Patent Description:
The propulsion system for commercial aircraft typically includes one or more aircraft engines, such as turbofan jet engines. The turbofan jet engine(s) may be mounted to a respective one of the wings of the aircraft, such as in a suspended position beneath the wing using a pylon. 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. Such fuel produces carbon dioxide upon combustion, and improvements to reduce such carbon dioxide emissions in commercial aircraft are desired. A hydrogen fuel may be utilized to achieve improvements in the emissions from commercial aircraft. <CIT> relates to a method and a device for producing ignitable fuel/air mixture including a fuel fraction which is a hydrogen or a gas mixture containing hydrogen and which is burnt in a burner arrangement for driving a thermal engine, in particular a gas turbine plant. <CIT> relates to a cryogenic fuel auxiliary power system for an engine including a cryogenic fuel supply, a first valve in fluid communication with the cryogenic fuel supply and configured to control a fuel flow, a first heat exchanger, configured to receive the fuel flow, in fluid communication with the first valve and a combustion chamber of the engine, and fuel cell in fluid communication between the first valve and the first heat exchanger.

Features and advantages of the present disclosure will be apparent from the following, more particular, 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.

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 noted above, a hydrogen fuel may be utilized to achieve improvements in the emissions from commercial aircraft. Hydrogen fuel, however, poses a number of challenges as compared to combustible hydrocarbon liquid fuel, such as Jet-A fuel or natural gas (NG). Hydrogen fuel, for example, is a reactive fuel that burns at higher temperatures than combustible hydrocarbon liquid fuel. Nitrogen oxide ("NOx") emission increases exponentially with high diatomic hydrogen (H<NUM>) content in fuel. When hydrogen fuel is used in current gas turbine engines with rich burn combustors, the higher combustion temperature requires additional water (or other diluent) additions to reduce the production of NOx, as compared to combustible hydrocarbon liquid fuel. Hydrogen fuel also has much higher flame speeds, which could impose an operability issue for combustors designed for Jet-A or NG fuel. For example, each of Jet-A fuel and NG may have a flame speed of about one meter per second, but a hydrogen fuel of diatomic hydrogen has a flame of about ten meters per second (see the comparison shown in <FIG>). The high flame speed of hydrogen makes it difficult to start up the engine with only hydrogen fuel due to potential risks of flashback or flameholding, imposing a safety issue. Therefore, combustor swirlers or premixers designed for conventional Jet-A or NG fuels must either be re-designed to stabilize hydrogen fueled flames, or an alternative fuel or diluent should be used to address the operability issue.

Utilizing hydrogen fuel in a gas turbine engine may require the use of large amounts of diluents, such as water. The use of diluents requires storage tanks to store the diluent and also requires the associated systems to introduce the diluent into the combustor and/or the hydrogen fuel, thus increasing the complexity and space requirements for a gas turbine engine using hydrogen fuel as compared to a gas turbine engine using a combustible hydrocarbon liquid fuel. These space requirements can be a particular disadvantage when using hydrogen fuel for applications such as aircraft, where space and weight are at a premium. The present disclosure discusses systems and methods that can be used to produce diluent from a combination of hydrogen fuel and air, reducing, or even eliminating, the need to store diluent onboard the aircraft using the gas turbine engine. In addition, this method of producing diluent enables starting-up a gas turbine engine with one hundred percent hydrogen fuel, which is used for power generation, and eliminates the need of an alternative fuel for start-up. In one embodiment, the present disclosure uses a catalytic reactor for a catalytic reaction between the oxygen in the air and hydrogen in the hydrogen fuel to produce water. This catalytically produced water can be used as the diluent. In addition, nitrogen can be used as a diluent and the nitrogen in the air used for the catalytic reaction is also used as a diluent.

