Double-walled tube for aircraft fuel system, aircraft fuel system and aircraft

Abstract

The invention relates to a double-walled tube for an aircraft fuel system, an aircraft fuel system and an aircraft. The double-walled tube includes 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 and via which fuel can flow through the double-walled tube in use. The double-walled tube also includes an outer wall disposed at least partially around the inner wall to define a void between the inner wall and the outer wall, the void being fluidly isolated from the interior region. The double-walled tube also includes at least one barrier that is openable to create a passage that fluidly connects the void to the interior region. The at least one barrier is configured to open when a pressure in the void is higher than a pressure in the interior region.

Description

Technical Field

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

[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 deliver fuel to various locations within the aircraft. For example, the fuel source may be located in the rear portion of the aircraft's fuselage, while the engine or 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 delivered through the aircraft fuel system at cryogenic conditions and / or high pressure. The liquid hydrogen fuel may also be stored in and delivered through the fuel system at or near saturation, such as at a temperature and pressure near the corresponding saturation temperature and saturation pressure associated with the liquid hydrogen fuel. Summary of the Invention

[0004] A first aspect of the present invention provides a double-walled pipe for an aircraft fuel system, the double-walled pipe 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 and enabling fuel to flow through the double-walled pipe via the interior region in use; an outer wall at least partially arranged around the inner wall to define a gap between the inner wall and the outer wall, the gap being fluidically isolated from the interior region; and at least one barrier capable of opening to form a passage connecting the gap fluidically to the interior region; wherein the at least one barrier is configured to open when the pressure in the gap is higher than the pressure in the interior region.

[0005] Providing at least one barrier between the void and the interior region (the at least one barrier may be referred to herein as an "openable barrier") can allow the pressure differential between the void and the interior region to decrease by opening the at least one barrier. This, in turn, can reduce the likelihood of a loss of integrity of the inner and / or outer walls due to such a pressure differential. 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 void.

[0006] The barrier can be configured to remain closed when the pressure in the void is less than the pressure in the interior region. In particular, the barrier can be configured to open in only one direction. That is, the barrier can be configured to open to allow fuel to flow from the void through the passageway to the interior region in only one direction. This can be achieved by having at least one component of the barrier be openable or rupturable only when the pressure on the side of the component in fluid communication with the void is greater than the pressure on the side of the component in fluid communication with the interior region. For example, the barrier can include a check valve that opens in only one direction and / or a rupture disk that preferably ruptures in only one direction. Providing such a one-way-openable barrier can allow a higher pressure to be maintained in the interior region during normal operation than in the void.

[0007] Providing a barrier configured to open when the pressure in the void exceeds the pressure in the interior region may be particularly advantageous for use in aircraft hydrogen fuel systems. To maintain the liquid phase, the liquid hydrogen fuel may need to be kept at cryogenic conditions. Exposure to higher temperatures may cause the liquid hydrogen fuel to transition to a vapor phase and expand, which may result in an increase in the pressure of the hydrogen fuel.

[0008] For example, this may occur when the inner wall ruptures to allow fuel to enter the void from the inner area. In this case, the hydrogen fuel escaping into the void may contact the outer wall, which may have a poorer thermal insulation than the inner wall with the atmosphere around the outer wall (for example, when there is no additional vacuum generated around the outer wall, or when the outer surface of the outer wall is in contact with ambient air). Ambient air may be at a higher temperature than the hydrogen fuel maintained under saturated conditions or near saturated conditions (for example, under cryogenic conditions) in the double-walled tube. Therefore, the contact of the hydrogen fuel with the outer wall may cause the temperature of the hydrogen fuel in the void to rise, which may cause some or all of the hydrogen fuel in the hydrogen fuel in the void to evaporate. This in turn increases the pressure in the void, particularly when the rupture in the inner wall is small enough to limit the pressure in the void when hydrogen flows back into the inner area. Therefore, in the case of increased pressure in the void, such as due to the evaporation of liquid hydrogen in the void, at least one barrier may be openable to better distribute the pressure in the double-walled tube. In this way, the outer wall can be arranged to have no ventilation device for releasing the pressure in the void to the atmosphere outside the double-walled tube. This can also avoid the need for a system for venting vapor from the atmosphere around the outer wall, such as to an exhaust port outside the fuel system and / or the aircraft. These factors, in turn, can reduce the weight, cost, and / or complexity of a fuel system including double-walled tubes.

