Fuel pre-heater

Abstract

A fuel pre-heater comprising a pressure vessel containing a combustion zone for the combustion of a fuel and an oxidant, and a heat exchanger comprising an inlet manifold for the delivery of a heat transfer medium to a heat exchanger matrix. The heat exchanger is arranged downstream of said combustion zone. The inlet manifold successively branches or furcates into a plurality of sub-tubes at nodes along the length of the inlet manifold.

Description

[0001] Fuel Pre-Heater

[0002] The present disclosure relates to a fuel pre-heater, a method for pre-heating fuel using said fuel pre-heater, as well as a system comprising said fuel-heater and an aircraft or other vehicle comprising such a system.

[0003] Summary

[0004] There has been growing interest in the use of low or zero carbon fuels in transport applications, in particular, aerospace applications. One such fuel is hydrogen. The volumetric energy density of hydrogen is however significantly lower than conventional kerosene based aerospace fuels. One way to address this lower volumetric energy density is to store the hydrogen in liquid cryogenic form.

[0005] In order to use the hydrogen fuel in a gas turbine engine for example, there is a need to bring the hydrogen from its storage conditions to ambient or near ambient temperatures.

[0006] The present disclosure seeks to overcome or at least ameliorate the problems associated with the prior art.

[0007] According to a first aspect of the disclosure, there is provided a fuel pre-heater comprising: a pressure vessel containing: a combustion zone for the combustion of a fuel and an oxidant; and a heat exchanger comprising an inlet manifold for the delivery of a heat transfer medium to a heat exchanger matrix; wherein the heat exchanger is arranged downstream of said combustion zone; and wherein the inlet manifold successively branches or furcates into a plurality of sub-tubes at nodes along the length of the inlet manifold.

[0008] The fuel may be hydrogen. The oxidant may be air. In use, the combustion products from the combustion zone flow over the heat exchanger in the fuel pre-heater. The heat transfer medium may be cryogenic fuel such as hydrogen for direct pre-heating of fuel or may be helium, argon, neon, nitrogen, or carbon dioxide where pre-heating of the fuel is done via an intermediate heat exchanger. Other heat transfer mediums may be used, in particular those which are chemically inert. The fuel pre-heater may have applications with other fuels than hydrogen.

[0009] The combination of a combustion zone with a heat exchanger with an inlet manifold which successively branches into a plurality of sub-tubes at nodes along the length of the inlet manifold, advantageously seeks to provide a compact and efficient heat exchanger with a small physical envelope.

[0010] The manifold may branch or furcate at two successive nodes along its length. The manifold may branch or furcate at three or four or more successive nodes along its length.

[0011] The successive nodes may be arranged spaced at intervals along the longitudinally extent of the fuel pre-heater.

[0012] The sub-tubes may extend generally longitudinally, for example, at angles less than 90 degrees to the longitudinal axis of the pre-heater.

[0013] The tubes of the tube matrix may extend generally longitudinally with respect to the fuel-pre- heater.

[0014] Optionally, the fuel pre-heater further comprising an inlet tube section fluidly coupled to the inlet manifold and extending from a location proximate the downstream end of said heat exchanger through the heat exchanger matrix to the inlet manifold of the heat exchanger.

[0015] In this way, the feed to the inlet manifold of the heat exchanger may be kept away from the oxidant or air inlet to the fuel pre-heater.

[0016] Optionally, the successive branching or furcation of the inlet manifold at said nodes along the length of the inlet manifold has a fractal or quasi-fractal form.

[0017] Such branching seeks to provide a short distance from inlet to the tube matrix. The flow of the combustion products from the combustion chamber may pass evenly between the sub-tubes of the manifold.

[0018] Optionally, the respective nodes at which furcation of branching occurs in each sub-tube is aligned in a common generally flat plane extending generally perpendicular to the longitudinal extent of the sub-tubes.

[0019] In this way, the branching can be generally uniform at each successive node thereby providing generally matching temperature profiles in each sub-tube.

[0020] Optionally, the heat exchanger matrix is fluidly coupled to an outlet manifold which successively consolidates at nodes along the length of the outlet manifold. Optionally, the tubes within the tube matrix are generally consistently spaced from one another along their length. This seeks to allow the even flow and distribution of the combustion products between the tubes of the tube matrix.

