Fuel circuit of a turbine engine

Abstract

A fuel circuit for a turbine engine is provided. The fuel circuit includes a fuel return valve connected to the main circuit and to a fuel tank, the valve being capable of adopting an open position in which the valve allows an excess quantity of fuel to be returned to the tank, and a closed configuration in which the return of fuel to the tank is blocked; a first hydraulic line connecting the valve to the main circuit, and including a first filter; a second hydraulic line connecting the valve to the main circuit, and including a second filter; and an intermediate hydraulic line connected to the first and second lines downstream from the filters, the first and second lines being hydraulically connected together by the intermediate line when the valve is in the closed configuration.

Claims

1. A turbine engine fuel circuit comprising: a fuel return valve configured to be connected firstly to a main fuel circuit of a turbine engine and secondly to a fuel tank, the fuel return valve being capable of adopting an open configuration in which the fuel return valve allows an excess quantity of fuel coming from the main fuel circuit to be returned to the fuel tank, and a closed configuration in which the return of fuel to the fuel tank is blocked; a first hydraulic line connecting the fuel return valve to the main fuel circuit and including a first filter; a second hydraulic line connecting the fuel return valve to the main fuel circuit and including a second filter; and an intermediate hydraulic line connected to the first hydraulic line downstream from the first filter, and connected to the second hydraulic line downstream from the second filter, the first and second hydraulic lines being hydraulically connected together by the intermediate hydraulic line when the fuel return valve is in the closed configuration; and wherein the first and second hydraulic lines are hydraulically connected together by the intermediate hydraulic line only when the fuel return valve is in the closed configuration.

2. The fuel circuit according to claim 1, wherein the intermediate hydraulic line passes through the inside of the fuel return valve, the hydraulic connection between the first and second hydraulic lines being established or interrupted by actuating the fuel return valve.

3. The fuel circuit according to claim 1, wherein the fuel return valve comprises a valve member that is movable between an open position corresponding to the open configuration of the fuel return valve, and a closed position corresponding to the closed configuration of the fuel return valve, the valve member defining a chamber via which the intermediate hydraulic line passes when the valve member is in the closed position.

4. The fuel circuit according to claim 1, including an adjustable constriction in the intermediate hydraulic line in order to modify the flow rate of fuel in said intermediate hydraulic line.

5. The fuel circuit according to claim 1, including first and second pressure regulators, the first regulator being arranged in the first hydraulic line between the point of connection, between the intermediate hydraulic line and the fuel return valve, and the second regulator being arranged in the second hydraulic line between the connection point of the intermediate hydraulic line and the fuel return valve.

6. The fuel circuit according to claim 1, wherein the main fuel circuit includes a low-pressure pump, a high-pressure pump, and a heat exchanger between the low-pressure pump and the high-pressure pump, and wherein the first hydraulic line is connected to the main fuel circuit upstream from the heat exchanger and the second hydraulic line is connected to the main fuel circuit downstream from the heat exchanger.

7. A turbine engine including a fuel circuit according to claim 1.

8. The fuel circuit according to claim 6, wherein the first hydraulic line is connected to the main fuel circuit between the low pressure pump and the heat exchanger.

9. The fuel circuit according to claim 6, wherein the second hydraulic line is connected to the main fuel circuit between the heat exchanger and the high-pressure pump.

10. The fuel circuit according to claim 6, wherein the main fuel circuit includes a hydraulic energy recovery member, situated between the low-pressure pump and the heat exchanger, and wherein the first hydraulic line is connected to the main fuel circuit between the low-pressure pump and the energy recovery member.

11. The fuel circuit according to claim 10, wherein the hydraulic energy recovery member is a jet pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings are diagrammatic and not to scale; they seek above all to show the principles of the invention.

(2) In the drawings, from one figure to another, elements (or element portions) that are identical are identified by the same reference signs.

(3) FIG. 1 shows a prior art example of a turbine engine fuel circuit.

(4) FIG. 2 shows an example of a turbine engine fuel circuit in accordance with the present description.

(5) FIG. 3 is a detail view of the figure to circuit.

DETAILED DESCRIPTION OF EMBODIMENT(S)

(6) Embodiments are described in detail below, with reference to the accompanying drawings. These examples show the characteristics and the advantages of the invention. Nevertheless, it should be recalled that the invention is not limited to these examples.

(7) FIG. 1 shows a prior art example of an airplane turbine engine fuel circuit. This prior art circuit is described above.

(8) FIG. 2 shows a fuel circuit 101 for a turbine engine, more particularly for an airplane turbojet. The circuit 101 comprises a main circuit 102 extending between the fuel tank 110 of the airplane and the combustion chamber 111 of the turbojet.