A particular example of suitable applications for producing diluent from the air and hydrogen fuel is in gas turbine engines used on aircraft, as the diluent storage systems can be reduced or limited, freeing up space and reducing the weight of the engine components. <FIG> is a perspective view of an aircraft <NUM> that may implement various preferred embodiments. The aircraft <NUM> includes a fuselage <NUM>, 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>. The fuel 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 each wing <NUM> and a portion of the fuel tank <NUM> is located in the fuselage <NUM> between the wings <NUM>. The fuel tank <NUM>, however, may be located at other suitable locations in the fuselage <NUM> or the wing <NUM>. The fuel tank <NUM> may also be located entirely within the fuselage <NUM> or the wing <NUM>. The fuel tank <NUM> may also be separate tanks instead of a single, unitary body, such as, for example, two 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). The engine <NUM> may be used in various other applications including stationary power generation systems and other vehicles beyond the aircraft <NUM> explicitly described herein, such as boats, ships, cars, trucks, and the like. The engines described herein are gas turbine engines, but the embodiments described herein also may be applicable to other engines where hydrogen is used as a fuel.

For the embodiment depicted, the engine <NUM> is a high bypass turbofan engine. The engine <NUM> may also be referred to as a turbofan engine <NUM> herein. <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 cross-sectional view of <FIG> is taken along line <NUM>-<NUM> in <FIG>. 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> that defines an annular inlet <NUM>. The outer casing <NUM> encases, in a serial flow relationship, a compressor section including a booster or low-pressure (LP) compressor <NUM> and a high-pressure (HP) compressor <NUM>, a combustion section (also referred to herein as a combustor <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 combustor <NUM>, and the turbine section together define at least in part a core air flowpath <NUM> extending from the annular inlet <NUM> to the jet exhaust nozzle section <NUM>. The turbofan engine <NUM> 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> in a spaced-apart manner. 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> is provided, circumferentially surrounding 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 plurality of fuel nozzles <NUM> that inject fuel into a combustion chamber <NUM> of the combustor <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 LP compressor <NUM> to one or both of the HP turbine <NUM> or 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 startup 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>, and <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>, as discussed below. Additionally, the turbofan engine <NUM> may include one or more heat exchangers <NUM> within, for example, the turbine section or jet exhaust nozzle section <NUM> for extracting waste heat from an airflow therethrough to also provide heat to various heat sinks, such as the vaporizers <NUM>, discussed below.

The turbofan engine <NUM> discussed herein is, however 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. In such a manner, 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 shaft driving the fan, such as the LP shaft <NUM>), may be 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 or gas turbine engines with annular-can or can combustors for power generation applications. 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>, and <NUM>, discussed above.

The engine <NUM> may include an engine controller <NUM>, schematically shown in <FIG>, configured to control various systems of the engine <NUM>. The engine controller <NUM> may also be communicatively coupled to other controllers of the aircraft <NUM>. Such controllers may include, for example, a controller that is part of the flight control system for the aircraft <NUM>, such as a flight controller.

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>, cause 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>.

<FIG> is a schematic view of the fuel system <NUM> according to an embodiment of the present disclosure. The fuel system <NUM> of this embodiment is configured to store the fuel for the engine <NUM> (<FIG> and <FIG>) in the fuel tank <NUM> and to deliver the fuel to the engine <NUM> via the 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>. As discussed above, the engine <NUM>, and in particular the combustor <NUM> discussed herein may be particularly suited for use with hydrogen fuel (diatomic hydrogen) or, in other embodiments, hydrogen enriched fuels. In the embodiments shown in <FIG>, the fuel is a hydrogen fuel comprising hydrogen, more specifically, diatomic hydrogen. In some embodiments, the hydrogen fuel may consist essentially of hydrogen.

