Patent Description:
The propulsion system for commercial aircraft typically includes one or more aircraft engines, such as turbofan jet engines. These engines may be powered by aviation turbine fuel, which is, typically, a combustible hydrocarbon liquid fuel, such as a kerosene-type fuel, having a desired carbon number and carbon-to-hydrogen ratio. Such fuel produces carbon dioxide upon combustion, and improvements to reduce or to eliminate such carbon dioxide emissions in commercial aircraft are desired.

<CIT> discloses a fuel delivery system for a gas turbine designed to efficiently transfer from one type of fuel to a separate fuel. A nitrogen purge system purges the high hydrogen fuel gas lines to the combustors and/or flushes the naphtha lines with distillate.

<CIT> discloses a gas turbine combustor including a fuel injector having a plurality of annular fuel injection portions in each of which multiple fuel injection holes are formed.

Features and advantages of the present disclosure will be apparent from the following description of various exemplary embodiments, as illustrated in the accompanying drawings, wherein like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements.

Features, advantages, and embodiments of the present disclosure are set forth or apparent from a consideration of the following detailed description, drawings, and claims. Moreover, it is to be understood that the following detailed description is exemplary and intended to provide further explanation without limiting the scope of the disclosure as claimed.

Various embodiments are discussed in detail below. While specific embodiments are discussed, this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without departing from the scope of the present disclosure.

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

For example, with regard to a gas turbine engine, forward refers to a position closer to an engine inlet and aft refers to a position closer to an engine nozzle or an exhaust.

The terms "directly upstream" or "directly downstream," when used to describe the relative placement of components in a fluid pathway, refer to components that are placed next to each other in the fluid pathway without any intervening components between them other than an appropriate fluid coupling, such as a pipe, a tube, a valve, or the like, to fluidly couple the components. Such components may be spaced apart from each other with intervening components that are not in the fluid pathway.

The terms "coupled," "fixed," "attached," "connected," and the like, refer to both direct coupling, fixing, attaching, or connecting as well as indirect coupling, fixing, attaching, or connecting through one or more intermediate components or features, unless otherwise specified herein.

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

Accordingly, a value modified by a term or terms, such as "about," "approximately," and "substantially" is not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value, or the precision of the methods or the machines for constructing or manufacturing the components and/or systems. For example, the approximating language may refer to being within a one, two, four, ten, fifteen, or twenty percent margin in either individual values, range(s) of values, and/or endpoints defining range(s) of values.

Here and throughout the specification and claims, range limitations are combined and interchanged. Such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.

To reduce carbon dioxide emissions from commercial aircraft, a hydrogen fuel may be used. Hydrogen fuel, however, poses a number of challenges as compared to combustible hydrocarbon liquid fuel. For example, hydrogen fuel has a relatively low boiling point, and, in its gaseous form, hydrogen fuel has a much lower power density. Hydrogen fuel, when in a gaseous form, also tends to seep through materials and attachment points between components without leaving residue. Hydrogen fuel is colorless and odorless. Hydrogen fuel is also highly reactive (relative to other fuels, such as Jet-A fuel) with a wide range of flammability limits.

The present disclosure discusses ways to improve the use of hydrogen fuel systems and, particularly, such fuel systems used in aircraft. The various embodiments, as described herein and as shown in the figures, describe a hydrogen fuel purge system that may be used to actively purge the fuel lines, the fittings, the valves, the sensors, and the components that receive hydrogen in the case of a leak. The purge may be carried away immediately and exhausted externally.

The hydrogen fuel systems discussed herein include hydrogen fuel purge systems that are particularly suited for use on aircraft. <FIG> is a perspective view of an aircraft <NUM> that may implement various preferred embodiments. The aircraft <NUM> includes a fuselage <NUM>, a pair of wings <NUM> attached to the fuselage <NUM>, and an empennage <NUM>. The aircraft <NUM> also includes a propulsion system that produces a propulsive thrust required to propel the aircraft <NUM> in flight, during taxiing operations, and the like. The propulsion system for the aircraft <NUM> shown in <FIG> includes a pair of engines <NUM>. In this embodiment, each engine <NUM> is attached to one of the wings <NUM> by a pylon <NUM> in an under-wing configuration. Although the engines <NUM> are shown attached to the wing <NUM> in an under-wing configuration in <FIG>, in other embodiments, the engine <NUM> may have alternative configurations and be coupled to other portions of the aircraft <NUM>. For example, the engine <NUM> may additionally or alternatively include one or more aspects coupled to other parts of the aircraft <NUM>, such as, for example, the empennage <NUM> and the fuselage <NUM>.

As will be described further below with reference to <FIG>, the engines <NUM> shown in <FIG> are gas turbine engines that are each capable of selectively generating a propulsive thrust for the aircraft <NUM>. The amount of propulsive thrust may be controlled at least in part based on a volume of fuel provided to the gas turbine engines <NUM> via a fuel system <NUM> (see <FIG>). In the embodiments discussed herein, the fuel is a hydrogen fuel that is stored in a fuel tank <NUM> of the fuel system <NUM>. As shown in <FIG>, at least a portion of the fuel tank <NUM> is located in the fuselage <NUM> and, in this embodiment, entirely within the fuselage <NUM>. The fuel tank <NUM>, however, may be located at other suitable locations in the fuselage <NUM> or the wing <NUM>, such as with a portion of the fuel tank <NUM> in the fuselage <NUM> and a portion of the fuel tank <NUM> in the wing <NUM>. Alternatively, the fuel tank <NUM> may also be located entirely within the the wing <NUM>. In the embodiment shown in <FIG>, a single fuel tank <NUM> is used, and the fuel tank <NUM> is located within the fuselage such that, relative to the forward direction and the aft direction, the fuel tank <NUM> is located at the wing center of lift. Any suitable number of fuel tanks <NUM> may be used, however, including a plurality of fuel tanks <NUM>. The plurality of fuel tanks <NUM> may include, for example, a forward fuel tank and an aft fuel tank. The forward fuel tank and the aft fuel tank may be located in the fuselage <NUM> and balanced about the wing center of lift to promote the stability of the aircraft <NUM> during flight. In another example, the plurality of fuel tanks <NUM> may include two separate tanks each located within a corresponding wing <NUM>.