[0021] Optionally, the tubes within the tube matrix are generally straight, curved, wavy or a combination thereof.

[0022] Optionally, the tube matrix comprises a plurality of modules arranged to form a generally ringshaped structure within said pressure vessel.

[0023] Such modules facilitate the manufacture and assembly of the heat exchanger and can allow faulty modules to be removed and replaced more readily.

[0024] Optionally, the fuel pre-heater further comprises an injector plate for the delivery of oxidant to said combustion zone.

[0025] Optionally, the injector plate is formed integrally with an oxidant inlet opening of the fuel-preheater.

[0026] Optionally, the fuel pre-heater further comprising a flow liner around said combustion zone. This flow liner seeks to maintain the hot combustion products from the combustion chamber away from the outer skin of the pressure vessel.

[0027] Optionally, the fuel pre-heater further comprising thermal insulation between the flow liner and the inner surface of the pressure vessel. Such insulation may serve to protect the pressure vessel material from the hot combustion products and allow less material to be used for the pressure vessel.

[0028] Optionally, the fuel pre-heater comprising a bypass channel for directing excess oxidant (oxidant that is not combusted) to an inner surface of the pressure vessel. This bypass channel may feed excess oxidant, such as air to keep the inner surface of the pressure vessel cool.

[0029] Such an oxidant channel may provide additional thermal protection to the pressure vessel material.

[0030] Optionally, a fluid drain hole is provided in said pressure vessel. The drain hold may serve to allow condensate to exit the pre-heater downstream of the heat exchanger and avoid the formation of frost which could impede the performance of the heat exchanger. The drain hold may be provided on the underside of the pre-heater so that gravity assists in removing the condensate.

[0031] Optionally, the fuel pre-heater further comprising an exhaust outlet. This allows the combustion products to exit the pre-heater. The exhaust outlet may be provided directly opposite the drain hole.

[0032] Optionally, a helical tube section is fluidly coupled to the outlet of the heat exchanger. The helical tube section seeks to allow for thermal expansion of the heat exchanger.

[0033] Optionally, the heat exchanger is fixed axially at its upstream end.

[0034] Optionally, the inlet manifold to said heat exchanger is generally rigid with respect to the pressure vessel.

[0035] Optionally, fins are provided extending from tube surfaces.

[0036] Optionally, the injector plate is formed integrally with said pressure vessel. This can serve to reduce part count and resultant weight.

[0037] Optionally, the fuel pre-heater further comprising a compliant ceramic filler between the heat exchanger and internal surface of the flow liner. This filler may serve to protect the internal surface of the flow liner and prevent combustion products from bypassing the heat exchanger.

[0038] Optionally, the fuel is hydrogen.

[0039] Optionally, the heat transfer medium is a cryogenic fuel, such as hydrogen. In this arrangement, the fuel is used to directly cool the heat exchanger of the fuel pre-heater.

[0040] Optionally, the heat transfer medium is one of helium, argon, neon, nitrogen, carbon dioxide, or another chemically inert fluid. In this arrangement, the heat transfer medium may warm the fuel via an intermediate heat exchanger. The intermediate heat exchanger may be provided externally to the fuel pre-heater.

[0041] According to a second aspect of the present disclosure, there is provided a system comprising: a fuel pre-heater according to the first aspect or any optional feature thereog; a fuel storage device; an oxidant compressor coupled via a shaft with a turbine driven by a main combustor; wherein the main combustor is fluidly coupled to the fuel storage device.

[0042] Advantageously, the system may provide for pre-heating of the fuel which fuel is used for the main combustor. A portion of the pre-heated fuel may be supplied to the pre-heater for combustion with oxidant in the combustion zone.

[0043] A fuel pump may be provided to pump fuel from the fuel storage device to the fuel pre-heater or to an intermediate heat exchanger. A fuel metering unit may control the fuel supplied to the system, the fuel pre-heater or the intermediate heat exchanger.

[0044] The oxidant in the compressor may be air. The fuel may be hydrogen.

