Method for determining fuel density for metering fuel in a fuel supply circuit of an aircraft engine

Abstract

The invention relates to a method for metering fuel in a fuel supply circuit of an aircraft engine, the circuit comprising a metering device for a fuel circuit of an aircraft engine, the metering device comprising, downstream of a fuel pumping system and upstream of an injector: a fuel inlet (E), a metering device (FMV) and a shut-off device (HPSOV) arranged in series, a regulating valve (VR) arranged on a fuel recirculation branch, so that any excess fuel supplied by the pumping system is fed back into the fuel circuit, wherein at least one flow metering sensor (WFM1) is arranged on the recirculation branch and a density value of the metered fuel is determined based on the measurement value of the sensor, and the metering device is controlled based on the fuel density value thus determined.

Description

Technical Field

[0001] The present invention generally relates to the supply of fuel to aircraft engines, and in particular to turbines.

[0002] The invention relates to a method for metering fuel and a circuit for supplying fuel to an aircraft engine. Background Art

[0003] Aircraft engines are usually equipped with a specific fuel metering system, which is called a Fuel Metering Unit (FMU) or a Hydro Mechanical Unit (HMU).

[0004] The metering system performs several functions. It regulates the flow of fuel to the combustion chamber, particularly in the event of overspeed (engine speed exceeding the permissible speed), and cuts off the flow of fuel to the combustion chamber (engine shutdown). The metering system also ensures the pressurization of the engine's fuel system.

[0005] Typically, a mass flow meter is inserted between the metering system FMU and the device for injecting fuel into the combustion chamber.

[0006] The information provided by the mass flow meter is sent to the engine's control computer EEC, but is never used in the engine regulation loop: this information is transmitted by the EEC to the aircraft computer for display in the cockpit.

[0007] The flow information used to control the metering of the metering unit FMU is itself generally obtained independently of the flow measurement provided by the engine flow meter.

[0008] Due to position sensors of the linear variable displacement transducer (LVDT) type, the metered flow rate is usually reconstructed from the position of the metering actuator.

[0009] However, the metered flow value thus calculated is relatively inaccurate.

[0010] The most significant inaccuracies are related to the variability in the type of fuel used for combustion and the range of temperatures over which the fuel may operate.

[0011] This is Figure 1 , in which different fuel density values ​​for different types of fuel are represented as a function of temperature.

[0012] As shown in the figure, at low temperatures, the density fluctuation from one fuel to another can be as high as 12.5%; at high temperatures it can be as high as 15%.

[0013] However, it is not uncommon to find only one type of fuel in all tanks of an aircraft. Different airports or maintenance operation centers do not need to refill tanks with the same fuel as the one previously introduced.

[0014] To avoid engine operability problems associated with over- or under-metering of fuel, particularly during the starting or deceleration phases, and more generally to avoid any risk of misfire, stalling, or lockup, engines are designed and certified to receive a wide range of fuel types for combustion, and across the entire temperature range they may encounter. This also applies to the fuel circuit and its inherent equipment components, which are also designed to function with each possible fuel. These equipment components are adapted to their inherent characteristics (density, lubrication power, PCI).

[0015] Consequently, variations in fuel type and temperature can produce significant inaccuracies in metered flow rates that now require over-scaling of the engine and its equipment components.

[0016] The cited French patent applications FR 3 053 396 A1 and FR 3 069 021 A1 are also known. Summary of the Invention

[0017] The general object of the present invention is to propose a method for regulating the fuel flow with greater metering accuracy.

[0018] Another object of the invention is to enable the dimensions of the engine and of the supply circuit to be optimized and their mass to be increased.

[0019] Another object of the invention is to enable the dimensioning of the metering actuator and engine elements independently of the properties and temperature of the fuel.

[0020] The increase in metering accuracy is reflected in a better dimensioning of the engine, for example, in particular in a better dimensioning of the air compression module of the engine.

[0021] A more optimized compressor is more efficient and improves the engine's specific fuel consumption.

[0022] This also reduces the amount of fuel to be carried for similar maneuvers.

[0023] In addition, the resulting increase in mass results in a reduction in the power delivered by the engines to ensure the thrust of the aircraft.

[0024] In addition to the reduced size of the engine, fuel consumption will also be lower.

[0025] The improved metering accuracy also makes it possible to reduce the amount of fuel recirculated into the fuel circuit, which is limited by the need to cool the engine oil.

[0026] Furthermore, the fact that less fuel is recirculated leads to a simplification of the fuel system and thus to an increase in mass.