Although the aircraft <NUM> shown in <FIG> is an airplane, the embodiments described herein may also be applicable to other aircraft <NUM>, including, for example, helicopters and unmanned aerial vehicles (UAV). The aircraft discussed herein are fixed-wing aircraft or rotor aircraft that generate lift by aerodynamic forces acting on, for example, a fixed wing (e.g., wing <NUM>) or a rotary wing (e.g., rotor of a helicopter), and are heavier-than-air aircraft, as opposed to lighter-than-air aircraft (such as a dirigible). In addition, the embodiments described herein may also be applicable to other applications where hydrogen is used as a fuel. The engines described herein are gas turbine engines, but the embodiments described herein also may be applicable to other engines. Further, the engine, specifically, the gas turbine engine, is an example of a power generator using hydrogen as a fuel, but hydrogen may be used as a fuel for other power generators, including, for example, fuel cells (hydrogen fuel cells). Such power generators may be used in various applications including stationary power-generation systems (including both gas turbines and hydrogen fuel cells) and other vehicles beyond the aircraft <NUM> explicitly described herein, such as boats, ships, cars, trucks, and the like.

<FIG> is a schematic, cross-sectional view of one of the engines <NUM> used in the propulsion system for the aircraft <NUM> shown in <FIG>. The engine <NUM> shown in <FIG> is a high-bypass turbofan engine. The engine <NUM> may also be referred to as a turbofan engine <NUM> herein. The turbofan engine <NUM> has an axial direction A (extending parallel to a longitudinal centerline <NUM>, shown for reference in <FIG>), a radial direction R, and a circumferential direction. The circumferential direction (not depicted in <FIG>) extends in a direction rotating about the axial direction A. The turbofan engine <NUM> includes a fan section <NUM> and a turbomachine <NUM> disposed downstream from the fan section <NUM>.

The turbomachine <NUM> depicted in <FIG> includes a tubular outer casing <NUM> (housing or nacelle) that defines an annular inlet <NUM>. The outer casing <NUM> encases, in a serial flow relationship, a compressor section including a booster or a low-pressure (LP) compressor <NUM> and a high-pressure (HP) compressor <NUM>, a combustion section <NUM>, a turbine section including a high-pressure (HP) turbine <NUM> and a low-pressure (LP) turbine <NUM>, and a jet exhaust nozzle section <NUM>. The compressor section, the combustion section <NUM>, and the turbine section together define at least in part a core air flow path <NUM> extending from the annular inlet <NUM> to the jet exhaust nozzle section <NUM>. The turbofan engine further includes one or more drive shafts. More specifically, the turbofan engine includes a high-pressure (HP) shaft or spool <NUM> drivingly connecting the HP turbine <NUM> to the HP compressor <NUM>, and a low-pressure (LP) shaft or spool <NUM> drivingly connecting the LP turbine <NUM> to the LP compressor <NUM>.

The fan section <NUM> shown in <FIG> includes a fan <NUM> having a plurality of fan blades <NUM> coupled to a disk <NUM> spaced apart in a circumferential direction around the disk <NUM>. The fan blades <NUM> and the disk <NUM> are rotatable, together, about the longitudinal centerline (axis) <NUM> by the LP shaft <NUM>. The disk <NUM> is covered by a rotatable front hub <NUM> aerodynamically contoured to promote an airflow through the plurality of fan blades <NUM>. Further, an annular fan casing or outer nacelle <NUM>, circumferentially surrounds the fan <NUM> and/or at least a portion of the turbomachine <NUM>. The nacelle <NUM> is supported relative to the turbomachine <NUM> by a plurality of circumferentially spaced outlet guide vanes <NUM>. A downstream section <NUM> of the nacelle <NUM> extends over an outer portion of the turbomachine <NUM> so as to define a bypass airflow passage <NUM> therebetween.

The turbofan engine <NUM> is operable with the fuel system <NUM> and receives a flow of fuel from the fuel system <NUM>. As will be described further below, the fuel system <NUM> includes a fuel delivery assembly <NUM> providing the fuel flow from the fuel tank <NUM> to the engine <NUM>, and, more specifically, to a fuel manifold <NUM> (not labeled in <FIG>, see <FIG>) of the combustion section <NUM> of the turbomachine <NUM> of the turbofan engine <NUM>.

The turbofan engine <NUM> also includes various accessory systems to aid in the operation of the turbofan engine <NUM> and/or an aircraft including the turbofan engine <NUM>. For example, the turbofan engine <NUM> may include a main lubrication system <NUM>, a compressor cooling air (CCA) system <NUM>, an active thermal clearance control (ATCC) system <NUM>, and a generator lubrication system <NUM>, each of which is depicted schematically in <FIG>. The main lubrication system <NUM> is configured to provide a lubricant to, for example, various bearings and gear meshes in the compressor section, the turbine section, the HP spool <NUM>, and the LP shaft <NUM>. The lubricant provided by the main lubrication system <NUM> may increase the useful life of such components and may remove a certain amount of heat from such components. The compressor cooling air (CCA) system <NUM> provides air from one or both of the HP compressor <NUM> or the LP compressor <NUM> to one or both of the HP turbine <NUM> or the LP turbine <NUM>. The active thermal clearance control (ATCC) system <NUM> cools a casing of the turbine section to maintain a clearance between the various turbine rotor blades and the turbine casing within a desired range throughout various engine operating conditions. The generator lubrication system <NUM> provides lubrication to an electronic generator (not shown), as well as cooling/heat removal for the electronic generator. The electronic generator may provide electrical power to, for example, a start-up electrical motor for the turbofan engine <NUM> and/or various other electronic components of the turbofan engine <NUM> and/or an aircraft including the turbofan engine <NUM>.