[0045] A bleed from the oxidant compressor may be supplied to the fuel pre-heater to allow combustion in the combustion zone.

[0046] Optionally, the fuel storage device is fluidly coupled to the fuel pre-heater for providing fuel to the combustion zone of the fuel pre-heater. This may be after the fuel has passed through the intermediate heat exchanger when present.

[0047] Optionally, the fuel storage device is fluidly coupled to the inlet manifold of the heat exchanger of the fuel pre-heater. In this way, the fuel is directly heated in the heat exchanger of the fuel preheater by the combustion zone products.

[0048] Optionally, the fuel storage device is fluidly coupled to an intermediate heat exchanger and a heat transfer medium supply is fluidly coupled to the intermediate heat exchanger and said inlet manifold of the heat exchanger of the fuel pre-heater. In this arrangement, no fuel is supplied to the heat exchanger of the fuel pre-heater but rather the fuel is heated indirectly by an intermediate heat transfer medium.

[0049] According to a third aspect of the present disclosure, there is provided a method of pre-heating a fuel using the fuel pre-heater according to the first aspect or any optional feature thereof or a system according to the second aspect or any optional feature thereof. Using the fuel pre-heater can provide an effective, compact and efficient means of pre-heating fuel.

[0050] According to a fourth aspect of the present disclosure, there is provided a transport vehicle, comprising a fuel pre-heater according to the first aspect or any optional feature thereof or a system according to the second aspect or any optional feature thereof. The transport vehicle may include a land, sea or aerospace vehicle.

[0051] Brief Description of the Drawings

[0052] The present disclosure will be described purely by way of example with reference to and as illustrated in the accompanying drawings where:

[0053] Figure 1 is a partially cut away view of a fuel pre-heater comprising a heat exchanger;

[0054] Figure 2 is an enlarged view of the heat exchanger shown in Figure 1 ;

[0055] Figure 3 is a cross-section of the heat exchanger shown in Figures 1 and 2;

[0056] Figure 4 is a schematic flow diagram showing a system incorporating the fuel pre-heater as shown in Figure 2.

[0057] Figure 5 shows a schematic flow diagram showing a system incorporating the fuel pre-heater as shown in Figure 2 with an intermediate heat exchanger;

[0058] Figure 6 shows a partially cut away view of a further example fuel pre-heater comprising a heat exchanger; and

[0059] Figure 7 shows an external view of the fuel pre-heater of Figure 6.

[0060] Detailed Description

[0061] Figure 1 shows a partially cut away view of a fuel pre-heater 1 of the present disclosure. The fuel pre-heater comprises a pressure vessel 2, which in the example, is formed as a cylindrical tube. The pressure vessel 2 may be formed of any suitable material, for example a stainless steel. At a first, upstream end 3 of the pressure vessel 2 is an oxidant inlet opening 4, which in the example is supplied with air. Downstream of the inlet opening 4 is provided an injector plate 6 comprising a plurality of apertures or air ports 7 through which the oxidant may pass. In the example, each of the apertures 7 in the injector plate 6 is provided with two fuel injectors for the delivery of fuel. Downstream of the injector plate 6, a combustion zone 9 is provided within which the supplied oxidant, in this case air, combusts with the supplied fuel. Around the combustion zone 9 a flow liner 8 is provided. The flow liner 8 is formed as a cylindrical tube spaced from the inner surface of the pressure vessel 2. Sandwiched between the flow liner 8 and the internal surface 10 of the pressure vessel 2, insulation 25 may be provided. Downstream of the combustion zone 9, a heat exchanger 5 is provided. The heat exchanger 5 is supplied with an inlet tube section 12 which originates downstream of the heat exchanger 5 and passes through end plate 13 of the pressure vessel through the middle of the heat exchanger 5 to the upstream end of the heat exchanger 5. The inlet tube section 12 is fluidly coupled with an inlet manifold 11 which serves initially to turn the fluid provided to the heat exchanger 5 through 180 degrees.