[0009] The barrier is openable to provide access through the inner wall, which can provide a compact arrangement in the double-walled pipe.

[0010] Optionally, the barrier is configured to open when the pressure in the void exceeds the pressure in the interior region by an amount greater than a threshold pressure differential. This can allow the at least one barrier to passively open in the event of an increase in the pressure differential between the void and the interior region. This can provide a simple, self-contained arrangement that does not require any external input, such as from a control circuit, to operate. This can reduce potential failure modes of the at least one barrier and / or reduce the cost, weight, and / or complexity of the double-walled pipe.

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

[0012] For example, the interior region may carry fuel from an aircraft fuel system, such as pressurized hydrogen fuel. A vacuum (or another pressure lower than the pressure in the interior region) may be maintained in the void, for example to thermally 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 this case, an increase in the pressure differential between the interior region and the void, such as due to an increase in pressure in the interior region rather than in the void, may not cause the barrier to open. This, in turn, may allow a vacuum to be maintained in the void.

[0013] Thus, the barrier can only open or rupture if the pressure of the void relative to the interior region increases, causing the pressure differential between the void and the interior region to exceed a threshold pressure differential. As discussed above, this may occur due to damage or rupture in the interior wall, which results in the ingress of fuel into the void.

[0014] Therefore, at least one barrier can be openable to allow fuel in the void to flow back into the interior area, thereby reducing the pressure in the void. This can reduce the pressure acting on the outer wall, which can reduce the likelihood of loss of integrity of the outer wall. As described above, such an arrangement can reduce the pressure in the void without requiring a ventilation system to vent fuel in the void to the exterior of the double-walled pipe and / or the fuel system and / or the atmosphere outside the aircraft. This can improve the safety of the double-walled pipe and / or a fuel system including the double-walled pipe. It can also reduce the cost, weight, and / or complexity of the double-walled pipe and / or such a fuel system including the double-walled pipe.

[0015] Optionally, the threshold pressure differential is lower than a burst pressure differential between the void and the external region surrounding the outer wall. Optionally, the burst pressure differential is a pressure differential between the void and the external region that would cause or increase the risk of a partial loss of integrity of the outer wall. For example, the burst pressure differential may be a pressure differential that may increase the risk of rupture of the outer wall, such as a rated pressure differential between the void and the external region.

[0016] By ensuring that the threshold pressure differential is below the burst pressure differential, the at least one barrier can reduce the pressure in the void before it becomes large enough to damage the outer wall. This can help ensure that no fuel can escape through the outer wall into the external area. This, in turn, can improve the safety of the double-walled tube, particularly when the fuel is liquid hydrogen.

[0017] Optionally, at least one barrier comprises a rupturable barrier. In other words, at least one barrier may not be resealable once opened. Such a rupturable barrier may have no moving parts, or have fewer moving parts than, for example, an openable and closable valve. Fewer moving parts can reduce the likelihood of gas leakage through at least one barrier and / or can improve the reliability and / or life of at least one barrier. This may be particularly advantageous for use in aircraft hydrogen fuel systems because hydrogen particles are smaller than conventional fuel particles (such as kerosene) and therefore can leak through smaller gaps and spaces than conventional fuel particles. In addition, providing a rupturable barrier with fewer moving parts or no moving parts can also reduce the cost, weight and / or complexity of double-walled pipes and / or fuel systems including double-walled pipes.

[0018] Optionally, at least one barrier comprises a rupture disk. If provided, the rupture disk will comprise a rupturable barrier. For example, if provided, the rupturable barrier may comprise a membrane that fails upon a predetermined pressure differential, such as a threshold pressure differential, across the membrane. In this case, it will be understood that the membrane can withstand a pressure differential between the void and the interior region that results in a first force acting on the membrane from the interior region in a first direction toward the void, but can rupture upon a pressure differential between the void and the interior region that results in a second force, having a magnitude less than the first force, acting on the membrane from the void in a second direction toward the interior.