Heat from these accessory systems <NUM>, <NUM>, <NUM>, <NUM>, and other accessory systems may be provided to various heat sinks as waste heat from the turbofan engine <NUM> during operation, such as to various vaporizers <NUM>, <NUM>, as discussed below with regard to <FIG>. Additionally, the turbofan engine <NUM> may include one or more heat exchangers <NUM> within, for example, the core air flow path <NUM>, such as the turbine section or the jet exhaust nozzle section <NUM>. Such heat exchangers <NUM> may be used to extract waste heat from an airflow therethrough also to provide heat to various heat sinks, such as the vaporizers <NUM>, <NUM>, discussed below.

The turbofan engine <NUM> discussed herein is provided by way of example only. In other embodiments, any other suitable engine may be utilized with aspects of the present disclosure. For example, in other embodiments, the engine may be any other suitable gas turbine engine, such as a turboshaft engine, a turboprop engine, a turbojet engine, and the like. Still further, in other embodiments, the gas turbine engine may have other suitable configurations, such as other suitable numbers or arrangements of shafts, compressors, turbines, fans, etc. Further, although the turbofan engine <NUM> is shown as a direct drive, fixed-pitch turbofan engine <NUM>, in other embodiments, a gas turbine engine may be a geared gas turbine engine (i.e., including a gearbox between the fan <NUM> and the shaft driving the fan, such as the LP shaft <NUM>), or a variable pitch gas turbine engine (i.e., including a fan <NUM> having a plurality of fan blades <NUM> rotatable about their respective pitch axes), etc. Further, still, in alternative embodiments, aspects of the present disclosure may be incorporated into, or otherwise utilized with, any other type of engine, such as reciprocating engines, as discussed above. Additionally, in still other exemplary embodiments, the exemplary turbofan engine <NUM> may include or be operably connected to any other suitable accessory systems. Additionally, or alternatively, the exemplary turbofan engine <NUM> may not include or be operably connected to one or more of the accessory systems <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, discussed above.

The engine <NUM> may also include an engine controller <NUM>. The engine controller <NUM> is configured to operate various aspects of the engine <NUM> and the fuel system <NUM>, including, for example, opening and closing valves, such as a shut-off valve <NUM> or diverter valves <NUM>, <NUM>, operating metering valve <NUM>, operating the vaporizers <NUM>, <NUM>, and operating pumps <NUM>, <NUM> (<FIG>). In this embodiment, the engine controller <NUM> is a computing device having one or more processors <NUM> and one or more memories <NUM>. The processor <NUM> can be any suitable processing device, including, but not limited to, a microprocessor, a microcontroller, an integrated circuit, a logic device, a programmable logic controller (PLC), an application-specific integrated circuit (ASIC), and/or a Field Programmable Gate Array (FPGA). The memory <NUM> can include one or more computer-readable media, including, but not limited to, non-transitory computer-readable media, a computer-readable non-volatile medium (e.g., a flash memory), a RAM, a ROM, hard drives, flash drives, and/or other memory devices.

The memory <NUM> can store information accessible by the processor <NUM>, including computer-readable instructions that can be executed by the processor <NUM>. The instructions can be any set of instructions or a sequence of instructions that, when executed by the processor <NUM>, causes the processor <NUM> and the engine controller <NUM> to perform operations. In some embodiments, the instructions can be executed by the processor <NUM> to cause the processor <NUM> to complete any of the operations and functions for which the engine controller <NUM> is configured, as will be described further below. The instructions can be software written in any suitable programming language or can be implemented in hardware. Additionally, and/or alternatively, the instructions can be executed in logically and/or virtually separate threads on the processor <NUM>. The memory <NUM> can further store data that can be accessed by the processor <NUM>.

The technology discussed herein makes reference to computer-based systems and actions taken by, and information sent to and from, computer-based systems. One of ordinary skill in the art will recognize that the inherent flexibility of computer-based systems allows for a great variety of possible configurations, combinations, and divisions of tasks and functionality between components and among components.

<FIG> is a schematic view of the fuel system <NUM> according to an embodiment of the present disclosure. The fuel system <NUM> is configured to store the hydrogen fuel for the engine <NUM> in the fuel tank <NUM> and to deliver the hydrogen fuel to the engine <NUM> via a fuel delivery assembly <NUM>. The fuel delivery assembly <NUM> includes tubes, pipes, and the like, to fluidly connect the various components of the fuel system <NUM> to the engine <NUM>. The fuel tank <NUM> may be configured to hold the hydrogen fuel at least partially within the liquid phase, and may be configured to provide hydrogen fuel to the fuel delivery assembly <NUM> substantially completely in the liquid phase, such as completely in the liquid phase. For example, the fuel tank <NUM> may have a fixed volume and contain a volume of the hydrogen fuel in the liquid phase (liquid hydrogen fuel). As the fuel tank <NUM> provides hydrogen fuel to the fuel delivery assembly <NUM> substantially completely in the liquid phase, the volume of the liquid hydrogen fuel in the fuel tank <NUM> decreases and the remaining volume in the fuel tank <NUM> is made up by, for example, hydrogen in the gaseous phase (gaseous hydrogen). As used herein, the term "substantially completely" as used to describe a phase of the hydrogen fuel refers to at least <NUM>% by mass of the described portion of the hydrogen fuel being in the stated phase, such as at least <NUM>%, such as at least <NUM>%, such as at least <NUM>%, such as at least <NUM>%, such as at least <NUM>%, or such as at least <NUM>% by mass of the described portion of the hydrogen fuel being in the stated phase.