The fuel tank <NUM> may be configured to hold the hydrogen fuel at least partially in 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 -<NUM> 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 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, etc., configured to carry the hydrogen fuel between the fuel tank <NUM> and the engine <NUM>. The fuel delivery assembly <NUM> thus provides a flow path of the hydrogen fuel from the fuel tank <NUM> to the engine <NUM>. The hydrogen fuel is delivered to the engine by the fuel delivery assembly <NUM> in the gaseous phase, the supercritical phase, or both (at least one of the gaseous phase and the supercritical phase). The fuel system <NUM> thus includes a vaporizer <NUM> in fluid communication with the fuel delivery assembly <NUM> to heat the liquid hydrogen fuel flowing through the fuel delivery assembly <NUM>. The vaporizer <NUM> is positioned in the flow path of the hydrogen fuel between the fuel tank <NUM> and the engine <NUM>. The vaporizer <NUM> may be positioned at least partially within the fuselage <NUM> or the wing <NUM>, such as at least partially within the wing <NUM>. The vaporizer <NUM> may, however, be positioned at other suitable locations in the flow path of the hydrogen between the fuel tank <NUM> and the engine <NUM>. For example, the vaporizer <NUM> may be positioned external to the fuselage <NUM> and the wing <NUM> and positioned at least partially within the pylon <NUM> or the engine <NUM>. When positioned in the engine <NUM>, the vaporizer may be located in the nacelle <NUM>, for example. Although only one vaporizer <NUM> is shown in <FIG>, the fuel system <NUM> may include multiple vaporizers <NUM>. For example, when a vaporizer <NUM> is positioned in the engine <NUM> or in the pylon <NUM> and functions as a primary vaporizer configured to operate once the engine <NUM> is in a thermally stable condition, another vaporizer <NUM> is positioned upstream of the primary vaporizer and proximate to the fuel tank <NUM> and functions as a primer vaporizer during start-up (or prior to start-up) of the engine <NUM>.

The vaporizer <NUM> is in thermal communication with at least one heat source <NUM>, <NUM>. In this embodiment, the vaporizer <NUM> is in thermal communication with a primary heat source <NUM> and an auxiliary heat source <NUM>. In this embodiment, primary heat source <NUM> is waste heat from the engine <NUM>, and the vaporizer <NUM> is, thus, thermally connected to at least one of the main lubrication system <NUM>, the compressor cooling air (CCA) system <NUM>, the active thermal clearance control (ATCC) 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, 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 auxiliary heat source <NUM>, to the vaporizer <NUM>, in order to facilitate operation of the vaporizer <NUM>.

The vaporizer <NUM> may be heated by any suitable heat source, and, in this embodiment, for example, the auxiliary heat source <NUM> is a heat source external to the engine <NUM>. The auxiliary 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 auxiliary heat source <NUM> may be integral to the vaporizer <NUM>, such as when the vaporizer <NUM> includes one or more electrical resistance heaters, or the like, that are powered by the electrical power source. In this configuration the auxiliary heat source <NUM> may provide heat for the 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>.

As noted, the vaporizer <NUM> is in communication with the flow of the hydrogen fuel through the fuel delivery assembly <NUM>. The vaporizer <NUM> is configured to draw heat from at least one of the primary heat source <NUM> and the auxiliary heat source <NUM> to heat the flow of hydrogen fuel from a substantially completely liquid phase to a substantially completely gaseous phase or to a substantially completely supercritical phase.

The fuel system <NUM> also includes a high-pressure pump <NUM> in fluid communication with the fuel delivery assembly <NUM> to induce the flow of the hydrogen fuel through the fuel delivery assembly <NUM> to the engine <NUM>. The high-pressure 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 high-pressure pump <NUM> may be configured to increase a pressure in the fuel delivery assembly <NUM> to a pressure greater than a pressure within the combustion chamber <NUM> of the combustor <NUM> of the engine <NUM>, and to overcome any pressure drop of the components placed downstream of the high-pressure pump <NUM>.

The high-pressure pump <NUM> is positioned within the flow of hydrogen fuel in the fuel delivery assembly <NUM> at a location downstream of the vaporizer <NUM>. In this embodiment, the high-pressure 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 high-pressure pump <NUM> is positioned within the engine <NUM>. With the high-pressure pump <NUM> located in such a position, the high-pressure pump <NUM> may be any suitable pump configured to receive the flow of hydrogen fuel in substantially completely a gaseous phase or a supercritical phase. In other embodiments, however, the high-pressure pump <NUM> may be positioned at other suitable locations, including other positions within the flow path of the hydrogen fuel. For example, the high-pressure pump <NUM> may be located upstream of the vaporizer <NUM> and may be configured to receive the flow of hydrogen fuel through the fuel delivery assembly <NUM> in a substantially completely liquid phase.

