FR2969701A1 - Method for managing heat exchange between e.g. fuel in turbojet engine of airplane, involves controlling derivation of fraction of oil flow from exchanger, where derived fraction is equal to maximum fraction of oil flow - Google Patents

Abstract

The method involves determining temperature (Ta) of air supplied to an oil/air heat exchanger i.e. air cooled oil cooler (ACOC) (32). Derivation of a fraction of oil flow from the exchanger is controlled, where the derived fraction is equal to maximum fraction and lower than 100 percent of oil flow when the temperature of the air is less than a predetermined threshold temperature. The derivation of the fraction is allowed when the temperature of the air is lower than the threshold temperature, and fuel flow rate is greater than predetermined flow rate. An independent claim is also included for a system for managing heat exchange between fluids in an aeronautical turboshaft engine.

Description

Background of the invention

The invention relates to the management of heat exchanges between fluids in an aerospace turbomachine, in particular an aircraft turbine engine. In such a turbine engine, it is customary to include an oil / air exchanger and an oil / fuel exchanger in a lubricating and / or cooling oil circuit, the oil / air exchanger or ACOC ("Air Cooled Oil"). Cooler ") being upstream or downstream of the oil / fuel or FCOC exchanger (" Fuel Cooled Oil Cooler ") or MHX (" Main Heat eXchanger "), the oil / air exchanger is traversed or swept by a flow air from outside. In cold environment, a significant amount of the calories carried by the oil is dissipated in the oil / air exchanger, limiting the ability of the oil to heat the fuel in the oil / fuel exchanger. However, in such an environment, the water present in the fuel can freeze disturbing the fuel supply of the injectors of the combustion chamber of the turbine engine and disrupting the control 20 of various members with adjustable positions (often called "variable geometries" ") using the fuel as a hydraulic fluid. In cold environment, there is therefore a risk that the thermal exchanges between the oil and the fuel are insufficient to prevent the icing of the fuel. To solve this problem, it has been proposed to modulate the flow of air from the oil / air exchanger by means of a valve controlled so as to indirectly control the temperature of the fuel. However, this solution requires the installation of additional equipment, which is detrimental in terms of weight, cost and reliability, such equipment being sensitive to the ingestion of bodies or particles carried by the air, by example of ice or sand. Another known solution consists in providing a specific oil / fuel exchanger for the fuel used as hydraulic fluid for controlling variable geometries. The fuel flow rate is low compared to that of the fuel injectors, which reduces the risk of frost. However, this is also an additional equipment whose presence is detrimental in terms of weight, cost and reliability and the absence of frost in the fuel flow to the injectors is not guaranteed. It has also been proposed to add to the oil / air exchanger a bypass line and a valve to completely divert the oil out of the oil / air exchanger to ensure efficient heating of the fuel when needed. Such a need exists in a cold environment. However, there is then a risk of freezing of the oil present in the exchanger and no longer circulating, under the effect of the cooling air flow, resulting in congestion of the exchanger and inducing a delay in circulation. oil in the exchanger when it is again desired.