To store the hydrogen fuel substantially completely in the liquid phase, the hydrogen fuel is stored in the fuel tank <NUM> at very low (cryogenic) temperatures. For example, the hydrogen fuel may be stored in the fuel tank <NUM> at about negative two hundred fifty-three degrees Celsius or less at atmospheric pressure, or at other temperatures and pressures to maintain the hydrogen fuel substantially in the liquid phase. The fuel tank <NUM> may be a double-walled cryogenic storage tank made from known materials such as titanium, Inconel®, aluminum, or composite materials. The fuel tank <NUM> and the fuel system <NUM> may include a variety of supporting structures and components to facilitate storing the hydrogen fuel in such a manner.

The liquid hydrogen fuel is supplied from the fuel tank <NUM> to the fuel delivery assembly <NUM>. The fuel delivery assembly <NUM> may include one or more lines, conduits, pipes, etc., configured to carry the hydrogen fuel between the fuel tank <NUM> and the engine <NUM>. The fuel delivery assembly <NUM> provides a flow path of the hydrogen fuel from the fuel tank <NUM> downstream to the engine <NUM>. Herein, the terms "downstream" and "upstream" may be used to describe the position of components relative to the direction of flow of the hydrogen fuel in the flow path of the fuel delivery assembly <NUM>. The fuel delivery assembly <NUM> may also include various valves (for example, shut-off valve <NUM>) and other components to deliver the hydrogen fuel to the engine <NUM> that are not shown in <FIG>. The fluid lines discussed herein, particularly, those conveying liquid hydrogen, may be vacuum jacketed pipes.

The fuel tank <NUM> in this embodiment is a hydrogen fuel source, and the fuel delivery assembly <NUM> is configured to receive hydrogen fuel from the fuel tank <NUM> (hydrogen fuel source) and to provide the hydrogen fuel from the hydrogen fuel source to the engine <NUM> (power generator), and, more specifically, a fuel input array (e.g., the fuel manifold <NUM> and the fuel nozzles <NUM>, discussed further below) of the engine <NUM>. The fuel system <NUM> may include a shut-off valve <NUM>, positioned, for example, in the pylon <NUM> or at another position between the fuel tank <NUM> and the engine <NUM> that can be used to isolate and to disconnect the fuel tank <NUM> from the components of the fuel delivery assembly <NUM> that are downstream of the shut-off valve <NUM>. The shut-off valve <NUM> may, thus, be positioned to isolate the components of the fuel system <NUM> that are located in the engine from the components of the fuel system <NUM> located in the remaining portion of the aircraft <NUM>.

The hydrogen fuel is delivered to the engine <NUM> by the fuel delivery assembly <NUM> in the liquid phase, the gaseous phase, the supercritical phase, or both of the gaseous phase and the supercritical phase. The fuel system <NUM>, thus, includes at least one vaporizer <NUM>, <NUM> in fluid communication with the fuel delivery assembly <NUM> to heat the liquid hydrogen fuel flowing through the fuel delivery assembly <NUM>. In the embodiment shown in <FIG>, the fuel system <NUM> includes two vaporizers, a main vaporizer <NUM> and a secondary vaporizer <NUM>. Each vaporizer <NUM>, <NUM> is positioned in the flow path of the hydrogen fuel between the fuel tank <NUM> and the engine <NUM>. In the embodiment shown in <FIG>, each vaporizer <NUM>, <NUM> is positioned at least partially within the engine <NUM>. When positioned in the engine <NUM>, the vaporizers <NUM>, <NUM> may be located in the nacelle <NUM>, for example. The vaporizers <NUM>, <NUM> may, however, be positioned at other suitable locations in the flow path of the hydrogen between fuel tank <NUM> and the engine <NUM>. For example, the vaporizers <NUM>, <NUM> may be positioned external to the engine <NUM> and positioned in the fuselage <NUM>, the wing <NUM>, or the pylon <NUM>.

Each vaporizer <NUM>, <NUM> is in thermal communication with at least one heat source, such as a primary heat source <NUM>, a secondary heat source <NUM>, or both. In this embodiment, the primary vaporizer <NUM> is configured to operate once the engine <NUM> is in a thermally stable condition and the primary heat source <NUM> is waste heat from the engine <NUM>. The main vaporizer <NUM> is, thus, thermally connected to at least one of the main lubrication system <NUM>, the compressor cooling air system <NUM>, the active thermal clearance control system <NUM>, the generator lubrication system <NUM>, and the heat exchangers <NUM> to extract waste heat from the engine <NUM> to heat the hydrogen fuel. In such a manner, it will be appreciated that the vaporizer <NUM> is configured to operate by drawing heat from the primary heat source <NUM> once the engine <NUM> is capable of providing enough heat, via the primary heat source <NUM>, to the vaporizer <NUM>, in order to facilitate operation of the vaporizer <NUM>.

The secondary vaporizer <NUM> of this embodiment is a combination start-up and trim vaporizer that may used to heat the liquid hydrogen fuel flowing through the fuel delivery assembly <NUM> when the main vaporizer <NUM> is not sufficient to heat the hydrogen fuel. During start-up of the engine <NUM>, for example, the engine <NUM> may not be in a thermally stable condition, and the secondary vaporizer <NUM> is used during start-up (or prior to start-up) to heat the hydrogen fuel instead of the main vaporizer <NUM>. In this example, the secondary vaporizer <NUM> operates as a start-up vaporizer. In another example, the main vaporizer <NUM> may not be heating the hydrogen fuel to the desired temperature and, thus, the secondary vaporizer <NUM> operates as a trim vaporizer to add supplemental heat to the hydrogen fuel and heat the hydrogen fuel to the desired temperature. Such a condition may occur when, for example, the heat provided by the primary heat source <NUM> to the main vaporizer <NUM> is not sufficient to heat the hydrogen fuel to the desired temperature.

