Double-walled heat exchanger for a fuel conditioning system

Abstract

The present invention relates to a heat exchanger for a fuel conditioning system of a turbine engine, the heat exchanger comprising: - a circulation space for a fuel to be heated, delimited by a first wall; - a circulation space for a hot fluid, delimited by a second wall; and - an exchange space between the circulation space for a fuel and the circulation space for a hot fluid, the exchange space being suitable for containing an inert gas and being delimited by the first wall and the second wall, the first wall and the second wall being connected by arms, and the exchange space being configured so that, during operation, the hot fluid heats the fuel by heat conduction.

Description

[0001] DESCRIPTION

[0002] TITLE: DOUBLE-WALLED HEAT EXCHANGER FOR A FUEL CONDITIONING SYSTEM

[0003] TECHNICAL FIELD

[0004] This disclosure relates to the field of aircraft comprising one or more turbomachines powered by fuel stored in a cryogenic tank. More specifically, this disclosure relates to a fuel conditioning system for supplying fuel to an aircraft turbomachine.

[0005] STATE OF THE ART

[0006] A fuel, particularly hydrogen, for powering an aircraft turbomachine can be stored in liquid form to limit the size and mass of the aircraft's tanks. For example, the fuel can be stored at a temperature of around 20 to 22 Kelvin (-253 to -251 °C) in a cryogenic tank on the aircraft.

[0007] It is possible to implement a conditioning system comprising a fuel circuit connected, at the inlet, to the cryogenic tank and, at the outlet, to the combustion chamber of the turbomachine. In order to be injected into the combustion chamber of the turbomachine while ensuring optimal combustion, the fuel must be conditioned, i.e. pressurized and heated.

[0008] In order to limit the energy consumption of the turbomachine, it is possible to use the heat from the hot gases produced by the turbomachine to heat the fuel circulating in the conditioning system.

[0009] However, it is necessary to avoid contamination between the fuel and an oxidant (such as the air contained in hot gases). Indeed, a mixture of fuel and air can easily ignite. The use of a conventional heat exchanger in which the oxidant and the fuel to be heated are separated by a single wall does not avoid this risk. Indeed, a break in the wall would induce the contamination to be avoided. GENERAL STATEMENT

[0010] One aim of the presentation is to propose a system reducing the risks of contamination of the fuel supplying a turbomachine during heating of the fuel by a flow of hot air from the engine.

[0011] To this end, according to one aspect of the present disclosure, a heat exchanger is proposed for a fuel conditioning system of a turbomachine, the heat exchanger comprising: a space for circulation of a fuel to be heated delimited by a first wall; a space for circulation of a hot fluid delimited by a second wall; and an exchange space between the space for circulation of a fuel and the space for circulation of a hot fluid, the exchange space being adapted to contain an inert gas and is delimited by the first wall and the second wall, the first wall and the second wall being connected by arms, the exchange space being configured so that in operation, the hot fluid heats the fuel by heat conduction.

[0012] This allows the fuel to be heated by reusing the heat produced by the turbomachine while limiting the risk of fuel contamination by the hot fluid coming from the turbomachine. The presence of a double wall separating the fuel flow from the hot fluid prevents fuel contamination by the hot fluid in the event of rupture of either the first or second wall.

[0013] In addition, such an exchanger makes it possible to dispense with the use of an intermediate circuit comprising a circulation loop for a heat transfer fluid, such an intermediate circuit necessarily comprising a pump for the circulation of the heat transfer fluid in order to promote convection in the heat transfer fluid and two separate exchangers between the intermediate circuit and the fuel and the hot fluid.

