Safety marking for hydrogen fuel systems

Abstract

A hydrogen fuel including a safety marker, and methods and apparatus for adding a safety marker to a hydrogen fuel. The hydrogen fuel can be stored in a tank in a liquid phase, and then heated to at least one of a gaseous phase and a supercritical phase. The safety marker can be added to the hydrogen fuel when the hydrogen fuel is in at least one of the gaseous phase and the supercritical phase after heating the hydrogen fuel. The hydrogen fuel can be delivered to a power generator, such as a gas turbine engine, in at least one of the gaseous phase and the supercritical phase. The safety marker can be a visual safety marker, such as an inert gas or a scent agent.

Description

TECHNICAL FIELD

[0001] The preferred embodiments described herein relate to fuel systems, and more particularly to fuel systems for aircraft. BACKGROUND

[0002] Propulsion systems for commercial aircraft typically include one or more aircraft engines, such as turbofan jet engines. The turbofan jet engines can be mounted to a respective wing of the aircraft, such as suspended beneath the wing using a pylon in a suspended position. These engines can be powered by aviation turbine fuel, which is typically a combustible hydrocarbon liquid fuel having a desired carbon number, such as a kerosene-type fuel. Aviation turbine fuel is a relatively power-dense fuel that is relatively easy to transport and remains in a liquid phase under most environmental operating conditions of the aircraft. This fuel produces carbon dioxide when combusted, and improvements are needed to reduce such carbon dioxide emissions in commercial aircraft. SUMMARY

[0003] According to an embodiment, a fuel includes hydrogen and a visual security marking, the visual security marking being an inert gas.

[0004] According to an embodiment, a fuel system for a vehicle having a generator, the fuel system including: a fuel tank for storing a hydrogen fuel in a liquid phase; a fuel delivery assembly extending from the fuel tank to a generator, the fuel delivery assembly being configured to provide the hydrogen fuel from the fuel tank to the generator; a vaporizer in communication with the fuel delivery assembly for heating the hydrogen fuel in the liquid phase to at least one of a gaseous phase and a supercritical phase, the vaporizer being located between the fuel tank and the generator; a security marking tank for storing a security marking; and a security marking delivery assembly extending from the security marking tank to the fuel delivery assembly, the security marking delivery assembly (i) connecting to the fuel delivery assembly at a security marking introduction location, and (ii) being configured to add a security marking to the hydrogen fuel when the hydrogen fuel is in the at least one of the gaseous phase and the supercritical phase, the security marking introduction location being a location at or upstream of the vaporizer.

[0005] Additional features, advantages, and embodiments of the present disclosure are set forth in the detailed description, drawings, and claims that follow. Moreover, it should be appreciated that the foregoing Summary and the following detailed description are examples only and are intended to provide further explanation without limiting the scope of the present disclosure as claimed. BRIEF DESCRIPTION OF DRAWINGS

[0006] The foregoing and other features and advantages will be apparent from the following more particular description of various exemplary embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same, similar and / or corresponding parts throughout the drawings.

[0007] Figure 1 is a schematic perspective view of an aircraft having a fuel system in accordance with an embodiment of the disclosure.

[0008] Figure 2 is a schematic cross-sectional view taken along line 2-2 in Figure 1 is a schematic cross-sectional view taken along line 2-2 in Figure 1 is a schematic cross-sectional view taken along line 2-2 in

[0009] Figure 3 is a schematic view of a fuel system including a safety tag introduction system in accordance with an embodiment of the disclosure.

[0010] Figure 4 is a schematic view of a fuel system in which a vaporizer is in a different location in the fuel system than in Figure 3 is a schematic view of a fuel system in which a vaporizer is in a different location in the fuel system than in

[0011] Figure 5 is a schematic view of a fuel system in which a vaporizer is in another different location in the fuel system than in Figure 3 and Figure 4 is a schematic view of a fuel system in which a vaporizer is in another different location in the fuel system than in

[0012] Figure 6 is a flowchart showing a method of adding a safety tag to hydrogen fuel in a fuel delivery system as shown in Figure 3

[0013] is a schematic view of a fuel system in which a safety tag introduction system is connected to the fuel system at a different location in the fuel system than in Figure 7 Figure 3 is a schematic view of a fuel system including a safety tag separation and recovery system in accordance with an embodiment of the disclosure.

[0014] Figure 8 is a flowchart showing a method of removing a safety tag from hydrogen fuel in a fuel delivery system as shown in

[0015] Figure 9 Figure 8 is a flowchart showing a method of removing a safety tag from hydrogen fuel in a fuel delivery system as shown in

[0016] Figure 10 is a schematic view of a fuel system in which a separator of a safety tag separation and recovery system is connected to the fuel system at a different location in the fuel system than in Figure 9

[0017] Figure 11 ​​​is a schematic of a fuel system including a safety tag separation and recovery system according to another embodiment of the present disclosure.

[0018] Figure 12 is a schematic of a fuel system including a safety tag separation and recovery system according to a further embodiment of the present disclosure. DETAILED DESCRIPTION

[0019] Various embodiments are discussed in detail below. Although specific embodiments are discussed, this is for illustrative purposes only. Those skilled in the relevant art will recognize that other components and configurations can be used without departing from the spirit and scope of this disclosure.

[0020] To reduce carbon dioxide emissions for commercial aircraft, hydrogen fuel can be used. However, hydrogen fuel presents many challenges compared to combustible carbon-hydrogen liquid fuels. 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 also tends to seep into attachment points between materials and components when in gaseous form without leaving a residue. Additionally, hydrogen fuel is colorless and odorless. When hydrogen fuel burns, it has a flame that is not visible to the naked eye under normal lighting conditions.

[0021] The present disclosure discusses methods of improving the safety of hydrogen fuel systems and, in particular, of such fuel systems used in aircraft. Preferred embodiments described herein relate to safety tags used in hydrogen fuel systems and, in particular, to hydrogen fuel systems for aircraft. As discussed above, hydrogen fuel is colorless and odorless, and when hydrogen fuel burns, it has a flame that is not visible to the naked eye under normal lighting conditions. This presents a safety issue because personnel around the aircraft, such as maintenance workers or other ground personnel, can not be able to detect a leak or even the presence of a hydrogen fire. In the present disclosure, safety tags are added to the hydrogen fuel to alert personnel of a leak. One such safety tag discussed herein is a visual safety tag, such as an inert gas, added to the hydrogen fuel. The visual safety tag makes the flame of the hydrogen visible to the naked eye under normal lighting conditions, such as sunlight. Another such safety tag discussed herein is an odorant that enables personnel to smell the hydrogen fuel when a leak occurs. Various safety tags are discussed herein and can be used individually or in any combination. For example, both a visual safety tag and an odorant can be used.

