CRYOGENIC TANK

Abstract

A cryogenic tank for storing cryogenic fluids is disclosed. The cryogenic tank is typically configured to be mounted on a vehicle for supplying cryogenic fuel to a propulsion system of the vehicle. The cryogenic tank comprises an inner vessel for containing cryogenic fluids and an outer vessel surrounding the inner vessel to define a vacuum insulating volume therebetween. The outer vessel is configured to transmit static and/or dynamic loads, while the inner vessel is partially or completely isolated from such loads.

Claims

1. An aircraft, comprising: an airframe configured to transmit aircraft flight loads, a propulsion system, and a cryogenic tank supplying the propulsion system, the cryogenic tank comprising an inner vessel defining a closed volume configured to carry a cryogenic fuel; and an outer vessel enclosing the inner vessel to define an insulating volume therebetween, the insulating volume comprising a vacuum, and the outer vessel comprising a vessel mount structurally connecting the inner vessel to the outer vessel and configured to isolate the inner vessel from static and/or dynamic loads carried by the outer vessel, wherein the outer vessel of the cryogenic tank comprises an integral structural member of the airframe.

2. The aircraft according to claim 1, wherein the outer vessel further comprises a panel having one or more reinforcing members projecting inwardly from the panel into the insulating volume.

3. The aircraft according to claim 1, wherein the outer vessel comprises an outer surface, the outer surface forming an aerodynamic surface of the aircraft.

4. The aircraft according to claim 1, wherein a face of the outer vessel comprises propulsion system mounts to which the propulsion system is connected.

5. The aircraft according to claim 4, wherein the outer vessel comprises a lower panel, an upper panel, an end cap, and a bulkhead, wherein the propulsion system mounts are provided on the bulkhead and do not extend into the insulating volume.

6. The aircraft according to claim 1, wherein the outer vessel includes a stiffening member or a panel of the airframe.

7. The aircraft according to claim 1, wherein the airframe comprises a wing spar, and a mounting member structurally connects the outer vessel of the cryogenic tank to the wing spar.

8. The aircraft according to claim 1, wherein the airframe includes a wing box having a front spar, a rear spar, an upper cover, and a lower cover, and the two or more longitudinally spaced mounting locations comprise locations for connecting respectively to the front spar and the rear spar.

9. The aircraft according to claim 8, wherein the outer vessel transfers a portion of propulsion system loads through the outer vessel and into the rear spar.

10. The aircraft according to claim 1, wherein the outer vessel further comprises a mounting member for structurally connecting the outer vessel of the cryogenic tank to the airframe at two or more longitudinally-spaced mounting locations, the mounting member configured to transfer the static and/or dynamic loads between the two or more longitudinally-spaced mounting locations thereby permitting transfer of the static and/or dynamic loads from the airframe through the outer vessel in a longitudinal direction.

11. The aircraft according to claim 10, wherein the airframe includes a fuselage section comprising a series of frames supporting an outer skin and the two or more longitudinally spaced mounting locations comprise mounting locations for connecting respectively to two respective frames of the series of frames.

12. The aircraft according to claim 10, wherein the cryogenic tank is integrated into the airframe to form a fuselage section of the aircraft and wherein the two or more longitudinally spaced mounting locations comprise mating joints with first and second fuselage sections of the airframe.

13. The aircraft according to claim 1, wherein the vessel mount comprises a fixed mount at one axial end of the inner vessel and a floating mount at another axial end of the inner vessel and wherein the fixed mount comprises a rigid connection between the inner vessel and the outer vessel through which conduits of an aircraft fuel system enter the inner vessel.

14. The aircraft according to claim 1, wherein the outer vessel comprises a flange extending outwardly from and longitudinally along the outer vessel and comprising the two or more longitudinally spaced mounting locations for connecting the cryogenic tank to the airframe.

