Aircraft engine fuel supply

Fueling of an aircraft engine

The invention relates to a fuel supply device of an aircraft engine, in particular, but not exclusively, to a gas turbine aircraft engine.

Typically, such a feeding device typically comprises a volumetric gear pump driven by the motor through an accessory drive box coupled to a motor shaft. The volumetric pump receives fuel that comes from a fuel circuit of the aircraft through a priming pump. An electrohydraulic control metering valve is mounted in a supply line that joins the volumetric pump outlet to an engine combustion chamber. A fuel return circuit with a governed variable opening bypass valve is connected between the outlet and the inlet of the volumetric pump. The bypass valve is hydraulically governed to maintain the pressure drop through the dosing valve at a constant or near constant value that allows to facilitate the desired fuel flow corresponding to the position of the dosing valve. An engine overspeed or overspeed valve can be mounted in a series feed line or bypass with the metering valve to send a decrease in fuel flow in response to the detection of excessive speed or thrust that can be translate into a failure of the dosing valve or its control. A shut-off valve is generally provided in series with the dosing and overspeed valves to shut down the engine due to interruption of the fuel supply by direct command from a pilot station. It may refer in particular to documents EP 1 355 054 and US 2004/0117102.

It has also been proposed to fuel a gas turbine engine by means of a centrifugal pump that makes it possible to supply fuel at a given pressure depending on the speed of rotation of the pump. EP 1 344 917 shows the use of a centrifugal pump of this type that is driven by an electric motor under the command of an electronic control circuit, which allows the speed of the pump to be regulated, hence the pressure of the fuel at The output of this. This same document also shows an electric gear pump that runs in parallel with the centrifugal pump to ensure a priming function and permanently facilitate a minimum fuel flow, the centrifugal pump and the volumetric pump being fed by a low pressure priming pump .

US 3 946 551 shows a fuel supply device with an electric control fin pump mounted in series with a centrifugal pump driven by the engine. The electric control fin pump has the function of placing the fuel at a pressure of necessary value during engine start-up (starting assistance) and ensuring the dosing of the fuel. An assembly of this type has several drawbacks. With the electric control fin pump running permanently to ensure dosing, it must have a large displacement to accept the maximum fuel flow. Thus, it must be sized accordingly. In addition, with a large displacement pump, the accuracy of dosing at low rotation speed is lower, while precise regulation at the start-up phase is also required. On the other hand, in case of failure of the fin pump, there is no fuel dosage.

The document "Patent Abstracts of Japan" vol. 200, No. 02, dated February 29, 2000 (JP 11 303 652) shows a fuel supply circuit to a gas turbine with two pumps mounted in parallel, a main pump driven by the gas turbine and a secondary pump driven by electric motor. The secondary pump is used for cold start while the main pump can be used in case of hot start. There is no indication about the main pump or about an eventual switching of operation between the pumps.

As for EP 0 657 651, this shows an association of a centrifugal pump and a start-up assistance pump, the latter being mechanically drawn in the same tree as the centrifugal pump. An out-of-circuit setting of the assistance pump forces it to be emptied so as not to allow fuel to stagnate and become hot in high-speed rotary equipment. The mechanical drag of the assistance pump and the need to empty it complicate the realization of the pumping group.

From EP 0 377 292, on the other hand, a gaseous fuel supply device to a turbine with regulation of the gas flow by a governed variable opening valve that receives the gas under constant pressure is known.

Object and summary of the inveneian

The aim of the invention is to provide a fuel supply device to an aircraft engine with better optimization in terms of mass and power consumption compared to the state of the art.

This objective is achieved thanks to a feeding device according to claim 1.

The use of a centrifugal pump driven by mechanical coupling rather than by an electric motor makes it possible to use the mechanical power provided by the motor as much as possible by avoiding an intermediate transformation into electrical energy, an inevitable source of loss of performance and increase in mass.

The assistance pumping group allows the centrifugal pump to be supplied when its engine drag is non-existent or insufficient to facilitate the minimum fuel pressure to the fuel flow regulation circuit.