[0014] Advantageously, but optionally:

[0015] - the exchange space is a cavity comprising cells between the first wall and the second wall, the cells being delimited by the arms and being configured to store the inert gas;

[0016] - the first wall comprises first fins for increasing the heat exchange by conduction between the inert gas and the fuel, the first fins extending perpendicularly projecting from the first wall into the fuel circulation space;

[0017] - the second wall comprises second fins for increasing the heat exchange by conduction between the hot fluid and the inert gas, the second fins extending perpendicularly projecting from the second wall into the circulation space of a hot fluid;

[0018] - the first fins and / or the second fins are straight, wavy or polyhedral pins or plates;

[0019] - the first fins and / or the second fins respectively have several alignments parallel to each other and offset from each other;

[0020] - the first fins have several straight, curved or polyhedral alignments, parallel to each other, to form labyrinthine fuel circulation channels along the first wall;

[0021] - the arms can be pawns, plates, polyhedral walls, crossed plates forming lattice cells, double cones or cylinders;

[0022] - the exchanger comprises a control device configured to, in operation, control a pressure of the inert gas in the exchange space, the control device being further configured to detect a variation in the pressure of the gas in the exchange space relative to a determined threshold.

[0023] According to another aspect, a fuel conditioning system is provided for supplying a turbomachine with a fuel stored in a cryogenic tank, the system comprising: an exchanger as previously described, the fuel circulation space comprising an inlet and an outlet; a first fuel circuit comprising an inlet connected to the cryogenic tank and an outlet connected to the inlet of the fuel circulation space; and a second fuel circuit comprising an inlet connected to the outlet of the fuel circulation space and an outlet connected to a turbomachine.

[0024] Advantageously but optionally: - the conditioning system comprises a heat circuit, the heat circuit connecting the circulation space of a hot fluid to a hot source;

[0025] - the inert gas contained in the exchange space is helium, neon, argon, krypton, xenon or nitrogen.

[0026] According to another aspect, there is provided an assembly comprising a turbomachine and a conditioning system as previously described, the circulation space of a hot fluid being in fluid communication with a hot part of the turbomachine and the circulation space of a fuel in fluid communication with a fuel supply of the turbomachine.

[0027] DESCRIPTION OF FIGURES

[0028] Figure 1 illustrates an aircraft schematically.

[0029] Figure 2 illustrates a schematic sectional view of an aircraft propulsion unit;

[0030] Figure 3 schematically illustrates a fuel conditioning system;

[0031] Figure 4a illustrates a sectional view of a plate heat exchanger according to a first embodiment;

[0032] Figure 4b illustrates a sectional view of a tubular heat exchanger according to a second embodiment;

[0033] Figure 5 schematically illustrates a sectional view of a heat exchanger according to a third embodiment;

[0034] Figure 6a, Figure 6b, Figure 6c and Figure 6d illustrate a top view of different fins and fin arrangement on the first wall, according to different embodiments of the present disclosure;

[0035] Figure 7a, Figure 7b and Figure 7c illustrate a top view of different fins and fin arrangement on the second wall, according to different embodiments of the present disclosure;

[0036] Figure 8a, Figure 8b and Figure 8c illustrate a sectional view of different arm arrangements in the exchange space, according to different embodiments of the present disclosure. In all the figures, similar elements bear identical references.

[0037] DETAILED DESCRIPTION

[0038] The present disclosure relates to a fuel conditioning system 3 for an engine 2 of an aircraft 100, such as an airplane as illustrated in FIG. 1. Such an aircraft 100 comprises an airframe which, in the case of an airplane, is composed of a fuselage, a wing structure comprising two wings, empennages, flight control surfaces and landing gear.

[0039] The engine 2 (or turbomachine) is configured to be fixed to the airframe of the aircraft 100, for example under its wings, in the case of an airplane, and this by means of a pylon (or mast). The propulsion unit 1 can also be mounted on the wing of the airplane or at the rear of its fuselage, or even be integrated into its fuselage.

[0040] Engine 2 may be a twin-spool, twin-flow, direct-drive ducted turbojet engine as described below, but may also have a different number of spools and / or flows, and / or be another type of turbojet engine, such as a geared turbojet engine or a turboprop engine, with or without afterburner, ducted or unducted.

[0041] Unless otherwise specified, the terms "upstream" and "downstream" are used in reference to the overall direction of airflow through the propulsion unit 1 in operation.

