Double-wall pipe for aircraft fuel system

Abstract

To provide a double-wall pipe or an aircraft fuel system comprising the double-wall pipe improved in the safety and reduced in the cost, weight and complexity.SOLUTION: A double-wall pipe for an aircraft fuel system is disclosed. The double-wall pipe includes an inner wall. The inner wall defines a first open end, a second open end, and an inner region connecting the first open end to the second open end. Via the inner region, a fuel is flowable through the double-wall pipe during use. The double-wall pipe also includes an outer wall disposed at least in part around the inner wall to define a space, between the inner wall and the outer wall, that is fluidically isolated from the inner region. The double-wall pipe includes at least one barrier that is openable to create a passage that fluidically connects the space to the inner region. The at least one barrier is configured to open when a pressure in the space is higher than a pressure in the inner region.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a double-walled pipe for an aircraft fuel system, to an aircraft fuel system comprising such a double-walled pipe, and to an aircraft comprising such an aircraft fuel system. [Background technology]

[0002] An aircraft fuel system typically includes a fuel source, such as a fuel tank, and one or more supply lines for supplying fuel from the fuel source to one or more engines of the aircraft. The fuel lines may be configured to transport fuel to different locations within the aircraft. For example, the fuel source may be in the aft portion of the aircraft's fuselage, while the engines may be located on the aircraft's wings.

[0003] Some aircraft fuel systems are configured to utilize liquid hydrogen fuel, which may be stored in and transported through the aircraft fuel system under cryogenic conditions and / or under high pressure. Liquid hydrogen fuel may also be stored in and transported through the fuel system at or near a saturated condition, such as at temperatures and pressures near the respective saturation temperatures and saturation pressures associated with the liquid hydrogen fuel. Summary of the Invention [Means for solving the problem]

[0004] A first aspect of the present invention provides a double-walled pipe for an aircraft fuel system comprising: an inner wall defining a first open end, a second open end, and an interior region connecting the first open end to the second open end, through which fuel may flow in use through the double-walled pipe; an outer wall disposed around at least a portion of the inner wall, the outer wall disposed to define an interspace between the inner wall and the outer wall that is fluidly isolated from the interior region; and at least one barrier openable to form a passageway fluidly connecting the space to the interior region; the at least one barrier configured to open when pressure in the space is higher than pressure in the interior region.

[0005] By providing at least one barrier (sometimes referred to herein as an "openable barrier") between the space and the interior region, the pressure difference between the space and the interior region can be reduced by opening the at least one barrier, thereby reducing the likelihood that such pressure difference will compromise the integrity of the interior and / or exterior walls. In other words, the at least one openable barrier can provide a fail-safe in the event of an abnormal increase in pressure within the space.

[0006] The barrier may be configured to remain closed when the pressure in the space is less than the pressure in the internal region. In particular, the barrier may be configured to open only in one direction, i.e. to allow fuel to flow through the passage only in one direction, from the space to the internal region. This may be due to a component that is only openable or rupturable when the pressure on the side of the at least one barrier component in fluid communication with the space is greater than the pressure on the side of said component in fluid communication with the internal region. For example, the barrier may comprise a check valve that opens only in one direction and / or a rupture disk that is preferentially rupturable only in one direction. By providing such a barrier that is openable in one direction, a higher pressure can be maintained in the internal region than in the space during normal operation.

[0007] Providing a barrier configured to open when the pressure in the space is greater than the pressure in the interior region can be particularly advantageous for use in aircraft hydrogen fuel systems. Liquid hydrogen fuel may need to be maintained under cryogenic conditions to remain in the liquid phase. Exposure to higher temperatures may cause the liquid hydrogen fuel to transition to a gas phase and expand. This may cause the pressure of the hydrogen fuel to increase.

[0008] For example, this may occur in the case of a break in the inner wall that allows fuel to pass from the interior region to the space. In such a case, hydrogen fuel leaking into the space may come into contact with the outer wall, which may be less insulated from the atmosphere surrounding the outer wall than the inner wall (e.g., if no additional vacuum is created around the outer wall or if the outer surface of the outer wall is in contact with the ambient air). The ambient air is likely to be at a higher temperature than the hydrogen fuel in the double-walled tube that is maintained at or near saturated conditions (e.g., under cryogenic conditions). Thus, contact of the hydrogen fuel with the outer wall may cause an increase in the temperature of the hydrogen fuel in the space, which may vaporize some or all of the hydrogen fuel in the space. This may increase the pressure in the space, especially if the break is small enough to restrict the flow of hydrogen gas from the space back to the interior region. Thus, the at least one barrier may open to better distribute the pressure in the double-walled tube in the event of an increase in pressure in the space, such as due to evaporation of liquid hydrogen in the space. In this manner, the outer wall may be provided without any vents to release pressure within the space to the atmosphere outside the double-walled tube, and this may avoid the need for a system to vent vapors away from the atmosphere surrounding the outer wall, such as to an exhaust outside the fuel system and / or aircraft. These factors may reduce the weight, cost, and / or complexity of a fuel system that includes a double-walled tube.

[0009] The barrier can be opened to provide a passageway through the inner wall to provide a compact arrangement within the double walled tube.

[0010] Optionally, the barriers are configured to open when the pressure in the space is higher than the pressure in the interior region by an amount greater than a threshold pressure difference. This may allow the at least one barrier to passively open when the pressure difference between the space and the interior region increases. This may provide a simple and self-contained configuration that does not require any external input, such as from a control circuit, for operation. This may reduce the possibility of failure modes of the at least one barrier and / or reduce the cost, weight, and / or complexity of the double-walled tube.