According to a preferred embodiment of the feeding device, the assistance pumping group comprises a volumetric pump and an overpressure gate having a first inlet connected to the outlet of the volumetric pump, a second inlet connected to the fuel circuit of the aircraft and an outlet attached to the volumetric pump inlet, putting the gate in communication its first input with its output when the pressure difference between its first input and its second input exceeds a predetermined threshold.

Preferably, then, the inlet of the volumetric pump is connected to the high pressure outlet of the centrifugal pump.

According to another preferred embodiment of the feeding device, the assistance pumping group comprises a second centrifugal pump and an electric control circuit for dragging the second centrifugal pump at a speed that facilitates said predetermined minimum pressure.

According to another preferred embodiment of the feeding device, the assistance pumping group comprises a regenerative pump instead of the volumetric pump of the first embodiment.

The choice of the type of assistance pump will be linked to the type of aircraft. Thus, this last preferred embodiment is intended more particularly for aircraft that have a gas turbine located above the tank (such as helicopters, seaplanes, etc.).

Preferably, stop means of the assistance pumping group are provided when the fuel pressure supplied to the flow regulation circuit or when the engine speed exceeds a predetermined pressure or regime threshold.

Restarting means of the assistance pumping group may be provided when the fuel pressure supplied to the flow regulation circuit or the engine regime is made below a predetermined pressure or regime threshold.

Because the fuel flow regulating device comprises a fuel flow measurement device and a governed variable opening valve, as well as a control system attached to the flow measurement device and the valve to govern it is a function of a fuel flow setpoint value, the flow regulation therefore does not need a fuel return circuit with a bypass valve between the outlet and the inlet of the main feed pump.

The flow measurement device can be a mass flowmeter, a volumetric flowmeter or a hybrid device that allows a flow measurement from the knowledge of the pressure coffe and the passage section through this device.

The use of a mass flow rate can allow a more precise regulation of the fuel flow rate compared to the use of a volumetric flowmeter. In fact, the need for the engine is generally expressed in mass of fuel. If the flow measurement is volumetric, a mass to volume conversion is necessary, but the accuracy of the regulation is affected by the uncertainty about the volumetric mass of the fuel, and this volumetric mass may vary depending on the external conditions and the embarked fuel.

According to yet another particularity of the supply circuit, the valve is an electrically governed direct control valve.

The control system may comprise a local feedback loop attached directly to the flow measurement device and the valve. By local loop is understood here an electronic feedback circuit outside the electrical module box of the automatic motor regulation system with full FADEC authority ("Full Authority Digital Engine Control").

Advantageously, the fuel flow regulation device comprises:

a fuel flow measurement device in the fuel supply line,

a first governed variable opening valve mounted on a feed line,

a control system attached to the flow measurement device and the first valve to govern this is in order to provide the engine with a desired fuel flow,

a second governed variable opening valve mounted in the supply line in series with the first, and

control means of the second valve that make it possible to provide the engine with an adjustable reduced fuel flow in response to a detection of overspeed or overspeed of the engine.

The first and second valves can be electrically governed direct control valves.

Brief deseripeian of the drawings

The invention will be better understood by reading the description made below, by way of indication but not limitation, referring to the accompanying drawings, in which:

Figure 1 illustrates an embodiment of a fuel supply device according to the invention;

Figure 2 illustrates the variations in the pressure time facilitated by the centrifugal pump and a pump start-up pump group;

Fig. 3 is a partial diagram illustrating a variant embodiment of the assistance pumping group of the fuel supply device of Fig. 1; and

Figures 4 and 5 are partial diagrams illustrating variants of realization of the fuel flow regulation circuit of the fuel supply device of Figure 1.

Detailed deseripeian of ways of performing of the inveneian

The fuel supply circuit 10 of Figure 1 receives fuel that comes from a fuel circuit 11 of an airplane and facilitates a fuel flow to a fuel injection system 12 of a gas turbine combustion chamber of an engine 14 which equips the aircraft, observing that the described feeding device can be used for aircraft engines other than gas turbine aircraft engines, for example helicopter engines.