The secondary vaporizer <NUM> is thermally coupled to a secondary heat source <NUM>. With the secondary vaporizer <NUM> operating as a combination start-up and trim vaporizer, the secondary heat source <NUM> is preferably a heat source external to the engine <NUM> that may provide heat for the secondary vaporizer <NUM> independent of whether or not the engine <NUM> is running and can be used, for example, during start-up (or prior to start-up) of the engine <NUM>. The secondary heat source <NUM> may include, for example, an electrical power source, a catalytic heater or burner, and/or a bleed airflow from an auxiliary power unit. The secondary heat source <NUM> may be integral to the secondary vaporizer <NUM>, such as when the secondary vaporizer <NUM> includes one or more electrical resistance heaters, or the like, that are powered by the electrical power source.

As noted above, the vaporizers <NUM>, <NUM> may be thermally coupled to any suitable heat source. For example, the main vaporizer <NUM> and/or the secondary vaporizer <NUM> may be thermally coupled to both waste heat from the engine <NUM> and a heat source external to the engine <NUM>. In the embodiment shown in <FIG>, the main vaporizer <NUM> and the secondary vaporizer <NUM> are located in series relative to the flow of hydrogen in the fuel delivery assembly <NUM>, with the secondary vaporizer <NUM> being downstream from the main vaporizer <NUM>. Other arrangements of the vaporizers <NUM>, <NUM> may be used, however, such as the main vaporizer <NUM> and the secondary vaporizer <NUM> being arranged in parallel to each other, as shown in <FIG> is a schematic view of a fuel system 200a with the main vaporizer <NUM> and the secondary vaporizer <NUM> arranged in parallel. Although the arrangements of vaporizers <NUM>, <NUM> differ between <FIG> and <FIG>, the remaining components of the fuel system 200a are the same or similar to the components shown in <FIG>.

<FIG>, <FIG>, and <FIG> show additional arrangements of vaporizers in a fuel system 200b, 200c, 200d. <FIG>, <FIG>, and <FIG> are schematic views of the fuel system 200b, 200c, 200d. In the arrangement shown in <FIG> and <FIG>, a plurality of secondary vaporizers <NUM> are used, with one being a start-up vaporizer 223a and the other being a trim vaporizer 223b. In the embodiments shown in <FIG> and <FIG>, the secondary vaporizer <NUM> is positioned to receive hydrogen fuel from the same hydrogen source (e.g., fuel tank <NUM>) as the main vaporizer <NUM>. The start-up vaporizer 223a may, however, be positioned to receive hydrogen fuel from a secondary hydrogen fuel source <NUM> that is different than the main vaporizer <NUM>. The secondary hydrogen fuel source <NUM> may be attached to the main fuel tank (fuel tank <NUM>) or be a secluded tank. Using a secondary hydrogen fuel source <NUM> allows the delivery system for the hydrogen fuel to be sized only to handle a limited fuel flow (up to idle, for example). Using the secondary hydrogen fuel source <NUM> helps size and optimize the heat source <NUM> and the start-up vaporizer 223a to better align with starting requirements.

The trim vaporizer 223b may be positioned in series with the main vaporizer <NUM>, as shown in <FIG>, or in parallel with the main vaporizer <NUM>, as shown in <FIG>. In another alternative arrangement, the trim vaporizer 223b may be omitted, as shown in <FIG>. Although the arrangements of vaporizers <NUM>, <NUM> in <FIG> differ the arrangement shown in <FIG>, the same or similar components of the fuel system <NUM> shown in <FIG> may be used in the arrangements of the fuel system 200b, 200c, 200d shown in <FIG>. The following discussion will focus on <FIG>, but it also applies to the arrangements shown in <FIG>.

As shown in <FIG>, the fuel delivery assembly <NUM> also includes a pump <NUM> to induce the flow of the hydrogen fuel through the fuel delivery assembly <NUM> to the engine <NUM>. The pump <NUM> may generally be the primary source of pressure rise in the fuel delivery assembly <NUM> between the fuel tank <NUM> and the engine <NUM>. The pump <NUM> may be configured to increase a pressure in the fuel delivery assembly <NUM> to a pressure greater than a pressure within a combustion chamber of the combustion section <NUM> of the engine <NUM> (<FIG>). In this embodiment, the pump <NUM> is positioned within the flow of hydrogen fuel in the fuel delivery assembly <NUM> at a location upstream of the main vaporizer <NUM>. In this embodiment, the pump <NUM> is positioned external to the fuselage <NUM> and the wing <NUM>, and is positioned at least partially within the pylon <NUM>, or at least partially within the engine <NUM>. More specifically, the pump <NUM> is positioned within the engine <NUM>. With the pump <NUM> located in such a position, the pump <NUM> may be any suitable pump configured to receive the flow of hydrogen fuel in substantially completely a liquid phase. In other embodiments, however, the pump <NUM> may be positioned at any other suitable locations, including other positions within the flow path of the hydrogen fuel. For example, the pump <NUM> may be located downstream of the main vaporizer <NUM> and may be configured to receive the flow of hydrogen fuel through the fuel delivery assembly <NUM> in a substantially completely a gaseous phase or a supercritical phase.

