Method for controlling the fuel flow of a helicopter turbomachine

Abstract

The present invention relates to a 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 method comprising the following steps: - calculating a fuel flow rate setpoint in accordance with a desired speed of the turbomachine (4); - calculating 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 model of the turbomachine influencing the temperature in the combustion chamber; - correcting the fuel flow rate setpoint of the fictitious fuel flow rate; - controlling the fuel metering device so that it injects into the combustion chamber a quantity of fuel in accordance with the corrected fuel flow rate setpoint (C2). Figure for abstract: Fig. 2

Description

Title of the invention: Method for controlling the fuel flow of a helicopter turbomachine Technical field

[0001] This disclosure relates to the field of helicopter engines and more particularly relates to a turbomachine for a helicopter. STATE OF THE ART

[0002] 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.

[0003] The operating principle is as follows: the fresh air entering the turbomachine is compressed due to the rotation of the compressor before being sent to a combustion chamber where it is mixed with a fuel. The burnt gases due to the combustion are then evacuated at high speed towards the turbine of the gas generator.

[0004] 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.

[0005] 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 member, such as the rotor of the helicopter.

[0006] 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 rate of fuel injected into the combustion chamber.

[0007] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various restrictions on carbon emissions have been, are being or will be adopted by various states. In particular, an ambitious standard applies both to new types of aircraft and those in circulation requiring the implementation of technological solutions in order to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0008] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. The Applicant takes into account consideration of 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.

[0009] 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.

[0010] This sustained research and development work covers new generations of aircraft engines, the lightening of aircraft, in particular through the materials used and lighter on-board equipment, the development of the use of electrical technologies to ensure propulsion, and, as essential complements to technological progress, aeronautical biofuels.

[0011] 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. PRESENTATION OF THE INVENTION

[0012] 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 the performance during transient engine speeds.

[0013] 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:

[0014] - calculation of a fuel flow setpoint in accordance with a desired speed of the turbomachine;

[0015] - calculation of a fictitious fuel flow corresponding to an increase or di reducing 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;

[0016] - correction of the fuel flow setpoint of the fictitious fuel flow;

[0017] - control of the fuel metering device so that it injects into the chamber of combustion of a quantity of fuel in accordance with the corrected fuel flow setpoint.

[0018] The invention is advantageously supplemented by the following characteristics, taken alone or in any of their technically possible combinations:

[0019] - the thermal model of the turbomachine comprises at least one thermal model extrinsic to the turbomachine which comes from a thermal model of an energy source extrinsic to the operation of the turbomachine.

[0020] - the turbomachine comprises a heat exchanger configured to take air cold, at the inlet of the turbomachine and to inject the air taken, after passing through the heat exchanger in the combustion chamber, the extrinsic thermal model including the temperature of the injected air.

[0021] - the temperature of the injected air is calculated using a behavior model thermal model 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.

[0022] - the thermal model of the heat exchanger is a mapping, a calculation analytics or a neural network that has been subject to machine learning or fuzzy logic.

[0023] - the heat exchanger is an air-air exchanger, the primary fluid being gases exhaust of the turbomachine, the secondary fluid being the air at the inlet of the turbomachine.

[0024] - 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.

[0025] - the extrinsic model includes a temperature resulting from a measurement using of a turbomachine temperature sensor.

[0026] 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.

[0027] According to a third aspect, the invention relates to a turbomachine comprising a regulation system according to the second aspect of the invention.

[0028] According to a fourth aspect, the invention relates to a helicopter comprising a turbomachine according to the third aspect of the invention. DESCRIPTION OF FIGURES

[0029] 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 drawings. annexed on which:

[0030] [Fig.l] illustrates a helicopter schematically.

[0031] [Fig.2] illustrates a schematic sectional view of a helicopter turbomachine which includes a heat exchanger.

[0032] [Fig. 3] illustrates a method for regulating the fuel flow in a turbomachine according to a first embodiment of the invention;

[0033] [Fig.4] illustrates a method for regulating the fuel flow in a turbomachine according to a second embodiment of the invention;

[0034] [Fig.5] and [Fig.6] illustrate in detail steps of the method illustrated in [Fig.4],

[0035] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION Helicopter

[0036] [Fig.l] 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 [Fig.l], 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 [Fig.l] 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. Turbomachine

[0037] [Fig. 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.

[0038] 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.

[0039] The turbomachine 4 has an air inlet 10 through which the fresh air F1 enters the gas generator 40.

[0040] 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.

[0041] 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 in rotation and, consequently, the centrifugal compressor 4L.

[0042] 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.

[0043] 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.

[0044] 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. Fuel flow regulation

[0045] The quantity of fuel required is dependent on the desired speed for the turbomachine. This quantity is tabulated, calculated and is stored in a computer 60 (comprising a processor) which provides fuel flow instructions to the fuel metering device 50.

[0046] The applicant has identified that this quantity can be adjusted as a function of the temperature prevailing inside the combustion chamber and in particular as a function of parameter(s) influencing this temperature. The hotter it is there, the faster the temperature rise in the combustion chamber 42 will be.

[0047] In this respect, a method for regulating the quantity of fuel is implemented by the computer 60 in relation to FIGS. 3 and 4.