The circuit 10 comprises a centrifugal pump 100 which constitutes the main pump of the circuit. The pump 100 has an inlet 100a connected to the fuel circuit 11 and a high pressure outlet 100b which facilitates fuel at a pressure depending on the speed of rotation of the pump. The pump is driven by mechanical connection with the motor accessories drag module 16 coupled to its turbine.

An assistance pumping group 110 comprises a volumetric pump 112 having an inlet 112a connected to the outlet of the centrifugal pump 100, an electric motor 114 for driving the pump 112 governed by an electric control circuit 115 and an overpressure gate 116.

Pump 112 is for example a gear pump. Between the outlet 100b of the pump 100 and the inlet 112a of the pump 112, a filter 118 may be mounted to protect it against any solid particles transported by the fuel from the circuit 11. The operation of the centrifugal pump 100 does not result affected by such particles.

The electric control circuit 115 is connected to an automatic regulation system 15 with full authority of the motor 14, or FADEC, to command the operation of the pump 112. This control circuit 115 could also be integrated in the regulation system 15.

The overpressure gate 116 has a first inlet 116a connected to the outlet 112b of the pump 112, a second inlet 116b connected to the fuel circuit of the aircraft and which facilitates a reference pressure to the gate 116, and an outlet 116c attached to the pump 112a 112a. The overpressure gate is regulated to open and communicate the first input 116a with the outlet 116c when the pressure difference between inputs 116a and 116b exceeds a predetermined threshold. To make the gate 116, a distributor 117 subjected, on the one hand, to the outlet pressure of the pump 112, through a pressure tap 116d and, on the other, to the pressure on the increased second inlet 116b may be used in a force exerted by a spring.

The outlet 100b of the centrifugal pump 100 is connected by a backstop gate 102 to the input of a fuel flow regulation circuit 120 provided to the fuel injection system 12, while the outlet 112b of the pump 112 is connected to the input of regulation circuit 120.

The operation is as follows.

The overpressure gate 116 is regulated to open at a pressure corresponding to a predetermined minimum pressure Pm that allows to meet the minimum fuel requirement of the engine 14 at startup.

The volumetric pump 112 is started and dragged at a speed that makes it possible to facilitate a fuel flow that exceeds the initial need of the engine 14 set by the regulating system 120, so that the pressure at the outlet 112b of the pump 112 reaches almost instantly at the minimum pressure Pm (see curve A in Figure 2) that causes the overpressure gate 116 to open. The pressure at the outlet 100b of the centrifugal pump begins to increase with the start of the engine 14 (see curve B in Figure 2) but does not initially cover the need for fuel pressure. The pressure at the outlet 112b of the pump 112 is then regulated to the pressure value Pm, the fuel supplied by the pump 112 circulated in a closed circuit and not supplied to the injection system 12 between the outlet and the inlet of the pump 112 a through the gate 116. The backstop 102 prevents the return of the fuel provided by the pump 112 to the centrifugal pump 100.

The pumping group 110 thus ensures a start-up assistance function, allowing the gate 116 to convert the volumetric pump 112 into a pump that facilitates a fuel pressure, in the same way as a centrifugal pump. However, contrary to what can happen with a centrifugal pump, the operation of the volumetric pump 112 is not affected by the presence of air or steam in the fuel initially taken out of circuit 11.

The pressure at the outlet of the pump 100 increases when the engine speed increases and when this pressure exceeds the value Pm, the backstop 102 opens (transition point T of Figure 2). The pressure provided to the flow regulation circuit 120 is then that provided by the centrifugal pump 100.

In Figure 2, the bold parts of curves A and B represent the fuel pressure provided to the regulation circuit 120. The pump assembly 100, pumping group 110 and gate 102 behaves like a pumping system that allows a transition by preponderance between pumps 112 and 100, the fuel pressure given to the regulation circuit being the highest of the pressures provided in parallel to the output of pumps 112 and 100.