15. The aircraft according to claim 1, wherein the outer vessel comprises an upper panel and a lower panel, the upper panel comprising an outwardly extending flange portion that overlaps with a corresponding region of the lower panel to thereby join the upper panel and lower panel and provide a flange extending outwardly from the outer vessel.

16. The aircraft according to claim 15, wherein at least one of the flange portion and corresponding region comprises an elongate sealing channel, the elongate sealing channel configured to comprise an elastomeric elongate sealing component or an elongate bead of curable sealing material to provide a fluid-tight seal between the upper panel and the lower panel.

17. The aircraft according to claim 1, wherein the vessel mount comprises a fixed mount at one axial end of the inner vessel and a floating mount at another axial end of the inner vessel, and wherein the floating mount comprises: a first mounting member connected to the inner vessel, and a second mounting member connected to the outer vessel, the first mounting member and second mounting member being interconnected to permit relative linear and/or rotational movement therebetween, and a bushing comprising a thermal insulating material for limiting heat transfer between the first mounting member and the second mounting member.

18. The aircraft according to claim 1, wherein the outer vessel is formed from a composite material and the inner vessel is formed from a metal.

19. An aircraft, comprising: an airframe configured to transmit aircraft flight loads, a propulsion system, and a cryogenic tank supplying the propulsion system, the cryogenic tank comprising an inner vessel defining a closed volume configured to carry a cryogenic fuel; an outer vessel enclosing the inner vessel to define an insulating volume therebetween, the insulating volume comprising a vacuum, and the outer vessel comprising a mounting member for structurally connecting the outer vessel of the cryogenic tank to the airframe at two or more longitudinally spaced mounting locations, the mounting member configured to transfer static and/or dynamic loads between the two or more longitudinally spaced mounting locations thereby permitting transfer of the static and/or dynamic loads from the airframe through the outer vessel in a longitudinal direction; and a vessel mount structurally connecting the inner vessel to the outer vessel and configured to isolate the inner vessel from said static and/or dynamic loads carried by the outer vessel.

20. An aircraft, comprising: an airframe configured to transmit aircraft flight loads, a propulsion system, and a cryogenic tank supplying the propulsion system, the cryogenic tank comprising an inner vessel defining a closed volume configured to carry a cryogenic fuel; an outer vessel enclosing the inner vessel to define an insulating volume therebetween, the insulating volume comprising a vacuum, a mounting member for structurally connecting the outer vessel of the cryogenic tank to the airframe, the mounting member permitting transfer of static and/or dynamic loads between the aircraft and the outer vessel; and a vessel mount structurally connecting the inner vessel to the outer vessel and configured to isolate the inner vessel from said static and/or dynamic loads carried by the outer vessel, wherein a forward face of the outer vessel comprises propulsion system mounts to which the propulsion system is connected.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0043] FIG. 1 schematically illustrates a number of features of a cryogenic tank;

[0044] FIG. 2 illustrates appropriate vacuum levels for the insulating volume;

[0045] FIG. 3 illustrates a cryogenic tank secured to a wing box of an aircraft;

[0046] FIG. 4 illustrates a cryogenic tank secured to a fuselage of an aircraft;

[0047] FIGS. 5A and 5B illustrate a cryogenic tank forming a fuselage section of an aircraft;

[0048] FIG. 6 provides an exploded view of the main components of the outer vessel of a cryogenic tank;

[0049] FIG. 7 provides a sectional view illustrating the attachment of the longitudinal flange of a cryogenic tank to an airframe of an aircraft;

[0050] FIG. 8 schematically illustrates a vessel mounting means of a cryogenic tank; and

[0051] FIGS. 9A, 9B and 9C schematically illustrate possible sealing configurations.

DETAILED DESCRIPTION

[0052] In general terms, the disclosure provides a cryogenic tank 100 for storage and dispensing of cryogenic fluids. For example, cryogenic fluid in the form of liquid hydrogen, or a mixture of liquid and gaseous hydrogen. In the illustrated embodiments the tank 100 is for mounting on an aircraft to supply fuel (in the form of cryogenic fluid) to an aircraft propulsion system. However, in other embodiments the tank 100 may be applied to marine, land or space vehicles. Moreover, the tank 100 may have utility in any application where weight and space/volume are important design factors.