As noted above, a diluent may be injected with the hydrogen fuel into the combustion chamber <NUM>. In this embodiment, diluent is produced using the hydrogen fuel, and, in some embodiments, diluent is not separately stored on the aircraft <NUM>, but rather, only produced as discussed herein. The fuel system <NUM> includes a catalytic reactor <NUM> that is used to produce the diluent. The catalytic reactor <NUM> is fluidly connected to the fuel delivery assembly <NUM>. In this embodiment, the catalytic reactor <NUM> is positioned in the flow path of the hydrogen fuel between the fuel tank <NUM> and the engine <NUM> downstream of the high-pressure pump <NUM> and upstream of a fuel metering valve <NUM> (discussed further below). The fuel delivery assembly <NUM> is configured to provide the catalytic reactor <NUM>, and the catalytic reactor <NUM> is configured to receive hydrogen fuel. In this embodiment, the catalytic reactor <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 catalytic reactor <NUM> is positioned within the engine <NUM>. In other embodiments, however, the catalytic reactor <NUM> may be positioned at other suitable locations, including other positions within the flow path of the hydrogen fuel.

The catalytic reactor <NUM> also includes an inlet <NUM>, through which air can be introduced to the catalytic reactor <NUM>. The catalytic reactor <NUM> is, thus, also configured to receive or draw air from an air source. The air source may be any suitable air source. In this embodiment, the air source is air flowing around or through the engine <NUM>. As shown in <FIG>, for example, the air is a portion of the air flowing through the core air flowpath <NUM>. More specifically, in this embodiment, the air is compressed air drawn from the compressor section or a position after the compressor section. In <FIG>, a port <NUM> is located downstream of the low-pressure (LP) compressor <NUM> and upstream of the high-pressure (HP) compressor <NUM>, and a portion of air compressed by the low-pressure (LP) compressor <NUM> is directed into the port <NUM> to be used in the catalytic reactor <NUM>. The location of the port <NUM> is illustrative and other suitable locations for the port <NUM> may be used. For example, the port <NUM> may be positioned in the core air flowpath <NUM> downstream of the high-pressure (HP) compressor <NUM> and upstream of the combustor <NUM>. The port <NUM> may also be positioned to receive air that has been compressed (or accelerated) by the fan section <NUM>, such as either in the bypass airflow passage <NUM> to receive bypass air or in the annular inlet <NUM>. Other suitable air sources include, for example, a back-up air supply for the engine <NUM> or even a dedicated port drawing air from outside the engine <NUM>.

The air and the hydrogen fuel are mixed in the catalytic reactor <NUM>, as schematically illustrated in <FIG>. The air includes (or contains) oxygen, more specifically, diatomic oxygen (O<NUM>), and the hydrogen fuel includes hydrogen, more specifically, diatomic hydrogen (H<NUM>). The catalytic reactor <NUM> also includes a catalyst such that when oxygen in the air mixes with hydrogen in the air, the oxygen and hydrogen undergo a catalytic reaction to produce water (H<NUM>O). The catalytic reactor <NUM> may include any catalyst suitable to promote the reaction between the oxygen and hydrogen to produce water. For example, the catalyst may be a metal catalyst and/or a ceramic catalyst. Metal catalysts may include, for example, at least one of the platinum group metals such as ruthenium, rhodium, palladium, osmium, iridium, and platinum. In addition, or in the alternative, the ceramic catalyst may include, for example, at least one transition metal oxide (e.g. Ni, Fe, Co). As another example of ceramic catalysts, a complex ceramic oxide catalyst based on perovskite or doped rare-earth oxides may be employed. The chemistry of ceramic based catalysts also can be a rich titanate oxide having, for example, the formula AXO<NUM>, where A is one of Ca, Ba, Sr, Cd, La, Pr, Gd, Sm, Y, or Nd and X is one of Fe, Mn, Cr, Al, Ti, Mn, or Nb. Other suitable catalysts may include copper cobaltite, lanthanum cobaltite, lanthanum ferrite, lanthanum manganite, and the like.