[0048] In a first step, a fuel flow rate setpoint C0 conforming to 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.

[0049] Next, the calculation (step CALC1) of a fictitious fuel flow rate cor responding 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.

[0050] 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.

[0051] 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.

[0052] In the case of a decrease in temperature, there is an equivalent quantity of fuel to be provided in addition to compensate for this decrease.

[0053] Then, the calculated fuel setpoint is corrected (CORR step) by this fictitious fuel flow.

[0054] Finally, the fuel metering device 50 is controlled (step COMM) so that it injects the fuel flow rate setpoint thus corrected into the combustion chamber 42.

[0055] According to a first embodiment as illustrated in [Fig.3], the method takes into account a first thermal model M of the turbomachine comprising only a model Ml 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.

[0056] According to a second embodiment illustrated in [Fig.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. The model M2 corresponds, for example, to a heat input into the combustion chamber which comes from an additional source such as a heat exchanger. Of course, any type of system capable of supplying heat to the combustion chamber can be provided.

[0057] Indeed, in this second embodiment, the turbomachine is equipped with a heat exchanger 46 (see [Fig.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 [Fig.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.

[0058] As known, a heat exchanger is characterized by means of a primary fluid which is used to heat a secondary fluid.

[0059] The heat exchanger 46 can be of several types: an air-air exchanger, an air-oil exchanger.

[0060] For example:

[0061] - In the case of an air-air exchanger, the primary fluid is made up of the gases exhaust 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 [Fig.2] downstream of the exhaust 45 of the turbomachine.

[0062] - In the case of an air-oil exchanger, the primary fluid is made up of the gases exhaust and the secondary fluid consists of oil from the turbomachine.

[0063] As illustrated in [Fig.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 Fl 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.

[0064] From this temperature, a fictitious fuel flow rate Cl is calculated.

[0065] This fictitious flow rate Cl can be positive or negative:

[0066] - When accelerating, the fictitious fuel flow Cl will be negative (due to thermal inertia) and so the fuel flow correction applied to the flow setpoint will be positive. It is the difference which defines the new C2 setpoint.

[0067] - At deceleration, the fictitious fuel flow will be positive (due to thermal inertia) and so the fuel flow correction applied to the flow setpoint will be negative. It is the difference which defines the new C2 setpoint.

[0068] The M2 model of the exchanger models in particular the thermal behavior of the heat exchanger and can take several forms: a map, an analytical calculation or a neural network that has been the subject of 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.

[0069] Alternatively, the M2 model of the exchanger is a temperature measurement.

[0070] Figure 5 schematically illustrates an embodiment of the M2 model of the thermal behavior of the heat exchanger. In this figure the symbol L signifies a mapping for steps S1 and S2.

[0071] The first flow F1 corresponds to the primary flow at the inlet of the exchanger and the second flow F4 corresponds to the flow at the outlet of the exchanger.

[0072] From the flow rates D_F1, D_F3 and temperatures T_F1, T_F3 of the primary flows and secondary and the thermal efficiency (Eff ) of the exchanger, the temperature T_F4 of the fluid at the outlet called stabilized is obtained (step SI) 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 E corresponds to a first-order dynamic filter whose time setpoint is equal to the value of the variable t46.

[0073] Figure 6 schematically illustrates the calculation of the fictitious fuel flow rate Cl (step CALC1). In this figure, the symbol E 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 SI 1) with the variation AT 4 the fictitious fuel flow rate Cl is obtained at the output.

Claims

Claims

1. A 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 method comprising the following steps: - calculating (CALCO) a fuel flow rate setpoint (CO) in accordance with a desired speed of the turbomachine (4); - calculating (CALC1) a fictitious fuel flow rate (Cl) 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 model of the turbomachine influencing the temperature in the combustion chamber; - correcting (CORR) the fuel flow rate setpoint of the fictitious fuel flow rate; - controlling (COMM) the fuel metering device so that it injects into the combustion chamber a quantity of fuel in accordance with the corrected fuel flow rate setpoint (C2).

2. Method according to claim 1, in which the thermal model (M') of the turbomachine (4) comprises at least one thermal model extrinsic to the turbomachine (4) which is derived from a thermal model (M2) of an energy source extrinsic to the operation of the turbomachine.

3. Method according to claim 2, in which the turbomachine (4) comprises a heat exchanger (46) configured to take cold air (Fl), at the inlet (10) of the turbomachine and to inject the taken air, after passing through the heat exchanger (46) into the combustion chamber (42), the extrinsic thermal model comprising the temperature of the injected air.

4. Method according to claim 3, 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).

5. The method of claim 4, wherein the thermal model (M2) of the heat exchanger (46) is a mapping, an analytical calculation or a neural network having been subject to machine learning or fuzzy logic.

6. Method according to one of claims 3 to 5, 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).

7. Method according to one of claims 3 to 5, 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).

8. Method according to one of claims 2 to 7, in which the extrinsic model comprises a temperature resulting from a measurement by means of a temperature sensor of the turbomachine (4).

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

10. Turbomachine (4) comprising a regulation system (60) according to claim 9.

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

Images