[0053] The tank 100 is illustrated schematically in FIG. 1, which shows an inner vessel 10 supported within an outer vessel 30, and an insulating volume 50 therebetween. The insulating volume 50 is maintained at a vacuum, or near vacuum, to provide thermal insulation between the inner 10 and outer 30 vessels. As illustrated in FIG. 2, an appropriate target vacuum pressure is considered to be 103 mBar (approximately 0.75 mTorr), though a pressure of 10 mTorr or less may be sufficient.

[0054] The inner vessel 10 comprises a fluid-tight reservoir for containing liquid hydrogen 12 and gaseous hydrogen 14. The fluid 12, 14 within the inner vessel 10 is typically at an above atmospheric pressure, and the inner vessel 10 thus forms a pressure vessel. The inner vessel 10 may have any one of a number of geometries appropriate to pressure vessels suitable for containing cryogenic fluids. In the illustrated embodiments the inner vessel 10 has a generally cylindrical central portion centred on a longitudinal axis 16, the central portion being capped at each end by two domed or convex end caps. This shape has been demonstrated to provide optimised structural performance for most applications.

[0055] The outer vessel 30 can have any one of a number of geometries appropriate to the application of the tank 100. For example, the outer vessel 30 may have an outer geometry optimised for aerodynamic performance in aircraft applications. The outer vessel 30 preferably has a generally cylindrical, or near-cylindrical, inner volume to provide a structurally optimised shape that minimises weight. In some aircraft applications the tank 100 may be designed to be mounted to an aircraft wing, while in others it may be mounted to an aircraft fuselage. In some cases the outer vessel 30 may be incorporated into the aircraft airframe structure, for example by incorporating fuselage frames, wing spars or ribs, or other structural airframe features.

[0056] Three example configurations for the outer vessel 30 are illustrated in FIGS. 3, 4 and 5A-B.

[0057] In FIG. 3 the tank 100 is mounted underneath a wing box 200 of a wing. As is typical of known wings, the wing box 200 includes a front spar 210, rear spar 220, upper cover 230 and lower cover 240. The wing box may be stiffened by ribs (not shown). The outer vessel 30 of the tank 100 comprises three pairs of mounting locations at which the tank 100 is mounted to the wing box 200: a pair of front spar mounting locations 60 provide a connection to a lower region of the front spar 210; a pair of rear spar mounting locations 62 provide a connection to a lower region of the rear spar 230; and a pair of aft mounting locations 64 provide a connection to an upper region of the rear spar 230 via a rear support truss 66. The aft mounting locations 64 and rear support truss 66 are included to avoid anticipated excitation-vibration issues, particularly in large tanks with a long longitudinal length, but it should be understood that they may be omitted in some embodiments. Of course, yet further mounting locations may be provided in yet further embodiments

[0058] The forward face of the outer vessel 30 carries a pair of propulsion system mounts 68 to which the propulsion system (not shown) of the aircraft is connected. These pinned fittings transfer a portion of the propulsion system loads through the outer vessel 30 and into the rear spar 220. The propulsion system mounts 68 may comprise a machined metallic (e.g. aluminium) fitting that is fastened to the front bulkhead 46 of the outer vessel 30. The fasteners do not penetrate the bulkhead 46 (i.e. do not extend into the insulating volume 50) in order to avoid creating a leak path should removal/replacement of the mounts 68 be required. Alternatively, the mounts 68 may be formed integrally with the bulkhead 46.

[0059] A fairing (not shown) may conceal forward and rear portions of the tank 100 to improve its aerodynamic performance. In some embodiments there may be fewer than, or more than, two propulsion system mounts 68. In particular, some embodiments may have no propulsion system mounts.