To promote the catalytic reaction, the catalytic reactor <NUM> preferably operates at an elevated temperature, such as from two hundred degrees Celsius to one thousand degrees Celsius. The catalytic reaction is exothermic and, thus, the elevated temperature is maintained during normal operation. During start up (or prior to start-up), the catalyst (catalytic reactor <NUM>) may be heated by a heat source to raise the temperature to the desired elevated temperature. Suitable heat sources include, for example, a glow plug, an electrical power source, and/or a bleed airflow from an auxiliary power unit, to obtain the temperature in the catalytic reactor <NUM> initially.

The catalytic reactor <NUM> is configured to catalytically react at least a portion of the oxygen in the air with at least a portion of the hydrogen in the hydrogen fuel to produce water. At least a portion of the oxygen in the air reacts with hydrogen in the hydrogen fuel to produce water. In some embodiments, the oxygen in the air is substantially completely reacted with hydrogen in the hydrogen fuel. As used herein, the term "substantially completely", as used to describe the amount of a particular element or molecule, refers to at least <NUM>% by mass of the described portion of the element or molecule, 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 element or molecule. The water produced by the catalytic reaction of oxygen with hydrogen in the catalytic reactor <NUM> is referred to herein as catalytically produced water. The catalytically produced water is used as a diluent, and the catalytic reactor <NUM> is configured to output diluent comprising the catalytically produced water.

The air also includes (or contains) nitrogen, more specifically, diatomic nitrogen (N<NUM>) and other minor constituents (e.g., Ar and CO<NUM>). It has been found that nitrogen can be used as a diluent with hydrogen fuel. <FIG> is a bar chart showing flame speed in meters per second for different fuels and fuel diluent mixtures. As shown in <FIG>, hydrogen fuel that consists essentially of diatomic hydrogen has a flame speed of about ten meters per second. Mixing the hydrogen with a percentage (by mass) of diatomic nitrogen can reduce the flame speed, such as to about seven meters per second for <NUM>% nitrogen (and <NUM>% hydrogen), to about four meters per second for <NUM>% nitrogen (and <NUM>% hydrogen), and to about one and a half meters per second for <NUM>% nitrogen (and <NUM>% hydrogen). The nitrogen in the air may also be used as a diluent in the fuel. The nitrogen is received by the catalytic reactor <NUM>, but, in this embodiment, does not undergo any reactions. The catalytic reactor <NUM> is configured to output diluent comprising the nitrogen, more specifically, diatomic nitrogen (N<NUM>). In this embodiment, the nitrogen from the air is mixed with the catalytically produced water and the catalytic reactor <NUM> is configured to output diluent comprising nitrogen from the air and the catalytically produced water.

As shown in <FIG>, the combustor <NUM> is fluidly coupled to the fuel delivery assembly <NUM> and the fuel tank <NUM> via the catalytic reactor <NUM> and, thus, receives hydrogen fuel via the catalytic reactor <NUM>. In this embodiment, only a portion of the hydrogen is reacted with the oxygen from the air in the catalytic reactor <NUM>, and the catalytic reactor <NUM> is configured to output hydrogen (hydrogen fuel) as well as the diluent. The diluent and hydrogen fuel are mixed in the catalytic reactor <NUM> to form a fuel and diluent mixture.

As noted above, only a portion of the hydrogen received by the catalytic reactor <NUM> is reacted with the oxygen in this embodiment. The amount of oxygen in the reactor thus controls the amount of water produced, and the amount of oxygen is controlled by the amount of air provided to the catalytic reactor <NUM>, or received by the catalytic reactor <NUM>. In addition, controlling the amount of air also controls the amount of nitrogen that can be used as a diluent.

<FIG> is a line graph illustrating the percentage of diluent in the fuel and diluent mixture as a function of inlet air fraction. The inlet air fraction is the amount of air to total amount of air and hydrogen fuel introduced to the catalytic reactor <NUM> at a given time (the mole percentage of air at the inlet of the catalytic reactor <NUM>). As can be seen from <FIG>, increasing the inlet air fraction increases the amount of diluent produced.

