Plant for heating a cryogenic fuel

Description

FIELD OF THE INVENTION

[0001] The invention lies in the field of aircraft turbomachines.

[0002] The present invention relates more specifically to an installation for heating a cryogenic fuel supplying the combustion chamber of an aircraft turbomachine, and also relates to an aircraft turbomachine operating with this cryogenic fuel and equipped with such an installation. STATE OF THE ART

[0003] The use of cryogenic fuel to power the combustion chamber of an aircraft turbomachine is well known. One such cryogenic fuel is, for example, liquid natural gas (known by the acronym "LNG"). Such a fuel is less expensive than conventional kerosene and further limits CO2 emissions. Indeed, LNG emits 25% less CO2 per unit of energy.

[0004] However, LNG must be transported in liquid form for the volume to be transported in an aircraft to be acceptable. Its liquefaction temperature at one bar (10 5 < Pascal) is minus 161 °C. However, it is preferable to inject LNG in gaseous form into the combustion chamber, as this has many advantages. It is therefore necessary to vaporize it, pressurize it and heat it until it reaches the injection temperature, which is around 50 °C.

[0005] In the state of the art, it has been envisaged to heat the cryogenic fuel by passing it through a heat exchanger, inside which circulated air from the exhaust gases of the turbomachine nozzle. However, there is then the risk that the water vapor present in these exhaust gases will turn into ice on the wall of said heat exchanger.

[0006] It has also been considered to heat the cryogenic fuel by passing it through a heat exchanger, inside which circulated oil, for example lubricating oil for the accessories present in the said turbomachine. However, due to the extremely low temperature of the cryogenic fuel, there is a risk that the lubricating oil will be too cooled and become too viscous to be used again to lubricate these accessories.

[0007] In addition, a rapid injection of cryogenic fuel in the liquid state onto the hot walls of the oil / cryogenic fuel exchanger causes vaporization of part of this liquid. The gas formed accumulates in the circulation circuit of said cryogenic fuel and the pressure inside it increases. This prevents the liquid cryogenic fuel from circulating. It is therefore necessary to start by sending the liquid cryogenic fuel with a low flow rate into the oil / cryogenic fuel exchanger so that the gas formed can be evacuated while the wall of said exchanger cools down to the temperature of the cryogenic fuel. Then, only the two-phase oil / cryogenic fuel exchanger is operational.

[0008] For any liquid, the temperature at which this liquid vaporizes, as well as the energy required for this vaporization, depend on the pressure at which it is found. In this case, if the cryogenic fuel is pressurized only upstream of the exchanger, that is to say while it is still in the liquid phase, to avoid a compressor downstream of the exchanger, then its state change temperature, as well as the energy required for its state change, are no longer freely controllable but are imposed by the pressure of the fuel in the liquid state, upstream of the exchanger. Management of the system is complicated if many two-phase exchangers are present.

[0009] Finally, it might be desirable to use the fuel in the combustion chamber not in the gaseous state but in the supercritical fluid state, which is not provided for in the aforementioned state of the art. As a reminder, it should be noted that the fuel reaches the supercritical fluid state when it is brought to a temperature above its critical temperature and to a pressure above its critical pressure.

[0010] Documents EP 3 623 604 and EP 3 623 602 already disclose an installation that allows the cryogenic fuel used to supply the combustion chamber of a turbomachine to be heated. However, it does not describe the fact that the installation includes an expansion tank, nor the control of the pump to maintain the heat transfer fluid at a pressure such that it remains in the liquid state.

[0011] GB 2 131 094 also discloses an installation for preheating fuel used in a turbomachine. However, this installation uses a conventional non-cryogenic fuel and a pressure accumulation device that is not located upstream of the pump. STATEMENT OF THE INVENTION

[0012] A first aim of the invention is to develop an installation for heating a cryogenic fuel supplying the combustion chamber of an aircraft turbomachine, which does not have the aforementioned drawbacks.

[0013] Another aim of the invention is that such an installation operates in an ecologically and economically interesting manner.

