aspect of the present disclosure is provided. The method 400 can be used to operate a fuel system in accordance with one or more of the exemplary embodiments described above with reference to Figures 1 to 9 a fuel system described. However, in other example aspects, the method 400 can be used to operate a fuel system having any other suitable configuration.

[0131] The method 400 includes priming a fuel delivery assembly of the fuel system with a starting fluid at (402), and supplying a hydrogen fuel stream from a fuel tank of the fuel system to an engine through the fuel delivery assembly at (404).

[0132] For the depicted example aspect, the starting fluid includes hydrogen fuel, and priming the fuel delivery assembly at (402) includes heating a hydrogen fuel stream from the fuel tank using a first vaporizer during a first operating condition of the engine at (406). Additionally, for the depicted example aspect, supplying the hydrogen fuel stream from the fuel tank to the engine at (404) includes heating the hydrogen fuel stream from the fuel tank using a second vaporizer during a second operating condition of the engine at (408). More specifically, for the depicted example aspect, supplying the hydrogen fuel stream from the fuel tank to the engine at (404) further includes heating the hydrogen fuel stream from the fuel tank using a third vaporizer during a third operating condition of the engine at (410).

[0133] For the depicted example aspect, the first vaporizer is a starting vaporizer and the first operating condition is a pre-start operating condition of the engine. The pre-start operating condition of the engine can be an operating condition before supplying hydrogen fuel to the engine for combustion. Additionally, for the depicted example aspect, the second vaporizer is a supplementary vaporizer and the second operating condition is a start operating condition of the engine. Additionally, still for the depicted example aspect, the third vaporizer is a main vaporizer and the third operating condition is a thermally stable operating condition of the engine.

[0134] It should be noted that each vaporizer can be configured to receive heat from different heat sources to be operable during different operating conditions of the engine. For example, a starting vaporizer can be configured to receive heat from a heat source external to the engine, such that heating the hydrogen fuel stream from the fuel tank at (406) can include providing heat from a heat source external to the engine to a first vaporizer. Similarly, a supplementary vaporizer can also be configured to receive heat from a heat source external to the engine, such that heating the hydrogen fuel stream from the fuel tank at (408) can include providing heat from a heat source external to the engine to a second vaporizer. Additionally, a main vaporizer can be configured to receive heat from a heat source internal to the engine, such that heating the hydrogen fuel stream from the fuel tank at (410) can include providing heat from the engine to a third vaporizer. Heat sources external to the engine can include, for example, one or more catalytic heat sources or burners, bleed air streams from an auxiliary power unit, resistance heaters, etc. Heat sources internal to the engine can include, for example, one or more waste heat sources of the engine, such as one or more of the heat sources described above with reference to Figure 2 the one or more heat sources.

[0135] It should be noted that although method 400 includes a separate starting vaporizer and a separate supplementary vaporizer, in other exemplary aspects of method 400, the fuel system can include a single vaporizer that performs the functions of the starting vaporizer and the supplementary vaporizer, and the single vaporizer is configured to receive heat from a heat source external to the engine. Such an exemplary aspect of method 400 can still include a separate main vaporizer.

[0136] In this way, it should be understood that Figure 11 the exemplary method 400 is capable of providing heat to the hydrogen fuel stream from the fuel tank through the fuel delivery assembly under various operating conditions of the engine. For example, Figure 11 the example method 400 can allow the fuel delivery assembly to be primed with hydrogen fuel before operating the engine, can allow the hydrogen fuel stream from the fuel tank to be heated before the engine operates under thermally stable operating conditions, and can also allow the hydrogen fuel stream from the fuel tank to be effectively heated by utilizing waste heat from the engine after the engine reaches thermally stable operating conditions.

[0137] Now referring to Figure 12 , a flowchart of a method 500 for operating a fuel system of a vehicle having an engine is provided. Method 500 can operate with a fuel system configured in a manner similar to one or more of the exemplary fuel systems described above with reference to Figures 1 to 9 . However, in another exemplary aspect, method 500 can be used with a fuel system having any other suitable configuration.

[0138] Method 500 includes, during operation of the engine at (502), supplying a hydrogen fuel stream from a fuel tank of a fuel system to the engine via a fuel delivery assembly.

[0139] The method further includes terminating, at (504), the hydrogen fuel stream from the fuel tank to the engine via the fuel delivery assembly. In certain exemplary aspects, terminating the hydrogen fuel stream at (504) can include terminating, at (506), the hydrogen fuel stream from the fuel tank to the engine in response to receiving a command to shut down the engine, or terminating, at (508), the hydrogen fuel stream from the fuel tank to the engine in response to an uncommanded shutdown of the engine. Additionally, for certain exemplary aspects, terminating the hydrogen fuel stream from the fuel tank to the engine at (504) can include shutting down one or more pumps (e.g., a high-pressure pump, and if provided, a low-pressure pump) in communication with the fuel delivery assembly.

[0140] Furthermore, it should be understood that for Figure 12 the exemplary method 500 depicted, method 500 further includes discharging, at (510), a remaining volume of hydrogen fuel from the fuel delivery assembly. The remaining volume of hydrogen fuel refers to the volume of hydrogen fuel in the fuel delivery assembly after terminating the hydrogen fuel stream from the fuel tank to the engine at (504). In this manner, it should be understood that for the depicted exemplary aspects, discharging the remaining volume of hydrogen fuel from the fuel delivery assembly at (510) includes discharging, at (512), the remaining volume of hydrogen fuel from the fuel delivery assembly after terminating, at (504), the hydrogen fuel stream from the fuel tank to the engine via the fuel delivery assembly.

