Method for controlling the fuel flow rate of a helicopter turbine engine

Abstract

The present invention relates to a computer-implemented method for controlling the flow rate of fuel injected into a combustion chamber (42) of a turbine engine (4) of a helicopter (1) by means of a fuel metering device (50), the method comprising the following steps: - calculating a fuel flow rate setpoint in accordance with a desired speed of the turbine engine (4); - calculating a virtual fuel flow rate corresponding to an increase or decrease in the temperature in the combustion chamber according to a thermal model (M, M') of the turbine engine comprising an intrinsic thermal model of the turbine engine influencing the temperature in the combustion chamber; - correcting the fuel flow rate setpoint of the virtual fuel flow rate; - controlling the fuel metering device so that it injects an amount of fuel that complies with the corrected fuel flow rate setpoint (C2) into the combustion chamber.

Description

[0001] DESCRIPTION

[0002] TITLE: METHOD FOR CONTROLLING THE FUEL FLOW OF A HELICOPTER TURBOMACHINE

[0003] TECHNICAL FIELD

[0004] This presentation concerns the field of helicopter engines and more particularly concerns a turbomachine for a helicopter.

[0005] STATE OF THE ART

[0006] A turbomachine for a helicopter comprises a gas generator and a free turbine driven in rotation by the gas flow generated by the gas generator. The gas generator comprises at least one compressor stage (centrifugal or axial or mixed) and a turbine coupled in rotation.

[0007] The operating principle is as follows: fresh air entering the turbomachine is compressed by the rotation of the compressor before being sent to a combustion chamber where it is mixed with fuel. The burnt gases from the combustion are then evacuated at high speed to the gas generator turbine.

[0008] A first expansion then occurs in the gas generator turbine, during which the latter extracts the energy necessary to drive the compressor. The gas generator turbine does not absorb all the energy from the burnt gases and the excess energy constitutes the gas flow generated by the gas generator.

[0009] The latter therefore provides kinetic energy to the free turbine so that a second expansion occurs in the free turbine which transforms the energy of the gas into rotational kinetic energy in order to drive a receiving organ, such as the rotor of the helicopter.

[0010] Obviously, the turbomachine is designed to operate within prescribed limits, the maintenance of the turboshaft engine within such limits being carried out by acting mainly on the flow of fuel injected into the combustion chamber.

[0011] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various carbon emission restrictions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new aircraft types and those already in operation, requiring the implementation of technological solutions to ensure their compliance with current regulations. Civil aviation has been mobilizing for several years now to contribute to the fight against climate change.

[0012] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences with the aim of improving the energy efficiency of aircraft.

[0013] Consequently, the Applicant is constantly working to reduce its negative climate impact by using methods and operating virtuous development and manufacturing processes and minimizing greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0014] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to ensure propulsion, and, as an essential complement to technological progress, aeronautical biofuels.

[0015] In particular, to improve the operability of a turbomachine, it becomes crucial to optimize the fuel regulation logic by taking into account the thermal state of the turbomachine and / or any other additional source of energy.

[0016] PRESENTATION OF THE INVENTION

[0017] The invention proposes a solution aimed at taking into account the thermal state of the turbomachine and / or another additional source of energy in controlling the regulation of the fuel flow in order to optimize performance during transient engine conditions.

[0018] To this end, according to a first aspect of the invention, a computer-implemented method is proposed for regulating the flow rate of fuel injected into a combustion chamber of a helicopter turbomachine by means of a fuel metering device, the method comprising the following steps:

[0019] - calculation of a fuel flow setpoint in accordance with a desired speed of the turbomachine;

[0020] - calculation of a fictitious fuel flow rate corresponding to an increase or decrease in the temperature in the combustion chamber based on a thermal model of the turbomachine comprising an intrinsic thermal model of the turbomachine influencing the temperature in the combustion chamber;

[0021] - correction of the fuel flow setpoint of the fictitious fuel flow;

[0022] - control of the fuel metering unit so that it injects into the combustion chamber a quantity of fuel in accordance with the corrected fuel flow setpoint.

[0023] The invention is advantageously supplemented by the following characteristics, taken alone or in any of their technically possible combinations: - the thermal model of the turbomachine comprises at least one thermal model extrinsic to the turbomachine which is derived from a thermal model of an energy source extrinsic to the operation of the turbomachine.

[0024] - the turbomachine comprises a heat exchanger configured to take cold air from the inlet of the turbomachine and to inject the taken air, after passing through the heat exchanger into the combustion chamber, the extrinsic thermal model comprising the temperature of the injected air.