[0011] Optionally, the barrier is configured to remain closed when pressure in the interior region is greater than pressure in the space by an amount equal to or greater than a threshold pressure difference.

[0012] For example, the interior region may carry a fuel, such as pressurized hydrogen fuel, in an aircraft fuel system. A vacuum (or a pressure lower than the pressure in the interior region) may be maintained in the space to insulate the fuel in the interior region from the atmosphere surrounding the outer wall, which in use may be at a higher temperature than the fuel passing through the double-walled tube. In such a case, the barrier may not open if an increase in pressure difference between the interior region and the space would, for example, increase the pressure in the interior region but not in the space. This may allow the vacuum in the space to be maintained.

[0013] Thus, the barrier can only open or rupture in the event of a pressure increase in the space relative to the interior region, which causes a pressure difference between the space and the interior region to exceed a threshold pressure difference, which may occur by a break or rupture of the inner wall, as described above, causing fuel to enter the space.

[0014] Thus, the at least one barrier is openable to allow fuel in the space to pass back to the interior region, reducing the pressure in the space. This can reduce the pressure acting on the exterior wall and reduce the possibility of compromising the integrity of the exterior wall. Such a configuration can allow the pressure in the space to be reduced without the need for a vent system to vent the fuel in the space to the outside of the double-walled tube and / or to the atmosphere outside the fuel system and / or aircraft, as described above. This can improve the safety of the double-walled tube and / or fuel system comprising the double-walled tube. This can also reduce the cost, weight, and / or complexity of such a fuel system comprising the double-walled tube.

[0015] Optionally, the threshold pressure difference is less than a burst pressure difference between the space and an exterior region surrounding the exterior wall. Optionally, the burst pressure difference is a pressure difference between the space and the exterior region that causes or increases the risk of a partial total loss of integrity of the exterior wall. For example, the burst pressure difference may be a pressure difference that may increase the risk of rupture of the exterior wall, such as a rated pressure difference between the space and the exterior region.

[0016] By ensuring that the threshold pressure difference is less than the breakdown pressure difference, the at least one barrier can reduce the pressure in the space before it becomes large enough to cause damage to the outer wall. This can help to prevent fuel from leaking through the outer wall to the outside area. The safety of the double-walled tube can be improved, especially when the fuel is liquid hydrogen.

[0017] Optionally, the at least one barrier comprises a rupturable barrier. In other words, the at least one barrier may not be resealable once opened. Such a rupturable barrier may have no moving parts or may have fewer moving parts than, for example, an openable and closable valve. Fewer moving parts may reduce the possibility of gas leakage through the at least one barrier and / or improve the reliability and / or lifespan of the at least one barrier. This may be particularly advantageous for use in aircraft hydrogen fuel systems, since hydrogen particles are smaller than conventional (e.g., kerosene) fuel particles and may leak through smaller gaps and spaces than conventional fuel particles. Furthermore, providing a rupturable barrier with fewer or no moving parts may also reduce the cost, weight, and / or complexity of the double-walled tube and / or the fuel system comprising the double-walled tube.

[0018] Optionally, at least one barrier comprises a rupture disk. When the rupture disk is provided, it comprises a rupturable barrier. For example, when the rupturable barrier is provided, it may comprise a membrane that breaks at a predetermined pressure difference across the membrane, such as a threshold pressure difference. In this case, it is understood that the membrane can withstand the pressure difference between the space and the interior region, which causes a first force to act on the membrane in a first direction, i.e., from the interior region toward the space, but can rupture when the pressure difference between the space and the interior region causes a second force to act on the membrane in a second direction, i.e., from the space toward the interior region.

[0019] Rupture disks can provide almost instantaneous response to the rapid increase in pressure difference between space and internal region, and can improve the robustness of double-walled pipes against damage associated with the inner wall that separates space and external region. Rupture disks can have fewer moving parts, reduced size, cost, and / or weight, improved ease of maintenance, improved response time, and / or improved airtightness compared to other barriers such as electronic valves or check valves. Thus, rupture disks can provide an efficient and reliable solution for mitigating the adverse effects of pressure difference between space and internal region.

[0020] Optionally, a vacuum or partial vacuum exists within the space. As mentioned above, this may improve insulation of fuel, which may be cryogenic liquid hydrogen, flowing through the interior region in use. A barrier that is only openable in one direction may allow such a vacuum to be maintained within the space even when high pressure fuel passes through the interior region.

[0021] Optionally, the at least one barrier comprises a plurality of barriers, each of the plurality of barriers being openable to form a respective passageway fluidly connecting the space to the interior region. For example, a double-walled tube may comprise a pair of barriers, each of which is openable to form a respective passageway (e.g., a respective passageway through an inner wall) between the space and the interior region. This may provide improved redundancy, for example, in the event of failure of one of the pair of barriers.

[0022] Optionally, the pair of barriers, if provided, are disposed on opposite sides of the interior region. Alternatively, the pair of barriers may be disposed axially adjacent to one another relative to the interior wall.

[0023] Optionally, the space is a first space and the outer wall defines a second space between the inner wall and the outer wall, the second space being fluidly isolated from the interior region and the first space.

[0024] The second space may be axially adjacent to the first space. In such a case, the double-walled tube may include a seal, such as an annular seal, separating the first and second spaces. Alternatively, the second space may be circumferentially adjacent to the first space. The first and second spaces may be diametrically opposed. When the first and second spaces are circumferentially adjacent and / or diametrically opposed, the seal, if provided, may include one or more axial seals separating the first and second spaces.