[0014] To this end, the invention relates to an installation for heating a cryogenic fuel supplying the combustion chamber of an aircraft turbomachine, this installation comprising: a storage tank for said cryogenic fuel in the liquid state, a supply pipe configured to connect said tank to said combustion chamber of the aircraft turbomachine, a closed circuit for circulating a heat transfer fluid, a cryogenic fuel / heat transfer fluid heat exchanger and at least one heat transfer fluid / working fluid heat exchanger, mounted in series on said closed circuit, the cryogenic fuel / heat transfer fluid heat exchanger making it possible to heat the cryogenic fuel by a heat input provided by the heat transfer fluid.

[0015] According to the invention, this closed circuit for circulating the heat transfer fluid comprises a pump for circulating said heat transfer fluid and a closed expansion tank, connected to said closed circuit upstream of said pump relative to the direction of circulation of the heat transfer fluid in the closed circuit and said pump is controlled by a central unit so as to ensure a flow rate of heat transfer fluid inside the closed circuit which makes it possible to cool the working fluid(s) and to heat the cryogenic fuel, depending on the operating phases of the aircraft and so that the closed expansion tank maintains the heat transfer fluid circulating in said closed circuit at a pressure such that it remains in the liquid state and does not change phase.Said installation comprises at least two heat transfer fluid / working fluid heat exchangers, including a heat transfer fluid / air heat exchanger taken from the outlet of the turbomachine compressor and a heat transfer fluid / turbine blade cooling air heat exchanger. The heat transfer fluid / air heat exchanger taken from the outlet of the turbomachine compressor is arranged upstream of the heat transfer fluid / turbine blade cooling air heat exchanger or upstream of the heat transfer fluid / turbine blade cooling air heat exchanger and the other heat transfer fluid / working fluid heat exchangers, relative to the direction of circulation of the heat transfer fluid in the closed circuit.

[0016] Thanks to these characteristics of the invention, it is possible on the one hand to recover heat from different hot sources present in the aircraft and to transfer it to the heat transfer fluid which circulates in the closed circuit, on the other hand to maintain this heat transfer fluid in the liquid single-phase state with only a fluctuation of its temperature and finally to then have only one heat exchanger with the cryogenic fuel, in which the heating of this fuel takes place.

[0017] According to a first variant embodiment of the invention, the installation comprises a pump arranged on the supply pipe between said tank and the heat exchanger, this pump is a high pressure pump making it possible to compress the cryogenic fuel to the liquid state to bring it to a pressure higher than its critical pressure and said cryogenic fuel / heat transfer fluid heat exchanger is a supercritical heat exchanger which makes it possible to heat the cryogenic fuel to a temperature higher than its critical temperature to bring it to the supercritical fluid state before its introduction into the combustion chamber.

[0018] According to a second variant embodiment of the invention, the installation comprises a pump arranged on the supply pipe between said tank and the heat exchanger, this pump is a pump which makes it possible to compress the cryogenic fuel to the liquid state to bring it to a pressure lower than its critical pressure and said cryogenic fuel / heat transfer fluid heat exchanger is a two-phase heat exchanger, which makes it possible to heat the cryogenic fuel by a heat input provided by said heat transfer fluid, to change this cryogenic fuel from the liquid state to the gaseous state, before its introduction into the combustion chamber.

[0019] According to other advantageous and non-limiting characteristics of the invention, taken alone or in combination: the working fluid of the heat transfer fluid / working fluid heat exchanger is chosen from the air taken from the outlet of the turbomachine compressor, the lubricating oil, the cooling air of the blades of the turbine of the turbomachine and the exhaust gas at the outlet of the nozzle of the turbomachine; it comprises a heat transfer fluid / exhaust gas heat exchanger at the outlet of the nozzle of the turbomachine and this is mounted in series with the heat transfer fluid / air taken from the outlet of the compressor of the turbomachine, so as to be located downstream of the latter with respect to the direction of circulation of the heat transfer fluid in the closed circuit;it comprises at least the heat transfer fluid / air heat exchanger taken from the turbomachine compressor outlet, a heat transfer fluid / oil heat exchanger, the heat transfer fluid / air heat exchanger for cooling the turbine blades and a heat transfer fluid / exhaust gas heat exchanger at the nozzle outlet of the turbomachine, mounted in series on the closed circuit for circulating the heat transfer fluid; it comprises the heat transfer fluid / air heat exchanger taken from the turbomachine compressor outlet, a heat transfer fluid / oil heat exchanger, the heat transfer fluid / air heat exchanger for cooling the turbine blades and a heat transfer fluid / exhaust gas heat exchanger at the nozzle outlet of the turbomachine, mounted in series and in this order, on the closed circuit for circulating the heat transfer fluid;it comprises at least two heat transfer fluid / working fluid heat exchangers and for at least one of these two heat transfer fluid / working fluid exchangers, an on / off valve is mounted on said closed circuit upstream of said heat transfer fluid / working fluid heat exchanger and a bypass circuit connects a point of said closed circuit located upstream of this on / off valve to a point of said closed circuit located downstream of said heat transfer fluid / working fluid heat exchanger and this bypass circuit is provided with an on / off valve; the cryogenic fuel is liquefied natural gas or liquid hydrogen. said cryogenic fuel / heat transfer fluid two-phase heat exchanger is a plate exchanger. ;