Object and summary of the invention

The present invention is intended in particular to ensure in a cold environment a sufficient heating of the fuel to prevent icing without providing additional equipment such as a modulating valve of the air flow to the oil / air exchanger or a specific oil / fuel exchanger for the fuel used as hydraulic fluid, and without risk or practically without risk of congestion of the oil / air exchanger. This object is achieved by a method for managing heat exchanges between fluids in an aeronautical turbomachine comprising: at least one oil circuit intended to be traversed by an oil flow; an oil / air exchanger mounted in the oil circuit and arranged to receive a flow of cooling air; a bypass line for diverting at least a fraction of the oil flow from the oil / air exchanger; and an oil / fuel exchanger mounted in the oil circuit and arranged to be traversed by a flow of fuel flowing in a fuel line feeding injectors of a combustion chamber of the turbomachine, a method according to which representative information is used 35 of the temperature of the air brought to the oil / air exchanger and it favors the Ilduflage Lat Latter in llunlantant I ~ j diversion of a fraction of the oil flow out of the exchanger oil / air, the fraction derived oil flow being at most equal to a maximum fraction less than 80% of the oil flow when the air temperature is below a predetermined temperature threshold. Thus, in a particularly cold environment, a minimum oil flow continues to pass through the oil / air exchanger, eliminating the risk of congestion thereof. The maximum fraction of the oil flow can be chosen at most equal to 90%. Thus, the ability of the fuel to heat the oil is largely preserved. According to a particularity of the method, fuel flow information representative of the fuel flow circulating in the fuel line is also used and the derivation of a fraction of the flow of oil derived from the oil / air exchanger is controlled. in the limit of said maximum fraction when the air temperature is below the predetermined temperature threshold and when the fuel flow rate is below a predetermined flow rate threshold. According to another particularity of the process, it is possible to completely bypass the oil flow from the oil / air exchanger when the air temperature is below the predetermined temperature threshold and when the fuel flow is not lower than the predetermined temperature threshold. at the predetermined flow threshold. The predetermined fuel flow rate threshold may be selected at an intermediate value between the flow rate value corresponding to the cruising speed and the flow rate value corresponding to the full speed. Thus, in a particularly cold environment, the oil flow can be completely derived from the oil / air exchanger and allow efficient heating of the fuel when the flow thereof is high, typically at takeoff. Since the operating phases with a high fuel flow rate are of limited duration, the risk of freezing of the oil remaining in the exchanger is reduced or even zero. In addition, such operating phases generally take place at low altitude so that the temperature of the air brought to the oil / air exchanger is higher than that of cruising altitude. This is all the more noticeable when the air supplied to the hu- man heat exchanger is exhausted after having passed through the fan of the distributor and has thus been warmed by its passage in the fan rotating at high speed. The predetermined temperature threshold is chosen at a value for example between -20 ° C and -50 ° C. According to another particularity of the method, information representative of the fuel temperature feeding the injectors is used and the fraction of oil flow derived from the oil / air exchanger is controlled to bring the temperature of the fuel to a value as low as as high as possible, within a predetermined set point temperature, regardless of the air temperature. The predetermined set temperature Tc may be such that Tc = Tk-AT where Tk is the coking temperature of the fuel and AT a safety margin for example between 0 ° C and 50 ° C. The present invention also aims to provide a system 15 for carrying out the method. This object is achieved by means of a system for managing heat exchange between fluids in an aerospace turbomachine, comprising: an oil circuit intended to be traversed by a flow of lubricating and / or cooling oil; oil / air exchanger mounted in an oil circuit, arranged to receive a flow of cooling air, - an oil bypass line out of the oil / air exchanger, - a variable position valve to make varying a fraction of the oil flow circulating in the oil circuit and derived from the oil / air exchanger by the bypass line, - a control circuit of the variable position valve, - a mounted oil / fuel exchanger in the oil circuit and connected to a fuel line to be traversed by a fuel flow supplying injectors of a combustion chamber of the turbomachine, - an air temperature sensor capable of providing information representing the temperature of the air supplied to the oil / air exchanger, and a fuel temperature sensor capable of supplying information representative of the temperature of the fuel supplied to the injectors of the combustion chamber, in which system the circuit of the variable position valve is connected to the air temperature sensor and is arranged to promote heating of the fuel by controlling the diversion of a fraction of the oil flow from the oil / air exchanger, while now the fraction of oil flow derived at most equal to a maximum fraction less than 100 ° Io of oil flow when the air temperature is below a predetermined temperature threshold. According to a feature of this system, the control circuit of the variable position valve is arranged to receive further information representative of the fuel flow in the fuel line and to control said valve to maintain the flow fraction of the fuel. oil derived from the oil / air exchanger within the limit of said maximum fraction when the air temperature is below the predetermined temperature threshold and when the fuel flow is below a predetermined flow rate threshold. Preferably then, the control circuit of the variable position valve is arranged to allow the derivation of the entire flow of oil out of the oil / air exchanger when the air temperature is below the predetermined temperature threshold. and when the fuel flow is not below the predetermined flow rate threshold. According to yet another particularity of the system, the control circuit of the variable position valve is arranged to control said valve in order to bring the temperature of the fuel as high as possible within the limit of a predetermined set temperature. whatever the air temperature. The invention also relates to an aerospace turbine engine 0 comprising such a system.