Changing the amount of diluent may be desirable based on the operating condition of the engine <NUM>. For example, during start-up or other operating conditions such as taxiing when the flow rate of air through the combustion chamber <NUM> is relatively low, the amount of diluent can be a relatively high inlet air fraction to reduce the flame speed of the hydrogen fuel (see, e.g., <FIG>). For the engine operating condition when the aircraft <NUM> is cruising, however, the air speed flowing through the combustion chamber <NUM> is relatively high and, thus, the amount of diluent is a relatively low inlet air fraction, allowing the flame speed to be fast. Controlling the amount of diluent in this way also helps to avoid problems such as lean blowout of the flame, which can occur when the flame speed is too low relative to the air flow speed, and flashback, which can occur when the flame speed is too high relative to the air flow speed.

Any suitable device may be used to control the amount of air provided to the catalytic reactor <NUM> and received by the catalytic reactor <NUM>. In this embodiment, an air control valve <NUM> is fluidly coupled to the catalytic reactor to control the amount of air received by the catalytic reactor <NUM>. Any suitable valve may be used for air control, such as a throttle valve, a damper, and the like. The air control valve <NUM> is schematically shown after the port <NUM> and in the inlet <NUM> of the catalytic reactor <NUM>, but the air control valve <NUM> may be located at other suitable positions such as at the port <NUM>. The engine controller <NUM> may be configured to control the air control valve <NUM> based, for example, on the operating condition of the engine <NUM> and/or aircraft <NUM>, as discussed above.

The catalytic reactor <NUM> may have a relatively large pressure drop. As shown in <FIG>, the fuel delivery assembly <NUM> may also include a booster pump <NUM>, in some embodiments, to further induce the flow of the hydrogen fuel through the fuel delivery assembly <NUM> to the engine <NUM>, and, more specifically, to the components in the flow path of the fuel and diluent mixture that are downstream of the catalytic reactor <NUM>. The booster pump <NUM> may be positioned within the flow of the fuel and diluent mixture at a location downstream of the catalytic reactor <NUM>. In this embodiment, the booster pump <NUM> is positioned upstream of the fuel metering valve <NUM>.

The fuel system <NUM> also includes a metering unit in fluid communication with the fuel delivery assembly <NUM>. Any suitable metering unit may be used including, for example, a fuel metering valve <NUM> placed in fluid communication with the fuel delivery assembly <NUM>. The fuel delivery assembly <NUM> is configured to provide the fuel metering valve <NUM>, and the fuel metering valve <NUM> is configured to receive hydrogen fuel. In this embodiment, the fuel metering valve <NUM> is fluidly coupled to the catalytic reactor <NUM> and positioned downstream of the catalytic reactor <NUM> and the booster pump <NUM>, and the hydrogen fuel provided to, and received by, the fuel metering valve <NUM> is from the fuel and diluent mixture output from the catalytic reactor <NUM>. The fuel metering valve <NUM> is further configured to provide the flow of the fuel and diluent mixture to the engine <NUM> in a desired manner. The fuel metering valve <NUM> is configured to provide a desired volume of the fuel and diluent mixture, 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 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 fuel metering valve <NUM> changes the volume of fuel (and diluent) provided to the combustion chamber <NUM> of the combustor <NUM> and, thus, changes the amount of propulsive thrust produced by the engine <NUM> to propel the aircraft <NUM>.

<FIG> also shows the combustor <NUM> of the engine <NUM> according to an embodiment of the present disclosure. <FIG> is a cross-sectional view of the combustor <NUM>. The combustor <NUM> includes a combustor liner <NUM>. The combustor liner <NUM> of this embodiment has a combustor inner liner 154A and a combustor outer liner 154B. A combustion chamber <NUM> is formed within the combustor liner <NUM>. The combustor liner <NUM>, and, thus, also the combustion chamber <NUM>, has a forward end <NUM> and an outlet <NUM>. A fuel nozzle <NUM> is positioned at the forward end <NUM> of the combustion chamber <NUM>. The fuel nozzle <NUM> of this embodiment is part of a swirler/fuel nozzle assembly <NUM>. In this embodiment, the combustor <NUM> is an annular combustor <NUM> and a plurality of fuel nozzles <NUM> is arranged in an annular configuration with the plurality of fuel nozzles <NUM> (the swirler/fuel nozzle assemblies <NUM>) aligned in a circumferential direction of the combustor.