[0060] In FIG. 4 the tank 100 is mounted beneath a fuselage section 300 of an aircraft. As is typical of known fuselages, the fuselage section 300 includes a series of circular frames (not shown) supporting an outer skin 310 that is stiffened by longitudinal stringers (not shown). The outer vessel 30 of the tank 100 comprises two pairs of mounting locations at which the tank 100 is mounted to two respective frames of the fuselage section: a pair of forward mounting locations 70; and a pair of rear mounting locations 72. A fairing 320 conceals forward and rear portions of the tank 100 to improve its aerodynamic performance.

[0061] FIGS. 5A and 5B shows the tank 100 integrated into a fuselage of an aircraft so that the outer vessel 30 of the tank forms a fuselage section 300 of the aircraft connected between a first mating fuselage section 330 and a second mating fuselage section 332. In these embodiments annular flanges 33 provide forward and aft mounting locations. In these embodiments the annular flanges 33 extend outwardly at the forward and aft ends of the outer vessel 30 to form a mating joint with the first 330 and second 332 fuselage sections, respectively. Thus, the annular flanges provide an integral butt-strap or lap joint. The joints may be fastened with fasteners, or by any other appropriate fastening means.

[0062] In the embodiment illustrated in FIG. 5A a longitudinal flange 32 extending outwardly from an upper region of the outer vessel 30 may provide a mounting location for systems and/or control components (e.g. cabling or ducting) passing through the fuselage. A fairing 340 encloses the upper region of the tank 100 to conceal the flange 32 and the systems and/or control components to improve aerodynamic performance. In other embodiments the longitudinal flange 32 and the fairing 340 may be omitted, as shown in FIG. 5B.

[0063] In preferred embodiments the outer vessel 30 will be formed from a material with similar thermal properties to that of the airframe components to which it is connected, in order to avoid thermal loading effects. For example, the outer vessel 30 and airframe components may be formed from a reinforced fibre composite material, such as a carbon fibre reinforced composite material.

[0064] The outer vessel 30 is distinguished by its integral flanges, including longitudinal flanges 32 and annular flanges 33. The mounting locations may be provided on the integral flanges, and/or the integral flanges may provide mounting sites for structural, systems or other components. In particular, the integral flanges may be joined to structural airframe components to enable load transfer between the outer vessel 30 and the airframe.

[0065] The longitudinal flanges 32 extend longitudinally along the outer vessel, and upon which the mounting locations are provided. That is, the outer vessel 30 comprises a pair of outwardly extending longitudinal flanges 32, each flange providing one of each of the pairs of mounting locations described above. In the FIG. 3 embodiment each flange carries one of: the pair of front spar mounting locations 60; the pair of rear spar mounting locations 62; and the (optional) pair of aft mounting locations 64. In the FIG. 4 embodiment each flange carries one of: the pair of forward mounting locations 70; and the pair of rear mounting locations 72. Thus, the flanges 32 each provide a mounting member for mounting the tank 100 to an airframe of an aircraft. The flanges 32 may also provide mounting locations for other structural components, or for systems components.

[0066] The two annular flanges 33 (seen most readily in FIGS. 5A to 5C, but present in all illustrated embodiments) extend around an outer periphery of the outer vessel 30. As described below, the annular flanges 33 are formed at a join between the upper 38 and lower 34 panels and the end cap 44, and at a corresponding join between the upper 38 and lower 34 panels and the bulkhead 46.

[0067] The integral flanges 32, 33 may be shaped such that they have a greater height, thickness, volume and/or surface area in the region of a mounting location. In this way, secondary joining parts such as butt-straps can be eliminated, thus saving weight and design complexity. The flanges 32, 33 are also typically shaped to enable sealing at the joint between the flange and airframe structure. For example, where the flange provides a lap joint the flange may be shaped to provide a sufficient lapped area to enable adequate sealing. Similarly, the flange may be shaped to provide a close fit with adjoining structural components, as shown in FIG. 3. Thus, additional aerodynamic panels for sealing can also be eliminated.