[0019] The rupture disk can provide an almost instantaneous response to a rapid increase in the pressure differential between the void and the interior region, which can improve the resiliency of the double-walled pipe to failures associated with the inner wall separating the void and the exterior region. Compared to other barriers, such as electronic valves or check valves, the rupture disk can have fewer moving parts, reduced size, cost, and / or weight, improved ease of maintenance, improved response time, and / or improved sealing. Thus, the rupture disk can provide an effective and reliable solution to mitigate the adverse effects of the pressure differential between the void and the interior region.

[0020] Optionally, a vacuum or partial vacuum exists in the void. As mentioned above, this can improve thermal insulation against the fuel, which may be cryogenic liquid hydrogen, flowing through the interior region during use. A barrier that is openable in only one direction can also allow such a vacuum to be maintained in the void even when high-pressure fuel is passing through the interior region.

[0021] Optionally, the at least one barrier comprises a plurality of barriers, and each of the plurality of barriers is openable to create a respective passageway fluidically connecting the void to the interior region. For example, a double-walled pipe may comprise a pair of barriers, each of which is openable to create a respective passageway between the void and the interior region, such as a respective passageway through the inner wall. This may provide improved redundancy, such as in the event of failure of one barrier of the pair.

[0022] Optionally, a pair of barriers, where provided, are arranged on opposite sides of the interior region.Alternatively, the pair of barriers may be arranged axially adjacent to each other relative to the interior wall.

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

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

[0025] By isolating the first and second voids from each other, in the event of a fault that causes a pressure change in one of the first and second voids, pressure can be maintained in the other of the first and second voids. This can limit the propagation of a fault associated with the first or second void to other portions of the double-walled pipe, such as the other of the first and second voids, or to other portions of a system including the double-walled pipe.

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

[0027] Optionally, the at least one barrier comprises at least one first void barrier, the passage comprises a first void passage connecting the first void fluid to the interior region, and the double-walled tube comprises at least one second void barrier, the at least one second void barrier being openable to create a second void passage connecting the second void fluid to the interior region.

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

[0029] In this manner, each of the first and second interstitial barriers can be openable to equalize the pressure between the interior region and the corresponding first and second interstitial barriers and / or reduce a pressure differential between the interior region and the corresponding first and second interstitial barriers. This can allow a pressure increase in one of the first and second interstitial spaces, such as caused by a failure of a portion of the inner wall separating the interior region from the corresponding first and second interstitial spaces, to be reduced without affecting the pressure in the other of the first and second interstitial spaces. This can improve the safety and / or reliability of the double-walled pipe.

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

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

[0032] Optionally, the outer wall defines one or more further voids between the inner wall and the outer wall, wherein the or each further void is fluidly isolated from the interior region.

[0033] Optionally, the or each additional void is fluidly isolated from the void defined between the inner wall and the outer wall. For example, the one or more additional voids may include a third void adjacent to or spaced apart from the first void and / or the second void and fluidly isolated from the first void and the second void. The third void may be axially or circumferentially adjacent to one or both of the first void and the second void.

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

[0035] The double-walled pipe may include one or more additional void barriers. The additional void barrier or each additional void barrier may be openable to create a corresponding additional void passageway that fluidly connects the corresponding additional void to the interior region. Alternatively, the one or more additional void barriers include one or more groups (e.g., pairs) of additional void barriers. Alternatively, each barrier in a group of additional void barriers may be openable to create a corresponding additional void passageway that fluidly connects one of the one or more additional voids to the interior region.

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

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

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

[0039] An aircraft fuel system may include a fuel supply unit comprising a fuel tank and one or more fluid propulsors for moving fluid from the fuel tank toward one or more engines. The fuel supply unit may include a sealed housing within which the fuel tank and the one or more fluid propulsors are located. The sealed housing may isolate the fuel tank and the one or more fluid propulsors from atmospheric fluid surrounding the fuel supply unit. The double-walled pipe may be configured to enable fuel to be transferred from the fuel supply unit through an interior region toward the one or more engines.