Brief description of the drawings

The invention will be better understood on reading the description given below, by way of indication but not limitation, with reference to the accompanying drawings in which: - Figure 1 is a very simplified view of an aircraft turbine engine; FIG. 2 is a simplified diagram showing an embodiment of a system of the invention; FIG. 3 is a simplified diagram showing another embodiment of a system according to the invention; FIG. 4 is a simplified flowchart showing an embodiment of the method according to the invention; and FIG. 5 is a simplified diagram showing yet another embodiment of a system according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A field of application of the invention is that of aircraft turbine engines such as for example that shown very schematically in Figure 1. The invention is however applicable to other aviation turbomachines such as helicopter turbines. The turbine engine of FIG. 1 comprises a combustion chamber 1, the combustion gases coming from the chamber 1 driving a high pressure turbine (HP) 2 and a low pressure turbine (LP) 3. The turbine 2 is coupled by a shaft to a high pressure compressor (HP) 4 supplying the combustion chamber 1 with pressurized air while the turbine 3 is coupled by another shaft to a fan 5 at the engine inlet. A gearbox 6, or accessory relay box, is connected by a mechanical power take-off 7 to a turbine shaft and comprises a set of gears for driving various equipment, in particular pumps and at least one generator. electi ical. In FIG. 2, the reference numeral 10 designates a fuel circuit which receives fuel from a tank 20 to deliver a controlled fuel flow rate to a line 22 supplying a fuel supply manifold 24 of a plurality of engines. injectors 26 of the combustion chamber 1. The fuel circuit 10 comprises in known manner, from upstream to downstream in the direction of flow of the fuel, a low pressure pump 12, a high pressure pump 14 and a Fuel metering unit (FMU) 16. Between the low pressure pump 12 and the high pressure pump 14, the fuel passes through an oil / fuel heat exchanger or FCOC ("Fuel Cooled Oil Cooler") 34. At the output of the high pressure pump, the fuel flow can be divided into a first fraction fed to the metering unit 16 to provide the regulated fuel flow to the combustion chamber and a second fraction available on a line 18 as that e hydraulic fluid for different components such as actuators or servovalves. Other devices such as a filter unit, a shut-off valve, a flow meter (not shown) are usually included in the fuel system.

Also in known manner, there is provided an oil circuit 30 which receives at input 30a a flow of lubricating oil and / or cooling. This flow of oil can be constituted by the joining of different streams from different sets using lubricating oil and / or cooling, the circulation of the oil being provided by pumps (not shown). Thus, in addition to the oil used for the lubrication and cooling of the engine itself, including shaft bearings of turbines and compressors, the overall oil flow may include oil used for the lubrication of the relay box of accessories and oil used for the lubrication and cooling of one or more electric generators. The oil arriving at the inlet 30a passes through an air / oil heat exchanger or ACOC ("Air Cooled Oil Cooler") 32 and the exchanger FCOC 34, before being returned from an outlet to the different sets of the turbine engine using the oil.