As discussed above, the compressor section, the combustor <NUM>, and the turbine section form, at least in part, the core air flowpath <NUM> extending from the annular inlet <NUM> to the jet exhaust nozzle section <NUM>. Air entering through the annular inlet <NUM> is compressed by blades of a plurality of fans of the LP compressor <NUM> and HP compressor <NUM>. A portion of the compressed air (primary air) enters the forward end <NUM> of the combustion chamber <NUM>. Fuel is injected by the fuel nozzle <NUM> into the primary air and mixed with the primary air. As noted above, the fuel nozzle <NUM> of this embodiment is part of a swirler/fuel nozzle assembly <NUM>. The swirler/fuel nozzle assembly <NUM> includes a swirler <NUM> that is used to generate turbulence in the primary air. The fuel nozzle <NUM> injects fuel into the turbulent airflow of the primary air and the turbulence promotes rapid mixing of the fuel with the primary air.

The mixture of fuel and compressed air is combusted in the combustion chamber <NUM>, generating combustion gases (combustion products), which accelerate as the combustion gases leave the combustion chamber <NUM>. The products of combustion are accelerated as the products are expelled through the outlet <NUM> to drive the engine <NUM>. The primary air thus flows in a bulk airflow direction from the forward end <NUM> of the combustion chamber <NUM> to the outlet <NUM>. The combusted fuel air mixture is then accelerated through the outlet <NUM> to turn the turbines (e.g., drive the turbine blades) of the HP turbine <NUM> and the LP turbine <NUM>. As discussed above the HP turbine <NUM> and the LP turbine <NUM>, among other things, drive the LP compressor <NUM> and HP compressor <NUM>.

As noted above, the diluent is mixed with the hydrogen fuel as a fuel and diluent mixture. The fuel nozzle <NUM> injects the fuel and diluent mixture into the combustion chamber <NUM>, and, in this embodiment, the diluent is injected into the forward end <NUM> of the combustion chamber <NUM> using the fuel nozzle <NUM>.

<FIG> is a schematic view of the fuel system <NUM> and the combustor <NUM> according to another embodiment of the present disclosure. In the embodiment shown in <FIG>, the fuel nozzle <NUM> is configured to inject both fuel and diluent into the combustion chamber <NUM>, but other suitable configurations may be used, including, for example, separate fuel and diluent nozzles. Such a configuration is shown schematically in <FIG>. The components that are the same or similar to the components described above with reference to <FIG> have the same reference numeral in <FIG>, and a detailed description these components is omitted. The fuel nozzle <NUM> of the embodiment shown in <FIG> is configured to inject fuel into the combustion chamber <NUM>. At least one separate nozzle, a diluent nozzle <NUM>, is configured to inject diluent into the combustion chamber <NUM>. In this embodiment, the catalytic reactor <NUM> is configured to produce diluent comprising nitrogen from the air and catalytically produced water. As in the embodiment discussed above, hydrogen from the hydrogen fuel is catalytically reacted with oxygen in the air to produce water, but the amount of hydrogen fuel supplied to the catalytic reactor <NUM> is controlled such that the output of the catalytic reactor <NUM> is substantially completely diluent. When the output is not completely diluent the remainder of the output may be hydrogen (H<NUM>) from the hydrogen fuel or oxygen (O<NUM>) from the air depending upon which of these two molecules is provided in excess (e.g., an amount greater than the sociometric amount).

Any suitable means may be used to control the amount of hydrogen fuel provided to, or received by, the catalytic reactor <NUM>. In this embodiment, a hydrogen control valve <NUM> is fluidly coupled to the catalytic reactor <NUM> to control the amount of hydrogen received by the catalytic reactor <NUM>. In <FIG>, the hydrogen control valve <NUM> is shown schematically at the inlet to catalytic reactor <NUM>, but the hydrogen control valve <NUM> may be located at other suitable positions. The engine controller <NUM> may be configured to control the hydrogen control valve <NUM> in addition to the air control valve <NUM> based, for example, on the operating condition of the engine <NUM> and/or aircraft <NUM>, as discussed above.