[0042] The engine 2, as illustrated in FIG. 2, comprises, from upstream to downstream, a fan 20, a compressor section 22, comprising a low-pressure compressor 220 and a high-pressure compressor 222, a combustion chamber 24 and a turbine section 26, comprising a high-pressure turbine 262 and a low-pressure turbine 260. The fan 20, the rotor parts of the compressor section 22 and the rotor parts of the turbine section 26, are capable of being rotated about the longitudinal axis XX relative to the engine casing 23 and the fan casing 25. The upstream part of the nacelle 3 further defines an air inlet 29 through which the fan 20 draws in the air flow circulating through the propulsion unit 1. The combustion chamber 24 comprises a fuel injection rail and a plurality of ignition injectors.The injection rail and / or the ignition injectors are fuel-consuming components of the engine 2.

[0043] In operation, the fan 20 draws in a flow of air, a portion of which passes through the engine casing 23 from one side to the other and is successively compressed within the compressor section 22, ignited within the combustion chamber 24 by combustion of the fuel, and expanded within the turbine section 26 before being ejected from the engine 2. In this way, the propulsion unit 1 generates thrust. This thrust can, for example, be used for the benefit of the aircraft 100 on which the propulsion unit 1 is attached and fixed.

[0044] The fuel conditioning system 3 makes it possible to supply the injection rail of the combustion chamber 24 with fuel during operation of the engine 2 and thus allow the ignition of the air.

[0045] Fuel conditioning system

[0046] The fuel conditioning system 3, as illustrated in FIG. 3, comprises a fuel circuit 31, a heat circuit 32 and a heat exchanger 4.

[0047] The fuel circuit 31 is configured to conduct the fuel from a tank 33 to the engine 2, in other words to the injection rail. The fuel circuit 31 may comprise a first portion 34 called the first circuit 34, for connecting the tank 33 to the heat exchanger 4 and a second portion 35, called the second circuit 35, for connecting the heat exchanger 4 to the engine 2. Furthermore, the fuel circuit 31 may comprise at least one pump 36 for controlling the flow of fuel in the fuel circuit 31.

[0048] The heat circuit 32, or hot fluid circulation conduit, allows heat to be conducted to the heat exchanger 4 in order to heat the fuel of the regulation circuit. The heat circuit 32 connects the heat exchanger 4 to a heat source. The heat source may be the hot air flow leaving the turbine section 26. This allows for better energy efficiency by reusing heat produced by the operation of the engine 2 to heat the fuel supplying the engine 2.

[0049] Heat exchanger

[0050] The heat exchanger 4 is configured to heat the fuel circulating in the fuel circuit 31 in order to condition it. Indeed, to improve the operation of the engine 2, the fuel must be transmitted to the injection rail at a temperature between 150K and 350K (i.e. -123°C to 77°C) depending on the flight phase. Since the fuel can be stored in the tank 33 at a cryogenic temperature between -240°C and -260°C, it must be heated before being injected into the injection rail. The heat exchanger 4 therefore comprises a hot source, the hot fluid, and a cold source, the fuel. The hot fluid can be the gas circulating in the engine 2 and whose temperature at the outlet of the turbine section 26 can vary between 400°C and 600°C. The hot fluid includes, among other things, oxygen.

[0051] The fuel to be heated may be hydrogen or, for example, methane or any other type of fuel that can be used in an engine 2. The fuel must therefore not come into contact with the hot fluid in order to avoid any risk of ignition.

[0052] The heat exchanger 4, as illustrated by FIGS. 4A and 4B, comprises a space for circulation of a fuel 41 to be heated delimited by a first wall 44, a space for circulation of a hot fluid 42 delimited by a second wall 45 and an exchange space 43 between the space for circulation of a fuel 41 and the space for circulation of a hot fluid 42.

[0053] The circulation space for a fuel 41 to be heated may be a conduit, a pipe or any other type of space configured to allow the circulation of the fuel in the heat exchanger 4 in a sealed manner. Hereinafter, we will refer to it as a fuel line for simplicity. The fuel line 41 comprises an inlet connected to an outlet of the first circuit 34 of fuel 31, one inlet of which is connected to the cryogenic tank 33, and an outlet connected to an inlet of the second circuit 35 of fuel 31, one outlet of which is connected to the engine 2.

