Fuel conditioning system for powering an aircraft turboshaft engine and associated method

Abstract

A fuel conditioning system configured to supply an aircraft turboshaft engine positioned in an engine frame of reference with fuel from a cryogenic tank positioned in an aircraft frame of reference. The conditioning system comprises a fuel circuit through which a fuel flow circulates. The fuel circuit includes at least one first heat exchanger in the aircraft frame of reference and at least one second heat exchanger in the engine frame of reference. The first heat exchanger is connected to the second heat exchanger by a connecting pipe linking the aircraft frame of reference to the engine frame of reference. The system includes at least one heating coil wound around the connecting pipe so as to define a plurality of turns. The heating coil is configured to circulate a heating fluid so as to heat the connecting pipe. Abstract figure: Figure 3

Description

Title of the invention: Fuel conditioning system for powering an aircraft turboshaft engine and associated method. Technical field

[0001] The present invention relates to the field of aircraft comprising one or more turbomachines powered by fuel stored in a cryogenic tank.

[0002] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new types of aircraft and those already in service, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively working for several years now to contribute to the fight against climate change.

[0003] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors impacting all phases of design and development in order to obtain aeronautical components and products that are less energy-intensive, more environmentally friendly, and whose integration and use in civil aviation have moderate environmental consequences, with the aim of improving the energy efficiency of aircraft.

[0004] Consequently, the Applicant is constantly working to reduce its negative climate impact by using methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, in particular through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and, as essential complements to technological progress, aviation biofuels.

[0006] To this end, the invention is the result of technological research aimed at significantly improving aircraft performance and, in this sense, contributes to reducing the environmental impact of aircraft. For this purpose, the invention relates to the field of aircraft comprising one or more turbomachines powered by fuel stored in a cryogenic tank.

[0007] It is known to store fuel, particularly hydrogen, in liquid form to limit the size and mass of aircraft tanks. For example, fuel is stored at a temperature of around 20 to 22 Kelvin (-253 to -251°C) in a cryogenic tank on the aircraft.

[0008] In order to be injected into the combustion chamber of a turbomachine, the fuel must be conditioned, that is, pressurized and heated, to allow for optimal combustion. Conditioning is necessary, for example, to reduce the risk of icing, that is, the solidification of the water vapor contained in the air circulating in the turbomachine, particularly at the turbomachine's fuel injectors. With reference to [Fig. 1], a prior art SCAA conditioning system is shown, comprising a fuel circuit 101 connected at its inlet to a cryogenic tank R and at its outlet to the combustion chamber CC of a turbomachine M. A fuel flow Q circulating from upstream to downstream in the fuel circuit 101 passes successively through a mechanical pump 102 and a heating module 103. The pump 102 circulates the fuel flow from upstream to downstream.

[0009] As is known, a heating module 103 allows the circulation of one or more hot fluids to supply heat to the fuel flow Q. Each hot fluid can be either a heat transfer fluid or a fluid from a heat source available on board the aircraft (such as hot air, hot gases from the turbomachine outlet, hot engine oil, etc.). Due to the very low temperature of the fuel flow Q exiting the cryogenic tank R, there is a risk that the hot fluid circulating in the heating module 103 may freeze within the module, which could damage the heating module 103 or affect its efficiency.

[0010] With reference to [Fig. 2], a fuel conditioning system SCAA2 is known, comprising two separate heat exchangers 131, 132 mounted successively in the fuel circuit 101. The first heat exchanger 131, through which a hot fluid circulates, heats the fuel flow Q to a primary temperature T1, higher than the solidification temperature of the hot fluid, so that the fuel is in a gaseous state in a connecting pipe ZI linking the first heat exchanger 131 to the second heat exchanger 132. The second heat exchanger 132, through which a hot fluid circulates, heats the fuel flow to a secondary temperature T2, higher than the primary temperature TL. The fuel flow Q, having reached a sufficiently high temperature at the outlet of the second exchanger 132, can then be introduced into the turbomachine M.The fuel flow Q thus circulates from an aircraft reference frame RA, including the cryogenic tank R and the first heat exchanger 131, to a . RM engine reference, including the second heat exchanger 132 and the M engine.

[0011] The connecting pipe ZI allows the aircraft reference frame RA to be linked to the engine reference frame RM via a complex, compact connection path. The connecting pipe ZI is in contact with ambient air, which is susceptible to icing due to the low temperature of the fuel within the connecting pipe ZI.

[0012] In order to ensure the proper functioning of the fuel circuit 101, it is necessary to ensure the thermal insulation of the connecting pipe ZI.

