Device for heating a fuel in a supply circuit of an aircraft turbine engine, aircraft turbine engine and method for heating a corresponding fuel

Abstract

This device for heating a fuel in a supply circuit of an aircraft turbine engine comprises a first circuit (14) for circulation of oil, a second circuit (18) for circulation of fuel and a phase change material (PCM) in a heat exchange relationship with the first circuit and with the second circuit. The device further comprises a bypass circuit (17) configured to selectively divert oil away from the phase change material on the basis of the respective temperatures of the oil and of the phase change material.

Description

[0001] DESCRIPTION

[0002] TITLE: FUEL HEATING DEVICE

[0003] IN AN AIRCRAFT TURBOMACHINE FUEL SUPPLY CIRCUIT, AIRCRAFT TURBOMACHINE AND METHOD FOR HEATING A CORRESPONDING FUEL

[0004] technical field

[0005] The present invention relates to the thermal management of fuel in an aircraft turbomachine. More particularly, it relates to a fuel heating device in a turbomachine's fuel supply circuit.

[0006] State of the art

[0007] An aircraft turbomachine equipped with a thermal management system typically includes a first oil circulation loop ensuring the lubrication and cooling of the turbomachine engine components, such as bearings, bushings and the geared motor, and a second fuel circulation loop which ensures the supply of fuel to the turbomachine and the control of variable geometry components via servovalves.

[0008] The first oil circulation loop and the second fuel circulation loop are coupled by heat exchangers to ensure thermal management of the entire fluid system including oil and fuel.

[0009] Figure 1 shows the general architecture of a thermal management system for a turbomachine according to the state of the art.

[0010] In this figure, the first loop I is represented in which lubricating oil circulates between an engine 1 and a reservoir 2 under the action of pumps P, a second loop II extending between the aircraft's fuel tank(s) 3, the engine's combustion chambers 4 and variable geometry devices 5 controlled by servovalves 6.

[0011] In this thermal management system, the cooling of the oil circulating in the first loop is ensured by the fuel circulating in the second loop under the action of the pumps P, by means of a heat exchanger 9.

[0012] The two loops are further coupled by a controlled heater 10 which essentially ensures the heating of the fuel in cold ambient conditions in order to avoid any risk of fuel freezing which could cause malfunctions of the servovalves 6 and, consequently, of the variable geometry components 5.

[0013] Fuel circulation in the second loop II is controlled by a bypass valve 11. Pumps P control the flow of fuel and oil in circulation loops I, II and III.

[0014] In cold ambient conditions, particularly negative ones, the fuel stored in tank 3 of the aircraft, which may contain water, even in small quantities, is liable to freeze, particularly at the servovalves, which is liable to cause malfunctions.

[0015] The role of the pilot-operated heater 10 is then to heat the fuel so that it reaches a positive temperature at the servovalves. However, under certain conditions, the fuel may reach the aircraft's engine system at very low temperatures, which can reach -55°C.

[0016] For example, when the aircraft has been parked in extreme conditions, the increase in fuel flow, which can occur during certain phases of flight or taxiing when the first circulation loop is generally cold and has not yet had time to warm up, results in an increase in fuel flow in the heat exchanger 9 and, consequently, additional cooling of the oil due to this increase in fuel flow at very low temperature.

[0017] This is the case, for example, when switching from idle mode to takeoff mode, which is accompanied by a significant increase in fuel consumption.

[0018] The increase in fuel consumption also results in a decrease in the fuel temperature at the outlet of the controlled heater 10.

[0019] Figure 2 shows an example of the evolution of the oil temperature (Curve A) and the fuel temperature (Curve B) during an idle phase (phase PI), then during a takeoff phase (phase P2).

[0020] As can be seen, during the transition from idle to takeoff, there is a drop in the oil temperature at the engine inlet as well as a drop in the fuel temperature at the outlet of the pilot-operated heater 10, so that the oil loses a substantial part of its fuel heating capacity.

[0021] Under these conditions, the fuel cannot be heated optimally and a positive fuel temperature is not guaranteed at the servovalves.

[0022] Description of the invention

[0023] The aim of the invention is therefore to overcome this drawback and to propose a fuel heating device in a turbomachine supply circuit allowing to maximize the heat exchanges to the fuel.

[0024] The invention therefore aims at a device for heating fuel in the fuel supply circuit of an aircraft turbomachine, comprising a first oil circulation circuit, a second fuel circulation circuit, and a phase-change material placed in a heat exchange relationship between the first and second circuits. This device further comprises a bypass circuit configured to selectively divert oil away from the phase-change material depending on the respective temperatures of the oil and the phase-change material.