[0022] When hydrogen fuel is used as a fuel in aircraft applications, the hydrogen fuel is typically stored as a liquid. Except for helium, the safety tags discussed herein can not be suitable to add to and mix with the hydrogen fuel while the hydrogen fuel is in the liquid phase. The present disclosure discusses systems and methods of introducing safety tags into the fuel system and removing and reusing the safety tags.

[0023] The safety markings, fuel systems, and methods discussed herein are particularly suitable for use on an aircraft. Figure 1 is a perspective view of an aircraft 10 in which various preferred embodiments can be implemented. The aircraft 10 includes a fuselage 12, wings 14 attached to the fuselage 12, and a tail 16. The aircraft 10 also includes a propulsion system that generates propulsive thrust needed to propel the aircraft 10 in flight, during taxi operations, and the like. The propulsion system for the aircraft 10 shown in Figure 1 includes a pair of engines 100. In this embodiment, each engine 100 is attached to one of the wings 14 in a wing-under configuration by a pylon 18. Although the engines 100 are shown attached to the wings 14 in a wing-under configuration, in other embodiments, the engines 100 can have alternative configurations and be coupled to other portions of the aircraft 10. For example, the engines 100 can additionally or alternatively include one or more aspects coupled to other portions of the aircraft 10, such as the tail 16 and the fuselage 12. Figure 1

[0024] As will be further described below with reference to Figure 2 , Figure 1 the engines 100 shown in Figure 3 are gas turbine engines each capable of selectively generating propulsive thrust for the aircraft 10. The amount of propulsive thrust can be controlled based at least in part on a volume of fuel provided to the gas turbine engines 100 via a fuel system 200 (see Figure 1 ). In the embodiments discussed herein, the fuel is hydrogen fuel stored in fuel tanks 210 of the fuel system 200. As shown, at least a portion of the fuel tanks 210 is located in each wing 14, and a portion of the fuel tanks 210 is located in the fuselage 12 between the wings 14. However, the fuel tanks 210 can be located in other suitable locations in the fuselage 12 or wings 14. The fuel tanks 210 can also be entirely located within the fuselage 12 or wings 14. The fuel tanks 210 can also be separate tanks rather than a single unit, for example, two tanks each located within a respective wing 14.

[0025] Although Figure 1 ​The aircraft 10 shown is an airplane, but the embodiments described herein can also be applied to other aircraft 10, including, for example, helicopters and unmanned aerial vehicles (UAVs). The aircraft discussed herein are fixed-wing or rotary-wing aircraft that generate lift through aerodynamic forces acting on, for example, a fixed wing (e.g., wing 14) or a rotating wing (e.g., the rotor of a helicopter), and are heavier than air, not lighter than air (such as airships). Furthermore, the embodiments described herein can also be applied to other applications using hydrogen as fuel. The engine described herein is a gas turbine engine, but the embodiments described herein can also be applied to other engines. Further, the engine, specifically the gas turbine engine, is an example of a generator using hydrogen as fuel, but hydrogen can be used as fuel for other generators, including, for example, fuel cells (hydrogen fuel cells). Such generators can be used in a variety of applications, including stationary power generation systems (including gas turbines and hydrogen fuel cells) and other vehicles besides the aircraft 10 explicitly described herein, such as ships, vessels, automobiles, trucks, etc.

[0026] In the described embodiment, the generator is engine 100, and more particularly a high-bypass turbofan engine. Engine 100 may also be referred to herein as turbofan engine 100. Figure 2 Is Figure 1 A schematic cross-sectional view of one of the engines 100 used in the propulsion system of the aircraft 10 shown. The turbofan engine 100 has an axial direction A (extending parallel to the longitudinal centerline 101, in...) Figure 2 (The image shows the radial direction R and the circumferential direction for reference.) Circumferential direction ( Figure 2 (Not shown) extends in a direction of rotation about the axial direction A. The turbofan engine 100 includes a fan section 102 and a turbine 104 disposed downstream of the fan section 102.

[0027] Figure 2The depicted turbine 104 includes a tubular outer casing 106 defining an annular inlet 108. The casing 106 encloses, in serial flow relationship, a compressor section including a booster or low pressure (LP) compressor 110 and a high pressure (HP) compressor 112, a combustion section 114, a turbine section including a high pressure (HP) turbine 116 and a low pressure (LP) turbine 118, and an ejection exhaust nozzle section 120. The compressor section, the combustion section 114, and the turbine section together at least partially define a core air flowpath 121 extending from the annular inlet 108 to the ejection exhaust nozzle section 120. The turbofan engine further includes one or more drive shafts. More specifically, the turbofan engine includes a high pressure (HP) shaft or spool 122 drivingly connecting the HP turbine 116 to the HP compressor 112, and a low pressure (LP) shaft or spool 124 drivingly connecting the LP turbine 118 to the LP compressor 110.

[0028] Figure 2 The depicted fan section 102 includes a fan 126 having a plurality of fan blades 128 coupled in spaced relation to a disk 130. The fan blades 128 and disk 130 are rotatable together about a longitudinal centerline (axis) 101 by the LP shaft 124. The disk 130 is covered by a rotatable front hub 132 having an aerodynamic profile to facilitate airflow through the plurality of fan blades 128. Further, an annular fan casing or outer nacelle 134 is provided that circumferentially surrounds at least a portion of the fan 126 and / or the turbine 104. The nacelle 134 is supported relative to the turbine 104 by a plurality of circumferentially spaced outlet guide vanes 136. A downstream section 138 of the nacelle 134 extends over an exterior of the turbine 104 so as to define a bypass airflow passage 140 therebetween.

[0029] The turbofan engine 100 is operable with and receives a flow of fuel from a fuel system 200. As will be further described below, the fuel system 200 includes a fuel delivery assembly 202 that provides a flow of fuel from a fuel tank 210 to the engine 100, and more specifically to a fuel manifold 172 of the combustion section 114 of the turbine 104 of the turbofan engine 100. Figure 2 not labeled; see Figure 3 ).