[0013] It is known to use a connecting pipeline comprising an inner pipe through which the fuel flows and an outer pipe that is evacuated to provide thermal insulation and reduce the risk of icing with ambient air, which could damage the connecting pipeline. This has the disadvantage of increasing the weight of the connecting pipeline and thus increasing the aircraft's fuel consumption. It also has the disadvantage of requiring so-called "bayonet" fittings, known to those skilled in the art, to maintain a vacuum between the connected connecting pipelines. These bayonet fittings are complex to manufacture and install, and make handling and maintenance of the connecting pipeline more cumbersome.

[0014] To eliminate these drawbacks, it is known to use a connecting pipe with a single conduit and to insulate it by surrounding it with a layer of insulating material. However, these materials are very sensitive to surface defects, and a crack in the material exposes the outer wall of the pipe to the ambient air. The water present in the ambient air is then liable to freeze upon contact with the pipe through which the fuel flows.

[0015] The invention thus aims to eliminate at least some of these drawbacks, by proposing a simple temperature conditioning system that is not very sensitive to exposure to ambient air. PRESENTATION OF THE INVENTION

[0016] The invention relates to a fuel conditioning system configured to supply an aircraft turboshaft engine positioned in an engine frame of reference with fuel from a cryogenic tank positioned in an aircraft frame of reference. The conditioning system comprises a fuel circuit connected at the inlet to the cryogenic tank and at the outlet to the turboshaft engine, with a fuel flow circulating from upstream to downstream in the fuel circuit. The fuel circuit includes: • at least one first heat exchanger in the aircraft frame of reference. configured to heat the fuel flow, • at least one second heat exchanger in the engine reference system configured to heat the fuel stream before it feeds the aircraft turboshaft engine, • the first heat exchanger being connected to the second heat exchanger by at least one connecting pipe linking the aircraft reference frame to the engine reference frame.

[0017] The fuel conditioning system is notable in that it includes at least one heating coil wound around the connecting pipe so as to define a plurality of turns, the heating coil being configured to circulate a heating fluid so as to warm the connecting pipe.

[0018] The fuel conditioning system advantageously maintains the outer wall of the connecting pipe at a temperature above 0°C despite the temperature difference between the ambient air and the fuel flow circulating in said connecting pipe. The fuel conditioning system thus eliminates the formation of frost on the outer wall of the connecting pipe, thereby ensuring its thermal insulation. The fuel conditioning system advantageously allows the use of a cost-effective, compact, and easy-to-maintain single-walled pipe. Furthermore, the heating coil installation is simple, practical, and quick. The fuel conditioning system is ideal for connecting different reference points that are far apart with complex connecting paths.The heating coil can be wrapped around various types of connecting pipes, adapting to their geometry and route. Using a heating coil eliminates the need for full-length insulation covering the connecting pipe, thus reducing the cost and weight of thermal insulation.

[0019] In one aspect, the heating coil extends along the entire length of the connecting pipe. Thanks to this, the entire connecting pipe is protected from frost formation.

[0020] According to one aspect, the connecting pipe extends along a pipe axis, and the heating coil's turns are spaced along the pipe axis with a spacing between 5 mm and 100 mm. This reduces the mass of the heating coil while protecting the exposed portions of the connecting pipe's outer wall from freezing. The spacing takes advantage of thermal conduction through the connecting pipe's outer wall to heat the exposed portions.

[0021] According to one aspect, the fuel stream is hydrogen.

[0022] According to one aspect, the heating fluid has a temperature between 300 and 500 Kelvin. This optimizes the heating of the outer wall of the connecting pipeline, maintaining its temperature above 0°C. Furthermore, it allows the outer wall of the connecting pipeline to be heated without excessively warming the fuel flow, ensuring its transport under ideal conditions.

[0023] In one aspect, the heating fluid is fuel that has been preheated in the engine's reference frame. This advantageously reduces the aircraft's weight because it eliminates the need for a separate heating fluid tank. Furthermore, it eliminates the need for a dedicated heat exchanger for the heating fluid. Consequently, the risk of heating fluid icing in the heating coil is eliminated.

[0024] According to one aspect, the heating fluid is reinjected into the fuel circuit at the connecting pipe. This reduces the length of the heating coil for the heating fluid circulation by eliminating the need for a return line. This reduces the energy required for the fluid to pass through the second heat exchanger, thus lowering the aircraft's energy consumption. The heating circuit advantageously has a simpler structure and a shorter length.

[0025] The invention also relates to an aircraft comprising a fuel conditioning system as described above.