The ACOC 32 may be of the surface cooled type, with oil ducts in the air-swept chamber F on one side of the exchanger. dual-flow turbine engine with a "hot" primary flow through the HP compressor assembly, combustion chamber and HP and LP turbines and a "cold" secondary flow from the fan and bypassing this assembly, such an exchanger is for example housed on a wall of the secondary flow channel, immediately downstream of the blower The ACOC 32 may also be of the air / oil plate exchanger type housed for example in the blower housing, the air passing through the exchanger may then be taken from the blower housing. The secondary flow can then be re-injected into it, alternatively, the air passing through the heat exchanger can be taken outside the fan casing and subsequently discharged to the outside or injected into the secondary flow. electronic control or ECU 40 regulates the turbomachine. The ECU 40 is in particular connected to the fuel metering unit 16 for regulating the fuel flow rate supplied to the injectors at a desired setpoint as a function of the operating speed of the turbine engine. Thermal exchanges between fluids (fuel, oil, air) are managed by controlling the possible diversion out of the exchanger 20 ACOC 32 of all or part of the flow of oil circulating in the oil circuit. For this purpose, in the embodiment of FIG. 2, a three-way valve 36 is mounted in the oil circuit immediately downstream of the ACOC 32, the valve 36 having a first inlet 36a connected to the outlet of the ACOC oil 32, a second inlet 36b connected to a bypass line 38 connected to the oil circuit immediately upstream of the ACOC 32 and an outlet 36c connected to the oil circuit. The valve 36 is a controllable variable position that can take any position between a first end position in which the inlet 36b is closed and the inlet 36a is open (no oil bypass outside the ACOC 32) and a second extreme position in which the inlet 36a is closed and the inlet 36b is open (bypassing all the oil flow out of the ACOC 32). The valve 36 may be an electric valve or an electro-hydraulic valve using the fuel as a hydraulic fluid. A sensor 28 provides information representative of the temperature of the fuel injection fuel. the combustion chamber of the tulbemuteui. Ull such a capteul is usually present in a

turbine engine. The sensor 28 can be mounted on the pipe 22 immediately upstream of its connection with the supply nozzle 24 of the injectors 26. Alternatively, one or more sensors could be placed on the injectors or in the vicinity thereof. The value selected for the injected fuel temperature is then the highest value recorded or a value derived from the latter by application of a law preset for example experimentally to better reflect the actual value of the temperature of the fuel injected.

Another sensor 29 provides information representative of the temperature Ta of the cooling air supplied to the ACOC 32. A sensor usually present at the input of the engine may be used to provide information representative of the temperature (usually denoted T12) of the air entering the engine.

FIG. 3 illustrates an embodiment that differs from that of FIG. 2 in that the controlled-position valve associated with the ACOC 32 and driven by the ECU 40 is a three-way valve 36 'placed upstream of the ACOC 32. The valve 36 'has an input 36'a connected to the oil circuit, a first output 36'b connected to the input of the ACOC 32 and a second output 36'c connected to the input of the bypass line 38 'which connects to the oil circuit immediately downstream of the ACOC 32. The heat exchange management by controlling the valve 36 or 36' is carried out by means of a control circuit which is advantageously integrated in the ECU 40, being noted that a specific control circuit distinct from the ECU 40 could also be used. An operating mode of the control circuit is shown in FIG. 4. The information representative of Ta and Ti is used as well as advantageously an information representative of the flow rate Qc of the fuel flowing in the duct 22. This information representative of the flow rate Qc can be the flow rate setpoint function of the desired speed of the turbine engine and used to control the fuel metering unit 16. It is also possible to use information provided by a flowmeter mounted on line 22. A first test (step 50) consists of checking if one is in a particularly cold environment by comparing the temperature Ta with the leilperatule threshold Ib. tempetatut e 1-5 is chosen according to the risk of congealing of oil remaining in the ACOC 32 in the case where all the flow oil in the oil circuit is derived out of the ACOC 32 by the branch line 38 or 38 '. The threshold temperature Ts is for example chosen between -200C and -500C. If Ta> Ts in step 50, the temperature Tc is brought to as high a value as possible within the limit of a fuel set point Tc (step 52). Heating the fuel to as high a value as possible is indeed advantageous because it results in an increase in the energy supplied to the combustion chamber and makes it possible, for a given operating speed, to minimize the fuel consumption. The set value Tc is chosen such that Tc = Tk-AT, Tk being the fuel coking temperature and AT a safety margin which is preferably selected such that 00C <AT <50 ° C, more preferably such that ° C <AT <30 ° C.