[0141] Additionally, for example, in the depicted aspect, discharging the remaining volume of hydrogen fuel from the fuel delivery assembly at (510) includes providing, at (514), a purge fluid stream via the fuel delivery assembly. The purge fluid defines a freezing point.

[0142] In certain exemplary aspects, the freezing point of the purge fluid can be lower than the freezing point of the hydrogen fuel. For example, the purge fluid can be helium. In such an exemplary aspect, providing the purge fluid stream via the fuel delivery assembly at (514) can include providing, at (515), the purge fluid stream immediately after terminating, at (504), the hydrogen fuel stream from the fuel tank to the engine.

[0143] However, in another exemplary aspect, the purge fluid can define a freezing point greater than the freezing point of the hydrogen fuel. For example, in some exemplary aspects, the purge fluid can be nitrogen. For such exemplary aspects, to avoid the purge fluid freezing when contacting the remaining volume of hydrogen fuel, providing a purge fluid flow through the fuel delivery assembly at (514) can include providing a purge fluid flow through the fuel delivery assembly at (516) after a boil-off period that terminates at (504) the flow of hydrogen fuel from the fuel tank to the engine through the fuel delivery assembly. The boil-off period can be at least about two minutes to at most about two hours. In this way, it should be understood that providing a purge fluid flow to the fuel delivery assembly at (516) after the boil-off period can include providing a purge fluid flow through the fuel delivery assembly at (518) after the temperature of the remaining volume of hydrogen fuel in the fuel delivery assembly has increased to a temperature above the freezing temperature of the purge fluid. Method 500 can utilize one or more sensors to sense data indicative of the temperature of the remaining volume of hydrogen gas to determine whether the temperature of the remaining volume of hydrogen fuel in the fuel delivery assembly has increased to a temperature above the freezing temperature of the purge fluid, and can make a control decision based thereon.

[0144] Still referring to Figure 12 , in other exemplary aspects of method 500, other suitable ways can be additionally or alternatively provided for discharging the remaining volume of hydrogen fuel from the fuel delivery assembly at (510). For example, in some exemplary aspects, discharging the remaining volume of hydrogen fuel from the fuel delivery assembly at (510) can include operating the engine at (520) to combust at least a portion of the remaining volume of hydrogen fuel in the fuel delivery assembly. For example, operating the engine at (520) to combust at least a portion of the remaining volume of hydrogen fuel in the fuel delivery assembly can include operating the engine to combust at least 20% of the remaining volume of hydrogen fuel, such as at least 30% of the remaining volume of hydrogen fuel, such as at least 40%, such as at least 50%, such as at least 60%, such as at least 70%, such as at least 80%.

[0145] Additionally or alternatively, discharging the remaining volume of hydrogen fuel from the fuel delivery assembly at (510) can include discharging at least a portion of the remaining volume of hydrogen fuel in the fuel delivery assembly to the atmosphere at (522), recapturing at least a portion of the remaining volume of hydrogen fuel in the fuel delivery assembly at (524), or both.

[0146] The portion of the remaining volume of hydrogen fuel in the fuel delivery assembly that is discharged at (522) to, for example, the atmosphere can include at least about 20% of the remaining volume of hydrogen fuel, such as at least 30% of the remaining volume of hydrogen fuel, such as at least 40%, such as at least 50%, such as at least 60%, such as at least 70%, such as at least 80%, such as at least 90%. Additionally or alternatively, the portion of the remaining volume of hydrogen fuel in the fuel delivery assembly that is recaptured at (524) can include at least about 20% of the remaining volume of hydrogen fuel, such as at least 30% of the remaining volume of hydrogen fuel, such as at least 40%, such as at least 50%, such as at least 60%, such as at least 70%, such as at least 80%, such as at least 90%.

[0147] However, it should be understood that in Figure 12 other exemplary aspects of method 500, the method can include one or more additional or alternative steps to ensure that the hydrogen fuel within the fuel delivery assembly can be removed without, for example, freezing the fluid in the fuel delivery assembly.

[0148] For example, now referring to Figure 13 there is provided Figure 12 a flowchart of another exemplary aspect of method 500. Figure 13 The exemplary aspects of Figure 12 can be similar to Figure 13 the exemplary aspects of

[0149] However, it should be understood that for Figure 13Exemplary aspects of providing a hydrogen fuel stream from a fuel tank of a fuel system to an engine at (502) include providing a pre-purge stream of hydrogen fuel to a fuel delivery assembly at (526), the pre-purge stream of hydrogen fuel being heated to a pre-purge stream temperature. In this manner, it should be understood that providing the pre-purge stream of hydrogen fuel to the fuel delivery assembly at (526) includes heating the pre-purge stream of hydrogen fuel to the pre-purge stream temperature at (528) using, for example, a vaporizer such as a starting vaporizer. In this manner, method 500 can provide the pre-purge stream of hydrogen fuel relatively slowly to allow for sufficient heating of the pre-purge stream of hydrogen fuel at (528). For example, in certain exemplary aspects, providing the pre-purge stream of hydrogen fuel to the fuel delivery assembly at (526) includes providing the pre-purge stream of hydrogen fuel to the fuel delivery assembly at (530) at a flow rate less than the fuel flow rate to the engine during idle operation of the engine (e.g., at a rate equal to between 5% and 90% of the fuel flow rate to the engine during idle operation of the engine).