[0025] - the temperature of the injected air is calculated using a model of the thermal behavior of the heat exchanger, a primary fluid of the exchanger being a fluid intended to heat a secondary fluid which is the fluid taken, the thermal model of the turbomachine being configured to provide, from the temperatures of the primary and secondary flows and the inlet flow rates of the primary and secondary flows at the inlet of the heat exchanger, the temperature of the primary flow at the outlet of the heat exchanger.

[0026] - the thermal model of the heat exchanger is a mapping, an analytical calculation or a neural network that has been subject to machine learning or fuzzy logic.

[0027] - the heat exchanger is an air-air exchanger, the primary fluid being exhaust gases from the turbomachine, the secondary fluid being the air entering the turbomachine.

[0028] - the heat exchanger is an air-oil exchanger, the primary fluid being oil taken from the turbomachine, the secondary fluid being the air entering the turbomachine.

[0029] - the extrinsic model includes a temperature from a measurement using a turbomachine temperature sensor.

[0030] According to a second aspect, the invention relates to a fuel flow control system comprising a processor configured to implement a method according to the first aspect of the disclosure.

[0031] According to a third aspect, the invention relates to a turbomachine comprising a regulation system according to the second aspect of the invention.

[0032] According to a fourth aspect, the invention relates to a helicopter comprising a turbomachine according to the third aspect of the invention.

[0033] DESCRIPTION OF FIGURES

[0034] Other characteristics, aims and advantages will emerge from the following description, which is purely illustrative and not limiting, and which must be read in conjunction with the attached drawings in which:

[0035] Figure 1 illustrates a helicopter schematically. Figure 2 illustrates a schematic sectional view of a helicopter turbomachine which includes a heat exchanger.

[0036] Figure 3 illustrates a method for regulating the fuel flow in a turbomachine according to a first embodiment of the invention;

[0037] Figure 4 illustrates a method for regulating the fuel flow in a turbomachine according to a second embodiment of the invention;

[0038] Figure 5 and Figure 6 illustrate in detail steps of the process illustrated in Figure 4.

[0039] Throughout the figures, similar elements have identical references.

[0040] DESCRIPTION DETAILLEE

[0041] Figure 1 schematically illustrates a helicopter 1 equipped with a main rotor 2, for lift and propulsion, as well as an anti-torque rotor. In the example illustrated in Figure 1, the anti-torque rotor is a tail rotor 3 but it could be a rotor coaxial with the main rotor. The drive train of the helicopter comprises in particular a turbomachine 4 to provide the power necessary for the flight of the helicopter and a main gearbox 5 whose function is to transmit the power from the turbomachine 4 to the main rotor 2 and to the tail rotor 3 to set them in motion by mechanisms which are schematically represented in Figure 1 by a first shaft 6 mechanically coupled to the main rotor 2 and a second shaft 7 mechanically coupled to the tail rotor 3.The main gearbox 5 has a mechanical input 9 from which the internal gears are driven which operate the shafts 6 and 7 respectively coupled to the main rotor 2 and the tail rotor 3.

[0042] Turbomachine

[0043] Figure 2 schematically illustrates a turbomachine 4 intended to drive the main rotor 2 of a helicopter 1 in rotation. The turbomachine comprises a gas generator 40 and a free turbine 44 adapted to be driven in rotation by a flow F of gas generated by the gas generator 40. The free turbine 44 is mounted on a shaft (not shown) which is adapted to transmit the rotational movement to the main rotor 2 of the helicopter 1.

[0044] The gas generator 40 comprises a rotating shaft (not shown) on which a compressor 41 and a turbine 43 are mounted, as well as a combustion chamber 42 arranged axially between the compressor 41 and the turbine 43 when considering the direction of circulation of the gases in the turbomachine 4. The turbomachine 4 has an air inlet 10 through which the fresh air F1 enters the gas generator 40.

[0045] After its admission into the enclosure of the gas generator 40, the fresh air F1 is compressed by the compressor 41 which forces it towards the inlet of the combustion chamber 42 in which it is mixed with fuel.

[0046] The combustion which takes place in the combustion chamber 42 causes the burnt gases F2 to be evacuated at high speed towards the turbine 43, which has the effect of driving the shaft of the gas generator 40 and, consequently, the centrifugal compressor 41 into rotation.

[0047] The rotation speed of the shaft of the gas generator 40 depends, among other things, on the flow rate of fuel entering the combustion chamber 42. It is noted that despite the extraction of kinetic energy by the turbine 43, the flow of burnt gases F2 leaving the gas generator 40 has significant energy.

[0048] The flow of burnt gases F2 is directed towards the free turbine 44 which has the effect of causing an expansion in the free turbine 44 leading to the rotation of the turbine wheel and the main shaft 2 to which the turbomachine is intended to be connected.