[0040] In this way, the fuel supply unit can accommodate any fuel that leaks from the tank, fluid propeller and / or other components within the sealed housing of the fuel supply unit. This in turn can allow the use of pipes other than double-walled pipes within the fuel supply unit, and can also reduce the cost, weight and / or complexity of the fuel supply system. As described above, the double-walled pipe, which is designed to reduce the risk of fuel leaking therefrom even when the inner pipe ruptures, can then also be connected to transfer fuel to the outside of the sealed housing, although this area is not sealed from the atmosphere around the sealed housing. Alternatively, or in addition, the fuel supply unit can include double-walled pipes, which can further reduce the risk of fluid leaking into the atmosphere around 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 transferring fuel between components of the aircraft fuel system and / or other systems associated with the aircraft.

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

[0043] After the inner wall ruptures and / or at least one barrier opens, at least one pressure relief valve can allow excess pressure generated in the inner pipe to be released and / or vented to the outside atmosphere. This can improve the safety of the double-walled pipe. Optionally, the at least one pressure relief valve includes two or more pressure relief valves. This can provide improved redundancy in the event of a failure of one of the pressure relief valves.

[0044] Optionally, the aircraft fuel system includes a vent located externally of the double-walled pipe, and the at least one pressure relief valve is fluidly connected to the vent. Optionally, the vent is configured to discharge fuel received from the at least one pressure relief valve to the atmosphere external to the aircraft. In this manner, hydrogen fuel can be safely discharged from the aircraft and / or components of the fuel system or an engine of the aircraft.

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

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

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

[0048] The aircraft may include and / or benefit from any of the optional 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 should be understood that features associated with any of the first, second and third aspects may be combined with features associated with any of the first, second and third aspects to suit the specific implementation of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0051] Figure 1A schematic diagram of an example aircraft is shown;

[0052] Figure 2 Shown Figure 1 A schematic diagram of an example fuel system for an aircraft;

[0053] Figure 3 Shown Figure 2 A schematic diagram of example fuel lines for a fuel system of FIG. 1 ; and

[0054] Figures 4A to 4C Shown Figure 3 Schematic diagram of an example structure of a fuel line rupture disk. DETAILED DESCRIPTION

[0055] Figure 1 An example aircraft 1 is shown, including a fuel system 2 and an engine 3. Fuel system 2 is a liquid hydrogen fuel system, located at least partially toward the rear end of fuselage 4 of aircraft 1. Specifically, fuel system 2 includes a fuel tank 5 located at least partially within tail section 6 of the aircraft. Engine 3 is located on wing 7 of aircraft 1. Aircraft fuel system 2 includes fuel lines 10 for transferring fuel from fuel tank 5 to engine 3. It will be appreciated that in other examples, fuel tank 5 and / or engine 3 may be located in any other suitable location on or within the aircraft. Aircraft 1 may also include more than one engine 3 and / or more than one fuel tank 5. Fuel tank 5 is a double-walled fuel tank, comprising walls defining a cavity for storing fuel and an outer shell surrounding the cavity walls to define a space between the cavity walls and the outer shell. This space includes a vacuum that thermally insulates the fuel in the cavity. This arrangement reduces the possibility of fuel leaking from the fuel tank, for example due to a rupture in the cavity wall.

[0056] Figure 2 The schematic diagram of shows the aircraft fuel system 2 in more detail. The aircraft fuel system 2 includes a fuel supply unit 20, which includes a sealed housing 21. "Sealed" here means that the interior space 22 defined by the sealed housing is fluidly isolated from the atmosphere surrounding the sealed housing 21. The fuel supply unit 20 includes a fuel tank 5 with the sealed housing 21 mounted thereon and a centrifugal pump 25 located in the sealed housing 21. The sealed housing 21 is defined by a single wall and reduces the possibility of fuel leaking from components in 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 as being mounted to the fuel tank 5, in other examples, the fuel tank 5 may be enclosed 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. Return to Figure 2The fuel supply system includes a control system 40 configured to issue a pump control signal to operate the centrifugal pump 25 to move fuel from the fuel tank 5 toward the engine 3. In other words, the control unit 40 is communicatively coupled to the centrifugal pump 25.

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

[0058] The following will refer to Figure 3 The fuel line 10 will be described in more detail.