[0030] The turbofan engine 100 also includes various accessory systems to aid in the operation of the turbofan engine 100 and / or an aircraft including the turbofan engine 100. For example, the turbofan engine 100 can include a main lubrication system 152, a compressor cooling air (CCA) system 154, an active thermal gap control (ATCC) system 156, and an electric generator lubrication system 158, each of which is described in greater detail below. Figure 2The main lubrication system 152 is configured to provide lubricant to various bearings and gear meshes in, for example, the compressor section, the turbine section, the HP spool 122, and the LP spool 124. The lubricant provided by the main lubrication system 152 can increase the useful life of these components and can remove an amount of heat from these components. The compressor cooling air (CCA) system 154 provides air from one or both of the HP compressor 112 or the LP compressor 110 to one or both of the HP turbine 116 or the LP turbine 118. The active thermal gap control (ATCC) system 156 cools the casings of the turbine section to maintain the gap between the various turbine rotor blades and the turbine casings within a desired range under various engine operating conditions. The generator lubrication system 158 provides lubrication to the electronic generator (not shown), as well as provides cooling / heat removal for the electronic generator. The electronic generator can provide electrical power to, for example, a starter motor for the turbofan engine 100, and / or various other electronic components of the turbofan engine 100 and / or an aircraft that includes the turbofan engine 100.

[0031] As discussed below, heat from these accessory systems 152, 154, 156, 158 and other accessory systems can be provided to various heat sinks, such as to various vaporizers 220, as waste heat from the turbofan engine 100 during operation. In addition, the turbofan engine 100 can include one or more heat exchangers 162 within, for example, the turbine section or 120, for extracting waste heat from airflow passing therethrough in order to also provide heat to various heat sinks, such as the vaporizers 220, discussed below.

[0032] However, it should be understood that the turbofan engine 100 discussed herein is provided by way of example only. In other embodiments, any other suitable engine can be used with aspects of the present disclosure. For example, in other embodiments, the engine can be any other suitable gas turbine engine, such as a turboshaft engine, a turboprop engine, a turbojet engine, etc. In this manner, it should be further understood that in other embodiments, the gas turbine engine can have other suitable configurations, such as other suitable numbers or arrangements of shafts, compressors, turbines, fans, etc. Further, although the turbofan engine 100 is shown as a direct drive fixed pitch turbofan engine 100, in other embodiments, the gas turbine engine can be a geared gas turbine engine (i.e., include a gearbox between the fan 126 and the shaft (such as the LP shaft 124) that drives the fan), can be a variable pitch gas turbine engine (i.e., include a fan 126 having a plurality of fan blades 128 that are capable of rotating about their respective pitch axes), etc. Still further, in alternative embodiments, aspects of the present disclosure can be incorporated into or otherwise used with any other type of engine, such as a reciprocating engine, as discussed above. Additionally, in other example embodiments, the example turbofan engine 100 can include or be operatively connected to any other suitable accessory system. Additionally or alternatively, the example turbofan engine 100 can not include or be operatively connected to one or more of the accessory systems 152, 154, 156, 158, and 162 discussed above.

[0033] Figure 3is a schematic illustration of a fuel system 200 according to embodiments of the present disclosure, the fuel system 200 configured to store hydrogen fuel for an engine 100 in a fuel tank 210 and deliver the hydrogen fuel to the engine 100 via a fuel delivery assembly 202. The fuel delivery assembly 202 includes tubes, pipes, and the like to fluidly connect various components of the fuel system 200 to the engine 100. The fuel tank 210 can be configured to store hydrogen fuel at least partially within a liquid phase, and can be configured to provide the fuel delivery assembly 202 with hydrogen fuel that is substantially entirely in a liquid phase, such as entirely in a liquid phase. For example, the fuel tank 210 can have a fixed volume and contain a volume of hydrogen fuel in a liquid phase (liquid hydrogen fuel). As the fuel tank 210 provides hydrogen fuel to the fuel delivery assembly 202 substantially entirely in a liquid phase, the volume of liquid hydrogen fuel in the fuel tank 210 decreases and the remaining volume in the fuel tank 210 is made up of, for example, hydrogen in a gaseous phase (gaseous hydrogen). It should be understood that the term “substantially entirely” as used herein to describe a phase of hydrogen fuel means that at least 99% of the mass of the portion of hydrogen fuel is in the phase, such as at least 97.5% of the mass of the portion of hydrogen fuel is in the phase, such as at least 95% of the mass of the portion of hydrogen fuel is in the phase, such as at least 92.5% of the mass of the portion of hydrogen fuel is in the phase, such as at least 90% of the mass of the portion of hydrogen fuel is in the phase, such as at least 85% of the mass of the portion of hydrogen fuel is in the phase, or such as at least 75% of the mass of the portion of hydrogen fuel is in the phase.

[0034] To store hydrogen fuel substantially entirely in a liquid phase, the hydrogen fuel is stored in the fuel tank 210 at a very low (cryogenic) temperature. For example, the hydrogen fuel can be stored in the fuel tank 210 at approximately -253 degrees Celsius or below at atmospheric pressure, or at other temperatures and pressures, to substantially maintain the hydrogen fuel in a liquid phase. The fuel tank 210 can be made of known materials, such as titanium, aluminum, or composite materials. The fuel tank 210 and the fuel system 200 can include a variety of support structures and components to facilitate storing hydrogen fuel in this manner.

[0035] The liquid hydrogen fuel is supplied from the fuel tank 210 to the fuel delivery assembly 202. The fuel delivery assembly 202 can include one or more lines, conduits, and the like configured to carry hydrogen fuel between the fuel tank 210 and the engine 100. Thus, the fuel delivery assembly 202 provides a flow path for hydrogen fuel from the fuel tank 210 to the engine 100. In this document, the terms “downstream” and “upstream” can be used to describe the position of components relative to the flow direction of hydrogen fuel in the flow path of the fuel delivery assembly 202. The fuel delivery assembly 202 can also include various valves (e.g., valve 204) and other components to deliver hydrogen fuel to the engine 100 (inFigure 3 not shown).