[0025] By isolating the first and second spaces from each other, in the event of a breach causing a change in pressure in one of the first and second spaces, pressure may be maintained in the other of the first and second spaces, thereby limiting the propagation of a breach associated with either the first or second space to other parts of the double-walled tube, such as the other of the first and second spaces, or to other parts of a system comprising the double-walled tube.

[0026] It will be appreciated that the second space may benefit from any of the features and / or advantages associated with the first space discussed above.

[0027] Optionally, the at least one barrier comprises at least one first space barrier, the passageway comprises a first space passageway fluidly connecting the first space to the interior region, and the double-walled tube comprises at least one second space barrier openable to form a second space passageway fluidly connecting the second space to the interior region.

[0028] The barrier of the first space and the barrier of the second space may be fluidly connected to each other at their outlets via the interior region, in other words, each of the first space and the second space may be fluidly connectable to the same interior region defined by the inner wall via the respective barrier of the first space and the barrier of the second space.

[0029] In this way, each of the barriers of the first space and the second space can be opened to equalize the pressure between the internal region and the respective first and second spaces and / or to reduce the pressure difference. This may allow a pressure increase in one of the first and second spaces, for example due to a break in a portion of an inner wall separating the internal region from one of the respective first and second spaces, to be reduced without affecting the pressure in the other of the first and second spaces. This may improve the safety and / or reliability of the double-walled tube.

[0030] Optionally, the at least one second space barrier comprises a plurality of second space barriers.

[0031] It will be appreciated that the at least one second space barrier may benefit from any of the features and / or advantages associated with the first space barrier discussed above.

[0032] Optionally, the outer wall defines one or more further spaces between the inner wall and the outer wall, the further spaces being fluidly isolated from the interior region.

[0033] Optionally, the additional spaces are fluidly isolated from each other space defined between the inner and outer walls. For example, the one or more additional spaces may comprise a third space adjacent or spaced apart from the first and / or second spaces and fluidly isolated from the first and second spaces. The third space may be axially or circumferentially adjacent one or both of the first and second spaces.

[0034] It will be appreciated that the further space may benefit from any of the features and / or advantages associated with the first space and / or the second space discussed above.

[0035] The double-walled tube may comprise one or more further space barriers. The further space barriers may be openable to form a respective further space passageway fluidly connecting the respective further space to the interior region. Optionally, the one or more further space barriers comprise one or more sets (e.g. pairs) of further space barriers. Optionally, each barrier in a set of further space barriers is openable to form a respective further space passageway fluidly connecting one of the one or more further spaces to the interior region.

[0036] It will be appreciated that the further barrier may benefit from any of the features and / or advantages associated with the first barrier and / or the second barrier described above.

[0037] A second aspect of the present invention provides an aircraft fuel system comprising a fuel tank for storing fuel for an engine of an aircraft and a double-walled pipe of the first aspect of the present invention fluidly connected or connectable to the fuel tank.

[0038] The double-walled pipe may be configured to allow fuel to pass through the interior region into the fuel tank from a fuel supply system for supplying fuel to the fuel tank. Alternatively or additionally, the double-walled pipe may be configured to allow fuel to pass through the interior region from the fuel tank to one or more components downstream of the fuel tank, such as one or more engines of an aircraft.

[0039] The aircraft fuel system may include a fuel supply unit comprising a fuel tank and one or more fluid movers for moving fluid from the fuel tank towards the one or more engines. The fuel supply unit may include a sealed housing within which the fuel tank and one or more fluid movers are disposed. The sealed housing may fluidly isolate the fuel tank and one or more fluid movers from an atmosphere surrounding the fuel supply unit. The double walled tube may be configured to allow fuel to pass from the fuel supply unit to an interior region towards the one or more engines.

[0040] In this manner, the fuel supply unit may contain any fuel leakage from the tank, fluid mover, and / or other components within the sealed housing of the fuel supply unit. This allows pipes other than double-walled pipes to be used within the fuel supply unit, reducing the cost, weight, and / or complexity of the fuel supply system. The double-walled pipes, as described above, are designed to reduce the risk of fuel leakage even in the event of a break in the inner pipe, which is then connected to pass fuel from the atmosphere surrounding the sealed housing to an unsealed area outside the sealed housing. Alternatively, or in addition, the fuel supply unit may include double-walled pipes, which may further reduce the risk of fluid leakage to the atmosphere surrounding the fuel supply unit.

[0041] It will be appreciated that an aircraft fuel system may include any suitable number of such double-walled pipes for passing fuel between aircraft fuel system components and / or other systems associated with the aircraft.

[0042] Optionally, the aircraft fuel system comprises at least one pressure relief valve configured to fluidly connect the interior region to an atmosphere outside the double-walled tube.

[0043] The at least one pressure relief valve may allow excess pressure generated in the inner tube following rupture of the inner wall and / or opening of the at least one barrier to be relieved and / or vented to the outside atmosphere. This may improve the safety of the double-walled tube. Optionally, the at least one pressure relief valve comprises two or more pressure relief valves. This may provide improved redundancy in case one of the pressure relief valves breaks.

[0044] Optionally, the aircraft fuel system comprises an exhaust located external to the double-walled pipe, and the at least one pressure relief valve is fluidly connected to the exhaust. Optionally, the exhaust is configured to exhaust fuel received from the at least one pressure relief valve to an atmosphere external to the aircraft. In this manner, hydrogen fuel may be safely exhausted from the aircraft and / or components of the fuel system or engines of the aircraft.