[0059] Engine 3 is part of an engine unit 30 of aircraft 1. Engine unit 30 includes a nacelle 31 that defines an engine compartment 37. Nacelle 31 here provides a sealed housing that defines engine compartment 37, but in other examples, engine compartment 37 is partially open to the atmosphere surrounding nacelle 31. Engine unit 30 includes engine 3. Engine 3 includes an outlet 36 that opens to the atmosphere surrounding engine unit 30, allowing exhaust gases to pass from engine 3 to the atmosphere surrounding engine unit 30 to provide at least some of the motive force for moving aircraft 1, as will be known to those skilled in the art.

[0060] Engine unit 30 includes an engine line 33 configured to receive fuel from fuel supply unit 20 via fuel line 10. Engine unit 30 includes a second isolator 34 operable via a second isolator control signal received from control system 40 to selectively allow or prevent the flow of fuel from engine line 33 to engine 3. In other words, control system 40 is communicatively coupled to second isolator 34. Engine unit 30 also includes a first pressure relief valve 32a and a second pressure relief valve 32b, each fluidly connecting engine line 30 to an exhaust 35 located outside cabin 31. Specifically, exhaust 35 is located in a relatively "safe" environment outside engine unit 30 and, preferably, also outside aircraft 1 as a whole. First and second pressure relief valves 32a, 32b are configured to vent excess pressure in fuel system 2, and particularly in fuel line 10 and / or fuel line 33, to the atmosphere surrounding cabin 31 via exhaust 35.

[0061] In some examples, similar pressure relief valves are provided in the fuel line 10 or 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 and second pressure relief valves 32a, 32b.

[0062] Now go to Figure 3 , the fuel line 10 is described in more detail. The fuel line 10 is a double-walled pipe that includes an inner wall 11 defining a first open end 18a, a second open end 18b, and an interior region 14 that connects the first open end 18a to the second open end 18b. Fuel can flow from the fuel supply unit 20 to the engine unit 30 via or through the interior region 14. In particular, in use, fuel received from the centrifugal pump 25 through the first open end 18a is fed along the fuel line 11. Figure 3 The direction of the arrow marked 50 in FIG. 1 passes through the interior region 14 and enters the engine unit 30 through the second open end 18 b. In other words, the first open end 18 a is fluidly connected to the fuel supply unit 20 to receive the fuel stored in the fuel tank 5, and the second open end 18 a is fluidly connected to the engine unit 30 to transfer the fuel from the interior region 14 toward the engine 3.

[0063] Fuel line 10 also includes an outer wall 12 disposed about inner wall 11 to define a first annular gap 13a and a second annular gap 13b therebetween. First gap 13a and second gap 13b are each fluidically isolated from interior region 14 by the inner wall. First gap 13a and second gap 13b are fluidically isolated from each other by an annular seal 19 disposed between inner wall 11 and outer wall 12. A vacuum is maintained in each of first gap 13a and second gap 13b to thermally insulate the liquid hydrogen fuel flowing through interior region 14 from the external atmosphere surrounding the outer wall during use. In this case, the external atmosphere is ambient air. The ambient air is at a higher temperature than the liquid hydrogen flowing through interior region 14, maintaining the liquid hydrogen at or near saturation (and particularly at cryogenic conditions).

[0064] Fuel line 10 includes diametrically opposed first and second rupture disks 15a, 15b, each capable of opening to form a respective first and second passages 16a, 16b through inner wall 11, fluidly connecting first void 13a to interior region 14. Fuel line 10 similarly includes diametrically opposed third and fourth rupture disks 15c, 15d, each capable of opening to form a respective third and fourth passages 16c, 16d through inner wall 11, fluidly connecting second void 13b to interior region 14. First, second, third, and fourth rupture disks 15a, 15b, 15c, and 15d include respective first, second, third, and fourth membranes 17a, 17b, 17c, and 17d. Each membrane 17a, 17b, 17c, 17d is configured to rupture in response to a pressure differential across the respective membrane 17a, 17b, 17c, 17d exceeding a threshold pressure differential.