[0150] Furthermore, it should be understood that providing the pre-purge stream of hydrogen fuel to the fuel delivery assembly at (526) can occur as a first step in shutting down the engine. In this manner, it should be understood that providing the pre-purge stream of hydrogen fuel to the fuel delivery assembly at (526) includes providing the pre-purge stream of hydrogen fuel to the fuel delivery assembly at (532) in response to receiving a command to shut down the engine. Additionally, providing the pre-purge stream of hydrogen fuel to the fuel delivery assembly at (526) can include substantially completely filling the fuel delivery assembly with the pre-purge stream of hydrogen fuel at (534) such that the remaining volume of hydrogen fuel is the pre-purge stream of hydrogen fuel.

[0151] Still referring to Figure 13 exemplary aspects of method 500, it will be further understood that terminating the hydrogen fuel stream from the fuel tank to the engine at (504) includes terminating the hydrogen fuel stream from the fuel tank to the engine at (536) after providing the pre-purge stream of hydrogen fuel to the fuel delivery assembly.

[0152] Additionally, for Figure 13 exemplary aspects of method 500, discharging the remaining volume of hydrogen fuel from the fuel delivery assembly at (510) includes providing a purge fluid stream through the fuel delivery assembly at (514). In certain exemplary aspects, the purge fluid defines a freezing point temperature below the pre-purge stream temperature. For example, in certain exemplary aspects, the purge fluid defines a boiling point temperature below the pre-purge stream temperature. In this manner, method 500 can pre-purge the fuel delivery assembly with heated hydrogen fuel, allowing the fuel delivery assembly and the fluid therein to be heated to a temperature at which the subsequently provided purge fluid will not liquefy and / or freeze.

[0153] Operating a fuel system in accordance with one or more exemplary aspects of the method 500 can ensure that a minimal amount of hydrogen fuel is retained in the fuel delivery assembly after operation of the engine. This can prevent hydrogen fuel from permeating the fuel delivery assembly during non-operating cycles of the engine, potentially preventing hydrogen fuel from accumulating in undesired locations within the engine or elsewhere.

[0154] While specific features of various embodiments may be shown in some figures and not in others, this is merely for convenience. In accordance with the principles of the present disclosure, any feature of any figure may be referenced and / or claimed in combination with any feature of any other figure.

[0155] This written description uses examples to disclose the invention, including the best mode, and also enables any person skilled in the art to practice the invention, including making and using any device or system and performing any incorporated method. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. If these other examples include structural elements that are not different from the literal language of the claims, or if they include equivalent structural elements that are not substantially different from the literal language of the claims, then these other examples are intended to fall within the scope of the claims.

[0156] Further aspects of the invention are provided by the subject matter of the following clauses:

[0157] A fuel system for a vehicle having an engine, the fuel system comprising: a fuel tank for holding hydrogen fuel in a liquid phase; a fuel delivery assembly extending from the fuel tank to the engine for supplying hydrogen fuel from the fuel tank to the engine; a vaporizer in communication with the fuel delivery assembly for heating the liquid-phase hydrogen fuel to a gaseous phase, a supercritical phase, or both; and a high-pressure pump in fluid communication with the fuel delivery assembly at a location downstream of the vaporizer for directing a flow of hydrogen fuel through the fuel delivery assembly to the engine.

[0158] The fuel system according to one or more of these clauses, wherein the vehicle is an aircraft having a fuselage and wings, wherein the fuel tank is at least partially located within the fuselage, the wings, or both, and wherein the vaporizer is also at least partially located within the fuselage, the wings, or both.

[0159] The fuel system according to one or more of these clauses, wherein the vaporizer is a starting vaporizer, and wherein the fuel system further comprises a main vaporizer in communication with the fuel delivery assembly for heating the hydrogen fuel flowing through the fuel delivery assembly.

[0160] The fuel system according to one or more of these clauses, wherein the engine includes a heat source, and wherein the main vaporizer is in thermal communication with the heat source of the engine.

[0161] The fuel system according to one or more of these clauses, wherein the starting carburetor includes a heat source external to the engine or is in thermal communication with a heat source external to the engine.

[0162] The fuel system according to one or more of these clauses, further comprising: a supplementary carburetor in communication with the fuel delivery assembly for heating the hydrogen fuel flowing through the fuel delivery assembly, wherein the supplementary carburetor includes a heat source external to the engine or is in thermal communication with a heat source external to the engine.

[0163] The fuel system according to one or more of these clauses, wherein the carrier is an aircraft having a fuselage and wings, wherein the fuel tank is at least partially located within the fuselage, the wings, or both, wherein the starting carburetor is also at least partially located within the fuselage, the wings, or both, and wherein the main carburetor and the supplementary carburetor are both located external to the fuselage and wings of the aircraft.

[0164] The fuel system according to one or more of these clauses, wherein the carrier is an aircraft having a fuselage and wings, wherein the fuel tank is at least partially located within the fuselage, the wings, or both, wherein the starting carburetor is also at least partially located within the fuselage, the wings, or both, and wherein the main carburetor and the high-pressure pump are both located external to the fuselage and wings of the aircraft.

[0165] The fuel system according to one or more of these clauses, wherein the main carburetor is in communication with the fuel delivery assembly at a location downstream of the high-pressure pump.

[0166] The fuel system according to one or more of these clauses, wherein the main carburetor is in communication with the fuel delivery assembly at a location upstream of the high-pressure pump.

[0167] The fuel system according to one or more of these clauses, further comprising: a fuel metering unit in fluid communication with the carburetor and the fuel delivery assembly downstream of the high-pressure pump.