The fuel system <NUM> also includes a fuel metering unit in fluid communication with the fuel delivery assembly <NUM>. In this embodiment, the fuel metering unit is a metering valve <NUM> positioned downstream of the vaporizers <NUM>, <NUM> and the pump <NUM>. The metering valve <NUM> is configured to receive hydrogen fuel in a substantially completely gaseous phase, or in a substantially completely supercritical phase. The metering valve <NUM> is further configured to provide the flow of fuel to the engine <NUM> in a desired manner. More specifically, as depicted schematically in <FIG>, the metering valve <NUM> is configured to provide a desired volume of hydrogen fuel at, for example, a desired flow rate, to a fuel manifold <NUM> of the engine <NUM>. The fuel manifold <NUM> then distributes (provides) the hydrogen fuel received to a plurality of fuel nozzles <NUM> within the combustion section <NUM> of the engine <NUM>, where the hydrogen fuel is mixed with compressed air and the mixture of hydrogen fuel and compressed air is combusted to generate combustion gases that drive the engine <NUM>. Adjusting the metering valve <NUM> changes the volume of fuel provided to the combustion section <NUM> of the engine <NUM> and, thus, changes the amount of propulsive thrust produced by the engine <NUM> to propel the aircraft <NUM>.

The hydrogen fuel used in the engine <NUM> and in the fuel system <NUM> may be substantially pure hydrogen molecules (diatomic hydrogen). As diatomic hydrogen is the smallest molecule known to exist, hydrogen can be difficult to contain, particularly, in the gaseous form. Hydrogen, when in a gaseous form, also tends to seep through materials and attachment points between components without leaving residue. The hydrogen is prone to leak through conventional seals and other small orifices such as cracks that may form in the fuel system <NUM> over time. When hydrogen fuel is not being provided to the engine <NUM> for combustion, the hydrogen is purged from the fuel system <NUM>. The fuel system <NUM> of this embodiment includes a hydrogen fuel purge system <NUM> that is used to purge hydrogen fuel from at least a portion of the fuel system <NUM>. For example, a commercial aircraft <NUM> may land and, after pulling up to the gate, shuts down either for a temporary period of time before departing on another flight or for a longer time, such as overnight. The hydrogen fuel purge system <NUM> may be used to purge a portion of the fuel system <NUM> after shutdown.

The hydrogen fuel purge system <NUM> uses a purge fluid to remove the hydrogen fuel from at least a portion of the fuel system <NUM>. Any suitable purge fluid may be used, but, in the embodiments discussed herein, the purge fluid is a gas and will be referred to as a purge gas. The purge gas is preferably a substantially inert gas, and is not reactive, or is minimally reactive, with hydrogen. The inert gas may be a substantially thermally inert gas that does not encourage ignition or act as an oxidizer in any type of reaction with hydrogen as the fuel source to create combustion, flame, spark, or exothermic energy release. In some embodiments, the purge gas has a very low freezing point that is suitable for use in purging the low-temperature (cryogenic) systems of the fuel system <NUM>. Examples of suitable purge gases include noble gases, such as helium, neon, argon, krypton, xenon, and radon. Examples of thermally inert gases that may be used as the purge gas include carbon dioxide, carbon monoxide, and the like. Commonly known fire suppressants may also be used as the purge gas. These fire suppressants include, but are not limited to, halon, FS227, NAF S <NUM>, and NAF S <NUM>. Another suitable purge gas includes nitrogen gas, such as diatomic nitrogen.

The purge gas is provided to the hydrogen fuel purge system <NUM> by a purge gas source <NUM>. In some embodiments, the purge gas source <NUM> may be a tank that stores the purge gas. In other embodiments where the purge gas is nitrogen, the purge gas source <NUM> may be a nitrogen separator that is configured to extract (strip) nitrogen from the atmosphere or other nitrogen generation systems. Suitable nitrogen generation systems include, for examples, those used as part of existing fuel tank inerting systems or On-Board Inert Gas Generation Systems (OBIGGSs). The purge gas source <NUM> is shown in <FIG> as being located within the engine <NUM>, but the purge gas source <NUM> may be located at other suitable locations external to the engine <NUM>. For example, the purge gas source <NUM> may be positioned at other locations in the aircraft <NUM> including, for example, in the fuselage <NUM>, the wing <NUM>, or the pylon <NUM>.

The purge gas flows from the purge gas source <NUM> into a purge gas delivery assembly <NUM>. The purge gas delivery assembly <NUM> includes tubes, pipes, and the like, to fluidly connect the various components of the hydrogen fuel purge system <NUM> to the fuel system <NUM>. In the embodiments discussed herein, the purge gas delivery assembly <NUM> fluidly connects the purge gas source <NUM> to at least one position in the fuel system <NUM> and, more specifically, the fuel delivery assembly <NUM>. More specifically, in the embodiment shown in <FIG>, the purge gas delivery assembly <NUM> is fluidly coupled to the fuel delivery assembly <NUM> using a diverter valve <NUM>. The diverter valve <NUM> may be used to selectively couple the purge gas delivery assembly <NUM> to the fuel delivery assembly <NUM>. In a first position, the diverter valve <NUM> allows hydrogen fuel to flow through the fuel delivery assembly <NUM>, but, in a second position, the diverter valve <NUM> closes off a portion of the fuel system <NUM> and fluidly couples the purge gas source <NUM> to the fuel delivery assembly <NUM>.

The embodiment of <FIG> shows a plurality of diverter valves <NUM>. These diverter valves <NUM> are shown to illustrate various positions where the purge gas can be introduced into the fuel system <NUM>, but some of these diverter valves <NUM> may be omitted. The diverter valves <NUM> are positioned upstream of the metering valve <NUM>, the secondary vaporizer <NUM>, the main vaporizer <NUM>, and the pump <NUM>, respectively. A diverter valve <NUM> may be positioned directly upstream of each of these components as shown. The diverter valve <NUM> may be positioned in the second position to isolate the components upstream of the diverter valve <NUM>, allowing purge gas to be introduced at the diverter valve <NUM> and directed to the components downstream of the diverter valve <NUM>. Thus, the purge gas may be introduced upstream of the metering valve <NUM>, the secondary vaporizer <NUM>, the main vaporizer <NUM>, and/or the pump <NUM> and, in some embodiments, directly upstream of each of these components.