[0020] The invention also relates to an aircraft turbomachine.

[0021] According to the invention, this turbomachine comprises a combustion chamber supplied with cryogenic fuel and an installation for heating this cryogenic fuel as mentioned above. DESCRIPTION OF FIGURES

[0022] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which: [ Fig. 1 ] is a diagram representing an example of the construction of an aircraft turbomachine, here a double-flow, double-spool turbomachine. [ Fig. 2 ] is a diagram representing an exemplary embodiment of an installation for heating a cryogenic fuel, in accordance with the invention, this fuel being intended to supply the combustion chamber of an aircraft turbomachine. [ Fig. 3 ] is a diagram showing the operation of the installation of the figure 2, during takeoff of the aircraft. [ Fig. 4 ] is a diagram showing the operation of the installation of the figure 2 , during the ascent of the aircraft. [ Fig. 5 ] is a diagram showing the operation of the installation of the figure 2 , when the aircraft is cruising or in the descent phase, or when it is on the ground and the engine is idling. Fig. 6 ] is a top view of a stage of a plate exchanger used in the aforementioned installation. [ Fig. 7 ] is a top view of a floor adjacent to the plate heat exchanger floor of the figure 6 .

[0023] On the figures 3 to 5 , the installation is represented in a simplified manner. DETAILED DESCRIPTION OF THE INVENTION

[0024] For the record, we will briefly recall below the structure of a double-flow, double-body turbomachine, with reference to the figure 1 .

[0025] On this one, we can see a double flow turbomachine 1 with successively, in the direction of circulation of the air, that is to say from upstream (on the left in the figure) to downstream (on the right in the figure), an air inlet 10 and a fan 11, which delivers the air on the one hand into a primary vein 12 and on the other hand into a secondary vein 13. By "vein", we mean the volume through which an air flow circulates.

[0026] The air flow circulating in the primary vein 12 successively passes through a low pressure compressor 14a, a high pressure compressor 14b, a combustion chamber 15, a high pressure turbine 16a and a low pressure turbine 16b, before being ejected through a primary flow nozzle 120.

[0027] Furthermore, the secondary air flow circulating in the secondary vein 13 is ejected separately through a secondary flow nozzle 130, after passing through a series of guide vanes 131.

[0028] The installation 2 for heating a cryogenic fuel in accordance with the invention will now be described in connection with the figure 2 .

[0029] This installation 2 can be used with the turbomachine 1, as described previously in connection with the figure 1 . However, this installation 2 can also be used with another type of turbomachine, for example a single-spool turbomachine or a turbomachine comprising only one compressor and one turbine.

[0030] So, on the figure 2 , the turbomachine 1 is represented schematically, with a compressor bearing the general reference 14 and an expander bearing the general reference 16, arranged respectively upstream and downstream of the combustion chamber 15.

[0031] The installation 2 comprises a tank 20 for storing said cryogenic fuel in the liquid state. This fuel is, for example, liquefied natural gas or liquid hydrogen. This tank 20 is connected to the combustion chamber 15 by a pipe 21. A cryogenic fuel / heat transfer fluid heat exchanger 22 is mounted on the pipe 21 between the tank 20 and the combustion chamber 15. This heat exchanger 22 makes it possible to heat the cryogenic fuel before the latter is injected into the combustion chamber 15. For this purpose, an injector is provided on the pipe 21, downstream of the exchanger 22, although this is not shown in the figures.