[0065] Taking third membrane 17c as an example, third membrane 17c is configured to rupture in response to a pressure differential across third membrane 17c that causes the force acting on third membrane 17c in the direction from second void 13b to interior region 14 to exceed a threshold force. Third membrane 17c is configured to rupture in response to a pressure differential across third membrane 17c that causes the force acting on third membrane 17c in the direction from interior region 14 to second void 13b to have a magnitude equal to or greater than the threshold force. Specifically, third rupture disk 15c is configured to rupture when the pressure in second void 17c is greater than the pressure in interior region 14, but remain closed when the pressure in interior region 14 is greater than the pressure in second void 13b. This can be referred to as a "one-way" rupture disk and allows third rupture disk 15c to withstand the pressure differential across inner wall 11 caused by the flow of high-pressure liquid hydrogen fuel through interior region 14 while maintaining a vacuum in second void 13b. The first rupture disk 15 a , the second rupture disk 15 b , and the fourth rupture disk 15 d are similarly configured to be unidirectional, opening only when the pressure in the corresponding first and second interstices 13 a , 13 b is greater than the pressure in the interior region 14 .

[0066] Returning to the example of the third rupture disk 17c, in the event of a rupture or damage 51 in the inner wall, the pressure in the second void 13b may be increased to a level higher than the pressure of the fuel in the inner region 14. Figure 3As schematically shown in FIG, since the pressure in the inner region 14 is higher than the pressure in the second void 13b, such a rupture 51 may initially cause the fuel to flow from the inner region 14 into the second void 13b. However, when the hydrogen fuel—which may be below, at, or near its saturation temperature and / or saturation pressure in the inner region 14—enters the second void 13b through the rupture 51, the hydrogen fuel may experience a rapid drop in pressure, which may cause some or all of the hydrogen fuel to evaporate, thereby reducing the density of the hydrogen fuel. In addition, in the second void 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. Therefore, the rupture 51 in the inner tube 11 may cause the temperature and pressure in the second void 13b to increase rapidly (in milliseconds). This may cause the pressure in the second void 13b to increase to or above the pressure level in the inner region 14.

[0067] In some cases, when the rupture 51 is sufficiently large, the hydrogen fuel in the second void 13b can flow back into the interior region through the rupture 51 to balance the pressure between the second void 13 and the interior region 14. However, if the rupture 51 is sufficiently small, the flow of the hydrogen fuel returning through the rupture 51 (which is currently in the vapor phase in the second void 13b) 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 can result in a locally higher velocity of the gas flowing through the rupture from the third void 13b to the interior region 14. Since vapor or gaseous hydrogen fuel is compressible and has a lower density than liquid hydrogen fuel, the local velocity of the hydrogen fuel flowing through the rupture 51 is limited to the speed of sound of the hydrogen fuel (i.e., a local velocity of Mach number 1). Therefore, any increase in the pressure in the second void 13b that exceeds the increase in the local speed of sound of the hydrogen fuel flowing through the rupture 51 will not further increase the flow rate of the hydrogen fuel through the rupture. This phenomenon is known as "blocking." If the flow of hydrogen fuel from the second void 13b through the rupture 51 becomes blocked, further increases in the pressure in the second void 13 relative to the pressure in the interior region 14 will not be mitigated by an increase in the flow rate of the hydrogen fuel through the rupture 51. Thus, in the event of blocked flow through the rupture 51, a further increase in the temperature of the hydrogen fuel in the void may result in a further increase in the pressure of the hydrogen fuel in the second void 13b. For the sake of completeness, it should be noted that an increase in the pressure in the second void 13b may result in an increase in the density of the hydrogen fuel in the second void 13b, which in turn may increase the mass flow rate through the rupture 51 under blocked conditions. However, this effect may not be sufficient to prevent further pressure buildup in the second void 13b.

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

[0069] Fourth rupture disk 15d is similarly configured to rupture when the pressure differential between second void 13b and interior region 14 exceeds a threshold pressure differential, thereby providing redundancy in the event of a failure of third rupture disk 15c. Similarly, first rupture disk 15a and second rupture disk 15b are configured to rupture when the pressure differential between first void 13a and interior region 14 exceeds a threshold pressure differential, such as when the rupture causes the pressure in first void 13b to exceed the pressure in interior region 14.

[0070] It will be appreciated that the threshold pressure difference is less than a burst pressure difference between the respective first and second voids 13a, 13b and the atmosphere surrounding the outer wall 12 that would increase the risk of failure of the outer wall 12. In particular, the threshold pressure difference is a predetermined margin below the burst pressure, thereby increasing the safety of the fuel supply system 2.