[0168] The fuel system according to one or more of these clauses, wherein the fuel system is configured to supply the fuel metering unit with hydrogen fuel that is substantially entirely in the gaseous phase or substantially entirely in the supercritical phase.

[0169] The fuel system according to one or more of these clauses, wherein the carburetor is a starting carburetor, and wherein the fuel system further comprises: a main carburetor in communication with the fuel delivery assembly for heating the hydrogen fuel flowing through the fuel delivery assembly; and a controller operably communicating with the starting carburetor and the main carburetor, wherein the controller is configured to operate the starting carburetor when the engine is in a first operating condition and is further configured to operate the main carburetor when the engine is in a second operating condition.

[0170] The fuel system according to one or more of these clauses further includes: a supplementary vaporizer in communication with the fuel delivery assembly for heating the hydrogen fuel flowing through the fuel delivery assembly, wherein the controller is operably in communication with the supplementary vaporizer, and wherein the controller is further configured to operate the supplementary vaporizer when the engine is in a third operating condition.

[0171] The fuel system according to one or more of these clauses, wherein the first operating condition is a pre-start operating condition, the third operating condition is a start operating condition, and the second operating condition is a thermal stability operating condition.

[0172] The fuel system according to one or more of these clauses further includes: a purge assembly in fluid communication with the fuel delivery assembly for providing a purge fluid flow through the fuel delivery assembly during or after an engine shutdown.

[0173] The fuel system according to one or more of these clauses, wherein the purge fluid is an oxygen-free gas.

[0174] The fuel system according to one or more of these clauses, wherein the vaporizer is configured to heat a hydrogen fuel stream from a fuel tank to convert the hydrogen fuel stream from a substantially liquid phase to a substantially gas phase or a substantially supercritical phase.

[0175] The fuel system according to one or more of these clauses, wherein the vaporizer includes a heat source different from or in thermal communication with a waste heat source of the engine.

[0176] The fuel system according to one or more of these clauses, wherein the vaporizer utilizes a burner, a catalytic heater, a bleed air stream from an auxiliary power unit, or a resistance heater.

[0177] The fuel system according to one or more of these clauses further includes: an accumulator in fluid communication with the fuel delivery assembly for receiving an overflow of hydrogen fuel from the fuel delivery assembly.

[0178] The fuel system according to one or more of these clauses further includes: a fuel metering unit in fluid communication with the fuel delivery assembly downstream of the vaporizer and the high-pressure pump, wherein the accumulator is in fluid communication with the fuel delivery assembly at a location downstream of the high-pressure pump and upstream of the fuel metering unit.

[0179] The fuel system according to one or more of these clauses, wherein the fuel delivery assembly includes a recirculation flow path extending from a location downstream of the high-pressure pump to a location upstream of the high-pressure pump.

[0180] A fuel system according to one or more of these clauses, wherein the engine is a gas turbine engine and wherein the carrier is an aerial carrier.

[0181] A fuel system according to one or more of these clauses, further comprising a low-pressure pump in communication with the fuel delivery assembly at a location upstream of the carburetor.

[0182] A fuel system according to one or more of these clauses, wherein the fuel tank is a pressurized fuel tank.

[0183] A fuel system according to one or more of these clauses, wherein the carburetor is a dual-function carburetor configured to operate as a starting carburetor under pre-start operating conditions and as a main carburetor under thermally stable operating conditions.

[0184] A fuel system according to one or more of these clauses, wherein the carburetor is a dual-function carburetor configured to operate as a starting carburetor under pre-start operating conditions and as a supplementary carburetor under start operating conditions.

[0185] A method of operating a fuel system for a carrier having an engine, the method comprising: priming a fuel delivery assembly of the fuel system with a priming fluid defining a priming fluid phase change point; providing a hydrogen fuel stream from a fuel tank of the fuel system to the engine via the fuel delivery assembly, the hydrogen fuel in the fuel tank being at least partially in a liquid phase, and wherein providing the hydrogen fuel stream from the fuel tank comprises providing the hydrogen fuel stream from the fuel tank at a temperature equal to or higher than the priming fluid phase change point of the priming fluid.

[0186] A method according to one or more of these clauses, wherein the priming fluid phase change point is the priming fluid freezing point.

[0187] A method according to one or more of these clauses, wherein priming the fuel delivery assembly of the fuel system with the priming fluid comprises providing a priming fluid stream via the fuel delivery assembly, wherein the priming fluid freezing point is less than the freezing point of the hydrogen fuel.

[0188] A method according to one or more of these clauses, wherein the priming fluid is helium.

[0189] A method according to one or more of these clauses, wherein priming the fuel delivery assembly of the fuel system with the priming fluid comprises pre-priming the fuel delivery assembly with a pre-priming fluid defining a pre-priming fluid freezing temperature, wherein the pre-priming fluid freezing temperature is within 150 degrees Celsius of the freezing temperature of the hydrogen fuel.

[0190] The method according to one or more of these clauses, wherein the freezing temperature of the pre-perfusion fluid is within 100 degrees Celsius of the boiling point of the hydrogen fuel.

[0191] The method according to one or more of these clauses, wherein the freezing temperature of the pre-perfusion fluid is within 75 degrees Celsius of the boiling point of the hydrogen fuel.

[0192] The method according to one or more of these clauses, wherein perfusing the fuel delivery assembly of the fuel system with the starting fluid further comprises gradually supplying the starting fluid to the fuel delivery assembly to minimize freezing of the pre-perfusion fluid within the fuel delivery assembly.