[0032] Finally, a pump 23 is mounted on the pipe 21, preferably between the storage tank 20 and the heat exchanger 22. Its operation is controlled by a central unit 8, such as a computer.

[0033] According to a first embodiment, the pump is a high-pressure pump, which makes it possible to bring the cryogenic fuel beyond its critical pressure and the heat exchanger 22 is a so-called “supercritical” exchanger, because it makes it possible to bring the cryogenic fuel beyond its critical temperature. At the outlet of the exchanger 22, the fuel is therefore in the supercritical fluid state and is injected in this state into the combustion chamber 15.

[0034] For the record, the critical point of hydrogen is 32K (minus 241.15°C) and 12.8 bars (12.8.10 5< Pa) and the critical point of natural gas is 190 K (minus 83.15°C) and 46.8 bars (46.8.10 5< Pa).

[0035] According to a second variant embodiment, the pump 23 is a pump which makes it possible to pressurize the cryogenic fuel in the liquid state but at a pressure lower than its critical pressure in order to deliver the flow of cryogenic fuel necessary for the aircraft according to these flight phases (takeoff, cruising flight, landing, taxiing on the runway) and the heat exchanger 22 is a so-called “two-phase” exchanger, because it makes it possible to change the cryogenic fuel from the liquid state to the gaseous state (phase change), before its injection into the combustion chamber 15.

[0036] The installation 2 also includes a closed circuit 3 for circulating a liquid heat transfer fluid. The heat transfer fluid circulating therein is, for example, a halogenoalkane, known under the brand name “NOVEC 7500” marketed by the company 3M. However, any other heat transfer fluid, which remains in the liquid phase and which has sufficient thermal properties to ensure the heat exchanges which will be described later, can be used.

[0037] The circulation of the heat transfer fluid inside the closed circuit 3 is ensured by a pump 30, also controlled by the central unit 8.

[0038] A closed expansion vessel 31 is connected to the circuit 3, at a point located upstream of the circulation pump 30, relative to the direction of circulation of the heat transfer fluid in the closed circuit 3. This closed expansion vessel 31 makes it possible to maintain the heat transfer fluid which is in the circuit 3 under a pressure such that it remains in the liquid state and does not change phase.

[0039] The heat exchanger 22 is also mounted on the closed circuit 3 to carry out the heat exchange with the heat transfer fluid.

[0040] In addition, at least one heat transfer fluid / working fluid heat exchanger is mounted on the circuit 3, in series with the exchanger 22. Different working fluids can be used and are described below.

[0041] According to the invention, the circuit 3 is provided with at least one heat exchanger 4 “heat transfer fluid / air taken from the outlet of the compressor 14 of the turbomachine 1”. This air taken from the outlet of the compressor 14 is known by the English term “bleed”.

[0042] The exchanger 4 is connected at its inlet 41 to the hot air outlet of the compressor 14. The hot air circulates inside the heat exchanger 4 counter-current to the heat transfer fluid which circulates in the closed circuit 3. It leaves the exchanger 4 through the outlet 42, after having supplied heat to the heat transfer fluid. The air thus cooled can then be sent into the cabin 43 of the aircraft.

[0043] Advantageously, the installation 2 can also comprise a “heat transfer fluid / lubricating oil” heat exchanger 5. This exchanger 5 is connected at its inlet 51 to the lubricating oil network 50 of various mechanical elements of the turbomachine.

[0044] Inside the turbomachine, a certain number of mechanical elements must in fact be cooled by lubricating oil in order to maintain their mechanical integrity. These mechanical elements are for example a reducer of an accessory box or bearings supporting a rotating shaft. The oil, which has heated up in contact with these mechanical elements, enters the heat exchanger 5, provides heat to the heat transfer fluid circulating in the circuit 3 and leaves through the outlet 52 of the exchanger 5, in order to be returned to the lubricating oil network 50 and to be able to be used again in contact with these mechanical elements.