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

[0072] The increased heat transfer rate between the hydrogen fuel in the fuel line 10 and the atmosphere surrounding the outer wall 12 may cause the hydrogen fuel in the fuel line 10, such as between the first isolator 24 and the second isolator 34, to increase over time when closed. This excess pressure may be vented to the exhaust 35 through the first and second pressure relief valves 32a, 32b. Therefore, it will be understood that when the pressure differential across the first and second pressure relief valves 32a, 32b is less than the burst pressure, the first and second pressure relief valves 32a, 32b also open to maintain the integrity of the outer wall 12.

[0073] By providing first, second, third, and fourth rupture disks 15a, 15b, 15c, and 15d, a pressure relief valve between each of first and second voids 13a, 13b and the atmosphere surrounding outer wall 12 can be omitted. This results in a simpler system, requiring only first and second pressure relief valves 32a, 32b (or even only one pressure relief valve) and associated piping to discharge hydrogen fuel to exhaust 35. This is particularly advantageous when fuel line 10 includes a greater number of voids, which may be the case as the length of fuel line 10 increases. A greater number of voids can allow the effects of a rupture of inner wall 11 to be localized to a smaller area along fuel line 10. Providing each void in the fuel line with at least one rupture disk similar to the first through fourth rupture disks 15a, 15b, 15c, 15d significantly reduces the number of pressure relief valves and associated piping that would otherwise be required to vent each of the voids to the exhaust 35 (or another exhaust device) in the event of a rupture of the inner wall 11.

[0074] Figures 4A to 4C The example structure of the rupture disk is shown, which is the first rupture disk 15a here, but can be any one of the first to fourth rupture disks 15a, 15b, 15c, 15d or any other rupture disk in the fuel line 10. Here, for ease of understanding, Figures 1 to 3 The same features in Figures 4A to 4C The same reference numerals are provided in FIG.

[0075] Figure 4A A first rupture disk 60A is shown, comprising a first disk boss 61A welded to a proximal end near inner wall 11 and a first disk membrane 62A attached to first disk boss 61A. Here, first disk membrane 62A is located at the distal end of first disk boss 61A, away from inner wall 11, and is recessed toward interior region 14. The recessed first disk membrane 62A better resists pressure acting from interior region 14 toward first void 13a. This allows a vacuum to be maintained in first void 13a while high-pressure fuel passes through interior region 14, as discussed above. First disk membrane 62A is capable of rupturing in response to a force pushing first disk membrane 62A from first void 13a toward interior region 14.

[0076] Figure 4BA second rupture disk 60B is shown, comprising a second disk boss 61B welded to inner wall 11. Here, a second disk diaphragm 62B is instead attached to a second disk plug 63, which in turn is welded to second disk boss 61B at its distal end, facing away from inner wall 11. Second disk diaphragm 62B is attached to second disk plug 63 at its end proximal to inner wall 11. Furthermore, second disk diaphragm 62B is shaped and arranged so as to function in response to a pressure differential between first void 13a and interior region 14 in substantially the same manner as first disk diaphragm 62A, discussed above.

[0077] Figure 4C A third rupture disk 60C is shown, comprising a third disk boss 61C welded to inner wall 11. Here, a third disk diaphragm 62C is similarly attached to a third disk plug 64, but third disk plug 64 is instead secured to third disk boss 61C using a threaded connection 67. This can improve the ease of replacing third disk plug 64 and / or third disk diaphragm 62C in the event that third rupture disk 60C ruptures. Furthermore, third disk diaphragm 62C is shaped and arranged so as to function in substantially the same manner as second disk diaphragm 62B and first disk diaphragm 62A discussed above, in response to a pressure differential between first void 13a and interior region 14.

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

[0079] For example, while only first and second interstices 13a, 13b are shown and described above, fuel line 10 may include any other suitable number of interstices. The actual number of interstices may depend on the length of fuel line 10 required to fluidically connect fuel supply unit 20 to engine unit 30. Furthermore, the above description of the operation of first through fourth rupture disks 15a, 15b, 15c, 15d and first and second interstices 13a, 13b may be extrapolated to any number of such rupture disks and corresponding interstices included in fuel line 10. In fact, each interstice may be associated with only one rupture disk, or more than two rupture disks capable of opening to fluidically connect the corresponding interstices with interior region 14. Longer fuel line 10 may include more interstices and / or rupture disks, which may reduce the likelihood that the effects of a rupture of inner wall 11 will propagate along fuel line 10 to other components of fuel system 2.