[0054] The hot fluid circulation space 42 may be a conduit, a pipe or any other type of space configured to allow the hot fluid to circulate in the heat exchanger 4 in a sealed manner. Hereinafter, we will refer to it as a heat pipe for simplicity. The heat pipe 42 comprises an inlet connected to the heat circuit 32, one inlet of which is connected to a hot source of the engine 2, such as, for example, the air leaving the compressor, the engine oil 2, the air leaving the turbine section 26, etc.

[0055] The fuel line 41 defines a flow direction of the fuel A and the heat line 42 defines a flow direction of the hot fluid B. The flow direction of the fuel A can be in the same direction as the flow direction of the hot fluid B, in which case it is referred to as a co-current exchanger, or it can be opposite to the flow direction of the hot fluid B, in which case it is referred to as a counter-current exchanger, or it can be orthogonal to the flow direction of the hot fluid B, in which case it is referred to as a cross-current exchanger. The exchange space 43 is a cavity delimited by the first wall 44 and by the second wall 45. In other words, the exchange space 43 is formed by the first wall 44 and by the second wall 45, which simplifies the design of the exchange space 43 but also makes it possible to promote thermal conduction between the fuel line 41 and the heat line 42 through the exchange space 43.In addition, the exchange space 43 is adapted to contain an inert gas. The inert gas contained inside the exchange space 43 makes it possible to avoid any ignition in the event of contact with the fuel A or the hot fluid B. The inert gas is helium, neon, argon, krypton, xenon or nitrogen.

[0056] Thus, the exchange space 43 is a barrier between the fuel pipe 41 and the heat pipe 42 which makes it possible to avoid any risk of contamination between the hot fluid and the fuel. In other words, the fuel is separated from the hot fluid in the heat exchanger 4 by two walls. In the event of a leak through the first wall 44 or the second wall 45, the fuel will not mix with the hot fluid forming an oxidant. The presence of the exchange space 43 makes it possible to avoid ignition of the fuel in the event of a leak in the first wall 44 or the second wall 45.

[0057] The first wall 44 and the second wall 45 may be cylindrical and coaxial or flat and parallel. In this way, the heat exchanger 4 may be respectively a plate exchanger or a tubular exchanger etc. In the case of a plate heat exchanger, the fuel pipe 41 may be delimited by two first walls 44, each delimiting with a separate second wall 45 an exchange space 43, as illustrated in FIG. 4a (in this case, the fuel pipe 41 is symmetrically included between two exchange spaces 43 and two heat pipes 42). In any case, the exchange space 43 is delimited by the first wall 44 and the second wall 45 and thus included between the fuel pipe 41 and the heat pipe 42 so as to improve the heat exchange.

[0058] Thus, the heat exchanger 4 is a simple and compact double-walled exchanger. It allows efficient heat transfer between the hot fluid and the fuel, through the exchange space 43, in order to heat the fuel while limiting the risk of fuel contamination. The heat exchange between the hot fluid and the fuel is carried out by conduction from the first wall 44 to the second wall 45 via the inert gas, in other words the heat transfer in the exchange space 43 is carried out by thermal conduction. In addition, the first wall 44 may comprise fins 46 to increase the heat exchange by conduction between the first wall 44 and the fuel A, as illustrated in FIG. 5. The fins 46 of the first wall 44 extend projecting from the first wall 44 into the fuel line 41. The fins 46 may be straight plates, or pins of different shapes.The fins 46 can also be corrugated or polyhedral, in other words formed by plates which are not parallel to each other and joined end to end on the first wall 44, as illustrated by figures 6a, 6b and 6c.

[0059] The fins 46 may extend parallel to each other and in a plane parallel to the direction of flow of the fuel λ in the fuel line 41. The fins 46 may further have one or more straight, curved or polyhedral alignments, parallel to each other, so as to channel the flow of fuel λ along the first wall 44 and thus improve the heat exchange. The fins 46 may thus form a labyrinth on the first wall 44.

[0060] For example, the fins 46 may have several alignments perpendicular to the flow direction of the fuel λ and in which the fins 46 are uniformly spaced. The respective fins 46 of two neighboring alignments may have an offset in a direction perpendicular to the flow direction of the fuel flow λ. This makes it possible to further improve the heat exchange between the fuel flow λ and the first wall 44.