[0036] The hydrogen fuel is delivered by the fuel delivery assembly 202 to the engine in a gaseous phase, a supercritical phase, or both (at least one of the gaseous phase and the supercritical phase). Accordingly, the fuel system 200 includes a vaporizer 220 in fluid communication with the fuel delivery assembly 202 to heat the liquid hydrogen fuel flowing through the fuel delivery assembly 202. The vaporizer 220 is positioned in the flow path of the hydrogen fuel between the fuel tank 210 and the engine 100. In Figure 3 In the illustrated embodiment, the vaporizer 220 is positioned at least partially within the fuselage 12 or the wing 14, such as at least partially within the wing 14. However, the vaporizer 220 can be positioned in other suitable locations in the flow path of the hydrogen between the fuel tank 210 and the engine 100. For example, the vaporizer 220 can be positioned outside of the fuselage 12 and the wing 14 and at least partially positioned within the pylon 18, as shown in Figure 4 or at least partially positioned within the engine 100, as shown in Figure 5 For example, when positioned in the engine 100, the vaporizer can be located in the nacelle 134. Although only one vaporizer 220 is shown in Figure 3 However, the fuel system 200 can include multiple vaporizers 220. For example, when the vaporizer 220 is positioned in the engine 100 or in the pylon 18 and functions as a primary vaporizer configured to operate once the engine 100 is in a hot stable state, another vaporizer 220 is positioned upstream of the primary vaporizer and proximate to the fuel tank 210 and functions as a primary vaporizer during (or prior to) startup of the engine 100.

[0037] The vaporizer 220 is in thermal communication with at least one heat source 222, 224. In this embodiment, the vaporizer 220 is in thermal communication with a primary heat source 222 and a secondary heat source 224. In this embodiment, the primary heat source 222 is waste heat from the engine 100, and thus the vaporizer 220 is thermally coupled to at least one of the main lubrication system 152, the compressor cooling air (CCA) system 154, the active thermal gap control (ATCC) system 156, the generator lubrication system 158, and the heat exchanger 162 to extract waste heat from the engine 100 to heat the hydrogen fuel. In this manner, it should be understood that, in order to facilitate operation of the vaporizer 220, the vaporizer 220 is configured to operate by drawing heat from the primary heat source 222 once the engine 100 is able to provide sufficient heat to the vaporizer 220 via the heat source 224.

[0038] Vaporizer 220 can be heated by any suitable heat source, and in this embodiment, for example, auxiliary heat source 224 is a heat source external to engine 100. Auxiliary heat source 224 can include, for example, an electrical power source, a catalytic heater or burner, and / or bleed air from an auxiliary power unit. Auxiliary heat source 224 can be integral with vaporizer 220, such as when vaporizer 220 includes one or more electrically powered resistance heaters powered by an electrical power source, etc. In such a configuration, auxiliary heat source 224 can provide heat to vaporizer 220 independent of whether engine 100 is operating, and can be used, for example, during (or prior to) startup of engine 100.

[0039] As noted, vaporizer 220 is in communication with the flow of hydrogen fuel through fuel delivery assembly 202. Vaporizer 220 is configured to draw heat from at least one of primary heat source 222 and auxiliary heat source 224 to heat the flow of hydrogen fuel from a substantially entirely liquid phase to a substantially entirely gaseous phase or to a substantially entirely supercritical phase.

[0040] Fuel delivery assembly 202 also includes high pressure pump 230 to direct the flow of hydrogen fuel through fuel delivery assembly 202 to engine 100. High pressure pump 230 can generally be the primary source of pressure rise in fuel delivery assembly 202 between fuel tank 210 and engine 100. High pressure pump 230 can be configured to increase the pressure in fuel delivery assembly 202 to a pressure greater than the pressure within the combustion chambers of combustion section 114 of engine 100. For example, high pressure pump 230 can be configured to increase the pressure in fuel delivery assembly 202 to at least four hundred pounds per square inch ("psi"), such as to at least five hundred psi, such as to at least six hundred psi, such as to at least seven hundred psi, such as to at least seven hundred fifty psi, such as to up to two thousand psi.

[0041] High pressure pump 230 is positioned within the flow of hydrogen fuel in fuel delivery assembly 202 at a location downstream of vaporizer 220. In this embodiment, high pressure pump 230 is positioned external to airframe 12 and wings 14, and at least partially positioned within pylon 18, or at least partially positioned within engine 100. More specifically, high pressure pump 230 is positioned within engine 100. With high pressure pump 230 located in such a position, high pressure pump 230 can be any suitable pump configured to receive a flow of hydrogen fuel that is a substantially entirely gaseous phase or a supercritical phase. However, it should be appreciated that in other embodiments, high pressure pump 230 can be positioned in any other suitable location, including other locations within the flow path of hydrogen fuel. For example, high pressure pump 230 can be located upstream of vaporizer 220 and can be configured to receive a flow of hydrogen fuel that is a substantially entirely liquid phase through fuel delivery assembly 202.

[0042] Fuel system 200 also includes a fuel metering unit in fluid communication with fuel delivery assembly 202. In this embodiment, the fuel metering unit is metering valve 240 positioned downstream of vaporizer 220 and high pressure pump 230. Fuel system 200 is configured to provide metering valve 240, and metering valve 240 is configured to receive hydrogen fuel in a substantially entirely gas phase or a substantially entirely supercritical phase. Metering valve 240 is further configured to provide a flow of fuel to engine 100 in a desired manner. More particularly, as Figure 3 schematically depicted in FIG. 1, metering valve 240 is configured to provide a desired volume of hydrogen fuel to fuel manifold 172 of engine 100 at a desired flow rate, for example. Fuel manifold 172 then distributes the received hydrogen fuel to a plurality of fuel injectors 174 within combustion section 114 of engine 100, the hydrogen fuel mixes with compressed air at combustion section 114 of engine 100, and the mixture of hydrogen fuel and compressed air combusts to produce combustion gases that drive engine 100. Adjusting metering valve 240 changes the volume of fuel provided to combustion section 114 of engine 100, and thus the amount of propulsive thrust produced by engine 100 to propel aircraft 10.

[0043] The hydrogen fuel used in engine 100 and in fuel system 200 can be substantially pure hydrogen molecules (diatomic hydrogen). Hydrogen can be difficult to contain, especially in gaseous form, as diatomic hydrogen is the smallest molecule known to exist. Hydrogen also tends to seep into attachment points between materials and components when in gaseous form, without leaving a residue. Hydrogen is prone to leaking through conventional seals and other small orifices, such as cracks that can form in fuel system 200 over time. However, hydrogen burns with a nearly colorless flame that is invisible in sunlight and is an odorless and colorless gas. Thus, leaks can be difficult to detect.