[0045] According to the invention, the installation 2 also comprises a heat exchanger 6 “heat transfer fluid / turbine blade cooling air”. This exchanger 6 is connected at its inlet 61 to the cooling air circuit of the turbine blades 16 so as to recover this air once it has heated up in contact with said blades. This heated air provides heat to the heat transfer fluid circulating in the circuit 3 and comes out cooled, via the outlet 62 of the exchanger 6. It can then be returned to the blades of the turbine 16, to cool them.

[0046] Finally, advantageously, the installation 2 can also comprise a heat exchanger 7 “heat transfer fluid / exhaust gas at the outlet of the turbomachine nozzle”. This exhaust gas is taken from the outlet of the nozzle 120, that is to say the nozzle of the primary stream.

[0047] The exchanger 7 is connected at its inlet 71 to the nozzle 120. The hot air circulates inside the heat exchanger 7, counter-current to the heat transfer fluid which circulates in the closed circuit 3. It leaves through the outlet 72, after having supplied heat to the heat transfer fluid and is then ejected into the atmosphere via the downstream part of the nozzle.

[0048] It can thus be seen that the heat transfer fluid which leaves the two-phase heat exchanger 22 cooled is gradually reheated after each passage through one of the exchangers 4, 5, 6, 7 until it reaches a maximum temperature at the inlet 223 of the exchanger 22. The intensity of the heat transfer from the hot sources (i.e., the different working fluids circulating in the different exchangers 4, 5, 6 and 7) to the cold source (i.e., the liquid heat transfer fluid) is controlled by the flow rate of heat transfer fluid circulating in the closed circuit 3. This flow rate is itself controlled by the rotation speed of the pump 30. The higher the flow rate of the heat transfer fluid, the more heat it captures from the hot sources and the more its temperature increases.

[0049] The closed expansion tank 31 comprises two parts separated by an elastic membrane, the first part is connected to the circuit 3 and receives the heat transfer fluid and the second part is filled with compressed air (or gas). When the temperature of the heat transfer fluid increases following heat exchanges with at least one of the exchangers 4, 5, 6 or 7, this fluid expands and the first part of the expansion tank 31 collects the excess heat transfer fluid, thus avoiding an increase in the pressure in the circuit 3. Conversely, if the temperature of the heat transfer fluid decreases, the fluid compresses and the excess heat transfer fluid present in the expansion tank 31 returns to the circuit 3.

[0050] This expansion vessel 31 makes it possible to maintain the heat transfer fluid under sufficient pressure to increase its boiling point and prevent it from passing into the gaseous state. Consequently, the heat transfer fluid circulating in the circuit 3 varies only in temperature but its pressure remains constant and it remains permanently in the liquid phase.

[0051] Advantageously, the two-phase heat exchanger 22 is a plate exchanger. An exemplary embodiment of such a plate exchanger is shown in the figures 6 and 7 Such an exchanger consists of several superimposed plates made of a thermally good conductive material, generally metal, for example aluminum or stainless steel, these different plates being assembled together by welding, brazing or using joints.

[0052] One of the main advantages of this type of exchanger is the maximization of convective exchanges, compared to other types of exchangers. Finally, advantageously, in the embodiment shown in the figures, and in order to maximize heat transfer, the plates of each stage include a multitude of channels arranged to form V-shaped chevrons.

[0053] At a given stage of the two-phase heat exchanger 22, stage referenced 22a on the figure 6 , (and arranged between two neighboring plates), the cryogenic fuel in the liquid state enters through the inlet 221 of the exchanger 22, passes through this stage and leaves in the gaseous state through the outlet 222. At an immediately neighboring stage, referenced 22b on the figure 7 , the heat transfer fluid enters through the inlet 223 of the exchanger 22, passes through this stage and leaves through the outlet 224 (see also the diagram of the figure 2 ).

[0054] Preferably, and as shown in the figure 2 , the circuit 3 is equipped with the four types of exchangers 4, 5, 6 and 7 mentioned above and the different heat exchangers 4, 5, 6 and 7 are mounted in series on the closed circuit 3. Preferably again, they are mounted in this order, relative to the direction of circulation of the heat transfer fluid inside the closed circuit 3, from the outlet 224 of the heat exchanger 22 to the inlet 223.