[0193] The method according to one or more of these clauses, wherein the perfusion fluid is hydrogen fuel.

[0194] The method according to one or more of these clauses, wherein gradually supplying the starting fluid to the fuel delivery assembly comprises supplying the starting fluid to the fuel delivery assembly at a rate less than the fuel flow rate to the engine during idle operation of the engine.

[0195] The method according to one or more of these clauses, wherein perfusing the fuel delivery assembly of the fuel system with the starting fluid comprises pre-perfusing the fuel delivery assembly with a pre-perfusion fluid, wherein the pre-perfusion fluid is nitrogen.

[0196] The method according to one or more of these clauses, wherein pre-perfusing the fuel delivery assembly with the pre-perfusion fluid comprises providing the pre-perfusion fluid from a pre-perfusion fluid source, wherein the pre-perfusion fluid source is a fluid tank, an on-board nitrogen generation system, or both.

[0197] The method according to one or more of these clauses, wherein the starting fluid is hydrogen fuel, and wherein perfusing the fuel delivery assembly of the fuel system comprises heating a hydrogen fuel stream from a fuel tank to convert the hydrogen fuel stream from a liquid phase to a gas phase and providing the heated hydrogen fuel stream in the gas phase through the fuel delivery assembly as the starting fluid.

[0198] The method according to one or more of these clauses, wherein heating the hydrogen fuel stream from the fuel tank comprises heating the hydrogen fuel stream to a temperature higher than the freezing point of the gas in the fuel delivery assembly.

[0199] The method according to one or more of these clauses, wherein heating the hydrogen fuel stream from the fuel tank comprises using a vaporizer to heat the hydrogen fuel stream from the fuel tank.

[0200] The method according to one or more of these clauses, wherein the starting fluid is hydrogen fuel, wherein the fuel delivery assembly of the fuel injection system includes heating a hydrogen fuel stream from a fuel tank using a starting vaporizer, and wherein supplying the hydrogen fuel stream from the fuel tank to the engine includes heating the hydrogen fuel stream from the fuel tank using a main vaporizer.

[0201] The method according to one or more of these clauses, wherein heating the hydrogen fuel stream from the fuel tank using the main vaporizer includes supplying heat from the engine to the main vaporizer.

[0202] The method according to one or more of these clauses, wherein heating the hydrogen fuel stream from the fuel tank using the main vaporizer includes supplying heat from a heat source external to the engine to the main vaporizer.

[0203] The method according to one or more of these clauses, wherein the fuel delivery assembly of the fuel injection system includes heating a hydrogen fuel stream from a fuel tank using a starting vaporizer during pre-start operating conditions of the engine.

[0204] The method according to one or more of these clauses, wherein supplying the hydrogen fuel stream from the fuel tank to the engine includes supplying the hydrogen fuel stream from the fuel tank to the engine during operating conditions of the engine.

[0205] The method according to one or more of these clauses, wherein supplying the hydrogen fuel stream from the fuel tank to the engine during operating conditions of the engine includes heating the hydrogen fuel stream from the fuel tank using a supplementary vaporizer during start-up operating conditions of the engine, and heating the hydrogen fuel stream from the fuel tank using the main vaporizer during thermally stable operating conditions of the engine.

[0206] The method according to one or more of these clauses, wherein supplying the hydrogen fuel stream from the fuel tank of the fuel system to the engine through the fuel delivery assembly includes metering the hydrogen fuel stream with a flow metering unit.

[0207] The method according to one or more of these clauses, wherein supplying the hydrogen fuel stream from the fuel tank of the fuel system to the engine through the fuel delivery assembly includes providing a hydrogen fuel stream that is substantially completely in the liquid phase through an outlet of the fuel tank, and providing a hydrogen fuel stream that is substantially completely in the gas phase or substantially completely in the supercritical phase to the flow metering unit.

[0208] The method according to one or more of these clauses, further comprising: terminating the hydrogen fuel stream from the fuel tank to the engine through the fuel delivery assembly; and providing a purge fluid stream through the fuel delivery assembly after terminating the hydrogen fuel stream from the fuel tank to the engine.

[0209] The method according to one or more of these clauses, wherein terminating the hydrogen fuel flow from the fuel tank to the engine includes closing one or more pumps in communication with the fuel delivery assembly.

[0210] The method according to one or more of these clauses, wherein the fuel tank supplies hydrogen fuel to the fuel delivery assembly that is substantially entirely in the liquid phase.

[0211] A method of operating a fuel system for a vehicle having an engine, the method comprising: during operation of the engine, supplying a hydrogen fuel flow from a fuel tank of the fuel system to the engine through a fuel delivery assembly; terminating the hydrogen fuel flow from the fuel tank to the engine through the fuel delivery assembly; and discharging a remaining volume of hydrogen fuel from the fuel delivery assembly.

[0212] The method according to one or more of these clauses, wherein discharging the remaining volume of hydrogen fuel from the fuel delivery assembly includes discharging the remaining volume of hydrogen fuel from the fuel delivery assembly after terminating the hydrogen fuel flow from the fuel tank to the engine through the fuel delivery assembly.

[0213] The method according to one or more of these clauses, wherein discharging the remaining volume of hydrogen fuel from the fuel delivery assembly includes supplying a purge fluid flow through the fuel delivery assembly.

[0214] The method according to one or more of these clauses, wherein the purge fluid defines a freezing point, and wherein the freezing point of the purge fluid is less than the freezing point of the hydrogen fuel.