[0080] The first and second voids 13a, 13b described above are annular, but in other examples, they may be of any other suitable shape. Furthermore, while the paired rupture disks for each void are described and illustrated as diametrically opposed across interior region 14, in other examples, the rupture disks may be arranged in any other suitable arrangement, such as adjacent to each other on the same side of inner wall 11. The multiple rupture disks for a given void are herein of different types, such as from different manufacturers, to provide improved redundancy and reduce the potential for single points of failure. However, in other examples, the multiple rupture disks for a given void may be of the same type. The rupture disks for each interface described above also rupture at the same threshold pressure differential. In other examples, one rupture disk for a given void may rupture at a higher threshold pressure differential than another rupture disk for that void. This can similarly provide improved redundancy by allowing the respective rupture disks to rupture in response to further increases in pressure differential, such as in situations where rupture of one rupture disk is insufficient to relieve the pressure differential.

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

[0082] It will be appreciated that the principles described above can be applied to any suitable system in which one or more voids are defined between corresponding pairs of walls, such as in the double-walled fuel tank 5 described above, or other systems including more than two walls. In particular, such a rupture disk can be provided to fluidly couple any two spaces (e.g., a flow path and a void, a storage space and a void, or two voids) on either side of a wall when the pressure in a first of the spaces exceeds the pressure in the other space by a certain amount, and particularly when the pressure in the first of the spaces is less than 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 as meaning "and / or" unless explicitly stated otherwise.

Claims

1. A double-walled tube for an aircraft fuel system, the double-walled tube 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 and through which fuel can flow through the double walled tube in use; an outer wall disposed at least partially around the inner wall to define a void between the inner wall and the outer wall, the void being fluidly isolated from the interior region; as well as at least one barrier that is openable to create a passage fluidly connecting the void to the interior region; Therein, the at least one barrier is configured to open when a pressure in the void is higher than a pressure in the interior region.

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

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

4. The double-walled pipe according to claim 2 or claim 3, wherein: The threshold pressure differential is lower than a burst pressure differential between the void and an outer region surrounding the outer wall.

5. The double-walled pipe according to any one of claims 1 to 4, wherein: The at least one barrier comprises a rupturable barrier.

6. The double-walled pipe according to any one of claims 1 to 5, wherein: The at least one barrier includes a rupture disk.

7. The double-walled pipe according to any one of claims 1 to 6, wherein: A vacuum or a partial vacuum exists in the void.

8. The double-walled pipe according to any one of claims 1 to 7, wherein: The at least one barrier comprises a plurality of barriers, and each barrier of the plurality of barriers is openable to create a respective passageway fluidly connecting the void to the interior region.

9. The double-walled pipe according to any one of claims 1 to 8, wherein: The void is a first void, and the outer wall defines a second void between the inner wall and the outer wall that is fluidly isolated from the interior region and the first void.

10. The double-walled pipe according to claim 9, wherein: The at least one barrier comprises at least one first void barrier, the passage comprises a first void passage connecting the first void fluid to the interior region, and the double-walled tube comprises at least one second void barrier, the at least one second void barrier being openable to create a second void passage connecting the second void fluid to the interior region.

11. The double-walled pipe according to claim 9 or claim 10, wherein: The outer wall defines one or more further voids between the inner wall and the outer wall, wherein the or each further void is fluidly isolated from the interior region.

12. An aircraft fuel system comprising: a fuel tank for storing fuel for an engine of the aircraft; as well as The double-walled pipe according to any one of claims 1 to 11, which is fluidly connected or fluidly connectable to the fuel tank.

13. The aircraft fuel system of claim 12, comprising at least one pressure relief valve configured to fluidly connect the interior region to atmosphere outside the double walled tube.

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

15. An aircraft comprising a double wall pipe according to any one of claims 1 to 11 or an aircraft fuel system according to any one of claims 12 to 14.

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