[0055] Preferably, when there are at least two heat exchangers, among the aforementioned exchangers 4, 5, 6 and 7 and in order to be able to possibly select only some of them, it is possible to provide for at least one of these exchangers, an on / off valve, mounted upstream of this exchanger and a bypass circuit, which connects a point of the closed circuit 3 located upstream of this on / off valve and a point of the closed circuit 3 located downstream of said heat exchanger.

[0056] Thus, for example, the exchangers 4, 5, 6 and 7 are equipped with on / off valves, referenced respectively 44, 54, 64 and 74 and with bypass circuits, referenced respectively 45, 55, 65 and 75. In addition, each aforementioned bypass circuit 45, 55, 65 and 75 is equipped with an on / off valve 450, 550, 650 and 750.

[0057] All on / off valves 44, 54, 64, 74, 450, 550, 650 and 750 are controlled by the central unit 8.

[0058] THE figures 3 , 4 And 5 illustrate different operating situations of installation 2, depending on the aircraft's flight phases. In each of these figures, the circulation of the heat transfer fluid is represented by a thick line.

[0059] There figure 3 illustrates the situation during aircraft takeoff. In this case, valves 450, 54, 64 and 74 are open, while valves 44, 550, 650 and 750 are closed.

[0060] This eliminates the need for the 4 heat transfer fluid / air heat exchanger taken from the turbomachine compressor outlet. During takeoff, the air bleed is cut off to achieve maximum propulsion power. There is therefore no airflow to cool.

[0061] There figure 4 illustrates the situation during the climb of the aircraft after takeoff. In this case, valves 450, 54, 650, and 74 are open, while valves 44, 550, 64, and 750 are closed. This makes it possible to use neither the heat exchanger 4 for the coolant / air taken from the outlet of the turbomachine compressor, nor the heat exchanger 6 for the coolant / air cooling the turbine blades. Thus, after takeoff when the engine reaches its maximum temperature, the exchanger 6 can be closed to limit losses since the cooling function of the air cooling the blades is no longer necessary.

[0062] Finally, the Figure 5 illustrates the situation in flight or in the descent phase or even in the taxiing phase of the aircraft when the aircraft's turbomachine is operating at idle. In this case, valves 44, 54, 650 and 750 are open, while valves 450, 550, 64 and 74 are closed. This makes it possible to use neither the heat transfer fluid / turbine blade cooling air heat exchanger 6 nor the heat transfer fluid / exhaust gas heat exchanger 7 at the turbomachine nozzle outlet. Indeed, in the aforementioned situations, the cryogenic fuel flow is lower and it is sufficient to heat it using only exchangers 4 and 5. Exchanger 7 can thus be closed and the air from the nozzle bypasses this exchanger to limit the losses caused by its presence in the air flow.

[0063] According to an embodiment variant shown only on the figures 3 to 5, it is possible to provide a bypass pipe 32 in the closed circuit 3, this bypass pipe 32 joining a point located on the circuit 3 downstream of the circulation pump 30 and upstream of the exchanger 22 to a point located downstream of the exchanger 22 and upstream of the heat exchanger 4 heat transfer fluid / air taken from the outlet of the compressor of the turbomachine. A thermostatic valve 33 equipped with a temperature sensor 34 is provided on this bypass pipe. The thermostatic valve 33 is controlled as a function of the temperature and possibly other factors such as the flight phase, or start / restart. This bypass pipe 32 makes it possible to divert part of the flow which passes through the heat exchanger 22 during start-up or restart and during certain flight phases.

[0064] Below a certain temperature, the valve 33 is controlled to pass a portion of the heat transfer fluid flow into the bypass pipe 32 and no longer only into the exchanger 22, in order to control the phase change of the fuel or its supercritical state. It is also possible to provide that in a given temperature range and as the temperature detected by the sensor 34 increases, an increasing portion of the heat transfer fluid is directed into the bypass pipe 32.