[0215] The method according to one or more of these clauses, wherein the purge fluid is helium.

[0216] The method according to one or more of these clauses, wherein the purge fluid defines a freezing point, and wherein the freezing point of the purge fluid is greater than the boiling point of the hydrogen fuel.

[0217] The method according to one or more of these clauses, wherein the purge fluid is nitrogen.

[0218] The method according to one or more of these clauses, wherein supplying a purge fluid flow through the fuel delivery assembly includes supplying a purge fluid flow through the fuel delivery assembly after a vaporization period starting from when the hydrogen fuel flow from the fuel tank to the engine through the fuel delivery assembly is terminated.

[0219] The method according to one or more of these clauses, wherein the vaporization period is at least about two minutes to at most two hours.

[0220] The method according to one or more of these clauses, wherein providing a purge fluid flow through the fuel delivery assembly after a vaporization period from termination of the hydrogen fuel flow from the fuel tank to the engine through the fuel delivery assembly includes providing a purge fluid flow through the fuel delivery assembly after determining that the remaining volume of hydrogen fuel in the fuel delivery assembly has increased to a temperature above the freezing temperature of the purge fluid.

[0221] The method according to one or more of these clauses, wherein discharging the remaining volume of hydrogen fuel from the fuel delivery assembly includes operating the engine to combust the remaining volume of hydrogen fuel in the fuel delivery assembly.

[0222] The method according to one or more of these clauses, wherein discharging the remaining volume of hydrogen fuel from the fuel delivery assembly includes discharging the remaining volume of hydrogen fuel in the fuel delivery assembly to the atmosphere.

[0223] The method according to one or more of these clauses, wherein discharging the remaining volume of hydrogen fuel from the fuel delivery assembly includes recapturing at least a portion of the remaining volume of hydrogen fuel in the fuel delivery assembly.

[0224] The method according to one or more of these clauses, wherein terminating the hydrogen fuel flow from the fuel tank to the engine includes closing one or more pumps in communication with the fuel delivery assembly.

[0225] The method according to one or more of these clauses, wherein providing a hydrogen fuel flow from the fuel tank of the fuel system to the engine includes providing a pre-purge flow of hydrogen fuel to the fuel delivery assembly, the pre-purge flow of hydrogen fuel being heated to a pre-purge flow temperature.

[0226] The method according to one or more of these clauses, wherein providing a pre-purge flow of hydrogen fuel to the fuel delivery assembly includes substantially completely filling the fuel delivery assembly with the pre-purge flow of hydrogen fuel such that the remaining volume of hydrogen fuel is the pre-purge flow of hydrogen fuel.

[0227] The method according to one or more of these clauses, wherein terminating the hydrogen fuel flow from the fuel tank to the engine includes terminating the hydrogen fuel flow from the fuel tank to the engine after providing a pre-purge flow of hydrogen fuel to the fuel delivery assembly.

[0228] The method according to one or more of these clauses, wherein discharging the remaining volume of hydrogen fuel includes providing a purge fluid flow through the fuel delivery assembly.

[0229] The method according to one or more of these clauses, wherein the purge fluid defines a freezing point temperature lower than the pre-purge flow temperature.

[0230] The method according to one or more of these clauses, wherein the purge fluid defines a boiling point temperature below the pre-purge stream temperature.

[0231] The method according to one or more of these clauses, wherein providing a pre-purge stream of hydrogen fuel to the fuel delivery assembly includes heating the pre-purge stream of hydrogen fuel to the pre-purge stream temperature with a vaporizer.

[0232] The method according to one or more of these clauses, wherein providing a pre-purge stream of hydrogen fuel to the fuel delivery assembly includes providing a pre-purge stream of hydrogen fuel to the fuel delivery assembly in response to receiving a command to shut down the engine.

[0233] The method according to one or more of these clauses, wherein providing a pre-purge stream of hydrogen fuel to the fuel delivery assembly includes providing a pre-purge stream of hydrogen fuel to the fuel delivery assembly at a flow rate less than the flow rate of fuel to the engine during idle operation of the engine.

[0234] A fuel system for a vehicle having an engine, the fuel system comprising: a fuel tank for holding hydrogen fuel in a liquid phase; a fuel delivery assembly extending from the fuel tank to the engine for providing hydrogen fuel from the fuel tank to the engine; a first vaporizer in communication with the fuel delivery assembly for heating the liquid phase hydrogen fuel to a gaseous phase, a supercritical phase, or both when the engine is in a first operating condition; and a second vaporizer in communication with the fuel delivery assembly for heating the liquid phase hydrogen fuel to a gaseous phase, a supercritical phase, or both when the engine is in a second operating condition.

[0235] The fuel system according to one or more of these clauses, wherein the first vaporizer is a starting vaporizer, and wherein the first operating condition is a pre-start operating condition.

[0236] The fuel system according to one or more of these clauses, wherein the second vaporizer is a main vaporizer, and wherein the second operating condition is a thermally stable operating condition.

[0237] The fuel system according to one or more of these clauses, wherein the second vaporizer is in thermal communication with a heat source of the engine.

[0238] The fuel system according to one or more of these clauses, further comprising: a third vaporizer in communication with the fuel delivery assembly for heating the liquid phase hydrogen fuel to a gaseous phase, a supercritical phase, or both when the engine is in a third operating condition.

[0239] The fuel system according to one or more of these clauses, wherein the third vaporizer is a supplementary vaporizer, and wherein the third operating condition is a start-up operating condition.