[0044] A safety tag is added to the hydrogen fuel in fuel system 200. The added safety tag facilitates detection of leaks and helps prevent injury or other adverse events. Preferably, the added safety tag enables a user, such as a maintenance worker or other ground personnel around aircraft 10, to detect a hydrogen fuel leak and take appropriate action. Thus, a suitable safety tag enables the hydrogen fuel to be readily detected by human senses, such as olfactory or visual senses.

[0045] One such safety tag is a scent agent. Suitable scent agents include, for example, mercaptans or sulfides, such as hydrogen sulfide, benzyl mercaptide, dimethyl sulfide, diphenyl sulfide, and the like. Such scent agents can be suitable for this application because, if desired, these scent agents can be combusted with the hydrogen as fuel, and they produce a perceptible scent that can be readily detected by the human nose. Preferably, the scent agent is present in the fuel at 1 x 10 -9 mol / mol and 1 x 10-2 a molar fraction between 1 x 10

[0046] Another suitable safety marker is a molecule, compound, or element that can be added to the hydrogen fuel such that when the hydrogen fuel is combusted, the flame of the combusted hydrogen is visible to the naked eye, especially under sunlight. Preferably, the flame will emit light having a wavelength in the visible spectrum that provides a color to the flame. Such a safety marker can be referred to herein as a visual safety marker. Suitable visual safety markers are noble gases, such as helium, neon, argon, krypton, xenon, and radon. The addition of a noble gas to the hydrogen fuel will color the flame of the combusted hydrogen, making it visible to the naked eye under normal conditions, such as sunlight or other typical lighting conditions. Visibility to humans allows humans to avoid the flame or take other appropriate action. When a noble gas, especially helium, neon, argon, and xenon, is included in a flammable mixture, such as the hydrogen fuel discussed herein, a colored flame results even though the noble gas itself does not burn. The molecules of the noble gas are excited by the heat of the flame and emit a visible colored light that can be detected by the naked eye. Preferably, the noble gas is added to the hydrogen fuel in a molar fraction between 1 x 10 -10 and 1 x 10 - 2 a molar fraction between 1 x 10

[0047] As discussed above, preferably the hydrogen fuel is stored in the fuel tank 210 in a liquid phase. Helium is a safety marker that can be added to the hydrogen fuel while the hydrogen fuel is in a liquid phase, and the helium can remain suspended in the hydrogen fuel while the hydrogen fuel is a liquid. Thus, preferred embodiments include a fuel comprising hydrogen and helium. Other preferred embodiments include a fuel consisting essentially of hydrogen and helium, and a fuel consisting of hydrogen and helium. The hydrogen in the fuel, especially the hydrogen in liquid form, is diatomic hydrogen molecules. Preferably, these hydrogen fuels can be liquids that are stored in the fuel tank 210 and used in the fuel system 200 discussed herein.

[0048] Although the safety markers discussed herein can not be suitable for being added to and mixed with the hydrogen fuel while the hydrogen fuel is in a liquid phase, except for helium, these other safety markers can still be used with the fuel system 200 discussed herein.

[0049] Figure 6 is a flowchart showing a method of adding a safety marker to hydrogen fuel in a fuel delivery system. As Figure 3As shown, fuel system 200 can further include a safety marker introduction system 310, and the method of adding a safety marker to the hydrogen fuel will be described with reference to safety marker introduction system 310. However, it should be understood that the method of adding a safety marker to the hydrogen fuel is not limited to the particular components of safety marker introduction system 310, and the method can be implemented with other suitable components and configurations.

[0050] As discussed above, the liquid hydrogen fuel is stored in fuel tank 210 (step S405) and then flows into fuel delivery assembly 202. In step S410, the hydrogen fuel is then heated from a liquid to a gas by vaporizer 220 in the present embodiment. In this embodiment, vaporizer 220 heats the liquid fuel from a substantially entirely liquid phase to a substantially entirely gaseous phase or a substantially entirely supercritical phase. Once the fuel is heated to at least a partial gaseous phase, the safety marker discussed above can be added to the hydrogen fuel.

[0051] In step S415, at least one safety marker, such as an odorant or a visual safety marker, is added to the hydrogen fuel using safety marker introduction system 310 (see, e.g., Figure 3 ) in the present embodiment. Safety marker introduction system 310 includes a safety marker storage tank 312 that stores the at least one safety marker. The safety marker discussed herein can be stored in a gaseous form in safety marker storage tank 312. The safety marker flows from safety marker storage tank 312 into a safety marker delivery assembly 314. Safety marker delivery assembly 314 includes tubes, pipes, and the like to fluidly connect the various components of safety marker introduction system 310 to fuel system 200. The safety marker is introduced from safety marker delivery assembly 314 at a rate suitable to achieve the desired concentration discussed above. In the present embodiment, a nozzle 316 is used to inject the safety marker into the gaseous hydrogen fuel at the desired rate. For example, other suitable methods and devices, such as an entrainment method using an eductor, can also be used to introduce the safety marker into the hydrogen fuel. Safety marker introduction system 310 can also include a pump 318 to increase the pressure of the safety marker in safety marker delivery assembly 314 to a pressure greater than the pressure of fuel system 200 at the point of introduction so that the safety marker flows into fuel system 200.

[0052] To detect leaks and maximize the safety of fuel system 200, the safety marker is preferably introduced immediately after or even as the liquid hydrogen fuel is being heated to a gas. In the present embodiment, nozzle 316 is located in vaporizer 220 and the safety marker is supplied to vaporizer 220 in fuel system 200. In other embodiments, the safety marker can be added downstream of vaporizer 220, such as by being supplied to fuel delivery assembly 202, as Figure 7 shown. Figure 7 is a schematic view of fuel system 200, similar toFigure 3 As shown, but with an alternative security mark introduction point. Figure 7 In this configuration, nozzle 316 is a component directly following carburetor 220. Preferably, nozzle 316 will be located in a portion of fuel delivery assembly 202 near or even adjacent to carburetor 220. However, a safety mark can be added to the hydrogen fuel in fuel system 200 at any point where the fuel is gaseous. In another embodiment, for example, a safety mark can be added to the fuel tank. As discussed above, the remaining volume of fuel tank 210 not filled with liquid hydrogen fuel can be gaseous hydrogen. A safety mark can be added to this gaseous hydrogen.