[0026] The invention also relates to a method for conditioning fuel for an aircraft turboshaft engine from fuel taken from a cryogenic tank by means of a conditioning system as described above, the method comprising steps consisting of: • Circulate a flow of fuel through the connecting line, and • Circulating a heating fluid through the heating coil of in order to heat the connecting pipe. PRESENTATION OF THE FIGURES

[0027] The invention will be better understood upon reading the following description, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

[0028] Fig. 1 is a schematic representation of a fuel conditioning system according to a prior art.

[0029] Fig. 2 is a schematic representation of a fuel conditioning system according to a second prior art.

[0030] Fig. 3 is a schematic representation of a fuel conditioning system according to a first embodiment.

[0031] Fig. 4 is a schematic representation of a fuel conditioning system according to a second embodiment.

[0032] Fig. 5 is a schematic profile representation of a heating coil wound around a connecting pipe.

[0033] Fig. 6 is a schematic cross-sectional front view representation of a heating coil wound around a connecting pipe.

[0034] Fig. 7 is a schematic cross-sectional profile representation of a portion of a heating coil wound around a connecting pipe.

[0035] It should be noted that the figures set out the invention in detail to implement the invention, said figures being of course able to serve to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0036] With reference to [Fig. 3], the invention relates to a fuel conditioning system SC configured to supply an aircraft turboshaft engine T positioned in an engine frame of reference RM with fuel Fl from a cryogenic tank RI positioned in an aircraft frame of reference RA. The fuel stream Fl is stored at a temperature of approximately 20 to 22 Kelvin (-253 to -251°C) in the cryogenic tank RL

[0037] The engine reference frame RM comprises elements integrated by an engine manufacturer, while the aircraft reference frame RA comprises elements integrated by an aircraft manufacturer. The elements of the two reference frames RM and RA are subject to different constraints, particularly of pressure and temperature. Thus, the fuel Fl must be conditioned and maintained at a predetermined temperature and pressure to be used in the turboshaft engine T without being altered by environmental constraints during its transfer from the aircraft reference frame RA to the engine reference frame RM.

[0038] For this purpose, the conditioning system SC includes a fuel circuit CF connected at the inlet to the cryogenic tank RI and at the outlet to the turboshaft engine T. A fuel flow Fl circulates from upstream to downstream in the fuel circuit CF.

[0039] In this example, the CF fuel circuit is a cryogenic fuel circuit for an aircraft turbomachine, in particular in which the fuel Fl is hydrogen.

[0040] With reference to [Fig.3], the fuel circuit CF transports the fuel Fl from the aircraft reference frame RA to the engine reference frame RM.

[0041] The CF fuel circuit comprises, from an upstream to a downstream point: • a first heat exchanger 31 in the aircraft reference frame RA configured to heat the fuel flow Fl, and • a second heat exchanger 32 in the engine reference frame RM configured to heat the fuel flow Fl before supplying the aircraft turbo-engine T, • a connecting pipe 1 linking the first heat exchanger 31 to the second heat exchanger 32.

[0042] In this example, the CF fuel circuit includes a pump 4 which draws a flow of fuel Fl from the cryogenic RI reservoir to circulate it through the CF fuel circuit.

[0043] The aircraft reference frame RA includes the cryogenic tank RI and the first heat exchanger 31 so as to heat the fuel to a sufficient temperature to allow the fuel flow Fl to be routed between the two reference frames RA, RM via the connecting pipe 1.

[0044] The engine reference frame RM includes the second heat exchanger 32 and the turbomotor T. The second heat exchanger 32 is configured to heat the fuel to an optimal temperature for its combustion in the turbomotor T, for example, between 200K and 500K.

[0045] In this example, only two heat exchangers 31, 32 are present, but their number could be different. In this example, the first heat exchanger 31 raises the fuel Fl to a transport temperature between 80 and 200 Kelvin. The second heat exchanger 32 then raises its temperature to a service temperature between 200 and 500 Kelvin in order to supply the turboshaft engine T.

[0046] The connecting pipe 1 thus makes it possible to link the aircraft reference frame RA to the engine reference frame RM and can extend along complex-shaped circulation paths whose isolation and maintenance are complex as previously presented in the preamble.

[0047] In this example, with reference to [Fig.5] and [Fig.6], the connecting pipe 1 has an outer wall PI which extends along a pipe axis Xc from upstream to downstream, and in which the fuel FL flows. In this example, the connecting pipe 1 is rigid, but it could also be flexible in order to adapt to space constraints.

[0048] With reference to [Fig. 4], the fuel conditioning system SC comprises a heating coil 2 wound around the connecting pipe 1 so as to define a plurality of turns 21. The heating coil 2 is mounted on the connecting pipe 1 so as to heat its outer wall PI in order to prevent it from freezing upon contact with ambient air. Advantageously, the heating coil 2 also provides heat to the fuel Fl in the connecting pipe 1.