[0062] The inlet manifold 11 to the heat exchanger 5 successively branches or furcates into a plurality of sub-tubes at nodes along the length of the inlet manifold 11. In the example shown in Figure 1 , the inlet manifold 11 furcates initially at the first node 16 into six sub-tubes 17. While different branching or furcation patterns may be provided depending on the application, in the example shown, the six sub-tubes 17 each further split at a second node point 18 into three further subtubes 19 making a total of eighteen second sub-tubes. Each of these eighteen second sub-tubes 19 then subsequently splits or furcates at third node point 20 into four third sub-tubes 21 resulting in seventy-two third sub-tubes 21. The seventy-two third sub-tubes 21 then each further split at fourth node point 22 into three fourth sub-tubes 23 resulting in a total of two-hundred-and-sixteen fourth sub-tubes 23. The of two-hundred-and-sixteen fourth sub-tubes 23 are fluidly coupled to a tube matrix 14, which in the example comprises a plurality of straight tubes 24. The straight tubes 24 of the tube matrix 14 are generally consistently spaced from one another along their length. The tubes of the inlet manifold 11 and also the tubes 24 of the tube matrix 11 extend in a direction substantially parallel with the longitudinal axis of the fuel pre-heater 1 .

[0063] The tube matrix 14 may comprise a number of submodules. In the example, the tube matrix 14 comprises six modules which together form a generally ring-shaped structure which extends longitudinally within the cavity within the fuel pre-heater 1.

[0064] At the downstream side of the tube matrix 14, the tubes consolidate through an outlet manifold 15 in a similar manner to the tube furcation at the inlet manifold 11. In the example, the two- hundred-and-sixteen first outlet sub-tubes 27 which are fluidly coupled to the tubes 24 of the tube matrix 14, consolidate in seventy-two second outlet sub-tubes 29 at first outlet node point 26. The seventy-two second outlet sub-tubes 29 further consolidate at second outlet node point 28 into eighteen third outlet sub-tubes 31 and subsequently into six fourth outlet sub-tubes 33 at third outlet node point 30. Three of the six fourth outlet sub-tubes 33 then consolidate into a first single helical tube 34 at fourth outlet node point 32. The remaining three sub-tubes of the six fourth outlet sub-tubes 33 consolidate into a second helical tube 35. These two helical tubes 34, 35 are interwound with one another and exit the fuel pre-heater 1 in first and second outlet tube sections 36, 37 through end plate 13 of the fuel pre-heater 1. In the region of the helical tubes 34, 35, the pre-heater 1 is provided with a drain hole 38 which allows for liquid condensate to be removed from the fuel pre-heater 1. This prevents excessive accumulation of frost on the heat exchanger 5.

[0065] An exhaust outlet 39 is provided which is positioned in the example opposite the drain hole 38.

[0066] The pressure vessel 2 is formed of stainless steel and resists internal pressures of up to approximately 20 bar.

[0067] Figure 2 shows an enlarged view of the heat exchanger 5. As outlined above, the inlet and outlet manifolds 11 , 15 to the heat exchanger 5 are similar in design apart from the first furcation node and the last consolidation node. The successive branching and furcation or consolidation of the tubes in the inlet and outlet manifolds 11 , 15 at nodes along the length of the inlet or outlet manifolds has a fractal or quasi-fractal form. The branching structures can be split into layers where within each layer the number of tubes is constant, the tubes moving closing together or further apart depending on the design and performance requirements of the heat exchanger 5. The furcation / branching or consolidation of the tubes occurs at nodes along the length of the inlet and outlet manifolds 11 , 15. In the example, each set of nodes in adjacent sub-tubes are arranged on a common plane and with the exception in the example shown of the first furcation node and the last consolation node, the flow direction of fluid within the tubes is generally parallel with the central longitudinal axis of the tube matrix.

[0068] As the number of tubes increases in the branching sections, the size of the tubes decreases although the total flow area available for tube side flow increases.

[0069] Within the tube matrix 14, the tubes are laid out in a pattern that ensures a consistent spacing between the tubes and to control the gap between the outermost tubes and the flow liner 8. In the example shown, the tubes are laid out on an equilateral triangular grid centred on the unit axis giving a tube pattern with a rotational symmetry of six. While the number of sub-tubes at a node point can vary, in the example shown, the rotational symmetry of the inlet and outlet manifolds is maintained.