[0053] Figure 3 and 7 The safety marking system 310 shown is at least partially located within the fuselage 12 or wing 14, such as at least partially within the wing 14. However, the safety marking system 310 may be located in other suitable locations, such as outside the fuselage 12 and wing 14, and at least partially located within the pylon 18, such as... Figure 4 As shown, or at least partially located within engine 100, such as Figure 5 As shown. For example, when located in engine 100, the safety marker introduction system 310 can be located in engine compartment 134. Furthermore, Figure 3 The image shows a safety tag introduction system 310. This safety tag introduction system 310 can be used to add a mixture of safety tags, such as both an odorant and a visual safety tag, or it can be used to add a single safety tag. Multiple safety tag introduction systems 310 can also be used, for example, one for an odorant and another for a visual safety tag. In a preferred embodiment, the visual safety tag can be helium and is added to the liquid hydrogen fuel stored in the fuel tank 210. In this way, a single safety tag introduction system 310 is used to add the odorant.

[0054] like Figure 6 As shown, after adding a safety marker in step S415, hydrogen fuel is delivered to the generator in step S420. In this embodiment, the generator is engine 100. Delivering hydrogen fuel to engine 100 in step S420 may include increasing the pressure of the hydrogen fuel using a high-pressure pump 230 (step S423), metering the hydrogen fuel using a metering valve 240 (step S425), dispensing the hydrogen fuel into the fuel manifold 172 (step S427), and injecting the hydrogen fuel into the combustion zone 114 using a fuel nozzle 174 (step S429). After the fuel has been injected into the combustion zone 114, the hydrogen is burned in step S430, as discussed above.

[0055] Additives, such as safety markers, added to the hydrogen fuel can separate from the hydrogen gas. If the safety markers separate from the gaseous or supercritical hydrogen fuel in the fuel system 200, the safety markers can not have the desired effect of alerting personnel to a leak because the hydrogen fuel can escape without the safety markers. It is therefore preferred to include a plurality of turbulators 206 in the fuel delivery assembly 202 to create turbulence in the gaseous or supercritical hydrogen fuel stream. The turbulence promotes mixing of the hydrogen fuel with the safety markers to maintain the safety markers entrained in the hydrogen fuel. Delivering the hydrogen fuel to the engine 100 (step S420) can also include the step of adding turbulence to the hydrogen fuel (step S421).

[0056] Various suitable turbulators 206 can be used, including, for example, zigzag metal strips or helical (twisted) metal strips placed in the flow path of the hydrogen fuel (e.g., the fuel delivery assembly 202) to create turbulence in the hydrogen fuel stream. In other cases, however, other components of the fuel system 200 can act as turbulators 206. For example, the fuel system 200 can include various other components in the fuel delivery assembly 202 between the vaporizer 220 and the engine 100, such as the valve 204, and such components can generate turbulence in the hydrogen fuel stream and act as turbulators 206.

[0057] The safety markers can be combusted with the hydrogen fuel in the engine 100. However, some of the safety markers discussed above, such as inert gases, can be expensive, and therefore, rather than allowing the safety markers to remain in the hydrogen fuel through combustion, the safety markers can be removed from the hydrogen fuel prior to combustion. Furthermore, some of the safety markers discussed herein, such as odorants, can clog the fuel nozzles 174 and cause corrosion of turbine components, and therefore, it is preferred to remove the safety markers prior to the fuel nozzles 174. Figure 8 is a schematic diagram of the fuel system 200 including a safety marker separation and recovery system 320, and Figure 9 is a flowchart showing a method of removing safety markers from hydrogen fuel. Steps S405 through S420 can be the same when used with the method shown in Figure 6 Steps S405 through S420 can be the same when used with the method shown in

[0058] In step S440, the safety markers are separated from the hydrogen fuel. The safety marker separation and recovery system 320 includes a separator 322 in fluid communication with the fuel delivery assembly 202 to separate the safety markers from the hydrogen fuel. As discussed above, for as many of the fuel delivery assembly 202 as possible, the safety markers are preferably retained in the hydrogen fuel. As Figure 8As shown, in the fuel delivery assembly 202, the separator 322 is positioned in the flow path of the hydrogen fuel between the metering valve 240 and the fuel nozzle 174, and more specifically, in the flow path of the hydrogen fuel between the metering valve 240 and the fuel manifold 172. The separator 322 can be positioned at other suitable locations in the flow path of the hydrogen fuel. For example, the separator 322 can be positioned upstream of the metering valve 240, and preferably, directly before the metering valve 240 in the flow path of the hydrogen fuel in the fuel delivery assembly 202, as Figure 10 shown. Such a location can be advantageous to avoid problems with metering the hydrogen fuel and dispensing the hydrogen fuel to the fuel nozzle 174. Suitable separators 322 include, for example, a cyclone separator or a filtration system. An example of a suitable cyclone separator is the separation device disclosed in U.S. Patent No. 8,858,679, the entire disclosure of which is incorporated herein by reference. The filtration system can include at least one filter or membrane that allows the hydrogen fuel (diatomic hydrogen molecules) to pass through the filter or membrane, but prevents the safety tag from passing through. In some embodiments, multiple separators can be used, including, for example, both a cyclone separator and a filtration system.

[0059] After being separated in step S440, the safety tag is stored (step S450) in a recovered safety tag storage tank 324. The recovered safety tag storage tank 324 is fluidly coupled to the separator 322 by a recovered safety tag line 326. The recovered safety tag line 326 can be a suitable fluid connection, such as a tube, pipe, or the like. To reduce the size of the recovered safety tag storage tank 324, the safety tag separation and recovery system 320 can include a compressor 328 to compress the safety tag in the recovered safety tag storage tank 324, and the method Figure 9 shown) further includes a step of compressing the separated safety tag (step S445).