[0049] In operation, fuel is injected, by means of a fuel metering device 50, into the combustion chamber 42. The combustion releases energy which, by expansion of the gases in the turbine 43, drives the shaft of the gas generator 40. The same applies to the expansion of the gases in the turbine 44 which drives the main rotor 2.

[0050] Fuel flow regulation

[0051] The quantity of fuel required is dependent on the desired speed for the turbomachine. This quantity is tabulated, calculated and stored in a computer 60 (comprising a processor) which provides fuel flow instructions to the fuel metering unit 50.

[0052] The applicant has identified that this quantity can be adjusted according to the temperature prevailing inside the combustion chamber and in particular according to parameter(s) influencing this temperature. The hotter it is, the faster the temperature rise in the combustion chamber 42 will be.

[0053] In this respect, a method for regulating the quantity of fuel is implemented by the computer 60 in relation to figures 3 and 4.

[0054] In a first step, a fuel flow rate setpoint C0 in accordance with a desired speed of the turbomachine is calculated (step CALC0). This setpoint C0 depends on variables of the turbomachine measured by means of sensors (not shown) arranged in the turbomachine and a regulation law. This calculation is well known to those skilled in the art.

[0055] Then, the calculation is carried out (step CALC1) of a fictitious fuel flow rate corresponding to an increase or decrease in the temperature in the combustion chamber as a function of a thermal model M, M' of the turbomachine comprising an intrinsic thermal state of the turbomachine influencing the temperature in the combustion chamber.

[0056] In this step CALC1, the aim is to calculate a correspondence between this increase or decrease in temperature impacting the combustion chamber and a corresponding quantity of fuel.

[0057] In the case of an increase in temperature, there is an equivalent quantity of fuel whose combustion would have brought about this increase in temperature.

[0058] In the case of a decrease in temperature, there is an equivalent quantity of additional fuel to be provided to compensate for this decrease.

[0059] Then, the calculated fuel setpoint is corrected (CORR step) by this fictitious fuel flow.

[0060] Finally, the fuel metering device 50 is controlled (COMM step) so that it injects the fuel flow setpoint thus corrected into the combustion chamber 42.

[0061] According to a first embodiment as illustrated in Figure 3, the method takes into account a first thermal model M of the turbomachine comprising only a model M1 of the intrinsic thermal state of the turbomachine resulting from the thermal characteristics of its components specific to its operation: heat capacity of the materials, exchange coefficient with the air flow of the turbomachine radiated heat, etc.

[0062] According to a second embodiment illustrated in Figure 4, the method takes into account a second thermal model M' comprising both a model M1 of the intrinsic thermal state of the turbomachine resulting from its own thermal characteristics and at least one model M2 of an energy source extrinsic to the operation of the turbomachine.

[0063] The M2 model corresponds, for example, to a heat supply to the combustion chamber that comes from an additional source such as a heat exchanger. Of course, any type of system that can supply heat to the combustion chamber can be provided.

[0064] Indeed, in this second embodiment, the turbomachine is equipped with a heat exchanger 46 (see figure 2) adapted to inject air into the combustion chamber 42, this injected air F4 coming from the air taken F1 at the inlet of the turbomachine as visible in figure 2. As such, the turbomachine comprises pipes 47, 48 which make it possible on the one hand to take the air F1 at the inlet and on the other hand to inject the air F4 at the outlet of the exchanger 46 into the combustion chamber 42.

[0065] As known, a heat exchanger is characterized by means of a primary fluid which is used to heat a secondary fluid.

[0066] The heat exchanger 46 can be of several types: an air-air exchanger, an air-oil exchanger.

[0067] For example:

[0068] - In the case of an air-air exchanger, the primary fluid is constituted by the exhaust gases and the secondary fluid is constituted by the air flow taken from the inlet of the turbomachine. The air-air exchanger 46 is shown in Figure 2 downstream of the exhaust 45 of the turbomachine.

[0069] - In the case of an air-oil exchanger, the primary fluid is made up of the exhaust gases and the secondary fluid is made up of oil from the turbomachine.

[0070] As illustrated in Figure 4, the second thermal model M' takes into account in particular the model M1 of the turbomachine and a model M2 which models an additional source of energy (for example a heat exchanger). This model M2 takes as input characteristics of a first energy flow F1 from the turbomachine to provide as output characteristics of a second energy flow F4 which corresponds to the first energy flow to which energy is supplied. The second flow is therefore at a higher temperature than the first flow and is injected into the combustion chamber.

[0071] From this temperature, a fictitious fuel flow rate C1 is calculated.

[0072] This fictitious flow C1 can be positive or negative:

[0073] - During acceleration, the fictitious fuel flow C1 will be negative (due to thermal inertia) and therefore the fuel flow correction applied to the flow setpoint will be positive. This is the difference that defines the new setpoint C2.