[0027] Thus, according to one aspect, the invention proposes a method for metering fuel in a fuel supply circuit of an aircraft engine, said circuit comprising a metering device for a fuel circuit of an aircraft engine, said metering device comprising, downstream of a fuel pumping system and upstream of an injector:

[0028] - fuel inlet,

[0029] - metering and cutting elements arranged in series,

[0030] - A regulating valve is arranged on the fuel recirculation branch so that excess fuel supplied by the pumping system is discharged into the fuel circuit.

[0031] At least one flow metering sensor is arranged on the recirculation branch, and a density value of the metered fuel is determined based on a measurement value of said sensor, the metering member being controlled based on the fuel density value thus determined.

[0032] In particular, the mass flow rate and the volume flow rate are determined based on the signals measured by the flow metering sensor, and the density value of the metered fuel is determined to be equal to the ratio between the mass flow rate and the volume flow rate determined thereby.

[0033] The metered flow rate can be calculated by subtracting the recirculation flow rate seen by the flow metering sensor on the recirculation branch from the pumped flow rate.

[0034] As a variant, at least one flow metering sensor is arranged downstream of the metering device and, based on the measurement values ​​of this sensor, another density value of the metered fuel is determined, the metering member being controlled based on this fuel density value and on the fuel density value determined based on the measurement values ​​of a sensor arranged on the recirculation branch.

[0035] The invention also relates to a fuel supply circuit for an aircraft engine.

[0036] The invention relates to an aircraft engine, in particular a turbomachine comprising such a circuit and an aircraft comprising such an engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Other features and advantages of the present invention will become apparent from the following description which is intended to be illustrative only and non-limiting and which should be read in conjunction with the accompanying drawings, in which:

[0038] - Figure 1is a graph showing the density of different fuels as a function of temperature;

[0039] - Figure 2 is a schematic diagram of an example of a known general architecture of a fuel supply circuit of a combustion chamber of an aircraft engine;

[0040] - Figure 3 is a schematic diagram of a metrology system FMU associated with a sensor for implementing the present invention;

[0041] - Figure 4 The general principles for implementing the present invention are shown;

[0042] - Figure 5 The present invention is shown implemented by an engine control computer. DETAILED DESCRIPTION

[0043] Tips on the fuel supply circuit

[0044] Figure 2 The feed circuit shown corresponds to a generally known general architecture and comprises, in series in the direction of fuel flow, a low-pressure pump LP, a main heat exchanger FCOC or "fuel oil exchanger" with the fuel as cooling source, a fuel filter F, a high-pressure HP pump and a fuel metering unit FMU.

[0045] For example, the high-pressure HP pump is a gear pump whose fixed displacement is optimized according to the engine speed of the turbine at takeoff.

[0046] The high-pressure HP pump, in addition to supplying fuel to the combustion chambers, also supplies fuel to the engine's "variable geometry" GVs, which are machine parts or turbine parts that include movable elements and require variable hydraulic power to operate.

[0047] These equipment components or members GV may be of various types, such as cylinders, servo valves, adjustable compressor safety valves, compressor transient safety valves and / or air flow control valves for clearance control systems at the tips of rotor blades of a low-pressure turbine or a high-pressure turbine.

[0048] To this end, fuel is taken from the fuel supply circuit on a branch B for supplying the "variable geometry", which branch extends between a node E between the HP pump and the metering unit FMU and a node C between the low-pressure LP pump and the high-pressure HP positive displacement pump.

[0049] At node E, the feed circuit shown includes a self-cleaning filter FA for filtering a portion of the harvested fuel flow. This filter FA is cleaned by the fuel flow circulating in the feed circuit to the fuel metering unit FMU. Branch B may further include a heat exchanger ECT, upstream of the plant component GV, for temperature control of the harvested fuel.

[0050] The combustor supply circuit also includes a recovery circuit RE (also known as a fuel recirculation branch) that connects the fuel metering unit FMU to the supply circuit between the low-pressure pump LP and the heat exchanger FCOC (e.g., node C). Thus, excess fuel flow supplied to the fuel metering unit FMU can be returned upstream of the heat exchanger FCOC via this recovery circuit RE to the main fuel filter F and the high-pressure HP pump.

[0051] Thus, in operation, fuel from the tank R is sucked in by the low-pressure LP pump and pumped into the supply circuit. In this supply circuit, the fuel is first cooled in the main heat exchanger FCOC and then filtered in the fuel filter F. Downstream of this filter F, the fuel is sucked in by the high-pressure HP pump and pumped under high pressure towards a connection point (node ​​E), where part of the fuel flow is transferred from the supply circuit to the equipment component GV and passes through the self-cleaning filter FA.