[0065] The heating installation 2 according to the invention has the following advantages: It comprises only a single cryogenic fuel / heat transfer fluid heat exchanger 22 and it is possible to supply the heat necessary for heating the cryogenic fuel via a single closed circuit 3 inside which circulates a heat transfer fluid maintained in the liquid state and of which only the temperature varies. Unlike the prior art, where the cryogenic fuel was heated by passing through a heat exchanger, inside which circulated air from the secondary stream, the risk of freezing on the exchanger 22 is reduced here because the temperature of the heat transfer fluid which circulates inside the closed circuit 3 is easier to control. The pipe 21 is short, since it is necessary to provide only a single exchanger 22 between the tank 20 and the combustion chamber 15 and not several exchangers, as when it is desired to recover the calories from different working fluids.This limits the circulation of cryogenic fuel, particularly liquefied natural gas, in hot and therefore flammable areas of the aircraft. Furthermore, a two-phase heat exchanger, inside which a phase change occurs, is more difficult to control. Consequently, it is preferable to reduce their number. Furthermore, inside the pipe 21, it is only necessary to manage the pressure of the cryogenic fuel, via the pump 23, the temperature being managed by the heat provided by the heat transfer fluid circulating in the closed circuit 3. In the preferred embodiment of the installation 2, shown in the figure 2, the heat transfer fluid has already been heated by passing through the exchanger 4, before reaching the exchanger 5. Consequently, the oil brought through the exchanger 5 is cooled but to a temperature high enough to prevent it from freezing or solidifying. The heat exchangers 4, 5 and 6 make it possible to cool the various working fluids brought therein, depending on their cooling requirements. The heat exchanger 7 makes it possible to adjust the temperature of the heat transfer fluid circulating in the circuit 3, using a heat source (here the exhaust gases at the outlet of the nozzle 120 of the turbomachine), which on the one hand is permanent, as long as the aircraft is operating, and which on the other hand does not need to be cooled for the operating requirements of the aircraft. The heat exchanger 7 therefore constitutes a variable for adjusting the operation of the heating installation 2.

Claims

1. An installation (2) for heating cryogenic fuel supplying the combustion chamber (15) of an aircraft turbine engine (1), this installation (2) comprising: - a storage tank (20) for said cryogenic fuel in the liquid state, - a supply line (21) configured to connect said tank (20) to said combustion chamber (15) of the aircraft turbine engine, - a closed circuit (3) for circulation of a heat-transfer fluid, - a cryogenic fuel / heat-transfer fluid heat exchanger (22) and at least one heat-transfer fluid / working fluid heat exchanger (4, 5, 6, 7), mounted in series in said closed circuit (3), the cryogenic fuel / heat-transfer fluid heat exchanger (22) enabling heating of the cryogenic fuel by an input of heat delivered by the heat-transfer fluid, characterised in that the closed circuit (3) for circulation of the heat-transfer fluid comprises a pump (30) for circulating said heat-transfer fluid and a closed expansion vessel (31), connected to said closed circuit (3) upstream of said pump (30) with respect to the direction of circulation of the heat-transfer fluid in the closed circuit (3), and in that said pump (30) is controlled by a central unit (8) so as to ensure a heat-transfer fluid flow rate inside the closed circuit (3) which enables cooling of the working fluid or fluids and heating of the cryogenic fuel according to the operating phases of the aircraft, and so that the closed expansion vessel (31) keeps the heat-transfer fluid circulating in said closed circuit (3) at a pressure such that it remains in the liquid state and does not change phase, in that the installation (2) comprises at least two heat-transfer fluid / working fluid heat exchangers (4, 5, 6, 7), including a heat exchanger (4) between the heat-transfer fluid and the bleed air taken at the outlet of the turbine engine compressor and a heat exchanger (6) between the heat-transfer fluid and the air cooling the turbine blade and in that the heat exchanger (4) between the heat-transfer fluid and the bleed air taken at the outlet of the turbine engine compressor is disposed upstream of the heat exchanger (6) between the heat-transfer fluid and the air cooling the turbine blades or upstream of the heat exchanger (6) between the heat-transfer fluid and the air cooling the turbine blades and of the other heat-transfer fluid / working fluid heat exchangers (5, 7), with respect to the direction of circulation of the heat-transfer fluid in the closed circuit (3).