When the pump 100 has taken over from the pump 112, its operation can be stopped. The stop may be governed in response to the exceeding of a pressure threshold P1 at the outlet of the pump 100 or in response to an exceeding of a regime threshold V1 of the engine 14. This can be commanded by the automatic regulation system 15 acting on the electric control circuit 115 in response to information provided by a fuel pressure sensor or by a turbine speed sensor of the engine 14. The thresholds P1 and V1 can be chosen to correspond to a value greater than Pm.

It will be noted that the pumping group 110 can be used not only at start-up, but also during other phases of engine idling or low-speed operation in the event that the centrifugal pump 100 is then unable to facilitate the minimum pressure Pm of fuel. It is then sufficient to restart the engine 114 by the control circuit 115 if a decrease in fuel pressure is detected below a pressure threshold P'1 or a decrease in the engine speed below a regime threshold V'1 of the motor 14, the thresholds P'1 and V'1 being lower than P1 and V1 being chosen.

The pumping group 110 then behaves not only as a start-up assistance group, but also as a support group in the low engine regimes to facilitate under any circumstances a minimum sufficient fuel pressure.

In the embodiment illustrated in Figure 1, the pump 112 is connected to the fuel circuit 11 through the centrifugal pump that is "transparent" to the pump 112 at start-up. This connection allows the pump 112 to benefit from the increase in pressure caused by the pump 100 since it begins to be pulled.

Naturally, it would be possible to connect the inlet 112a of the pump 112 to the fuel circuit 11 through a filter, without passing through the centrifugal pump 100.

According to another variant embodiment, the volumetric pump 112 may be replaced by a regenerative pump, especially for aircraft that have a gas turbine located above the tank, such as helicopters, seaplanes, etc. .

In another embodiment illustrated in Figure 3, the assistance pumping group 110 comprises a centrifugal pump 212 whose inlet is connected to the fuel circuit 11 and which is driven by a motor 214 governed by an electronic control circuit 215 connected to the automatic engine regulation system 15 14. An anti-reverse gate 202 is mounted at the outlet of the pump 212. Centrifugal pump 212 is driven at a speed that facilitates the minimum pressure Pm as long as it cannot be facilitated by the centrifugal pump

100 The operation of the centrifugal pump 212 can be interrupted and restarted according to the needs in the same way as that of the pump 112 in the embodiment of Figure 1. This other embodiment is distinguished from the mode of Figure 1 by a Simplified construction of the assistance pumping group 110 but is only possible if the fuel circuit 11 is capable of providing an air-free or steam-free fuel even at start-up.

The fuel flow regulating circuit 120 in the conduit comprises a mass flowmeter 122 and a direct drive fuel valve 124 mounted in a conduit 126 connecting the pump 100 and the assistance pumping group 110 to the injection device 12 fuel. Flowmeter 122 is preferably mounted upstream of valve 124. In the conduit 110, upstream of the flowmeter 122, a thermal exchange circuit 128 can be inserted between the engine oil and the fuel oil, and a particle filter 130, such exchange circuits being well known Thermal and filter.

The valve 124 is for example an electric control valve. The opening of the valve is regulated by means of an electromechanical actuator 125 such as a jack or electric motor. The actuator 125 receives an electrical supply from an electrical circuit of the motor 14, for example from an integrated supply in the automatic motor control system 15 or from an electrical supply bus of the motor 14. By way of redundancy, two similar actuators 125, 125 'could be provided that work in parallel.

A local feedback loop 132 fed from an electrical circuit of the engine receives a signal provided by the mass flowmeter 122 representative of the actual mass flow of fuel in the conduit 126 and a signal provided by the automatic regulation system 15 of the engine and representative of the desired setpoint value of the mass fuel flow to be provided to the engine 14. The actuator 125 is sent according to the deflection detected between the actual and setpoint mass flows in order to regulate the flow to the desired setpoint value.