Although the purge gas may be used to push the hydrogen fuel through the fuel system <NUM> and out the fuel nozzles <NUM> for a venting operation, the hydrogen and purge gas are preferably vented overboard. The hydrogen fuel purge system <NUM> includes a vent line <NUM> that is used to vent the hydrogen fuel and to purge gas externally to the engine <NUM>. In this embodiment, the vent line <NUM> is fluidly coupled to a vent <NUM> having a vent opening on the exterior of the engine <NUM>, such as the outer casing <NUM> or the outer nacelle <NUM>, for example. The vent <NUM> may be located at other locations on the aircraft <NUM> including, for example, the wing <NUM> or a position on the fuselage <NUM>, such as on the empennage <NUM>, as shown in <FIG>. A diverter valve <NUM> is used to fluidly couple the fuel delivery assembly <NUM> to the vent line <NUM> and the vent <NUM>. The diverter valve <NUM> may be used to selectively couple the fuel delivery assembly <NUM> to the vent line <NUM> and the vent <NUM>. In a first position, the diverter valve <NUM> allows hydrogen fuel to flow through the fuel delivery assembly <NUM>, but, in a second position, the diverter valve <NUM> closes off a portion of the fuel system <NUM> and fluidly couples the fuel delivery assembly <NUM> to the vent line <NUM> and the vent <NUM>. In the embodiment shown in <FIG>, the diverter valve <NUM> is positioned upstream of the fuel manifold <NUM> and downstream of the metering valve <NUM>. In this way, the components upstream of the fuel input array, which, in this embodiment, are the fuel manifold <NUM> and the fuel nozzles <NUM>, can be purged of hydrogen fuel. Although only one vent <NUM> is shown, a plurality of vents <NUM> may be used. In such a configuration, the plurality of vents <NUM> may be connected to a single vent line <NUM>, but in other embodiments, each vent <NUM> may be fluidly connected to a corresponding vent line <NUM> and diverter valve <NUM> at a plurality of locations in the fuel delivery assembly <NUM>.

The hydrogen fuel purge system <NUM> also includes a pump <NUM> that is configured to increase the pressure of the purge gas to a pressure sufficient to push the hydrogen fuel through the fuel delivery assembly <NUM>, the vent line <NUM>, and out the vent <NUM>. One of the diverter valves <NUM> connected to the purge gas delivery assembly <NUM> is positioned in the second position and the diverter valve <NUM> connected to the vent line <NUM> is also positioned in the second position. The pump <NUM> may then be operated to push the purge gas and the hydrogen through the fuel delivery assembly <NUM> and out the vent <NUM>. In such a configuration, the vent <NUM> is fluidly coupled to the fuel delivery assembly <NUM> and configured to vent hydrogen fuel from the fuel delivery assembly <NUM> when the purge gas is provided to the fuel delivery assembly <NUM> from the purge gas source <NUM>.

As noted above, hydrogen is highly reactive and has wide flammability limits. When exposed to even a small amount of oxygen, hydrogen has a very low ignition energy requirement, even as little as a static spark. An anti-ignition system may, thus, be used to prevent ignition of the vented hydrogen and the ignition of hydrogen upstream of the vent <NUM>, including within the fuel delivery assembly <NUM>. Anti-ignition systems may include those that prevent sparks, such as grounding systems. In the embodiment shown in <FIG>, the anti-ignition system includes a flame arrestor <NUM>. The flame arrestor <NUM> is positioned in the vent line <NUM> proximate to the vent <NUM>. Any suitable flame arrestor <NUM> may be used. The flame arrestor <NUM> may be, for example, a serpentine passage formed in the vent line <NUM>, such as a P-trap, that prevents a continuous, unbroken gas path to the fuel delivery assembly <NUM>. Other suitable flame arrestors <NUM> may include a wire screen or a diffusion system where the vented gas bubbles through a liquid, such as water, before reaching the vent <NUM>.

In the embodiment shown in <FIG>, the purge gas delivery assembly <NUM> is also fluidly connected to the fuel delivery assembly <NUM> at a position between the diverter valve <NUM> connected to the vent line <NUM> and the fuel nozzles <NUM>. A check valve <NUM> is positioned in this line of the purge gas delivery assembly <NUM> to allow the purge gas to flow into the fuel delivery assembly <NUM>, but to prevent any back flow from the fuel delivery assembly <NUM> into the purge gas delivery assembly <NUM>. Introducing purge gas at this point allows the fuel array (e.g., the fuel manifold <NUM> and the fuel nozzles <NUM>) to remain charged with purge gas post-shutdown from the diverter valve <NUM> and the check valve <NUM> forward. With the diverter valve <NUM> connected to the vent line <NUM> in the first position, the vent line <NUM> and the vent <NUM> are closed, entrapping purge gas, as a buffer, between the upstream components of the fuel delivery assembly <NUM> and ambient air, which contacts fuel check valves <NUM> (only one shown in <FIG>). This entrapped purge gas may be monitored using a sensor, such as a pressure sensor, communicatively coupled to a controller, such as the engine controller <NUM>, to monitor the system integrity, for example. The engine controller <NUM> may, thus, sense a loss in pressure, which could indicate a leak in the fuel delivery assembly <NUM>.

<FIG> is a schematic view of the fuel system 200e having a plurality of vent connections to the fuel delivery assembly <NUM>. Other than the distinctions noted below, the remaining components and arrangement of the fuel system 200e are the same or similar to the components of the fuel system <NUM> shown in <FIG>. In the embodiment shown in <FIG>, one diverter valve <NUM> is shown to fluidly couple the fuel delivery assembly <NUM> to the vent <NUM> on the exterior of the aircraft <NUM>. In some embodiments, the fuel delivery assembly <NUM> may fluidly connect to the vent <NUM> at a plurality of locations. As shown in <FIG>, for example, one connection to the vent <NUM> is located as described above with respect to <FIG>, and the other connection to the vent <NUM> is downstream of the pump <NUM> and upstream of the vaporizers <NUM>, <NUM>.