If Ta <Ts, it is checked (step 54) if the fuel flow Q, is less than a threshold value Qcs. The threshold value Qcs is chosen greater than the fuel flow Qu, corresponding to the engine's cruising speed in flight and less than the fuel flow corresponding to a high speed, namely the take-off speed, or even the climb speed. For example, we can choose QOE such that 1.3 Qcn <Qcs <1.5 Qoe (exact?). If Qc <valve 36 or 36 'is controlled to bring the temperature T, to a maximum value possible, within the limit of a maximum fraction Qhdmax of the total flow of oil Qh derived from the ACOC 32 25 and within the limit of the setpoint Tc. The value Qhdmax is less than 100% of Qh, for example or more equal to 90% of Qh. The guarantee of maintaining a minimum oil circulation in the ACOC 32 makes it possible to combat the risk of freezing the oil exposed to the cooling air flow in a particularly cold environment while avoiding the icing of the fuel due to the fact that the possibility of deriving a very large part of the oil flow from the ACOC 32. If Q, Qcs, the valve 6 to 36 'is controlled, in order to optimize the heating of the fuel, (step 58 without limitation of the fraction of the oil fluea derived from the ACOC 32 but still maintaining the temperature Ti of the fuel higher than normal at the cooling stages at Qc are, at the same time, limited, and the temperature the air supplied to the ACOC is normally higher than when operating at Qc <QcS at cruising altitude, as already indicated.The risk of freezing of the oil remaining in the ACOC 32 is therefore very limited in the case where all or almost all the oil flow is derived from the ACOC 32 during these operating phases at Qc> Qcs- It is desirable that the heating of the fuel to the highest possible temperature not be done at the expense of maintaining the oil temperature within a range of desired values in each of the turbine engine assemblies using the oil. It is then possible to use sensors supplying the control circuit with information representative of the oil temperatures in these different assemblies so as to drive the valve 36 or 36 'in priority to maintain these temperatures within the desired limits, the valve 36 or 36' then being 15 piloted so as to derive all the oil flow out of the ACOC 32 (measured oil temperature too low) or to derive no fraction of the oil flow out of the ACOC 32 (too much oil temperature high). The piloting of the valve 36 or 36 'to ensure the heating of the fuel at the highest possible temperature, as described above, then only intervenes if the oil temperatures measured are within the desired limits. It will be noted that steps 54 and 58 are preferred but not necessary, a limitation to the value Qhdmax of the fraction of oil flow derived from the oil / air exchanger can be provided in cold environment regardless of the fuel flow.

In this case, the valve 36 or 36 'is controlled to control the temperature Ti according to step 52 or 56 depending on whether Ta <Ts or not. It would also be possible to use a variable-opening two-way valve 36 "mounted on a line 38" in branch of the ACOC 32, as shown in FIG. 5. The valve 36 "is driven by the ECU 40 as described for FIG. steps 52 and 56 depending on whether Ta <Ts or not, the passage section of the valve 36 "is controlled, taking into account the passage section of the oil flowx in the ACOC 32, so that the fraction 35 of the Derived oil flow remains within the limit of the maximum fraction I ~ <decreases Q of the total flow of oil in the oil circuit. Preferably, the passage section in the valve 36 "is chosen so that in full opening thereof, this fraction Qhdmax is reached or almost reached.

Claims (14)