[0052] The remaining portion of the fuel flow flows through the self-cleaning filter FA to the fuel metering unit FMU, after cleaning said filter FA. The unit FMU, for its part, in particular ensures the metering of the fuel flow supplied to the combustion chamber via the injector I, for example, via a flow meter DMT connected to the control computer EEC and an injection filter FI arranged upstream of the injector I.

[0053] Architecture of the FMU system

[0054] Figure 3 The metering system FMU shown is arranged in the fuel supply circuit of the engine, downstream of the fuel pumping system (HP pump) and upstream of the injectors I supplied by the metering system.

[0055] The regulating valve VR is located at the inlet of the metering system, on the branch that ensures the recirculation of fuel for discharge.

[0056] The regulating valve VR ensures a constant pressure difference across the FMU.

[0057] This regulating valve VR, often called a “bypass valve”, is a purely passive component which, thanks to the return pressure of the spring, enables a certain pressure difference to be maintained between the inlet of the FMU and the outlet of the SOV.

[0058] A spring in the valve (example below) acts on a piston (spool), which has fuel at different pressures on either side.

[0059] The flow rate itself is metered by a metering element, usually called a fuel metering valve (FMV). This element is controlled by the control computer EEC via a servo valve, which estimates the metered mass flow rate Q using the following formula for calculating the flow through the orifice:

[0060]

[0061] Where ΔP is the pressure difference, S is the surface of the holes that allow the fuel fluid to pass through the FMV, ρ is the density of the fluid, and K S It is a parameter related to FMV.

[0062] The metering member FMV generally includes a linear position sensor (linear variable differential transducer) (LVDT, Linear Variable Differential Transducer) (such as Figure 2 A movable valve core is associated with a rotary sensor (shown) or a rotary variable differential transducer (RVDT).

[0063] The position of the valve spool measured by the LVDT or RVDT sensor is transmitted to the control computer EEC, which controls the position of the valve spool via the servo valve ( Figure 2 The FMV (EHSV) in the control valve element controls the displacement of the valve element: Since the differential pressure remains constant, the metered flow rate varies with the position of the movable valve element.

[0064] As an output, the FMU includes a HPSOV valve (High Pressure Shut-Off Valve), which, on the one hand, enables pressurization of the fuel circuit and, on the other hand, shut-off of the injection flow (for example in the event of detection of an engine overspeed).

[0065] Like the metering member, the HPSOV shut-off valve includes a position sensor LVDT or RVDT that sends position information to the engine control computer EEC. The displacement of the HPSOV valve is controlled by the computer through the HPSOV EHSV servo valve.

[0066] Improved measurement accuracy

[0067] The metering system FMU is further supplemented by a flow meter sensor WFM1 which is arranged upstream of the regulating valve VR on the recirculation circuit RE.

[0068] This flow meter WFM1 enables the measurement of mass flow and volume flow.

[0069] These two pieces of information are processed by the EEC to determine the fuel density by simply dividing the measured mass flow by the also measured volume flow.

[0070] The mass flow sensor WFM1 is for example a sensor with two rotors of the type described in patent US 3.144.769, or a drum and impeller sensor as described in patent EP 0.707.199.

[0071] like Figure 4 As shown, in the case where sensor WFM1 includes a drum output (DRUM) and an impeller output (IMPELLER), the rotational speed of the drum and the impeller is proportional to the volume flow Qv, while the time offset ΔT between the drum and the impeller is proportional to the mass flow Qm.

[0072] like Figure 5 As shown, the computer EEC receives signals from its solenoids from the sensor WFM, these signals following the rotation of the drum (DRUM) and the rotation of the impeller (IMPELLER).

[0073] After filtering (F IMPELLER; F DRUM) and amplification (A IMPELLER; A DRUM), these signals are digitized (A / N). The EEC combines the drum and impeller signals to deduce the volume flow rate Qv through sensor WFM. This computer compares the drum and impeller signals to deduce the time offset ΔT between the drum and impeller rotations and the mass flow rate Qm, which is sent to the aircraft's computer.

[0074] The computer then calculates the ratio Qm / Qv corresponding to the fuel density.

[0075] Based on the fuel density thus determined, and the opening S of the metering member provided by the sensor LVDT, the computer EEC calculates the flow Q metered by the metering member using the following formula:

[0076]

[0077] This formula has been indicated above.