The at least one diluent nozzle <NUM> is fluidly connected to the output of the catalytic reactor <NUM> and receives the output of the catalytic reactor <NUM>, which, in this embodiment, is substantially completely diluent. The diluent nozzle <NUM> then injects diluent into the forward end <NUM> of the combustion chamber <NUM>. In some embodiments, a plurality of diluent nozzles <NUM> may be used, and a plurality of diluent nozzles <NUM> may also be used for each fuel nozzle <NUM>.

<FIG> is a schematic view of the fuel system <NUM> and the combustor <NUM> according to another embodiment of the present disclosure. In some embodiments, it may be beneficial to reduce the amount of hydrogen fuel flowing through the catalytic reactor <NUM> and provide some of the hydrogen fuel to the combustor <NUM> through a flow path that does not include the catalytic reactor <NUM>. Such a configuration is shown in <FIG>. The components that are the same or similar to the components described above with reference to <FIG> and <FIG> have the same reference numeral in <FIG>, and a detailed description these components is omitted. In the configuration shown in <FIG>, a portion of the hydrogen fuel flowing from the fuel tank <NUM> flows to the catalytic reactor <NUM> and the remaining portion bypasses the catalytic reactor <NUM> by flowing through a bypass flow path <NUM>. The output of the catalytic reactor <NUM> and the portion of the hydrogen fuel that flows through the bypass flow path <NUM> may be mixed in a fuel mixing assembly <NUM> located upstream of the fuel metering valve <NUM>. <FIG> shows the catalytic reactor <NUM> operating as described above with reference to <FIG>, and the output of the catalytic reactor <NUM> contains hydrogen which may be used as fuel. Alternatively, the catalytic reactor <NUM> may be configured and controlled as described above with reference to <FIG> to output diluent.

In the embodiments discussed above, the gas turbine engine <NUM> and combustor <NUM> have been described as using hydrogen fuel. The systems and methods to produce diluent discussed herein may be applicable to other fuels as well.

<FIG> is a schematic view of a fuel system <NUM> that provides a hydrogen enriched fuel, such as hydrogen enriched natural gas (CH<NUM>) to the combustor <NUM>. The components that are the same or similar to the components described above with reference to <FIG>, <FIG>, and <FIG> have the same reference numeral in <FIG>, and a detailed description these components is omitted. In the fuel system <NUM> shown in <FIG>, the fuel system <NUM> also includes a natural gas delivery assembly <NUM> that connects a source of natural gas (such as a natural gas storage tank <NUM>) to the fuel mixing assembly <NUM> where the natural gas is mixed with the hydrogen and diluent produced by the catalytic reactor <NUM>. In <FIG>, the hydrogen and diluent are provided to the fuel mixing assembly <NUM> from the catalytic reactor <NUM> and the bypass flow path <NUM> in the manner described above with reference to <FIG> The hydrogen fuel and diluent, however, may be provided to the fuel mixing assembly <NUM> using the catalytic reactor <NUM> and the fuel delivery assembly <NUM> configured in the manner as shown in <FIG> and <FIG>.

Claim 1:
A gas turbine engine (<NUM>) comprising:
a catalytic reactor (<NUM>) configured (i) to receive hydrogen fuel, (ii) to receive air containing oxygen, (iii) to catalytically react at least a portion of the oxygen in the air with at least a portion of the hydrogen in the hydrogen fuel to produce water, and (iv) to output diluent comprising the catalytically produced water;
an air control valve (<NUM>) fluidly coupled to the catalytic reactor (<NUM>) to control the amount of air received by the catalytic reactor (<NUM>);
a controller (<NUM>) configured to operate the air control valve (<NUM>), wherein the controller (<NUM>) is configured to adjust the amount of air received by the catalytic reactor (<NUM>) based on an operating condition of the gas turbine engine (<NUM>); and
a combustor (<NUM>) including (a) a combustion chamber (<NUM>) and (b) at least one nozzle (<NUM>, <NUM>) that is fluidly coupled to the catalytic reactor (<NUM>) to receive the diluent output by the catalytic reactor (<NUM>) and configured to inject diluent into the combustion chamber (<NUM>).