REVENDICATIONS1. A method for managing heat exchange between fluids in an aviation turbomachine comprising: at least one oil circuit (30) to be traversed by an oil flow (Oh); an oil / air exchanger (32) mounted in the oil circuit and arranged to receive a flow of cooling air; a bypass line (38; 38 '; 38 ") for diverting at least a fraction of the oil flow from the oil / air exchanger; and an oil / fuel exchanger (34) mounted in the oil circuit downstream of the air / fuel exchanger and arranged to be traversed by a flow of fuel flowing in a fuel line supplying the injectors of a combustion chamber of the turbomachine, characterized in that one uses information representative of the temperature (Ta) of the air fed to the oil / air exchanger and the heating of the fuel is promoted by controlling the diversion of a fraction of the oil flow from the oil / air exchanger (32), the fraction of derived oil flow being at most equal to a maximum fraction (Qhdmax) of less than 100% of the oil flow when the air temperature (Ta) is below a predetermined temperature threshold (Ts). 2. Method according to claim 1, characterized in that the maximum fraction of the oil flow (Ohdmax) is chosen at most equal to 90%. 3. Method according to any one of claims 1 and 2, characterized in that one further uses a fuel flow information (Oc) representative of the flow of fuel flowing in the fuel line and the control is carried out. deriving a fraction of the oil flow from the oil / air exchanger (32) within the limit of said maximum fraction (Qhdmax) when the air temperature (Ta) is below the predetermined temperature threshold (Ts) and when the fuel flow (Oc) is below a predetermined flow threshold (Ocs). 4. Method according to claim 3, characterized in that it allows the total derivation of the oil flow from the oil / air exchanger when the air temperature (Ta) is below the predetermined temperature threshold (Ts ) and when the fuel flow (Oc) is not below the predetermined flow threshold (Qcs), 5. Method according to any one of claims and 4, ~ aracterized in which th threshold c-IL2ii predetermined rate (Ocs) is: selected to an intermediate value between the flow rate value corresponding to the cruising speed and the flow value corresponding to full diet. 6. Method according to any one of claims 1 to 5, characterized in that the predetermined temperature threshold (Ts) is chosen at a value between -200C and -50'C. 7. Method according to any one of claims 1 to 6, characterized in that one uses a representative information of the fuel temperature (Ti) supplying the injectors and the control of the fraction of oil flow derived out the oil / air exchanger (32) for bringing the fuel temperature to as high a value as possible within the limit of a predetermined set temperature (Tc) regardless of the air temperature. 8. A method according to claim 7, characterized in that the predetermined set temperature Tc is such that Tc = Tk-AT where Tk is the coking temperature of the fuel and AT a safety margin. 9. Method according to claim 8, characterized in that the safety margin AT is such that O ° C <AT <50 ° C. 10. Thermal exchange management system between fluids 20 in an aviation turbine engine, comprising: - an oil circuit (30) to be traversed by a flow of lubricating oil and / or cooling - an oil / heat exchanger air (32) mounted in an oil circuit, arranged to receive a flow of cooling air, a line (38; 38 '; 38 ") of oil diversion from the oil / air exchanger, a variable position valve (36; 36 '; 36 ") for varying a fraction of the oil flow flowing in the oil circuit and derived from the oil / air exchanger by the bypass line; a circuit (40) for controlling the variable-position valve; an oil / fuel exchanger (34) mounted in the oil circuit and connected to a fuel line for the passage of a fuel flow supplying fuel injectors; a combustion chamber of the turbomachine, an air temperature sensor capable of supplying ir representative information of the temperature (Ta) of the air supplied to the oil / air exchanger, and - a fuel temperature sensor (28) capable of supplying information representative of the temperature of the fuel (Ti) supplied to the injectors of the combustion chamber, characterized in that the control circuit of the variable-position valve (36; 36 '; 36 ") is connected to the air temperature sensor (29) and is arranged to promote heating of the fuel by controlling the diversion of a fraction of the oil flow from the oil / air exchanger, while maintaining the fraction of oil flow derived at most equal to a maximum fraction (Qhdrnax) less than 100% of the oil flow when the air temperature (Ta) is below a predetermined temperature threshold (Ts). 11. System according to claim 10, characterized in that the control circuit of the variable position valve (36; 36 ") is arranged to receive further information representative of the fuel flow (Qc) in the fuel line and for controlling said valve to maintain the derived oil flow fraction out of the oil / air exchanger within the limit of said maximum fraction (Qhdmax) when the air temperature (Ta) is below the temperature threshold (Ts ) and when the fuel flow (Qc) is below a predetermined flow threshold (Qcs). 12. System according to claim 11, characterized in that the control circuit of the variable position valve (36; 36 ") is arranged to allow the diversion of the entire flow of oil out of the oil / air exchanger. when the air temperature (Ta) is below the predetermined temperature threshold (Ts) and when the fuel flow is not below the predetermined flow rate threshold. 13. System according to any one of claims 10 to 12, characterized in that the control circuit of the variable position valve (36; 36 '; 36 ") is arranged to control said valve in order to bring fuel (Ti) to a value as high as possible within the limit of a predetermined set temperature (Tc) regardless of the air temperature. 14. Aeronautical turbomachine comprising a heat exchange management system according to any one of claims 10 to 13.