[0045] Optionally, the aircraft fuel system comprises liquid hydrogen fuel in a fuel tank. The fuel tank may comprise a sealed pressure vessel configured to store the liquid hydrogen fuel. The aircraft fuel system may comprise insulation surrounding at least a portion of the fuel tank. The insulation may include a vacuum and / or any other suitable insulating material. The aircraft fuel system may comprise a temperature control system for regulating and / or maintaining a temperature of the fuel in the fuel tank. This may allow the liquid hydrogen to be better maintained under cryogenic conditions and may enhance the quality of the fuel in the fuel tank and / or the fuel delivered to the engine.

[0046] A third aspect of the invention provides an aircraft comprising a double-walled pipe of the first aspect of the invention, or an aircraft fuel system of the second aspect of the invention.

[0047] The aircraft may include one or more engines, and the double-walled pipe may be configured to allow fuel to pass through the interior region to the one or more engines. If provided, the aircraft fuel system may be configured to supply fuel to the one or more engines.

[0048] The aircraft may comprise and / or benefit from any of the features and / or advantages associated with the double-walled pipe of the first aspect or the fuel system of the second aspect described above.

[0049] It will be appreciated that features associated with any of the first, second and third aspects may be combined with other features associated with any of the first, second and third aspects, as appropriate to a particular implementation of the invention.

[0050] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0051] [Figure 1] FIG. 1 is a schematic diagram of an example aircraft.

[0052] [Diagram 2] FIG. 2 is a schematic diagram of an example fuel system for the aircraft of FIG.

[0053] [Diagram 3] FIG. 3 is a schematic diagram of an example fuel line of the fuel system of FIG.

[0054] [Figure 4A-4C] 4A to 4C are schematic diagrams of configuration examples of the rupture disk of the fuel line of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] FIG. 1 shows an example of an aircraft 1 comprising a fuel system 2 and an engine 3. The fuel system 2 here is a liquid hydrogen fuel system and is located at least partially towards the aft of the fuselage 4 of the aircraft 1. In particular, the fuel system 2 comprises a fuel tank 5 located at least partially in the tail 6 of the aircraft. The engine 3 is located on a wing 7 of the aircraft 1. The aircraft fuel system 2 comprises a fuel line 10 for transferring fuel from the fuel tank 5 to the engine 3. It will be understood that in other examples the fuel tank 5 and / or the engine 3 may be located in any other suitable location on or in the aircraft. The aircraft 1 may also comprise two or more engines 3 and / or two or more fuel tanks 5. The fuel tank 5 is here a double-walled fuel tank comprising a cavity wall defining a cavity for storing fuel and a shell surrounding the cavity wall so as to define a space between the cavity wall and the shell. This space is provided with a vacuum, which insulates the fuel in the cavity. This configuration reduces the possibility of fuel leaking from the fuel tank, such as by rupturing the cavity walls.

[0056] The aircraft fuel system 2 is shown in more detail in the schematic diagram of FIG. 2. The aircraft fuel system 2 comprises a fuel supply unit 20 comprising a sealed housing 21. In this context, "sealed" means that an interior space 22 defined by the sealed housing is fluidly isolated from the atmosphere surrounding the sealed housing 21. The fuel supply unit 20 comprises a fuel tank 5 to which the sealed housing 21 is attached, and a centrifugal pump 25 within the sealed housing 21. The sealed housing 21 is defined by a single wall to reduce the possibility of fuel leaking from components within the sealed housing 21, such as the centrifugal pump 25, to the atmosphere surrounding the sealed housing 21. Although the sealed housing 21 is shown attached to the fuel tank 5, in other examples, the fuel tank 5 may be surrounded by the sealed housing 21, which may further reduce the possibility of fuel leaking from the fuel tank 5 to the atmosphere surrounding the sealed housing 21. Returning to FIG. 2, the fuel supply system comprises a control system 40 configured to issue pump control signals such that operation of the centrifugal pump 25 moves fuel from the fuel tank 5 towards the engine 3. In other words, the control system 40 is communicatively coupled to the centrifugal pump 25 .

[0057] The fuel tank 5 is fluidly connected to a centrifugal pump 25 by a fuel tank line 23, here a single-walled tube. The pump 25 moves fuel through the fuel line 10 via a first isolator 24. The first isolator 24 is operable by a first isolator control signal received from a control system 40 to selectively allow or prevent the flow of fuel from the centrifugal pump 25 and / or the fuel tank 5 to the fuel line 10. In other words, the control system 40 is communicatively coupled to the first isolator 24.

[0058] The fuel line 10 is described in more detail below with respect to FIG.

[0059] The engine 3 is part of an engine unit 30 of the aircraft 1. The engine unit 30 comprises a nacelle 31 which defines an engine compartment 37. Here, the nacelle 31 provides an enclosed housing which defines the engine compartment 37, but in another example, the engine compartment 37 is partially open to the atmosphere surrounding the nacelle 31. The engine unit 30 comprises an engine 3. The engine 3 comprises an exhaust 36 which is open to the atmosphere surrounding the engine unit 30, so that exhaust gases can pass from the engine 3 to the atmosphere surrounding the engine unit 30, as is known to those skilled in the art, to provide at least part of the motive force for moving the aircraft 1.