[0068] In some embodiments the mounting locations are provided in the form of fasteners, e.g. pins or bolts, that pass through fastener holes in the flanges 32. One example is illustrated in FIG. 6, which shows fasteners in the form of pins 42 that connect the flanges 32 to a structural member of the airframe 400. In the illustrated arrangement the heads of the pins 42 are countersunk to avoid unwanted steps in the aerodynamic surface that could reduce aerodynamic performance. The pins 42 are located within tapered bushes 43 inserted into fastener holes in the flanges 32, to create a locating and locking feature for the pins 42. This design solution is considered particularly advantageous because it will not be subject to fatigue failure.

[0069] A key advantage of providing the mounting locations on the flanges 32 in this way is that the fasteners do not penetrate the insulating volume 50. This both avoids the creation of a potential leakage route for vacuum or cryogenic fluids and the possibility of outgassing at a fastener site causing an electro-magnetic hazard, or lightning strike risk.

[0070] In preferred embodiments the outer vessel 30 is assembled from four main structural components, as illustrated in FIG. 5: lower panel 34, upper panel 38, end cap 44 and bulkhead 46.

[0071] In the illustrated embodiment the lower panel 34 comprises a generally U-shaped member with a curved base 35 and a pair of upstanding opposing walls 36. The lower panel 34 is formed from a thin sheet, or panel, which in this embodiment is reinforced by longitudinal stringers 37. The upper panel 38 is generally W-shaped in cross-section, such that it has a curved top portion 39 sandwiched between two upstanding flange portions 40. Like the lower panel, the upper panel 38 is formed from a thin sheet or panel, which in this embodiment is reinforced by longitudinal stringers 37. In related embodiments the flange portions 40 (and their cooperating opposing walls 36) may be provided so that they are not parallel to one another as shown, but are instead formed at an angle to one another, for example at an acute angle so that they diverge in the manner of the arms of a V-shape. When assembled, the upper panel 38 is slotted into the lower panel 34 such that the flange portions 40 overlap with the upper portions of the upstanding walls 36 to form the longitudinal flanges 32 of the outer vessel 30. This is best understood by review of FIG. 6.

[0072] In some embodiments a series of fasteners (not shown) connect the flange portions 40 with the upstanding walls 36, with the benefit that this both avoids the creation of a potential leakage route for vacuum or cryogenic fluids and the possibility of outgassing at a fastener site causing an electro-magnetic hazard, or lightning strike risk. In other embodiments this connection may be provided by co-curing or co-bonding during manufacture of the outer vessel 30. In mechanically fastened embodiments the joint between the flange portions 40 and upstanding walls 36 is sealed by providing a layer of interfay sealant 48 between the mating faces. An aerodynamic seal 49 (which can be attached to the flange) fills a gap between each flange 32 and the aircraft aerodynamic surface.

[0073] An end cap 44 encloses one end of the tube-like volume formed by the assembled upper 38 and lower 34 panels, and a reinforced bulkhead 46 encloses the other end. Either or both of these parts may comprise outwardly-extending annular flanges 33 to permit mounting of structural or systems components of the tank 100 or the airframe 400. These outwardly-extending annular flanges 33 comprise an overlap (or lap joint) between upper 38 and lower 34 panels and the end cap 44 and a corresponding overlap (or lap joint) between upper 38 and lower 34 panels and the bulkhead 46. These joints can be fastened via mechanical fasteners, bonding or co-bonding. Where mechanical fasteners are used as the joining means, the fasteners do not protrude into the insulating volume 50 of the tank avoiding the creation of a potential leakage route for vacuum or cryogenic fluids and the possibility of outgassing at a fastener site causing an electro-magnetic hazard, or lightning strike risk.