[0070] The tubes of the tube matrix 14 may include partial or continuous fins that protrude from the otherwise circular tube surfaces, in order to better manage the temperature distribution and thermal stresses in the unit. The fins may join the tubes together along the triangular gridlines. The fins may be present for part or all of the length of the tubes within the tube matrix. Different designs of fin may be included at different axial positions. Figure 3 shows a cross section through the heat exchanger showing the internal tube passages. The heat exchanger 5, in particular the inlet and outlet manifold and tube matrix may be formed using a 3D printing process.

[0071] With reference to Figure 1 , in use, a heat transfer medium is supplied to the inlet tube section 12. The inlet tube section 12 flows through the centre of the tube matrix 14. At the upstream end of the heat exchanger 5, the inlet tube section 12 turns the flow of heat transfer medium through 180 degrees at a first node point 16 into six sub-tubes. The sub-tubes further furcate at subsequent nodes along their length before reaching the tubes 24 of the tube matrix 14. Fuel, which in the example is hydrogen, is supplied as a fuel to the injector plate 6. This hydrogen supplied to the injector plate 6 combusts with air supplied through the inlet opening 4 of the fuel pre-heater 1. The hot combustion gases subsequent flow over the outer surfaces of the heat exchanger 5 in order to increase the temperature of the heat transfer medium. In one example, the heat transfer medium is cryogenic hydrogen from a fuel store, of which a part is used for combustion in the preheater. In the example of hydrogen as the heat transfer medium, the hot combustion gases flowing over the surfaces of the heat exchanger bring the cryogenic supercritical hydrogen within the heat exchanger 5 to ambient conditions. The cryogenic supercritical hydrogen is generally at a temperature of 25 to 45 Kelvin and at a pressure of between 20 and 120 bar depending on the system specifics and throttle condition. The combustion products from the combustion zone 9 are typically at a temperature of between 800 and 1300 Kelvin. After passing over the heat exchanger 5, the combustion products exit via the exhaust outlet 39 at a temperature of between 500 and 800 Kelvin.

[0072] In the example, the injector plate 6 is of the micro-mix type. Hydrogen is injected at the injector plate 6 and the combustion happens on the downstream side of the injector plate 6 in the combustion zone 9.

[0073] The flow liner 8 with a circular cross-section extends downstream from the injector plate 6 and acts to contain the hot combustion gas and direct it towards the heat exchanger 5.

[0074] A seal 40 and mounts 41 are provided around the injector plate 6 that support both the flow liner 7 and the injector plate 6 and prevent air from bypassing.

[0075] The flow liner 7 is axially fixed at its upstream end but is free to expand axially at its downstream end to allow for thermal expansion. Insulation 25 is provided on the outside of the flow liner 8 to minimise heat transmission from the hot combustion gas to the outer pressure vessel 2. This seeks to ensure that an acceptable pressure vessel temperature is maintained. An alternative means to control the temperature of the pressure vessel can include, for example, allowing a small portion of the air approaching the combustion zone 9 to bypass and travel down the back side of the insulation 25 to remove any heat soaking therethrough.

[0076] There is a close fit between the outer heat exchanger tubes 24 and the inside of the flow liner 8. A compliant ceramic material can be used to fill the gaps and prevent direct contact between the heat exchanger 5 and the flow liner 7.

[0077] In the example shown, the inlet tube section 12 passes through the centre of the tube matrix 14. This advantageously allow the heat transfer medium inlet and outlet connectors to both be placed at the rear of the pressure vessel where the combustion gas is substantially cooler than in the region of the combustion zone. In an alternative configuration, heat transfer medium could be supplied through an inlet tube passing from the upstream end of the fuel pre-heater 1 through the centre of the injector plate 6 before connecting with the inlet manifold 11 of the heat exchanger 5.

[0078] As an alternative to hydrogen acting as the heat transfer medium, the heat exchanger 5 may be supplied with another fluid such as helium, argon, neon, nitrogen, or carbon dioxide. Other heat transfer mediums may be used, in particular those which are chemically inert. Heat transfer mediums other than the fuel to be preheated serve as an intermediate fluid requiring an additional heat exchanger to transfer heat between the intermediate fluid and the fuel to be preheated. Such an arrangement will be described in relation to Figure 5.