[0060] The engine unit 30 comprises an engine line 33 configured to receive fuel from the fuel supply unit 20 via the fuel line 10. The engine unit 30 comprises a second isolator 34 operable by a second isolator control signal received from the control system 40 to selectively allow or prevent the flow of fuel from the engine line 33 to the engine 3. In other words, the control system 40 is communicatively coupled to the second isolator 34. The engine unit 30 also comprises a first pressure relief valve 32a and a second pressure relief valve 32b, each of which fluidly connects the engine line 33 to an exhaust device 35 arranged outside the nacelle 31. In particular, the exhaust device 35 is arranged in a relatively "safe" environment outside the engine unit 30, preferably outside the entire aircraft 1. The first pressure relief valve 32a and the second pressure relief valve 32b are configured to exhaust excess pressure in the fuel system 2, in particular excess pressure in the fuel line 10 and / or the fuel line 33, via the exhaust device 35 to the atmosphere surrounding the nacelle 31.

[0061] In some examples, similar pressure relief valves are provided in the fuel line 10 or the fuel supply unit 20, such as upstream and / or downstream of the centrifugal pump 25 and / or the first isolator 24. Such pressure relief valves may be provided instead of or in addition to the first and second pressure relief valves 32a and 32b.

[0062] 3, the fuel line 10 will now be described in more detail. The fuel line 10 is a double-walled tube with an inner wall 11 defining a first open end 18a, a second open end 18b, and an interior region 14 connecting the first open end 18a to the second open end 18b. Fuel can flow from the fuel supply unit 20 through or through the interior region 14 to the engine unit 30. In particular, in use, fuel is received from the centrifugal pump 25 through the first open end 18a, passes through the interior region 14 in the direction of arrow 50 in FIG. 3, and enters the engine unit 30 through the second open end 18b. In other words, the first open end 18a is fluidly connected to the fuel supply unit 20 to receive fuel stored in the fuel tank 5, and the second open end 18b is fluidly connected to the engine unit 30 to pass fuel from the interior region 14 towards the engine 3.

[0063] The fuel line 10 also includes an outer wall 12 disposed around the inner wall 11 to define a first annular space 13a and a second annular space 13b between the inner wall 11 and the outer wall 12. The first space 13a and the second space 13b are each fluidly isolated from the interior region 14 by the inner wall. The first space 13a and the second space 13b are fluidly isolated from each other by an annular seal 19 disposed between the inner wall 11 and the outer wall 12. A vacuum is maintained in each of the first space 13a and the second space 13b to insulate the liquid hydrogen fuel flowing through the interior region 14, in use, from the external atmosphere surrounding the outer wall. The external atmosphere in this case is ambient air. The ambient air is at a higher temperature than the liquid hydrogen flowing through the interior region 14, while the liquid hydrogen is maintained at or near a saturated state (particularly a cryogenic state).

[0064] The fuel line 10 comprises a first rupture disk 15a and a second rupture disk 15b, which are diametrically opposed to each other, and each of these rupture disks can be opened to form a first passage 16a and a second passage 16b through the inner wall 11, which fluidly connects the first space 13a to the inner region 14. Similarly, the fuel line comprises a third rupture disk 15c and a fourth rupture disk 15d, which are diametrically opposed to each other, and each of these rupture disks can be opened to form a third passage 16c and a fourth passage 16d through the inner wall 11, which fluidly connects the second space 13b to the inner region 14. The first rupture disk 15a, the second rupture disk 15b, the third rupture disk 15c, and the fourth rupture disk 15d comprise a first membrane 17a, a second membrane 17b, a third membrane 17c, and a fourth membrane 17d, respectively. Each membrane 17a, 17b, 17c and 17d is configured to rupture in response to a pressure differential across the respective membrane 17a, 17b, 17c and 17d that exceeds a threshold pressure differential.

[0065] Taking the third membrane 17c as an example, the third membrane 17c is configured to rupture in response to a pressure difference across the third membrane 17c, which generates a force greater than a threshold force in the direction from the second space 13b to the internal region 14. The third membrane 17c is configured to remain closed in response to a pressure difference across the third membrane 17c, which generates a force on the third membrane 17c equal to or greater than the threshold force, from the internal region 14 to the second space 13b. Specifically, the third rupture disk 15c is configured to rupture when the pressure in the second space 13b is greater than the pressure in the internal region 14, but remain closed when the pressure in the internal region 14 is greater than the pressure in the second space 13b. This may be referred to as a "unidirectional" rupture disk, which allows the third rupture disk 15c to withstand the pressure difference across the inner wall 11 caused by high-pressure liquid hydrogen fuel flowing through the internal region 14 while a vacuum is maintained in the second space 13b. Similarly, the first rupture disk 15a, the second rupture disk 15b, and the fourth rupture disk 15d are configured to be unidirectional and open only when the pressure in the corresponding first space 13a and second space 13b is greater than the pressure in the internal region 14.

[0066] Returning to the example of the third rupture disk 15c, in the event of a break or rupture 51 in the inner wall, the pressure in the second space 13b may rise above the pressure of the fuel in the inner region 14. As shown diagrammatically in FIG. 3, such a rupture 51 may initially allow fuel to flow from the inner region 14 into the second space 13b due to the higher pressure present in the inner region 14 than in the second space 13b. However, the hydrogen fuel, which may be below or near the saturation temperature and / or pressure of the inner region 14, may experience a rapid drop in pressure upon passing through the rupture 51 into the second space 13b, which may cause some or all of the hydrogen fuel to vaporize and reduce the density of the hydrogen fuel. Furthermore, in the second space 13b, due to the loss of vacuum, the hydrogen fuel may experience an increased rate of heat transfer with the atmosphere surrounding the outer wall 12. Thus, the rupture 51 in the inner wall 11 may cause a rapid (on the order of milliseconds) increase in temperature and pressure in the second space 13b. This allows the pressure in the second space 13b to rise to a level higher than the pressure in the internal region 14.