Naturally, the regulation could be ensured by an electronic module integrated in the automatic regulation system 15 of the motor 14. The use of a local loop 132, outside the box of this electronic module, nevertheless allows avoiding the presence of connection of this last with flowmeter 122.

In the duct 126, downstream of the valve 124, a valve 134 of over-speed or over-thrust protection of the motor 14 is mounted. Advantageously, a direct-control valve with electromechanical actuator 135 may be used, similar to the valve 124 and to the actuator 125. The actuator 135 is sent from the automatic control system 15 of the engine 14 by a module different from that dedicated to the regulation by the valve 124, for safety purposes. By way of redundancy, two similar actuators 135, 135 'which operate in parallel can be provided.

In normal engine regime, according to the setpoint, the valve 134 is in the maximum opening position and the flow regulation is ensured by the valve 124.

The automatic regulation system 15 receives information representative of the engine regime, for example information representative of the rotational speed of the high pressure turbine. When a state of overspeed (or overshoot) is detected, that is to say a speed that exceeds the speed setpoint value beyond a given deviation, and cannot be corrected by action on the valve 124, the valve 134 is governed to reduce the fuel flow in the duct 126.

The automatic regulation system 15 can be programmed to bring the valve 134 to a predetermined partial safety shut-off position that makes it possible to facilitate a reduced fuel flow. The use for the valve 134 of a direct control valve is then advantageous because it allows the engine to be maintained by modifying the fuel flow rate at least in a reduced range. This modification can be carried out by the automatic regulation system 15 depending on a desired engine regime. Thus, following an overspeed detection, the valve 134 takes over from the valve 124 to continue authorizing a variation of the flow rate at least in a certain interval.

With respect to the state of the art systems in which the operation of the overspeed valve is in two states: (i) full opening or (ii) predetermined cut-off or opening, the possibility of a flow regulation after the overspeed or overspeed detection allows to conserve a motor thrust and avoid a situation in which a reduced flow imposed may not be acceptable by the engine under certain conditions.

In the duct 126, for example downstream of the valve 134, a shut-off valve 136 of the entire type is mounted

or nothing. The valve 136 can be governed by an electromechanical actuator 137. In a known way, the shut-off valve 136 can be operated by command from the automatic regulation system 15 of the engine or, as a priority, from the pilot position of the aircraft to switch off the engine 15 due to interruption of the fuel supply.

In a known manner also, in the duct 126, downstream of the valve 136, a mass total flowmeter 138 can be mounted to provide information on the cumulative consumption of the engine in mass of fuel.

The need for fuel in an engine translates into mass of fuel. The use of the mass flowmeter 122 thus allows, within the limit of its error range, a precise regulation of the fuel supply from a mass flow rate setpoint. The mass flow rate may be of the type described in US 2004/0123674 and US 2004/0129088.

It is possible, however, as shown in Figure 4, to replace the mass flow rate with a volumetric flowmeter 222. The actual volumetric flow rate information measured by the flowmeter 222 is transmitted to the automatic regulation system 15 of the engine 14. System 15 is programmed to translate the need of the engine into the volumetric flow rate of the setpoint from an estimated volumetric mass value of the fuel. Valve 124 of

5 Direct command is then governed by the system 15 to feedback the volumetric flow in the duct 126 to the desired setpoint value.

According to yet another embodiment, as shown in Figure 5, a device 322 can be used that allows a flow measurement from the knowledge of the pressure coffee P through the device 322, of the passage section of fuel through device 322 and the volumetric mass of the fuel. The flow rate is

10 determined by the measurement by a sensor (not shown) of the position of a valve whose load loss is imposed by a spring.

It will be noted that device 322 is known per se. It may refer to EP 1 344 917. The device 322 also has a construction analogous to the hydraulic dosing valves used in known systems of supplying fuel to aircraft engines, such as that of EP 1 355 054.

fifteen In the above description, the use of electric control valves 124, 134, 136 has been considered. In a variant, hydraulic control valves may be used.