[0079] Figure 4 shows a system diagram incorporating the fuel pre-heater shown in Figures 1 to 3 in which hydrogen is used as the heat transfer medium in heat exchanger 5. Liquid hydrogen is stored in a liquid hydrogen tank 42. Hydrogen is stored at a temperature of around 20 Kelvin and 1.5 bar. A liquid hydrogen pump 43 is fluidly connected to the liquid hydrogen tank 42. The liquid hydrogen pump 43 supplies cold, high pressure liquid hydrogen at a temperature of 35 Kelvin and a pressure of 80 bar. The hydrogen is then fed to the heat exchanger 5 of the fuel pre-heater 1. The operation of the fuel pre-heater 1 has been described in relation to Figures 1 to 3. The hydrogen exits the heat exchanger 5 as shown by stream 54 at ambient temperature for example at 273 Kelvin and at a pressure of 80 bar. The hydrogen passes through a fuel metering unit 44 which provides a small proportion of the now ambient hydrogen via stream 52 to the fuel preheater 1 combustor 45 in order to combust with supplied air. The majority and remainder of the ambient high pressure hydrogen is supplied to a combustion chamber 46 of a gas turbine engine 47. The gas turbine engine 47 comprises a compressor 48 coupled via a shaft 49 to turbine 50. The gas turbine engine 47 may comprise a single-spool or multiple spools. The compressor 48 compresses the air to 50 bar and a temperature of 850 Kelvin. A bleed supply 51 of air at 15 bar and 600 Kelvin from the compressor 28 is supplied to the fuel pre-heater combustor 45. The combustion products of the main combustor 46 are at a temperature of 1800 Kelvin and a pressure of 50 bar. The combustion products from the fuel preheater 1 exit at 53. It will of course be understood that different temperatures and pressures may be provided for within the system depending on the application requirements. The system or the fuel pre-heater may be incorporated into a vehicle, for example, an aerospace vehicle in order to provide ambient or near ambient hydrogen to fuel the propulsion units of the vehicle.

[0080] Figure 5 shows a system diagram incorporating the fuel pre-heater shown in Figures 1 to 3 in which an intermediate heat exchanger 56 is utilised to preheat the hydrogen fuel. Liquid hydrogen is stored in a liquid hydrogen tank 42. Hydrogen is stored at a temperature of around 20 Kelvin and 1.5 bar. A liquid hydrogen pump 43 is fluidly connected to the liquid hydrogen tank 42. The liquid hydrogen pump 43 supplies cold, high pressure liquid hydrogen at a temperature of 35 Kelvin and a pressure of 80 bar. The hydrogen is then fed into intermediate heat exchanger 56. As a heat transfer medium, a chemically inert fluid may be used. In the example, nitrogen acts as the heat transfer medium and is circulated using circulator 57 to the heat exchanger 5 of the fuel preheater 1. The intermediate fluid circulator 57 is shown as being positioned after the intermediate heat exchanger 56, as this minimises the temperature of the heat transfer medium and thereby minimises the compression work, but other locations are also possible.

[0081] The operation of the fuel pre-heater 1 has been described in relation to Figures 1 to 3, the only difference here being that fuel, in this case, hydrogen is not used as the heat transfer medium within the fuel-preheater heat exchanger 5. The warmed nitrogen at 80 bar and 400 Kelvin exits the heat exchanger 5 and passes via stream 58 to the intermediate heat exchanger 56 where heat is transferred to the cold high pressure liquid hydrogen. After being heated in the intermediate heat exchanger 56, the hydrogen passes via stream 55 through a fuel metering unit 44 which provides a small proportion of the now ambient hydrogen via stream 52 to the fuel preheater 1 combustor 45 in order to combust with supplied air. The majority and remainder of the ambient high pressure hydrogen is supplied to a combustion chamber 46 of a gas turbine engine 47. The gas turbine engine comprises a compressor 48 coupled via a shaft 49 to turbine 50. The compressor 48 compresses the air to 50 bar and a temperature of 850 Kelvin. A bleed supply 51 of air at 15 bar and 600 Kelvin from the compressor 48 is supplied to the fuel pre-heater combustor 45. The combustion products of the main combustor 46 are at a temperature of 1800 Kelvin and a pressure of 50 bar. The combustion products from the fuel preheater 1 exit at 53. It will of course be understood that different temperatures and pressures may be provided for within the system depending on the application requirements. There is significant scope for varying the intermediate fluid temperatures and mass flows relative to the hydrogen mass flow in order to obtain the best system level design, balancing the size and complexity of the pre-heater, intermediate heat exchanger, and intermediate fluid circulator.