[0067] In some cases, when the rupture 51 is sufficiently large, the hydrogen fuel in the second space 13b may flow back through the rupture 51 into the interior region, equalizing the pressure between the second space 13b and the interior region 14. However, when the rupture 51 is sufficiently small, the flow of hydrogen fuel (now in vapor phase in the second space 13b) back through the rupture 51 may be "choked," thereby limiting the amount of hydrogen fuel that can flow back into the interior region 14. It will be appreciated that, due to the principle of conservation of mass, a smaller rupture 51 may result in a locally higher velocity of gas flowing through the rupture from the second space 13b into the interior region 14. Because vapor or gaseous hydrogen fuel is compressible and has a lower density than liquid hydrogen fuel, the local velocity of hydrogen fuel flowing through the rupture 51 is limited to the speed of sound of the hydrogen fuel (i.e., a local velocity having a Mach number of 1). Thus, an increase in pressure in the second space 13b beyond the pressure that would cause a sonic local velocity of hydrogen fuel flowing through the rupture 51 will not further increase the flow of hydrogen fuel through the rupture. This phenomenon is known as "choking". When the flow of hydrogen fuel from the second space 13b through the rupture 51 is choked, the increase in the flow rate of hydrogen fuel through the rupture 51 will not mitigate a further increase in pressure in the second space 13b relative to the interior region 14. Thus, in the case of choked flow through the rupture 51, a further increase in the temperature of the hydrogen fuel in the space will further increase the pressure of the hydrogen fuel in the second space 13b. For completeness, it is noted that an increase in pressure in the second space 13b may cause an increase in the density of the hydrogen fuel in the second space 13b, which in turn may increase the mass flow in a choked condition through the rupture 51. However, this effect is likely to be insufficient to prevent a further pressure increase in the second space 13b.

[0068] When the pressure in the second space 13b becomes greater than the pressure in the interior region 14 by an amount greater than the threshold pressure difference, the third membrane 17c ruptures, forming a third passage 16c between the second space 13b and the interior region 14. The hydrogen fuel in the second space 13b can then pass through the third passage 16c, which has a larger cross-sectional area than the rupture portion 51, to reduce the pressure difference between the second space 13b and the interior region 14.

[0069] The fourth rupture disk 15d is also configured to rupture when the pressure difference between the second space 13b and the inner region 14 exceeds a threshold pressure difference, so that redundancy is obtained for the breakage of the third rupture disk 15c. Similarly, the first rupture disk 15a and the second rupture disk 15b are configured to rupture when the pressure difference between the first space 13a and the inner region 14 exceeds a threshold pressure difference, for example, when the rupture portion causes the pressure in the first space 13a to exceed the pressure in the inner region 14.

[0070] It will be understood that the threshold pressure difference is smaller than a burst pressure difference that increases the risk of damage to the outer wall 12, i.e., a burst pressure difference between each of the first space 13a and the second space 13b and the atmosphere surrounding the outer wall 12. In particular, the threshold pressure difference is a certain margin below the burst pressure, enhancing the safety of the fuel supply system 2.

[0071] In response to such a rupture 51, the first isolator 24 and / or the second isolator 34 may close to prevent backflow of fuel into the centrifugal pump 25 and / or to prevent gaseous hydrogen fuel from flowing towards the engine 3. In some examples, such a rupture may be detected by a change in pressure within the fuel supply system 2, such as using a pressure sensor (not shown), and / or by a change in temperature within the fuel supply system, such as using a temperature sensor (not shown).

[0072] Due to an increased rate of heat transfer between the hydrogen fuel in the fuel line 10 and the atmosphere surrounding the outer wall 12, the pressure of the hydrogen fuel in the fuel line 10, such as between the first and second isolators 24, 34, may increase over time when the isolators are closed. This excess pressure may be vented to the exhaust system 35 via the first and second pressure relief valves 32a, 32b. Thus, it will be appreciated that in order to maintain the integrity of the outer wall 12, the first and second pressure relief valves 32a, 32b are also adapted to open when the pressure differential across them is less than the burst pressure.

[0073] By providing the first rupture disk 15a, the second rupture disk 15b, the third rupture disk 15c and the fourth rupture disk 15d, it is also possible to omit the pressure relief valve between each of the first space 13a and the second space 13b and the atmosphere surrounding the outer wall 12. This leads to a simpler system that only requires the first pressure relief valve 32a and the second pressure relief valve 32b (or only one pressure relief valve) and the associated piping for venting the hydrogen fuel to the exhaust device 35. This is particularly advantageous when the fuel line 10 includes a larger number of spaces as the length of the fuel line 10 increases. The larger number of spaces allows the effect of the rupture of the inner wall 11 to be localized to a smaller area along the fuel line 10. By providing at least one rupture disk similar to the first rupture disk 15a, the second rupture disk 15b, the third rupture disk 15c and the fourth rupture disk 15d for each space in the fuel line, the number of pressure relief valves and associated piping that would be required to vent each of the spaces to the exhaust system 35 (or another exhaust system) in the event that the inner wall 11 ruptures is significantly reduced.