[0049] The heating coil 2 is configured to circulate a heating fluid F2 so as to heat the connecting pipe 1. For this purpose, it includes a input 22 connected to a heating source and an output 23, as will be described in more detail later.

[0050] With reference to [Fig.5] and [Fig.6], the heating coil 2 is wound around the connecting pipe 1 so as to be in contact with the connecting pipe 1. This allows the heat from the heating coil 2 to the outer wall PI of the connecting pipe 1 to be transmitted more efficiently by thermal conduction.

[0051] Preferably, the heating coil 2 is made of a metallic material, for example, aluminum or stainless steel, and the outer wall PI of the connecting pipe 1 is also made of a metallic material, for example, aluminum or stainless steel, to allow better thermal conduction.

[0052] Preferably, the heating coil 2 extends over the entire length of the connecting pipe 1 so as to avoid any risk of icing.

[0053] With reference to [Fig. 5], the turns 21 are spaced at a pitch L21 along the axis of the pipe Xc so as to be disjointed. Preferably, the pitch L21 is between 5 mm and 100 mm. Such a pitch L21 optimizes the mass of the heating coil 2 while allowing satisfactory heating of the connecting pipe 1, preventing icing between the turns 21.

[0054] Indeed, as illustrated in [Fig. 7], the turns 21 directly heat certain covered portions of the outer wall PI by thermal conduction. The uncovered portions P12 of the outer wall PI, which are not in contact with the turns 21 due to the presence of the spacing L21, are heated by thermal conduction through the outer wall PI thanks to the covered portions of the Pli. Thus, the uncovered portions P12 of the outer wall PI that are in contact with the ambient air are heated and do not frost up.

[0055] It goes without saying that the turns 21 could also be joined.

[0056] In this example, with reference to [Fig.5], the turns 21 are wound in a circular manner so as to conform to the shape of the connecting pipe 1. It goes without saying that the shape of the turns 21, and therefore of the heating pipe 2, could be different depending on the shape of the connecting pipe 1.

[0057] In this example, with reference to [Fig. 5], all the turns 21 of the heating coil 2 have a circular cross-section. This facilitates the manufacture of the heating coil 2. Alternatively, the cross-section of each turn 21 could vary depending on the area of ​​the connecting pipe 1 with which it is in contact, so as to better conform to its shape and optimize thermal conduction.

[0058] Preferably, with reference to Figures 3 and 4, the conditioning system SC includes a heating circuit CC in which the heating fluid F2 circulates. The heating coil 2 belongs to the heating circuit CC.

[0059] According to a first embodiment, with reference to [Fig. 3], the heating fluid F2 is a heat transfer fluid circulating in a closed loop in the heating circuit CC. In this embodiment, the heating fluid F2 is heated by a heat source 33, in particular, a heat exchanger extracting heat from the engine frame RM, preferably from the turboshaft engine T. The heating fluid F2 can be in the form of an inert gas, such as nitrogen or helium, or a liquid, such as oil.

[0060] According to a second embodiment, with reference to [Fig. 4], the heating circuit CC is fluidically connected to the fuel circuit CF. In this embodiment, the heating fluid F2 is fuel drawn from the outlet of the second heat exchanger 32 in the engine frame RM. The inlet 22 of the heating coil 2 is connected to the fuel circuit CF downstream of the second heat exchanger 32. The outlet 23 of the heating coil 2 is connected to the fuel circuit CF downstream of the first heat exchanger 31, specifically to the connecting pipe 1. This makes it possible to limit the length of the heating coil 2 for the circulation of the heating fluid by avoiding the need for a return pipe. This prevents disturbing the thermodynamic equilibrium of the fuel Fl before it passes through the first heat exchanger 31.The Fl fuel is thus heated and requires less heat from the second heat exchanger 32, thereby reducing energy expenditure.

[0061] Preferably, the heating circuit CC includes a heating fluid drive element F2, for example a pump, a compressor or a circulator to ensure flow in the heating coil 2.

[0062] A jet pump can be used to provide a vacuum to draw the fluid into the DC heating circuit.

[0063] Preferably, the heating fluid F2 has a heating temperature T2 between 300 and 500 Kelvin. The heating fluid F2 thus transmits its heat through the wall of the heating coil 2 to the outer wall PI of the connecting pipe 1 so as to prevent any icing of the outer wall PL. The outer wall PI of the connecting pipe 1 is advantageously maintained at a temperature above 275 Kelvin, even if the entire surface of the outer wall PI is not covered by coils 21.