[0061] As illustrated by Figure 6d, the fins 46 may further have one or more continuous alignments in order to form circulation channels, for example in a labyrinth, of the fuel flow A along the first wall 44. As illustrated by Figures 7a, 7b and 7c, the second wall 45 may also comprise fins 47 to increase the heat exchange by conduction between the hot fluid and the second wall 45. The fins 47 of the second wall 45 extend projecting from the second wall 45 into the heat pipe 42. The fins 47 may be straight plates, or pins of different shapes. The fins 47 may also be corrugated or polyhedral, in other words formed by plates that are not parallel to each other and joined end to end on the second wall 45.

[0062] The fins 47 may extend parallel to each other and in a plane parallel to the direction of flow of the hot fluid B in the heat pipe 42. The fins 47 may further have one or more alignments so as to channel the flow of fuel A along the first wall 44 and thus improve the heat exchange. For example, the fins 47 may have several alignments perpendicular to the direction of flow of the hot fluid B and in which the fins 47 are uniformly spaced. The respective fins 47 of two neighboring alignments may have an offset in a direction perpendicular to the direction of flow of the flow of hot fluid B.

[0063] The exchange space 43 is a honeycomb cavity and comprises: cells 48 between the first wall 44 and the second wall 45 and arms 49 connecting the first wall 44 to the second wall 45. The cells 48 are configured to store the inert gas. In other words, the exchange space 43 is configured to contain, in its cells 48, the inert gas. This makes it possible to promote heat exchange by conduction through the exchange space 43 while simplifying the heat exchanger 4 (by dispensing with a recirculation loop, a recirculation circuit and / or a convection system).

[0064] As illustrated by Figures 8a, 8b and 8c, the arms 49 can have different shapes so as to improve the thermal conduction and the resistance of the exchange space 43 in order to avoid leaks. The arms 49 can be in the form of a pin, a plate, a polyhedral wall (as illustrated particularly by Figure 8b), a crossed plate forming lattice cells 48, a double cone, a cylinder, etc. Thus, the heat exchange by conduction between the hot fluid and the fuel through the exchange space 43 is improved. Indeed, the heat transfer between the hot fluid and the fuel is a transfer by thermal conduction through the first wall 44, the arms 49 and the second wall 45. The heat exchanger 4 therefore does not require a pump for the inert gas which conducts heat by conduction and not by convection.The heat exchanger 4 is thus simpler and more compact than a system comprising an intermediate inert gas circuit comprising a heat exchanger with the hot fluid and a heat exchanger with the fuel as well as a pump to allow convection in the gas circuit between the two heat exchangers.

[0065] The inert gas confined in the exchange space 43 may be at a pressure higher than the pressure of the hot fluid in the heat pipe 42 and the pressure of the fuel in the fuel pipe 41. The pressure of the hot fluid in the heat pipe 42 may be between 0.15 bar and 1.5 bar, the pressure of the fuel in the fuel pipe 41 may be between 2 bar and 60 bar and the pressure of the inert gas in the exchange space 43 may be between 65 bar and 120 bar (in the absence of leakage). The inert gas is at supercritical conditions. For example, the pressure and temperature of the inert gas are respectively higher than the critical pressure and the critical temperature of the type of inert gas considered. This makes it possible to avoid condensation of the inert gas, which would cause a local pressure drop.Thus, in the event of a leak through the first wall 44 or the second wall 45, the pressurized inert gas escapes through the leak and thus prevents the fuel and the hot fluid from coming into contact.

[0066] Compared to a double-walled exchanger comprising, for example, a foam or a solid material in the exchange space 43, the presence of an inert gas in the exchange space 43 makes it possible to detect a leak by measuring the pressure of the gas in the exchange space 43.

[0067] The heat exchanger 4 may comprise a device 50 for controlling a pressure of the inert gas in the exchange space 43.