[0074] Figure 4A-4C show the exemplary structure of rupture disk, which is the first rupture disk 15a here, but can be any one of the first rupture disk 15a, the second rupture disk 15b, the third rupture disk 15c and the fourth rupture disk 15d or any other rupture disk in fuel line 10. Here, for ease of understanding, the same features in Figure 1-3 are given the same reference numbers in Figure 4A-4C.

[0075] FIG. 4A shows a first rupture disk 60A comprising a first disk boss 61A welded at a proximal end adjacent to the inner wall 11 and a first disk membrane 62A attached to the first disk boss 61A. Here, the first disk membrane 62A is located at a distal end of the first disk boss 61A distal from the inner wall 11 and is concave toward the inner region 14. The concave first disk membrane 62A better resists the pressure acting from the inner region 14 toward the first space 13a. This allows a vacuum to be maintained in the first space 13a while the high pressure fuel passes through the inner region 14, as described above. The first disk membrane 62A is rupturable in response to a force pushing the first disk membrane 62A from the first space 13a toward the inner region 14.

[0076] 4B shows a second rupture disk 60B with a second disk boss 61B welded to the inner wall 11. Here, the second disk membrane 62B is instead attached to a second disk plug 63, which is welded to the second disk boss 61B at a distal end of the second disk boss 61B distal from the inner wall 11. The second disk membrane 62B is attached to the second disk plug 63 at an end of the second disk plug 63 proximate to the inner wall 11. Otherwise, the second disk membrane 62B is shaped and arranged to function substantially similarly to the first disk membrane 62A described above in response to a pressure difference between the first space 13a and the interior region 14.

[0077] 4C shows a third rupture disk 60C with a third disk boss 61C welded to the inner wall 11. Here, the third disk membrane 62C is similarly attached to the third disk plug 64, but the third disk plug 64 is instead fixed to the third disk boss 61C by a screw connection 67. This can improve the ease of replacing the third disk plug 64 and / or the third disk membrane 62C in the event of the third rupture disk 60C being ruptured. Otherwise, the third disk membrane 62C is shaped and arranged to function substantially similarly to the second disk membrane 62B and the first disk membrane 62A described above in response to the pressure difference between the first space 13a and the inner region 14.

[0078] It will be understood that the above examples have been provided for illustrative purposes only and that modifications and variations are possible within the scope of the present invention as defined by the appended claims.

[0079] For example, although only the first space 13a and the second space 13b are shown and described above, the fuel line 10 may include any other suitable number of spaces. The actual number of spaces will depend on the length of the fuel line 10 required to fluidly connect the fuel supply unit 20 to the engine unit 30. Furthermore, the above description of the operation of the first rupture disk 15a, the second rupture disk 15b, the third rupture disk 15c and the fourth rupture disk 15d, and the first space 13a and the second space 13b can be extrapolated to any number of such rupture disks and corresponding spaces included in the fuel line 10. In fact, each space can be associated with only one rupture disk, or three or more rupture disks that can be opened to fluidly connect the respective space and the internal region 14. A longer fuel line 10 can include more spaces and / or rupture disks, which can reduce the possibility of the effect of the rupture of the inner wall 11 propagating to other components of the fuel system 2 along the fuel line 10.

[0080] The first space 13a and the second space 13b described above are annular, but in other examples, they may be any other suitable shape. Furthermore, although the pair of rupture disks for each space is described and shown as diametrically opposite across the inner region 14, the rupture disks may be arranged in any other suitable manner, such as adjacent to each other on the same side of the inner wall 11, in other examples. The multiple rupture disks for a given space are here different types of rupture disks, such as rupture disks from different manufacturers, to provide improved redundancy and reduce the possibility of a single point of failure. However, in other examples, the multiple rupture disks for a given space may be the same type of rupture disks. The rupture disks at each of the above-mentioned interfaces also rupture at the same threshold pressure difference. In other examples, one rupture disk for a given space may rupture at a higher threshold pressure difference than another rupture disk for the space. This can also provide improved redundancy by allowing each rupture disk to continue rupturing in response to a further increase in pressure difference, such as when the rupture of one rupture disk is insufficient to relieve the pressure difference.

[0081] In some examples, pressure relief valves similar to the first pressure relief valve 32a and the second pressure relief valve 32b are fluidly coupled to the fuel line 10, such as directly to the interior region 14, or are provided in the fuel supply unit 20, such as upstream and / or downstream of the centrifugal pump 25 and / or the first isolator 24. Such pressure relief valves may be provided instead of or in addition to the first pressure relief valve 32a and the second pressure relief valve 32b. In some examples, the centrifugal pump 25 is any other suitable type of pump, such as a gear pump or a piston pump.

[0082] It is understood that the above-mentioned principle can be applied to any suitable system in which one or more spaces are defined between each pair of walls, such as the above-mentioned double-walled fuel tank 5, or other systems that include two or more walls. Specifically, such rupture disks can be provided to fluidly couple any two spaces (for example, a flow path and a space, a storage space and a space, or two spaces) on either side of the wall, especially when the pressure in one space becomes a certain amount greater than the pressure in the other space, which is lower or equal to the pressure in the other space during normal use.