[0025] In one embodiment, the bypass circuit is placed between an inlet and an outlet of the first oil circulation circuit, so as to divert the oil circulation of the phase change material if the temperature of the oil is lower than that of the phase change material.

[0026] In one embodiment, the first and second circuits each comprise several branches extending in parallel, the parallel branches of the first circuit crossing the parallel branches of the second circuit, and wherein the phase-change material is disposed between the branches of the first and second circuits.

[0027] Advantageously, the phase change material is chosen based on the latent heat of phase change of the phase change material which corresponds to the oil temperature at the end of a predetermined operating phase of the turbomachine.

[0028] The invention also relates to a thermal management system for an aircraft turbomachine comprising a heating device as defined above.

[0029] It also relates to an aircraft turbomachine comprising such a thermal management system.

[0030] The invention also relates to a method for heating fuel in the fuel supply circuit of an aircraft turbomachine, wherein the fuel circulating in a fuel circulation loop is heated by oil circulating in an oil circulation loop, and wherein, during a first operating phase of the turbomachine, the thermal energy of the oil is stored in a phase-change material in a heat exchange relationship between the fuel circulation loop and the oil circulation loop, and during a second operating phase of the turbomachine, the thermal energy stored in the phase-change material is released back to the fuel. In one embodiment, when the oil temperature is lower than that of the phase-change material, the oil is diverted from the phase-change material.

[0031] Brief description of the drawings

[0032] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example and made with reference to the accompanying drawings in which:

[0033] - Fig. 1 and Fig. 2, which have already been mentioned, respectively illustrate the general architecture of a thermal management system for an aircraft turbomachine according to the state of the art and the evolution of the oil and fuel temperature during predetermined phases of turbomachine operation;

[0034] - Fig. 3 illustrates the structure of a fuel heating device according to the invention;

[0035] - Figure 4 illustrates the operation of the device shown in Figure 3; and

[0036] - Fig. 5 shows curves illustrating the operation of the device in Figure 3, as well as a fuel heating method according to the invention.

[0037] Detailed description

[0038] We will first refer to figure 3 which illustrates a fuel heating device according to an embodiment of the invention, designated by the general numerical reference 12.

[0039] Such a device 12 is intended to be integrated into a thermal management system of a turbomachine as illustrated in figure 1, between a first oil circulation loop which supplies the engine to ensure lubrication and cooling of the turbomachine engine elements and a second fuel circulation loop, which on the one hand supplies the combustion chambers 4 of the engine and on the other hand allows control of servovalves 6 piloting variable geometry devices 5.

[0040] The heating device 12 is for example integrated into the controlled heater 10 to ensure the heating of the fuel, particularly in cold conditions.

[0041] As can be seen, the heating device 12 includes a first oil circulation circuit 14, which includes an inlet 15 and an outlet 16 respectively connected to the oil circulation loop I, as well as a bypass circuit 17 extending between the inlet 15 and the outlet 16 so as to short-circuit the first oil circulation circuit 14.

[0042] The device 12 also includes a second fuel circulation circuit 18 in heat exchange relationship with the first oil circulation circuit 14 and which includes an inlet 19 and an outlet 20 each connected to the second fuel circulation loop.

[0043] In the embodiment illustrated in Figure 3, and in no way limitingly, the first oil circulation circuit 14 comprises a set of branches, such as 21, extending parallel between the inlet 15 and the outlet 16.

[0044] This is also the case for the second traffic circuit 18 which also includes a set of branches, such as 22, extending parallel between the entrance 19 and the exit 20.

[0045] The branches 21 of the first oil circulation circuit 14 are in heat exchange relationship with the branches 22 of the second fuel circulation circuit 18.

[0046] For example, branches 21 intersect branches 22. They are advantageously arranged perpendicularly to branches 22 of the second circuit 18. Branches 21 and 22 delimit between each other cells, such as 23, which are filled with a phase-change material (PCM) capable of changing from a solid to a liquid state, and vice versa, at a predetermined temperature, by absorbing or releasing energy in the form of latent heat. Examples include water, wax, phase-change hydrocarbons, or paraffin.

[0047] Of course, we do not depart from the scope of the invention when using other types of phase-change materials.