[0082] The system or the fuel pre-heater may be incorporated into a vehicle, for example, an aerospace vehicle in order to provide ambient or near ambient hydrogen to fuel the propulsion units of the vehicle.

[0083] Figure 6 shows a further example of a fuel pre-heater 101 with an injector plate 106 which is integral with inlet opening 104. This integrated part is provided at the inlet end 103 of the pressure vessel 102. The injector plate incorporates at its centre the same injector concept as the design of Figure 1 with a plurality of injector plate apertures 107. The integrated injector plate 106 and inlet opening 104 can be manufactured via additive manufacturing. This integrated part can replace the separate injector plate 6 and inlet opening 4 arrangement as shown in Figure 1.

[0084] In the example of Figure 6, the inlet opening 104 incorporates small circumferentially spaced air bypass channels 152 around its inner edge proximate to the upstream side of the injector plate 106. These small air bypass channels 152 allow a small amount of the incoming air to bypass the injector plate 106 and enter the space behind the flow liner 108 adjacent to internal surface 110. T o enable this air to flow, the thickness of the insulation 125 is reduced compared to the insulation 25 in Figure 1. The air entering the air bypass channels 152 provides cooling with the heat that soaks through the insulation 125 being absorbed by the cooler bypass air. This can allow the pressure vessel 102 to remain at approximately the temperature of the incoming bypass air, which allows for better control of the surface temperatures of the pressure vessel 102 which may be desirable in a typical aerospace application. As no heat needs to be rejected to the environment, the outside of the pressure vessel 102 is well insulated and the surface temperatures controlled. Air bypass holes 152 may be provided in the separate injector plate 6 as described in relation to Figure 1.

[0085] Apart from the intergrated injector plate 106 and inlet opening 104 and the air bypass channels 152, the fuel preheater 101 and its operation is the same as that described in relation to Figure 1 with the same heat exchanger 5 and can be provided in the systems described in relation to Figures 4 and 5. While no drain hole is shown in Figure 6, it should be understood that a drain hole can be also provided in the example of Figure 6 as described in relation to Figure 1. It will be understood that, although shown in the same example, the aspects of the integrated injector plate 106 and inlet opening 106 and the air bypass cooling as provided by air bypass holes 152 are not intrinsically linked and may be utilised separately or together. Figure 7 shows an external view of the example fuel preheater 101 of Figure 6 with air bypass holes 152 and integrated injector plate 106 and inlet 103.

[0086] The fuel pre-heater 1 and 101 of the present disclosure provide a compact and highly efficient apparatus to pre-heat the hydrogen fuel for use in aerospace applications.

Claims

Claims1. A fuel pre-heater comprising: a pressure vessel containing: a combustion zone for the combustion of a fuel and an oxidant; and a heat exchanger comprising an inlet manifold for the delivery of a heat transfer medium to a heat exchanger matrix; wherein the heat exchanger is arranged downstream of said combustion zone; and wherein the inlet manifold successively branches or furcates into a plurality of sub-tubes at nodes along the length of the inlet manifold.

2. A fuel pre-heater according to claim 1, further comprising an inlet tube section fluidly coupled to the inlet manifold and extending from a location proximate the downstream end of said heat exchanger through the heat exchanger matrix to the inlet manifold of the heat exchanger.

3. A fuel pre-heater according to any of the preceding claims, wherein the successive branching or furcation of the inlet manifold at said nodes along the length of the inlet manifold has a fractal or quasi-fractal form.