[0068] The control device 50 can control the pressure of the inert gas. The inert gas can have a constant volume in the exchange space 43 and a variable pressure depending on the operating conditions. The control device 50 is then configured to detect an abnormal pressure variation. Or, the inert gas can have a constant pressure and a variable volume thanks to an expansion tank 51. Depending on the thermal gradients, the volume of the inert gas varies in the exchange space 43 but at constant pressure (in the absence of a leak). The control device 50 is then configured to detect a pressure variation.

[0069] Thus, a leak in the exchange space 43 can be easily detected and taken into account. Detection of a leak can trigger the cutting off of the fuel supply.

Claims

CLAIMS 1. Heat exchanger (4) for a fuel conditioning system (3) of a turbomachine (2), the heat exchanger (4) comprising: - a circulation space for a fuel (41) to be heated delimited by a first wall (44); - a space for circulation of a hot fluid (42) delimited by a second wall (45); and - an exchange space (43) between the fuel circulation space (41) and the hot fluid circulation space (42), the exchange space (43) being adapted to contain an inert gas and is delimited by the first wall (44) and the second wall (45), the first wall (44) and the second wall (45) being connected by arms (49); the exchange space (43) being configured so that in operation, the hot fluid heats the fuel by heat conduction.

2. Exchanger (4) according to claim 1, in which the exchange space (43) is a cavity comprising cells (48) between the first wall (44) and the second wall (45), the cells (48) being delimited by the arms (49) and being configured to store the inert gas.

3. Exchanger (4) according to any one of claims 1 and 2, in which the first wall (44) comprises first fins (46) to increase the heat exchange by conduction between the inert gas and the fuel, the first fins (46) extending perpendicularly projecting from the first wall (44) into the fuel circulation space (41).

4. Exchanger (4) according to any one of claims 1 to 3, in which the second wall (45) comprises second fins (47) to increase the heat exchange by conduction between the hot fluid and the inert gas, the second fins (47) extending perpendicularly from the second wall (45) into the circulation space of a hot fluid (42).

5. Exchanger (4) according to any one of claims 3 to 4, in which the first fins (46) according to claim 3 and / or the second fins (47) according to claim 4, are straight, corrugated or polyhedral pins or plates.

6. Exchanger (4) according to any one of claims 3 to 5, in which the first fins (46) according to claim 3 and / or the second fins (47) according to claim 4, respectively present several alignments parallel to each other and offset from each other to improve heat exchange.

7. Exchanger (4) according to any one of claims 1 to 3, 5 and 6, in which the first fins (46) have several straight, curved or polyhedral alignments, parallel to each other, to form labyrinthine circulation channels for the fuel along the first wall (44).

8. Exchanger (4) according to any one of claims 1 to 7, in which the arms (49) can be pins, plates, polyhedral walls, crossed plates forming lattice cells (48), double cones or cylinders.

9. Exchanger (4) according to any one of claims 1 to 8, comprising a control device (50) configured to, in operation, control a pressure of the inert gas in the exchange space (43), the control device (50) being further configured to detect a variation in the pressure of the gas in the exchange space (43) relative to a determined threshold.

10. Fuel conditioning system (3) for supplying a turbomachine (2) with fuel stored in a cryogenic tank (33), the system (3) comprising: - an exchanger (4) according to one of claims 1 to 9, the fuel circulation space (41) comprising an inlet and an outlet; - a first fuel circuit (34) comprising an inlet connected to the cryogenic tank (33) and an outlet connected to the inlet of the fuel circulation space (41); and - a second fuel circuit (35) comprising an inlet connected to the outlet of the fuel circulation space (41) and an outlet connected to a turbomachine (2).

11. Conditioning system (3) according to claim 10, comprising a heat circuit (32), the heat circuit (32) connecting the circulation space of a hot fluid (42) to a hot source.

12. Packaging system (3) according to any one of claims 10 and 11, in which the inert gas contained in the exchange space (43) is helium, neon, argon, krypton, xenon or nitrogen.

13. Assembly comprising a turbomachine (2) and a conditioning system (3) according to any one of claims 10 to 12, the space for circulation of a hot fluid (42) being in fluid communication with a hot part of the turbomachine (2) and the space for circulation of a fuel (41) in fluid communication with a fuel supply of the turbomachine (2).

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