[0240] A fuel system according to one or more of these clauses, wherein the first carburetor is a starting carburetor, wherein the first operating condition is a pre-start operating condition, wherein the second carburetor is a main carburetor, and wherein the second operating condition is a thermally stable operating condition.

[0241] A vehicle comprising a fuel system according to one or more of these clauses.

[0242] A vehicle comprising a fuel system operated according to the method according to one or more of these clauses.

[0243] A fuel system comprising a controller, the controller comprising one or more processors and a memory, the memory storing instructions which, when executed, cause the fuel system to operate according to the method according to one or more of these clauses.

[0244] A further aspect of the present invention is provided by the subject matter of the following clauses:

[0245] 1. A fuel system for a vehicle having an engine, the fuel system comprising: a fuel tank for holding hydrogen fuel in a liquid phase; a fuel delivery assembly extending from the fuel tank to the engine for supplying the hydrogen fuel from the fuel tank to the engine; a first carburetor in communication with the fuel delivery assembly for heating the liquid-phase hydrogen fuel to a gas phase, a supercritical phase, or both when the engine is in a first operating condition; and a second carburetor in communication with the fuel delivery assembly for heating the liquid-phase hydrogen fuel to a gas phase, a supercritical phase, or both when the engine is in a second operating condition.

[0246] 2. The fuel system according to any preceding clause, wherein the first carburetor is a starting carburetor, and wherein the first operating condition is a pre-start operating condition.

[0247] 3. The fuel system according to any preceding clause, wherein the second carburetor is a main carburetor, and wherein the second operating condition is a thermally stable operating condition.

[0248] 4. The fuel system according to any preceding clause, wherein the second carburetor is in thermal communication with a heat source of the engine.

[0249] 5. The fuel system according to any preceding clause, further comprising: a third carburetor in communication with the fuel delivery assembly for heating the liquid-phase hydrogen fuel to a gas phase, a supercritical phase, or both when the engine is in a third operating condition.

[0250] 6. According to the fuel system described in any of the preceding clauses, wherein the third vaporizer is a supplementary vaporizer, and wherein the third operating condition is a starting operating condition.

[0251] 7. According to the fuel system described in any of the preceding clauses, wherein the first vaporizer is a starting vaporizer, wherein the first operating condition is a pre-start operating condition, wherein the second vaporizer is a main vaporizer, and wherein the second operating condition is a thermally stable operating condition.

[0252] 8. An engine for a vehicle, the vehicle including a fuel tank for holding hydrogen fuel in a liquid phase, the engine including: a turbine including a compressor section, a combustion section, and a turbine section arranged in a serial flow order, the combustion section including a plurality of fuel nozzles; and a fuel system including a fuel delivery assembly configured to extend from the fuel tank to the engine for supplying the hydrogen fuel from the fuel tank to the plurality of fuel nozzles of the turbine of the engine; a first vaporizer in communication with the fuel delivery assembly for heating the hydrogen fuel in the liquid phase to a gas phase, a supercritical phase, or both when the engine is in a first operating condition; and a second vaporizer in communication with the fuel delivery assembly for heating the hydrogen fuel in the liquid phase to a gas phase, a supercritical phase, or both when the engine is in a second operating condition.

[0253] 9. According to the engine described in any of the preceding clauses, wherein the first vaporizer is a starting vaporizer, and wherein the first operating condition is a pre-start operating condition.

[0254] 10. According to the engine described in any of the preceding clauses, wherein the second vaporizer is a main vaporizer, and wherein the second operating condition is a thermally stable operating condition.

[0255] 11. According to the engine described in any of the preceding clauses, wherein the second vaporizer is in thermal communication with a heat source of the engine.

[0256] 12. According to the engine described in any of the preceding clauses, further comprising: a third vaporizer in communication with the fuel delivery assembly for heating the hydrogen fuel in the liquid phase to a gas phase, a supercritical phase, or both when the engine is in a third operating condition.

[0257] 13. According to the engine described in any of the preceding clauses, wherein the third vaporizer is a supplementary vaporizer, and wherein the third operating condition is a starting operating condition.

[0258] 14. According to the engine described in any of the preceding clauses, wherein the first carburetor is a starting carburetor, wherein the first operating condition is a pre-start operating condition, wherein the second carburetor is a main carburetor, and wherein the second operating condition is a thermally stable operating condition.

[0259] 15. A method of operating a fuel system for a vehicle having an engine, the method comprising: providing a hydrogen fuel stream from the fuel tank of the fuel system to the engine through the fuel delivery assembly; heating the hydrogen fuel stream from the fuel tank using a first carburetor during a first operating condition of the engine; heating the hydrogen fuel stream from the fuel tank using a second carburetor during a second operating condition of the engine.

[0260] 16. According to the method described in any of the preceding clauses, wherein the first carburetor is a starting carburetor, and the first operating condition is a pre-start operating condition of the engine.

[0261] 17. According to the method described in any of the preceding clauses, wherein the second carburetor is a supplementary carburetor, and the second operating condition is a starting operating condition of the engine.

[0262] 18. According to the method described in any of the preceding clauses, further comprising: heating the hydrogen fuel stream from the fuel tank using a third carburetor during a third operating condition of the engine.

[0263] 19. According to the method described in any of the preceding clauses, wherein the third carburetor is a main carburetor, and the third operating condition is a thermally stable operating condition of the engine.