[0074] The bulkhead 46 is typically the final component to be assembled to enclose the outer vessel 30 around the inner vessel 10 and any systems components to be provided within the insulating volume 50.

[0075] FIGS. 9A-C illustrate possible configurations for this joint to provide adequate sealing of the insulating volume 50. The annular flange 33 is formed as a joint between mating annular flanges of the bulkhead 46 and the assembled upper 38 and lower 34 panels. A layer of interfay sealant 84 is provided between the mating surfaces.

[0076] In the arrangement shown in FIG. 9A an annular sealing channel 80 extends around the mating face of the annular flange of the bulkhead 46, an O-ring type seal 82 and/or bead of sealant material being provided within the sealing channel 80 during assembly to provide a fluid-tight seal between the bulkhead 46 and the assembled upper 38 and lower 34 panels.

[0077] In the arrangement shown in FIGS. 9B and 9C a bead of sealant material 86 is injected into the annular sealing channel 80 by a sealant gun 87 via one of a plurality of sealant ports 88. The sealant ports 88 comprise channels extending through the full thickness of the assembled upper 38 and lower 34 panels, with an opening configured to enable insertion of the nozzle of a sealant gun 87. When sealant material exits from another of the sealant ports 88 this indicates that the sealant channel 80 is adequately filled with sealant material.

[0078] This design in which the outer vessel 30 is assembled from a number of structural components simplifies the tooling required for its manufacture, while simultaneously providing a mounting member in the form of the longitudinal flanges 32 and annular flanges for mounting the tank 100 to the airframe and carrying flight loads, thermal loads and/or propulsion loads.

[0079] The inner vessel 10 is mounted within the outer vessel 30 by vessel mounting means located on the longitudinal axis 16, the vessel mounting means including a fixed mount 20 and a floating mount 24.

[0080] The fixed mount 20 is located at one axial end of the inner vessel 10 and provides a rigid connection between the two vessels, through which conduits 22 of the fuel systems enter the inner vessel 10. The conduits 22 in this embodiment include a refuel line 22a, liquid fuel outlet line 22b, pressure line 22c, and vent line 22d. The floating mount 24 at the other axial end of the inner vessel 10 provides a floating (or flexible) connection between the inner 10 and outer 30 vessels, that allows relative movement therebetween. Thus, the inner vessel 10 is isolated (either fully or partially) from loads carried by the outer vessel 30. That is, the inner vessel 10 experiences no or minimal distortion as a result of movement or deformation of the outer vessel 30 caused by flight loads, thermal loads, propulsion loads, or a combination of all three.

[0081] The floating mount 24 is illustrated in FIG. 7. A generally horizontally-orientated shaft 25 with an outer bearing surface is rigidly mounted to the domed end cap of the outer vessel 30 so that it projects inwardly into the insulating volume 50. A cooperating sleeve 26 with a cooperating inner bearing surface is able to slide along the bearing surface of the shaft 25 and rotate relative to it about the shaft's longitudinal axis. The sleeve 26 is rigidly mounted to the domed end cap of the inner vessel 30. The shaft 25 is formed either partially or fully from a thermally-insulating material such as a glass-fibre reinforced composite material (GFRP) in order to isolate the outer vessel 30 from the low temperatures of the cryogenic fluid contained by the inner vessel 10. In alternative embodiments, the shaft 25 may have an alternative orientation; for example, it may be generally vertically-orientated.

[0082] In preferred embodiments the outer vessel 30 is formed from a composite material. For example, the lower panel 34, upper panel 38 and end cap 44 may be moulded from a fibre reinforced composite material such as a carbon fibre reinforced material. The bulkhead 46 may be machine formed from a metal such as aluminium, or alternatively may be moulded from a fibre reinforced composite material. In some embodiments the lower panel 34, upper panel 38 and end cap 44 may be integrally formed. The inner vessel 10 is preferably formed from a metal such as aluminium, but in some embodiments may also be fibre reinforced material.