[0048] As illustrated in Figure 4, which shows the temperature variation as a function of the amount of heat stored in a phase change material, and on which sensible heat corresponds to a temperature rise of a material without a change of physical state while latent heat corresponds to a phase change of a material without a change in its temperature, a phase change material is capable of storing a large amount of thermal energy at a constant temperature which, depending on the phase change material, can range from -40°C to 150°C, in order to release it later.

[0049] Thus, the phase-change material of the heating device 12 can be used to store the thermal energy released when the fuel heating capacity is maintained, for example, during idle time on the ground. The phase-change material is particularly useful before entering operating phases in which the fuel heating capacity is no longer maintained, such as takeoff, which result in an increased fuel flow rate and, consequently, additional oil cooling due to the increased fuel flow at very low temperatures.

[0050] As an example, referring to Figure 5, in one implementation mode, during an idle operating phase (PI phase), the engine runs at low speed, and partially heats the oil and fuel.

[0051] During this idle phase (PI), in the first stage P'1, the oil temperature (curve A) and the fuel temperature (curve B) increase. The temperature of the phase-change material (curve C) also increases, through sensible heat transfer, i.e., without a physical phase transition. In the subsequent stage P'1, the oil and fuel temperatures continue to rise, and the thermal energy is stored in the phase-change material as latent heat, at a constant temperature.

[0052] During this period P”l, the phase change material, which advantageously has a phase change temperature chosen according to the needs of the thermal management system, for example between 0 and 100 °C, thus melts, which makes it possible to store at a constant temperature a significant amount of energy, for example on the order of a few hundred thousand kilojoules.

[0053] During a takeoff which, as previously indicated, is accompanied by an increase in fuel flow (phase P2), the energy stored in the phase change material is released as latent heat at constant temperature to the fuel (curve B').

[0054] During takeoff, the fuel flow rate can be multiplied by a factor of 2 to 20, and generally causes a drop of 5° to 30°C in the oil temperature.

[0055] If the temperature of the oil becomes lower than that of the phase change material, the bypass circuit 17 is implemented so that the oil no longer circulates in the heating device 12 and does not recover the energy stored in the phase change material, so that it is entirely available to heat the fuel.

[0056] The phase-change material then heats the fuel. It has been observed that a temperature increase of approximately 10 to 30°C can be achieved.

[0057] The heating device just described thus makes it possible to maximize the exchange of temperature to the fuel by storing the thermal energy which is available during less demanding engine operating phases, in which the fuel heating capacities are maintained, and then returning this energy to the fuel during more demanding operating phases in which the fuel heating capacities are not maintained, and this without having to size the controlled heater, by using a phase change material whose volume is smaller than that of a conventional heat exchanger.

Claims

fuel in a supply circuit of an aircraft turbomachine, characterized in that it comprises a first oil circulation circuit (14), a second fuel circulation circuit (18) and a phase change material (PCM) in a heat exchange relationship between the first circuit (14) and the second circuit (18), and in that it further comprises a bypass circuit (17) configured to selectively divert oil from the phase change material (PCM) according to the respective temperatures of the oil and the phase change material, the bypass circuit (17) being placed between an inlet (15) and an outlet (16) of the first circulation circuit, so as to divert the oil circulation from the phase change material if the temperature of the oil is lower than that of the phase change material.

2. Device according to claim 1, wherein the first and second circuits each comprise several branches (21, 22) extending in parallel, the parallel branches of the first circuit crossing the parallel branches of the second circuit, and wherein the phase-change material is disposed between the branches of the first and second circuits.

3. Device according to any one of claims 1 and 2, wherein the phase change material is chosen according to the latent heat of phase change of the phase change material which corresponds to the temperature of the oil at the end of an operating phase of the turbomachine.

4. Thermal management system of an aircraft turbomachine, characterized in that it comprises a heating device (12) according to any one of claims 1 to 3.

5. Aircraft turbomachine comprising a thermal management system according to claim 4.

6. A method for heating fuel in a fuel supply circuit of an aircraft turbomachine, wherein the fuel circulating in a fuel circulation loop (II) is heated by oil circulating in an oil circulation loop (I), wherein during a first operating phase of the turbomachine, the thermal energy of the oil is stored in a phase change material (PCM) in a heat exchange relationship between the fuel circulation loop and the oil circulation loop and, during a second operating phase of the turbomachine, the thermal energy stored in the phase change material is returned to the fuel, and wherein when the temperature of the oil is lower than the temperature of the phase change material, the oil is diverted from the phase change material.

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