[0074] - During deceleration, the fictitious fuel flow will be positive (due to thermal inertia) and therefore the fuel flow correction applied to the flow setpoint will be negative. This is the difference that defines the new setpoint C2.

[0075] The M2 model of the exchanger specifically models the thermal behavior of the heat exchanger and can take several forms: a map, an analytical calculation or a neural network that has been subject to machine learning or even fuzzy logic. The idea is that the model provides as output the temperature of the fluid injected into the combustion chamber.

[0076] Alternatively, the M2 model of the exchanger is a temperature measurement.

[0077] Figure 5 schematically illustrates a realization of the M2 model of the thermal behavior of the heat exchanger. In this figure the symbol Z signifies a mapping for steps S1 and S2.

[0078] The first flow F1 corresponds to the primary flow entering the exchanger and the second flow F4 corresponds to the flow leaving the exchanger.

[0079] From the flow rates D_F1, D_F3 and temperatures T_F1, T_F3 of the primary and secondary flows and the thermal efficiency (Eff) of the exchanger, the temperature T_F4 of the fluid at the outlet, called stabilized, is obtained (step S1) as well as a time constant t46 of the exchanger (step S2) which gives the time taken by the exchanger to stabilize in temperature. Then, the temperature T_F4 of the fluid at the outlet of the heat exchanger is obtained (step S3). Concerning step S3, the symbol Z corresponds to a first-order dynamic filter whose time setpoint is equal to the value of the variable t46.

[0080] Figure 6 schematically illustrates the calculation of the fictitious fuel flow rate C1 (step CALC1). In this figure, the symbol Z signifies a 3D map. From the engine speed R, the temperature Tin at the inlet 41 of the turbomachine and the atmospheric pressure, the partial derivative of the fictitious fuel flow rate AC2 with respect to the variation AT_4 of the temperature of the fluid at the outlet of the exchanger T_4 is obtained (step S10), by a simple multiplication (step S11) with the variation AT_4 we obtain at the output the fictitious fuel flow rate C1.

Claims

CLAIMS 1. Computer-implemented method for regulating the flow rate of fuel injected into a combustion chamber (42) of a turbomachine (4) of a helicopter (1) by means of a fuel metering device (50), the turbomachine (4) comprising a heat exchanger (46) configured to take cold air (F1), at the inlet (10) of the turbomachine and to inject the taken air, into the combustion chamber (42), after passing through the heat exchanger (46), the method comprising the following steps: - calculation (CALCO) of a fuel flow rate setpoint (CO) in accordance with a desired speed of the turbomachine (4); - calculation (CALC1) of a fictitious fuel flow rate (C1) corresponding to an increase or decrease in the temperature in the combustion chamber as a function of a thermal model (M') of the turbomachine comprising an intrinsic thermal model of the turbomachine influencing the temperature in the combustion chamber, the intrinsic thermal model taking into account the thermal characteristics of the components of the turbomachine, the thermal model further comprising a heat input into the combustion chamber coming from an additional heat source, the heat input coming from the temperature of the injected air; - correction (CORR) of the fuel flow setpoint of the fictitious fuel flow; - control (COMM) of the fuel metering unit so that it injects into the combustion chamber a quantity of fuel in accordance with the corrected fuel flow setpoint (C2).

2. Method according to claim 1, in which the temperature of the injected air is calculated by means of a model (M2) of the thermal behavior of the heat exchanger (46), a primary fluid of the exchanger being a fluid intended to heat a secondary fluid which is the fluid taken, the thermal model (M') of the turbomachine (4) being configured to provide from the temperatures of the primary and secondary flows and the inlet flow rates of the primary and secondary flows at the inlet of the heat exchanger (46) the temperature of the primary flow at the outlet of the heat exchanger (46).

3. Method according to claim 2, in which the thermal model (M2) of the heat exchanger (46) is a mapping, an analytical calculation or a neural network having been the subject of machine learning or fuzzy logic.

4. Method according to one of claims 1 to 3, in which the heat exchanger (46) is an air-air exchanger, the primary fluid being exhaust gases from the turbomachine (4), the secondary fluid being the air at the inlet of the turbomachine (4).

5. Method according to one of claims 1 to 4, in which the heat exchanger (46) is an air-oil exchanger, the primary fluid being oil taken from the turbomachine, the secondary fluid being the air at the inlet of the turbomachine (4).

6. Method according to one of claims 1 to 5, in which the heat input is characterized by a temperature resulting from a measurement by means of a temperature sensor of the turbomachine (4).

7. A fuel flow control system (60) comprising a processor configured to implement a method according to one of the preceding claims.

8. Turbomachine (4) comprising a regulation system (60) according to claim 7.

9. Helicopter comprising a turbomachine (4) according to the preceding claim.

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