[0064] Preferably, the heating fluid F2 circulates in the opposite direction to the fuel Fl circulating in the connecting pipe 1. This notably improves heat exchange.

[0065] An example of the implementation of a fuel conditioning process for a Aircraft turboshaft engine T from fuel Fl from a cryogenic tank RI by means of the SC conditioning system will be presented.

[0066] The process includes a step of circulating fuel Fl through the connecting pipe 1. For this purpose, the fuel is drawn from the tank RI and then heated by the first heat exchanger 31 so that the fuel temperature is between 80 and 200 K in the connecting pipe 1. Such a temperature is advantageous because it ensures that the cryogenic fuel vaporizes (or becomes supercritical steam), thus guaranteeing stability of its density with respect to temperature changes. This ensures better stability of the circuit as a whole despite the thermal inputs on the exposed sections and the sections covered and heated by the heating coil 2.

[0067] The process includes a step of circulating the heating fluid F2 through the heating coil 2 so as to heat the connecting pipe 1 and prevent it from freezing. For this purpose, as illustrated in [Fig. 4], hot fuel Fl is drawn downstream of the second heat exchanger 32 and then injected into the heating coil 2. The fuel Fl circulating in the heating coil 2 is then reinjected into the connecting pipe 1.

[0068] At the outlet of the connecting pipe, the fuel Fl has warmed up slightly and must be warmed up by the second heat exchanger 32 in order for the fuel Fl to be consumed.

[0069] Thanks to the invention, the connecting pipe 1 can conveniently link the two reference frames RA, RM by following complex paths, given its small size and optimal protection against icing. The use of a heating coil 2 eliminates the need for a protective covering over the entire connecting pipe 1, thus reducing cost and weight.

[0070] It goes without saying that the heating coil 2 could also be used to heat other components of the CF fuel circuit, for example, a valve, a compressor, a pump, or even a pipe fitting.

[0071] It goes without saying that the heating coil 2 could also be used to heat an oil circuit.

Claims

Demands

1. Fuel conditioning system (SC) configured to supply an aircraft turboshaft engine (T) positioned in an engine reference frame (RM) with fuel (Fl) from a cryogenic tank (RI) positioned in an aircraft reference frame (RA), the conditioning system (SC) comprising a fuel circuit (CF) connected inlet to the cryogenic tank (RI) and outlet to the turboshaft engine (T), a fuel flow (Fl) circulating upstream to downstream in the fuel circuit (CF), the fuel circuit (CF) comprising: • at least one first heat exchanger (31) in the aircraft reference frame (RA) configured to heat the fuel (Fl), • at least one second heat exchanger (32) in the engine reference frame (RM) configured to heat the fuel flow (Fl) before supplying the aircraft turboshaft engine (T),• the first heat exchanger (31) being connected to the second heat exchanger (32) by at least one connecting pipe (1) linking the aircraft frame of reference (RA) to the engine frame of reference (RM), system characterized in that it comprises at least one heating coil (2) wound around the connecting pipe (1) so as to define a plurality of turns (21), the heating coil (2) being configured to circulate a heating fluid (F2) so as to heat the connecting pipe (1).

2. Fuel conditioning system (SC) according to claim 1, wherein the heating coil (2) extends over the entire length of the connecting pipe (1).

3. Fuel conditioning system (SC) according to any one of claims 1 to 2, wherein, the connecting pipe (1) extending along a pipe axis (Xc), the turns (21) of the heating coil (2) are spaced along the pipe axis (Xc) by a spacing pitch (L21) between 5mm and 100mm.

4. Fuel conditioning system (SC) according to any one of claims 1 to 3, wherein the fuel stream (Fl) is hydrogen.

5. Fuel conditioning (SC) system according to one of the claims

6.

7.

8.

9. indications 1 to 4, in which the heating fluid (F2) has a temperature between 300 and 500 Kelvin. Fuel conditioning system (SC) according to any one of claims 1 to 5, wherein the heating fluid (F2) is fuel (Fl) previously heated in the engine reference frame (RM). Fuel conditioning system (SC) according to claim 6, wherein the heating fluid (F2) is reinjected into the fuel circuit (CF) at the connecting pipe (1). Aircraft comprising a fuel conditioning system (SC) according to any one of claims 1 to 7. A method for conditioning fuel for an aircraft turboshaft engine (T) from fuel (Fl) from a cryogenic tank (RI) using a conditioning system (SC) according to any one of claims 1 to 7, the method comprising steps consisting of: Circulate a flow of fuel (Fl) in the connecting pipe (1), and Circulate a heating fluid (F2) in the heating coil (2) so as to heat the connecting pipe (1).

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