In this configuration, different portions of the fuel delivery assembly <NUM> may be purged at different times or using different purge gases. Here, two different purge gases are used. One purge gas, such as nitrogen, is used for the components that are operated at higher temperatures when the hydrogen fuel is in a gaseous phase or a supercritical phase. Another purge gas, such as helium, may be used for the components that are operated at lower temperatures when the hydrogen fuel is in a liquid phase. The fuel delivery assembly <NUM> is fluidly coupled to a second purge gas source 310a that contains the second purge gas, such as helium. If nitrogen is used as a purge gas for the portions of the fuel system 200e that convey the hydrogen fuel in the liquid phase, there is a risk that some of the nitrogen purge gas may solidify in these components, forming, for example, nitrogen crystals in the fuel system 200e. In contrast, helium can remain suspended in the hydrogen fuel when the hydrogen fuel is a liquid, and, thus, helium may be preferred for the portions of the fuel delivery assembly <NUM> that convey the hydrogen fuel in the liquid phase. Because of the cost of helium, minimizing the use of helium may be preferred, and, thus, another purge gas, such as nitrogen, is used for other parts of the fuel system <NUM>.

<FIG> is a schematic cross-sectional view of a double-walled pipe <NUM> that may be used as part of the fuel delivery assembly <NUM> to convey the hydrogen fuel. In the embodiments discussed above, the purge gas may flow through the same passages of the fuel delivery assembly <NUM> as the hydrogen fuel, but in addition (or alternatively), the purge gas may flow through a separate passage such that the purge gas can be used as a buffer between the hydrogen fuel and the surrounding environment. In such a manner, the purge gas may be used to remove hydrogen that leaks from the hydrogen flow path through the vent <NUM>. The double-walled pipe <NUM> includes an inner wall <NUM> and an outer wall <NUM>. The inner wall <NUM> of this embodiment is annular and defines a hydrogen fuel flow path <NUM>. Hydrogen fuel flows through the hydrogen fuel flow path <NUM> as the hydrogen fuel is conveyed in the fuel delivery assembly <NUM> from the fuel tank <NUM> to the fuel nozzles <NUM>. The outer wall <NUM> circumscribes the inner wall <NUM> and defines an annular outer flow path <NUM> (or cavity) between the inner wall <NUM> and the outer wall <NUM>. In some embodiments, the outer flow path <NUM> may be subjected to a vacuum to help to maintain the temperature of the hydrogen fuel in the hydrogen fuel flow path <NUM>. In this embodiment, the hydrogen fuel flow path <NUM> is fluidly coupled to the purge gas source <NUM>, the vent line <NUM>, and the vent <NUM>. Such fluid connections may be made in a manner similar to that discussed above, but, in some embodiments, the diverter valves <NUM>, <NUM> may be omitted. The purge gas may then flow through the outer flow path <NUM> to remove any hydrogen in case of a leak. Accordingly, the outer flow path <NUM> is fluidly coupled to the purge gas source <NUM> to receive the purge gas and configured to direct the purge gas flow therethrough. The outer flow path <NUM> may also be fluidly coupled to the vent <NUM> to vent the purge gas flowing through the outer flow path <NUM>.

<FIG> is a schematic cross-sectional view of a triple-walled pipe <NUM> that may be used as part of the fuel delivery assembly <NUM> to convey the hydrogen fuel. In some embodiments, a triple-walled pipe <NUM> pipe may be used in portions of the fuel delivery assembly <NUM> in a manner similar to the double-walled pipe <NUM> shown in <FIG>. The triple-walled pipe <NUM> shown in <FIG> further includes a middle wall <NUM>. The middle wall <NUM> circumscribes the inner wall <NUM> and defines an annular middle flow path <NUM> (or cavity) between the inner wall <NUM> and the middle wall <NUM>. The outer wall <NUM> circumscribes both the middle wall <NUM> and the inner wall <NUM>, and the outer flow path <NUM> is formed between the middle wall <NUM> and the outer wall <NUM>. The middle flow path <NUM> may be a subjected to a vacuum to help to maintain the temperature of the hydrogen fuel in the hydrogen fuel flow path <NUM>.

Claim 1:
A hydrogen fuel system (<NUM>) for providing hydrogen to a power generator, the hydrogen fuel system (<NUM>) comprising:
a fuel delivery assembly (<NUM>) configured to receive hydrogen fuel from a hydrogen fuel source (<NUM>) and to provide the hydrogen fuel from the hydrogen fuel source (<NUM>) to the power generator;
a purge gas source (<NUM>) fluidly coupled to the fuel delivery assembly (<NUM>) and configured to provide a purge gas to the fuel delivery assembly (<NUM>);
a vent opening (<NUM>) fluidly coupled to the fuel delivery assembly (<NUM>) and configured to vent hydrogen fuel from the fuel delivery assembly (<NUM>) when the purge gas is provided to the fuel delivery assembly (<NUM>);
a vent line (<NUM>) fluidly connecting the fuel delivery assembly (<NUM>) to the vent opening (<NUM>)
a diverter valve (<NUM>) fluidly coupling the fuel delivery assembly (<NUM>) to the vent line (<NUM>), the diverter valve (<NUM>) including a first position and a second position, wherein, in the first position, the diverter valve (<NUM>) allows hydrogen fuel to flow through the fuel delivery assembly (<NUM>), and wherein, in the second position, the diverter valve (<NUM>) closes off a portion of the hydrogen fuel system (<NUM>) and fluidly couples the fuel delivery assembly (<NUM>) to the vent line (<NUM>); and
a fuel input array (<NUM>), the fuel delivery assembly (<NUM>) being selectively fluidly coupled to the vent opening (<NUM>) at a position upstream of the fuel input array (<NUM>).