[0083] It should be noted that the term "or" as used herein should be interpreted to mean "and / or" unless otherwise stated. [Aspect 1] 1. A double-walled pipe for an aircraft fuel system, comprising: an inner wall defining a first open end, a second open end, and an interior region connecting said first open end to said second open end, through which fuel can flow through said double-walled tube in use; an outer wall disposed about at least a portion of the inner wall such that the outer wall defines a space between the inner wall and the outer wall that is fluidly isolated from the interior region; and at least one barrier that is openable to form a passageway fluidly connecting the space to the interior region; The at least one barrier is configured to open when pressure in the space is greater than pressure in the interior region. [Aspect 2] 2. The double-walled pipe of claim 1, wherein the barrier is configured to open when the pressure in the space is greater than the pressure in the interior region by an amount greater than a threshold pressure difference. [Aspect 3] 3. The double-walled tube of embodiment 2, wherein the barrier is configured to remain closed when the pressure in the interior region is greater than the pressure in the space by an amount equal to or greater than the threshold pressure difference. [Aspect 4] 4. The double-walled pipe of any one of claims 2 to 3, wherein the threshold pressure difference is less than a burst pressure difference between the space and an outer region surrounding the outer wall. [Aspect 5]

[0023] Aspect 5. The double-walled pipe of any one of aspects 1-4, wherein the at least one barrier comprises a rupturable barrier. [Aspect 6] 6. The double-walled tube of any one of the preceding embodiments, wherein the at least one barrier comprises a rupture disk. [Aspect 7] 7. The double-walled tube of any one of aspects 1-6, wherein a vacuum or partial vacuum exists in the space. [Aspect 8] 8. The double-walled pipe of any one of aspects 1-7, wherein the at least one barrier comprises a plurality of barriers, each barrier of the plurality of barriers being openable to form a respective passageway fluidly connecting the space to the interior region. [Aspect 9] 9. The double-walled pipe of any one of aspects 1-8, wherein the space is a first space, and the outer wall defines a second space between the inner wall and the outer wall that is fluidly isolated from the interior region and the first space. [Aspect 10] The double-walled tube of claim 9, wherein the at least one barrier comprises at least one first space barrier, the passage comprises a first space passage fluidly connecting the first space to the interior region, and the double-walled tube comprises at least one second space barrier that is openable to form a second space passage fluidly connecting the second space to the interior region. [Aspect 11] A double-walled pipe as described in aspect 9 or 10, wherein the outer wall defines one or more additional spaces between the inner wall and the outer wall, and the additional space, or each of the plurality of additional spaces, is fluidly isolated from the interior region. [Aspect 12] a fuel tank for storing fuel for the aircraft's engines; 12. An aircraft fuel system comprising: the double-walled pipe according to any one of aspects 1 to 11, said double-walled pipe being fluidly connected or connectable to the fuel tank. [Aspect 13] 13. The aircraft fuel system of embodiment 12, comprising at least one pressure relief valve fluidly connecting the interior region to an atmosphere outside the double-walled tube. [Aspect 14] 14. The aircraft fuel system of claim 12 or 13, comprising liquid hydrogen fuel in the fuel tank. [Aspect 15] An aircraft comprising the double-walled pipe according to any one of aspects 1 to 11, or the aircraft fuel system according to any one of aspects 12 to 14.

Claims

1. 1. A double-walled pipe for an aircraft fuel system, comprising: an inner wall defining a first open end, a second open end, and an interior region connecting said first open end to said second open end, through which fuel can flow through said double-walled tube in use; an outer wall disposed about at least a portion of the inner wall such that the outer wall defines a space between the inner wall and the outer wall that is fluidly isolated from the interior region; at least one barrier openable to form a passageway fluidly connecting the space to the interior region; The at least one barrier is configured to open when pressure in the space is greater than pressure in the interior region.

2. The double-walled pipe of claim 1 , wherein the barrier is configured to open when pressure in the space is greater than pressure in the interior region by an amount greater than a threshold pressure difference.

3. The double-walled pipe of claim 2 , wherein the barrier is configured to remain closed when the pressure in the interior region is greater than the pressure in the space by an amount equal to or greater than the threshold pressure difference.

4. 4. The double-walled pipe of claim 2 or 3, wherein the threshold pressure difference is less than a burst pressure difference between the space and an outer region surrounding the outer wall.

5. The double-walled pipe of claim 1 , wherein the at least one barrier comprises a rupturable barrier.

6. The double-walled tube of claim 1 , wherein the at least one barrier comprises a rupture disk.

7. The double-walled tube of claim 1 , wherein a vacuum or partial vacuum exists within the space.

8. 2. The double-walled pipe of claim 1, wherein the at least one barrier comprises a plurality of barriers, each barrier of the plurality of barriers being openable to form a respective passageway fluidly connecting the space to the interior region.

9. 2. The double-walled pipe of claim 1, wherein the space is a first space and the outer wall defines a second space between the inner wall and the outer wall that is fluidly isolated from the interior region and the first space.

10. 10. The double-walled tube of claim 9, wherein the at least one barrier comprises at least one first space barrier, the passage comprises a first space passage fluidly connecting the first space to the interior region, and the double-walled tube comprises at least one second space barrier that is openable to form a second space passage fluidly connecting the second space to the interior region.

11. 11. The double-walled pipe of claim 9 or 10, wherein the outer wall defines one or more further spaces between the inner wall and the outer wall, the or each of the further spaces being fluidly isolated from the interior region.

12. a fuel tank for storing fuel for the aircraft engine; and a double-walled pipe as claimed in claim 1 fluidly connected or connectable to the fuel tank.

13. 13. The aircraft fuel system of claim 12, comprising at least one pressure relief valve fluidly connecting the interior region to an atmosphere external to the double-walled tube.

14. 14. An aircraft fuel system as claimed in claim 12 or 13, comprising liquid hydrogen fuel in the fuel tank.

15. An aircraft comprising a double-walled pipe according to claim 1 or an aircraft fuel system according to claim 12.

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