[0060] The safety tag stored in the recovered safety tag storage tank 324 can be subsequently recovered for reuse. In Figure 8 embodiments, the recovered safety tag storage tank 324 is shown in the engine 100. However, the recovered safety tag storage tank 324, as well as other components of the safety tag separation and recovery system 320, such as the compressor 328, can be at least partially positioned within the pylon 18, the wing 14, or the fuselage 12. In Figure 8 embodiments, the safety tag separation and recovery system 320 is configured such that the safety tag is removed from the recovered safety tag storage tank 324 and the aircraft 10 before the safety tag is reused. However, embodiments are not limited thereto. For example, as Figure 11As shown, the recovered security tag storage tank 324 can be fluidly coupled to the security tag introduction system 310 by, for example, a transfer line 332, and the security tags can be recovered and subsequently reused during operation of the aircraft 10. The transfer line 332 can be any suitable fluid connection, such as a pipe, tube, etc. The transfer line 332 is part of a security tag transfer system 330. For example, the security tag transfer system 330 can have other components for effecting the transfer of recovered security tags from the recovered security tag storage tank 324 to the security tag storage tank 312, such as a transfer pump 334 and a transfer valve 336. The transfer valve 336 can be opened and the transfer pump 334 operated to transfer the security tags from the recovered security tag storage tank 324 to the security tag storage tank 312 through the transfer line 332. Alternatively, the recovered security tag storage tank 324 can be omitted, and the recovered security tags can be returned to the security tag storage tank 312 after they are separated by the separator 322, as Figure 12 shown. Additionally, the separated security tags can be discharged to the environment, rather than being stored in the security tag storage tank 324 or otherwise reused.

[0061] The embodiments discussed above describe the use of security tags in a system in which hydrogen fuel is stored as a liquid in the fuel tank 210. However, the use of security tags discussed herein is not limited thereto, and they can be used with fuel systems 200 in which hydrogen fuel is stored in a gaseous phase. In such a system, the security tags can be added to the fuel prior to the fuel tank 210 being filled for storage in the fuel tank 210. In such a system, the vaporizer 220 and the security tag introduction system 310 can be omitted. Also as discussed above, the power generator is not limited to a gas turbine engine 100. Instead, the power generator can be a fuel cell in which hydrogen is provided to the fuel cell to generate electricity by reacting with air.

[0062] Other aspects of the disclosure are provided by the subject matter of the following clauses.

[0063] A fuel, the fuel comprising hydrogen and a visual security tag, the visual security tag being an inert gas.

[0064] The fuel of any of the preceding clauses, wherein the visual security tag has a mole fraction in the fuel of between 1 x 10 -10 mol / mol and 1 x 10 -2 mol / mol.

[0065] The fuel of any of the preceding clauses, wherein the hydrogen is a liquid and the visual security tag is helium.

[0066] The fuel of any of the preceding clauses, wherein the hydrogen produces a flame when the fuel is combusted, and the molecules of the noble gas are excited by heat of the flame to produce visible light.

[0067] The fuel of any of the preceding clauses, wherein the hydrogen produces a flame when the fuel is combusted, and the visual security marking is capable of coloring the flame of the fuel to be visible in sunlight.

[0068] The fuel of any of the preceding clauses, further comprising an odorant.

[0069] The fuel of any of the preceding clauses, wherein the odorant is one of a mercaptan or a sulfide.

[0070] An aircraft comprising a gas turbine engine, wherein a gas combusted by the engine comprises the fuel of any of the preceding clauses.

[0071] A fuel system for a vehicle having an electric generator, the fuel system comprising: a fuel tank for storing a hydrogen fuel in a liquid phase; a fuel delivery assembly extending from the fuel tank to an electric generator, the fuel delivery assembly being configured to provide the hydrogen fuel from the fuel tank to the electric generator; a vaporizer in communication with the fuel delivery assembly for heating the hydrogen fuel in the liquid phase to at least one of a gaseous phase and a supercritical phase, the vaporizer being located between the fuel tank and the electric generator; a security marking tank for storing a security marking; and a security marking delivery assembly extending from the security marking tank to the fuel delivery assembly, the security marking delivery assembly (i) connecting to the fuel delivery assembly at a security marking introduction location, and (ii) being configured to add a security marking to the hydrogen fuel when the hydrogen fuel is in the at least one of the gaseous phase and the supercritical phase, the security marking introduction location being the vaporizer or a location upstream of the vaporizer.

[0072] The fuel system of any of the preceding clauses, wherein the hydrogen fuel produces a flame when the fuel is combusted, and wherein the security marking is a visual security marking capable of making the flame of the hydrogen fuel visible in sunlight when the hydrogen fuel is combusted.

[0073] The fuel system of any of the preceding clauses, wherein the visual security marking is a noble gas.

[0074] The fuel system of any of the preceding clauses, wherein the visual security marking is added to have a concentration of 1 x 10 -10mol / mol and 1 x 10 -2 between 1 x 10

[0075] The fuel system of any of the preceding clauses, wherein the safety marker is a scent.

[0076] The fuel system of any of the preceding clauses, wherein the scent is one of a mercaptan or a sulfide.

[0077] The fuel system of any of the preceding clauses, wherein the fuel delivery assembly includes a turbulator downstream of the safety marker introduction location at which the safety marker delivery assembly is connected to the fuel delivery assembly, the turbulator configured to generate turbulence in the hydrogen fuel as the hydrogen fuel is delivered from the fuel tank to the power generator.

[0078] An aircraft comprising the fuel system of any of the preceding clauses, wherein the power generator is a gas turbine engine.

[0079] The aircraft of any of the preceding clauses, further comprising a fuselage and a wing connected to the fuselage, wherein the fuel tank is at least partially positioned within at least one of the fuselage and the wing.

[0080] The aircraft of any of the preceding clauses, wherein the vaporizer is at least partially positioned within at least one of the fuselage and the wing.

[0081] The aircraft of any of the preceding clauses, wherein the safety marker delivery assembly is at least partially positioned within at least one of the fuselage and the wing.

[0082] The aircraft of any of the preceding clauses, wherein the vaporizer is at least partially positioned within the gas turbine engine.

[0083] The aircraft of any of the preceding clauses, wherein the safety marker delivery assembly is at least partially positioned within the gas turbine engine.

[0084] The aircraft of any of the preceding clauses, further comprising a pylon connecting the gas turbine engine to the wing, wherein the vaporizer is at least partially positioned within the pylon.

[0085] The aircraft of any of the preceding clauses, further comprising a pylon connecting the gas turbine engine to the wing, wherein the safety marker delivery assembly is at least partially positioned within the pylon.