2. The installation according to claim 1, characterised in that it comprises a pump (23) disposed in the supply line (21) between said tank (20) and the heat exchanger (22), in that this pump (23) is a high-pressure pump which can compress the cryogenic fuel in the liquid state in order to bring it to a pressure greater than its critical pressure and in that said cryogenic fuel / heat-transfer fluid heat exchanger (22) is a supercritical heat exchanger which can heat the cryogenic fuel to a temperature greater than its critical temperature in order to bring it into the supercritical fluid state before its introduction into the combustion chamber (15).

3. The installation according to claim 1, characterised in that it comprises a pump (23) disposed in the supply line (21) between said tank (20) and the heat exchanger (22), in that this pump (23) is a pump which can compress the cryogenic fuel in the liquid state in order to bring it to a pressure less than its critical pressure and in that said cryogenic fuel / heat-transfer fluid heat exchanger (22) is a two-phase heat exchanger, which can heat the cryogenic fuel by an input of heat delivered by said heat-transfer fluid, in order to take this cryogenic fuel from the liquid state to the gaseous state, before its introduction into the combustion chamber (15).

4. The installation according to any one of the preceding claims, characterised in that the working fluid of the heat-transfer fluid / working fluid heat exchanger (4, 5, 6, 7) is chosen from the bleed air taken at the outlet of the turbine engine compressor, the lubricating oil, the cooling air of the turbine blades of the turbine engine and the exhaust gas at the outlet of the turbine engine nozzle.

5. The installation according to any one of the preceding claims, characterised in that it comprises a heat exchanger (7) between the heat-transfer fluid and the exhaust gas at the outlet of the turbine engine nozzle and in that this is mounted in series with the heat exchanger (4) between the heat-transfer fluid and the bleed air taken at the outlet of the turbine engine compressor, so as to be located downstream thereof with respect to the direction of circulation of the heat-transfer fluid in the closed circuit (3).

6. The installation according to any one of the preceding claims, characterised in that it comprises at least the heat exchanger (4) between the heat-transfer fluid and the bleed air taken at the outlet of the turbine engine compressor, a heat-transfer fluid / oil heat exchanger (5), the heat exchanger (6) between the heat-transfer fluid and the air cooling the turbine blades, and a heat exchanger (7) between the heat-transfer fluid and the exhaust gas at the outlet of the turbine engine nozzle, mounted in series in the closed circuit (3) for circulation of the heat-transfer fluid.

7. The installation according to claim 6, characterised in that it comprises the heat exchanger (4) between the heat-transfer fluid and the bleed air taken at the outlet of the turbine engine compressor, the heat-transfer fluid / oil heat exchanger (5), the heat exchanger (6) between the heat-transfer fluid and the air cooling the turbine blades and the heat exchanger (7) between the heat-transfer fluid and the exhaust gas at the outlet of the turbine engine nozzle, mounted in series and in this order in the closed circuit (3) for circulation of the heat-transfer fluid.

8. The installation according to any one of the preceding claims, characterised in that it comprises at least two heat-transfer fluid / working fluid heat exchangers (4, 5, 6, 7) and in that for at least one of these two heat-transfer fluid / working fluid heat exchangers (4, 5, 6, 7), an on-off valve (44, 54, 64, 74) is mounted in said closed circuit (3), upstream of said heat-transfer fluid / working fluid heat exchanger (4, 5, 6, 7), and in that a bypass circuit (45, 55, 65, 75) connects a point of said closed circuit (3) located upstream of this on-off valve (44, 54, 64, 74) to a point of said closed circuit (3) located downstream of said heat heat-transfer fluid / working fluid exchanger (4, 5, 6, 7) and in that this bypass circuit (45, 55, 65, 75) is provided with an on-off valve (450, 550, 650, 750).

9. The installation according to any one of the preceding claims, characterised in that the cryogenic fuel is liquefied natural gas or liquid hydrogen.

10. The installation according to claim 3, characterised in that said two-phase cryogenic fuel / heat-transfer fluid heat exchanger (22) is a plate exchanger.

11. An aircraft turbine engine (1), characterised in that it comprises a combustion chamber (15) supplied with cryogenic fuel and an installation (2) for heating this cryogenic fuel according to any one of claims 1 to 10.