4. A fuel pre-heater according to any of the preceding claims, wherein the respective nodes at which furcation or branching occurs in each sub-tube is aligned in a common generally flat plane extending generally perpendicular to the longitudinal extent of the sub-tubes.

5. A fuel pre-heater according to any of the preceding claims, wherein the heat exchanger matrix is fluidly coupled to an outlet manifold which successively consolidates at nodes along the length of the outlet manifold.

6. A fuel pre-heater according to any of the preceding claims, wherein the tubes within the tube matrix are generally consistently spaced from one another along their length.

7. A fuel pre-heater according to any of the preceding claims, wherein the tubes within the tube matrix are generally straight, curved, wavy or a combination thereof.

8. A fuel pre-heater according to any of the preceding claims, wherein the tube matrix comprises a plurality of modules arranged to form a generally ring-shaped structure within said pressure vessel.14RECTIFIED SHEET (RULE 91) ISA / EP9. A fuel pre-heater according to any of the preceding claims, further comprising an injector plate for the delivery of oxidant to said combustion zone.

10. A fuel pre-heater according to claim 10, wherein the injector plate is formed integrally with an oxidant inlet opening of the fuel-preheater.

11. A fuel pre-heater according to any of the preceding claims, further comprising a flow liner around said combustion zone.

12. A fuel pre-heater according to any of the preceding claims, further comprising thermal insulation within said pressure vessel.

13. A fuel pre-heater according to claim 11 , further comprising a bypass channel for directing oxidant to an inner surface of the pressure vessel.

14. A fuel pre-heater according to any of the preceding claims, wherein a fluid drain hole is provided in said pressure vessel.

15. A fuel pre-heater according to any of the preceding claims, further comprising an exhaust outlet.

16. A fuel pre-heater according to any of the preceding claims, wherein a helical tube section is fluidly coupled to the outlet of the heat exchanger.

17. A fuel pre-heater according to any of the preceding claims, wherein the heat exchanger is fixed axially at its upstream end.

18. A fuel pre-heater according to any of the preceding claims, wherein the inlet manifold to said heat exchanger is generally rigid with respect to the pressure vessel.

19. A fuel pre-heater according to any of the preceding claims, wherein fins are provided extending from tube surfaces.

20. A fuel pre-heater according to any of the preceding claims, wherein the injector plate is formed integrally with said pressure vessel.

21. A fuel pre-heater according to any of the preceding claims, further comprising a ceramic filler on the between the heat exchanger and internal surface of the pressure vessel.15RECTIFIED SHEET (RULE 91) ISA / EP22. A fuel pre-heater according to any of the preceding claims, wherein the fuel is hydrogen.

23. A fuel pre-heater according to any of the preceding claims, wherein the heat transfer medium is a cryogenic fuel, such as hydrogen.

24. A fuel pre-heater according to any of claims 1 to 22, wherein the heat transfer medium is one of helium, argon, neon, nitrogen, carbon dioxide, or another chemically inert fluid.

25. A system comprising: a fuel pre-heater according to any of the preceding claims; a fuel storage device; an oxidant compressor coupled via a shaft with a turbine driven by a main combustor; wherein the main combustor is fluidly coupled to the fuel storage device.

26. A system according to claim 25, wherein the fuel storage device is fluidly coupled to the fuel pre-heater for providing fuel to the combustion zone of the fuel pre-heater.

27. A system according to claim 25, wherein the fuel storage device is fluidly coupled to the inlet manifold of the heat exchanger of the fuel pre-heater.

28. A system according to any of claims 25 to 26, wherein the fuel storage device is fluidly coupled to an intermediate heat exchanger and a heat transfer medium supply is fluidly coupled to the intermediate heat exchanger and said inlet manifold of the heat exchanger of the fuel preheater.

29. A method of pre-heating a fuel using the fuel pre-heater of any of claims 1 to 24 or the system of any of claims 25 to 28.

30. A transport vehicle, comprising a fuel pre-heater according to any of the claims 1 to 24 or a system according to any of claims 25 to 28.16RECTIFIED SHEET (RULE 91) ISA / EP

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