[0086] A method of adding a safety marker to hydrogen fuel in a fuel delivery system, the method comprising: storing hydrogen fuel in a tank in a liquid phase; heating the hydrogen fuel in the liquid phase to at least one of a gaseous phase and a supercritical phase; delivering the hydrogen fuel in the at least one of the gaseous phase and the supercritical phase to a power generator; and adding a safety marker to the hydrogen fuel when the hydrogen fuel is in the at least one of the gaseous phase and the supercritical phase after heating the hydrogen fuel.

[0087] The method of any of the preceding clauses, wherein the safety marker is a visual safety marker that enables the flame of the hydrogen fuel to be visible in sunlight when the hydrogen fuel is combusted.

[0088] The method of any of the preceding clauses, wherein the visual safety marker is an inert gas.

[0089] The method of any of the preceding clauses, wherein the visual safety marker is added to have a mole fraction between 1 x 10 -10 mol / mol and 1 x 10 -2 mol / mol.

[0090] The method of any of the preceding clauses, wherein the safety marker is an odorant.

[0091] The method of any of the preceding clauses, wherein the odorant is one of a mercaptan or a sulfide.

[0092] The method of any of the preceding clauses, further comprising adding a turbulent flow to the hydrogen fuel as the hydrogen fuel is delivered.

[0093] A fuel, the fuel comprising hydrogen and a safety marker.

[0094] The fuel of any of the preceding clauses, wherein the hydrogen is diatomic hydrogen.

[0095] The fuel of any of the preceding clauses, wherein the safety marker is at least one of a visual safety marker and an odorant.

[0096] The fuel of any of the preceding clauses, wherein the safety marker is both a visual safety marker and an odorant.

[0097] The fuel of any of the preceding clauses, wherein the visual safety marker is an inert gas.

[0098] The fuel of any of the preceding clauses, wherein the visual safety marker is at least one of helium, neon, argon, krypton, xenon, radon.

[0099] The fuel according to any of the preceding clauses, wherein the odorant is at least one of a mercaptan, hydrogen sulfide, benzyl sulfide, dimethyl sulfide, and diphenyl sulfide.

[0100] The fuel according to any of the preceding clauses, wherein the safety marker is at least one of helium, neon, argon, krypton, xenon, radon, a mercaptan, hydrogen sulfide, benzyl sulfide, dimethyl sulfide, and diphenyl sulfide.

[0101] While the foregoing description has been directed to preferred embodiments, it is noted that other variations and modifications will be apparent to those skilled in the art and can be made without departing from the spirit or scope of the disclosure. Furthermore, features described with respect to one embodiment can be used in conjunction with other embodiments, even if not explicitly stated above.

Claims

1. A fuel, characterized by, The fuel includes hydrogen and a visual security marker, the visual security marker being a noble gas and having a mole fraction in the fuel between 1 x 10 -10 mol / mol and 1 x 10 -2 mol / mol.

2. The fuel of claim 1, wherein wherein the hydrogen is a liquid and the visual security marking is helium.

3. The fuel of claim 1, wherein wherein when the fuel burns, the hydrogen produces a flame and the molecules of the inert gas are excited by the heat of the flame to produce visible light.

4. The fuel of claim 1, wherein wherein when the fuel burns, the hydrogen produces a flame and the visual security marking is capable of coloring the flame of the fuel to be visible in sunlight.

5. The fuel of claim 1 wherein, further comprising an odorant.

6. The fuel of claim 5, wherein, wherein the odorant is one of a mercaptan or a sulfide.

7. An aircraft comprising a gas turbine engine, characterised in that, wherein the gas combusted by the engine comprises the fuel of claim 1.

8. A fuel system for a vehicle having an electric generator, characterized by, The fuel system comprises: a fuel tank for storing a hydrogen fuel in a liquid phase; a fuel delivery assembly extending from the fuel tank to a power generator, the fuel delivery assembly configured to provide the hydrogen fuel from the fuel tank to the power generator; a vaporizer in communication with the fuel delivery assembly for heating the hydrogen fuel in the liquid phase to at least one of a gaseous phase and a supercritical phase, the vaporizer located between the fuel tank and the power generator; a visual security marking tank for storing a visual security marking, the visual security marking being an inert gas; and a visual security marker delivery assembly extending from the visual security marker tank to the fuel delivery assembly, the visual security marker delivery assembly (i) connected to the fuel delivery assembly at a visual security marker introduction location, and (ii) configured to add a visual security marker to the hydrogen fuel at a mole fraction between 1 x 10 -10 mol / mol and 1 x 10 -2 mol / mol in the fuel when the hydrogen fuel is in the at least one of the gaseous phase and the supercritical phase, the visual security marker introduction location being a location at or upstream of the vaporizer.

9. The fuel system of claim 8, wherein, wherein when the fuel burns, the hydrogen fuel produces a flame, and wherein when the hydrogen fuel burns, the visual security marking is capable of making the flame of the hydrogen fuel visible in sunlight.

10. The fuel system of claim 8, wherein, wherein the fuel delivery assembly comprises a turbulator downstream of the visual security marking introduction location at which the visual security marking delivery assembly is connected to the fuel delivery assembly, the turbulator configured to generate turbulence in the hydrogen fuel as the hydrogen fuel is delivered from the fuel tank to the power generator.

11. An aircraft comprising a fuel system according to claim 8, characterized in that, wherein the power generator is a gas turbine engine.

12. The aircraft of claim 11, wherein, further comprising a fuselage and a wing connected to the fuselage, wherein the fuel tank is at least partially positioned within at least one of the fuselage and the wing.

13. The aircraft of claim 12, wherein, wherein the vaporizer is at least partially positioned within at least one of the fuselage, the wing, and the gas turbine engine.

14. The aircraft of claim 12, wherein, wherein the visual security marking delivery assembly is at least partially positioned within at least one of the fuselage, the wing, and the gas turbine engine.

15. The aircraft of claim 12, wherein, further comprising a pylon connecting the gas turbine engine to the wing, wherein the vaporizer is at least partially positioned within the pylon.

16. The aircraft of claim 12, wherein, further comprising a pylon connecting the gas turbine engine to the wing, wherein the visual security marking delivery assembly is at least partially positioned within the pylon.

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