[0078] The computer EEC then determines the control current CC for the FMV EHSV servo valve in order to adjust the displacement of the spool of the metering device FMV so that this displacement matches the metering to be controlled.

[0079] In this way, fuel metering control is more precise than is the case with conventional reconstructed metering flows.

[0080] In an advantageous embodiment, a mass flow sensor is also used downstream of the FMU to obtain a second flow value. This second value ensures redundancy.

[0081] It should be noted that this solution makes it possible to maintain the flow rate throughout the flight without exploring very low flows and without fast transients.

[0082] In particular, the calculated density is not disturbed by changes in engine speed and pressure deviations.

[0083] This increased metering accuracy allows for better sizing of the engine's air compression module. Thanks to the more optimized compressor, the engine's fuel consumption improves. This results in a reduced amount of fuel to be loaded, and an increase in the aircraft's mass, which in turn reduces the power required to maintain thrust.

[0084] Furthermore, due to the reduced size of the engine, fuel consumption is lower. Better metering also enables the amount of recirculated fuel to be reduced, which leads to a simplification of the fuel system and, in this case, an increase in the mass of the engine.

[0085] Furthermore, more precise knowledge of the fuel density makes it possible to significantly simplify the design of the temperature compensation in the hydraulic block. Figure 2 In the feed circuit of , the dimensions of the heat exchanger FCOC and the exchanger ECT can be smaller than in the case of the previous solutions.

[0086] In an advantageous embodiment, a mass flow sensor downstream of the FMU is also used to obtain a second flow density value. Figure 2 The WFM2 in the example is also a Crane-based sensor or similar. This sensor provides a second density value for redundancy.

[0087] As yet another variant, if the computer EEC knows the flow pumped by the pumping system downstream of the FMU, the metered flow to be transmitted to the computer can be calculated by subtracting the recirculation flow seen by sensor WFM1 from said pumped flow. The downstream sensor WFM2 can then be deleted.

Claims

1. A fuel metering method for metering fuel in a fuel supply circuit of an aircraft engine, the fuel supply circuit comprising a metering device for a fuel supply circuit of an aircraft engine, the metering device comprising, downstream of a fuel pumping system and upstream of an injector: - fuel inlet (E), - Metering element (FMV) and shut-off element (HPSOV) arranged in series, - a regulating valve (VR) arranged on the fuel recirculation branch, so that excess fuel provided by the fuel pumping system is discharged into the fuel supply circuit, wherein at least one flow metering sensor is arranged on the recirculation branch and upstream of the regulating valve, and a density value of the metered fuel is determined based on a measurement value of the flow metering sensor, and the metering member is controlled based on the fuel density value determined thereby, wherein the flow measurement sensor is a drum and impeller sensor, The fuel metering method comprises: - receiving a signal from the solenoid of the flow meter sensor, said signal following the rotation of the drum and the rotation of the impeller, - comparing the signals of the drum and the impeller to infer the mass flow rate and the volume flow rate, the mass flow rate being proportional to the time offset between the rotations of the drum and the impeller, and the volume flow rate being proportional to the rotational speed of the drum and the impeller, - calculating a density value of said metered fuel equal to the ratio between said mass flow rate and said volume flow rate determined thereby, wherein at least one flow metering sensor is arranged downstream of the metering device, and a further density value of the metered fuel is determined based on a measurement value of the flow metering sensor arranged downstream of the metering device, and the metering member is controlled based on the further density value of the metered fuel and the fuel density value determined based on the measurement value of the flow metering sensor arranged on the recirculation branch.

2. The fuel metering method according to claim 1, wherein: The metered flow is calculated by subtracting the recirculation flow measured by the flow metering sensor on the recirculation branch from the pumped flow.

3. A fuel supply circuit for an aircraft engine, comprising a metering device for a fuel supply circuit for an aircraft engine, the metering device comprising, downstream of a fuel pumping system and upstream of an injector: - fuel inlet (E), - Metering element (FMV) and shut-off element (HPSOV) arranged in series, - a regulating valve (VR) arranged on the fuel recirculation branch, so that excess fuel provided by the fuel pumping system is discharged into the fuel supply circuit, - a computer for controlling the metering member and the regulating valve, Therein, at least one flow metering sensor is arranged on the recirculation branch, and the computer is adapted to control the metering member by implementing the fuel metering method according to any one of claims 1 to 2.

4. An aircraft engine comprising a fuel supply circuit according to claim 3.

5. The aircraft engine according to claim 4, wherein: The aircraft engine is a turbine.

6. An aircraft comprising an aircraft engine according to claim 4.

Images