[0264] 20. According to the method described in any of the preceding clauses, wherein heating the hydrogen fuel stream from the fuel tank using the second carburetor during the second operating condition of the engine comprises providing heat from a heat source of the engine to the second carburetor.

Claims

1. A fuel system for a vehicle having an engine, characterized in that, The fuel system includes: A fuel tank for holding hydrogen fuel in a liquid phase; A fuel delivery assembly extending from the fuel tank to the engine for supplying the hydrogen fuel from the fuel tank to the engine; A first vaporizer in communication with the fuel delivery assembly for heating the liquid-phase hydrogen fuel to a gaseous phase, a supercritical phase, or both when the engine is in a first operating condition; and A second vaporizer in communication with the fuel delivery assembly for heating the liquid-phase hydrogen fuel to a gaseous phase, a supercritical phase, or both when the engine is in a second operating condition; A purge / priming assembly configured to provide a starting fluid flow or a pre-starting fluid flow to the fuel delivery assembly, wherein the purge / priming assembly is fluidly coupled to the fuel delivery assembly downstream of the first vaporizer and upstream of the second vaporizer.

2. The fuel system according to claim 1, wherein Wherein the first vaporizer is a starting vaporizer and wherein the first operating condition is a pre-start operating condition.

3. The fuel system according to claim 2, characterized in that, Wherein the second vaporizer is a main vaporizer and wherein the second operating condition is a thermally stable operating condition.

4. The fuel system according to claim 3, characterized in that, Wherein the second vaporizer is in thermal communication with a heat source of the engine.

5. The fuel system according to claim 1, characterized in that, Further comprising: A third vaporizer in communication with the fuel delivery assembly for heating the liquid-phase hydrogen fuel to a gaseous phase, a supercritical phase, or both when the engine is in a third operating condition.

6. The fuel system according to claim 5, characterized in that, Wherein the third vaporizer is a supplementary vaporizer and wherein the third operating condition is a start-up operating condition.

7. The fuel system according to claim 1, wherein Wherein the first vaporizer is a starting vaporizer, wherein the first operating condition is a pre-start operating condition, wherein the second vaporizer is a main vaporizer, and wherein the second operating condition is a thermally stable operating condition.

8. An engine for a vehicle, the vehicle including a fuel tank for holding hydrogen fuel in a liquid phase, characterized in that, The engine includes: A turbine including a compressor section, a combustion section, and a turbine section arranged in a serial flow order, the combustion section including a plurality of fuel nozzles; and A fuel system including: A fuel delivery assembly configured to extend from the fuel tank to the engine for supplying the hydrogen fuel from the fuel tank to the plurality of fuel nozzles of the turbine of the engine; A first vaporizer in communication with the fuel delivery assembly for heating the liquid-phase hydrogen fuel to a gaseous phase, a supercritical phase, or both when the engine is in a first operating condition; and A second vaporizer in communication with the fuel delivery assembly for heating the liquid-phase hydrogen fuel to a gaseous phase, a supercritical phase, or both when the engine is in a second operating condition; A purge / priming assembly configured to provide a starting fluid flow or a pre-starting fluid flow to the fuel delivery assembly, wherein the purge / priming assembly is fluidly coupled to the fuel delivery assembly downstream of the first vaporizer and upstream of the second vaporizer.

9. The engine according to claim 8, characterized in that, Wherein the first vaporizer is a starting vaporizer and wherein the first operating condition is a pre-start operating condition.

10. The engine according to claim 9, characterized in that, wherein the second vaporizer is the main vaporizer, and wherein the second operating condition is a thermally stable operating condition.

11. The engine according to claim 10, characterized in that, wherein the second vaporizer is in thermal communication with a heat source of the engine.

12. The engine according to claim 8, characterized in that, Further comprising: a third vaporizer in communication with the fuel delivery assembly for heating the hydrogen fuel in the liquid phase to the gaseous phase, supercritical phase, or both when the engine is in a third operating condition.

13. The engine according to claim 12, characterized in that, wherein the third vaporizer is a supplementary vaporizer, and wherein the third operating condition is a start-up operating condition.

14. The engine according to claim 8, characterized in that, wherein the first vaporizer is a starting vaporizer, wherein the first operating condition is a pre-start operating condition, wherein the second vaporizer is the main vaporizer, and wherein the second operating condition is a thermally stable operating condition.

15. A method of operating a fuel system for a vehicle having an engine, characterized in that, The method includes: providing a hydrogen fuel stream from a fuel tank of the fuel system to the engine via a fuel delivery assembly; heating the hydrogen fuel stream from the fuel tank using a first vaporizer during a first operating condition of the engine; and heating the hydrogen fuel stream from the fuel tank using a second vaporizer during a second operating condition of the engine; priming the fuel delivery assembly of the fuel system with a starting fluid.

16. The method according to claim 15, characterized in that, wherein the first vaporizer is a starting vaporizer, and the first operating condition is a pre-start operating condition of the engine.

17. The method according to claim 15, characterized in that, wherein the second vaporizer is a supplementary vaporizer, and the second operating condition is a start-up operating condition of the engine.

18. The method according to claim 15, wherein Further comprising: heating the hydrogen fuel stream from the fuel tank using a third vaporizer during a third operating condition of the engine.

19. The method according to claim 18, wherein wherein the third vaporizer is the main vaporizer, and the third operating condition is a thermally stable operating condition of the engine.

20. The method according to claim 15, wherein wherein heating the hydrogen fuel stream from the fuel tank using the second vaporizer during the second operating condition of the engine includes providing heat from a heat source of the engine to the second vaporizer.

Images