(9) Going from upstream to downstream, the main circuit 102 comprises: a low-pressure pump (or LP pump) 116 connected to the tank 110; a jet pump 119; a heat exchanger 112; a high-pressure pump (or HP pump) 118; and a metering unit 113 for feeding fuel to the combustion chamber 111. A filter (not shown) may be provided between the HP pump 118 and the metering unit 113.

(10) A recirculation loop 115 serves to return any excess fuel from the metering unit 113 to the jet pump 119. The jet pump 119 makes it possible to entrain in the flow of low-pressure fuel by using the flow of excess a high-pressure fuel as returned by the metering unit 113 via the loop 115. This increase in speed is then re-transformed into pressure by the diffuser of the jet pump 119. The jet pump 119 is activated or not activated depending on different stages of flight.

(11) The circuit 101 also includes an FRV that makes it possible to return an excess quantity of hot fuel 131 to the tank 110 after it has passed through the heat exchanger 112. The temperature of the fuel returned to the tank 110 via the FRV is lowered by mixing the hot fuel 131 taken downstream from the heat exchanger 112 with the cold fuel 121 taken upstream from the heat exchanger 112.

(12) Unlike the circuit of FIG. 1, the circuit 101 does not have a main filter associated with the heat exchanger 112, nor does it have a filter associated with the LP pump 116. In contrast, the circuit has first and second filters 125, 135 incorporated respectively in the first and second hydraulic lines 120, 130 connecting the FRV to the main circuit 102. It should also be observed that the FRV of the circuit 101 differs from that of the circuit 1 in FIG. 1, since the FRV of FIGS. 2 and 3 has an intermediate hydraulic line 150 passing therethrough, as explained below.

(13) The first hydraulic line, also referred to as the cold line 120, is used for conveying cold fuel 121 and it connects the FRV to the main circuit 102. From upstream to downstream, it comprises the filter 125 and a pressure regulator 123. This cold line 120 is connected to the main circuit 102 upstream from the heat exchanger 112, between the LP pump 116 and the jet pump 119.

(14) The second hydraulic line, also referred to as the hot line 130, serves to convey a hot fuel 131 and it connects the FRV to the main circuit 102. From upstream the downstream, it comprises the filter 135 and a pressure regulator 133. This hot line 130 is connected to the main circuit 102 between the heat exchanger 112 and the HP pump 118.

(15) An intermediate hydraulic line 150 extends between the hot and cold lines 130 and 120. This intermediate line 150 is connected to the cold line 120 at a connection point 151 situated downstream from the first filter 125, and more particularly situated between the first filter 125 and the first pressure regulator 123. Likewise, the link 150 is connected to the hot line 130 at a connection point 152 situated downstream from the second filter 135, and more particularly situated between the second filter 135 and the second pressure regulator 133.

(16) The hot and cold lines 120 and 130 are hydraulically connected together by the intermediate line 150 when the FRV is in the closed configuration. In contrast, when the FRV is in the open configuration, the connection between the hot and cold lines 120 and 130 is interrupted.

(17) The FRV, the intermediate line 150, the first pressure regulator 123, the second pressure regulator 133, the first filter 125, and the second filter 135 may constitute a non-separable assembly, referred to below as the fuel return system 155. The fuel return system 155 may be in the form of a unitary component having two fuel inlets (one inlet for hot fuel and one inlet for cold fuel) and one fuel outlet leading to the tank 110. The elements of the fuel return system 155 may be protected by a common housing. The fuel return system 155 may be mounted on the turbine engine.

(18) In this example, the intermediate line 150 passes via the inside of the FRV, the hydraulic connection between the lines 120 and 130 being established or interrupted by actuating the FRV. To do this, as shown in FIG. 3, the FRV has a valve member 160, also referred to as a slide, mounted to slide along an axis A. The valve member 160 is mounted to slide in a sheath 164 surrounding the outside of the valve member 160 and extending along the axis A.

(19) The valve member 160 is mounted facing an access opening 165 to the hydraulic line 109 leading to the tank 110. The valve member 160 is movable between an open position (to the right in FIG. 3) in which it does not close the opening 165, and a closed position (to the left in FIG. 3) in which it closes the opening 165, thus preventing fuel from returning to the tank 110. In FIG. 3, the valve member 160 is shown in the closed position. The valve member 160 thus performs an on/off function, being in a position that is either open or closed in the circuit for returning fuel to the airplane tank 110. The valve member 160 is electrically or hydraulically controlled by a control device 172. The valve member 160 is also mounted on a spring 163 urging the valve member 160 towards its closed position. The control device 172 therefore needs to generate a force that is greater than the return force of the spring in order to open the FRV.

(20) The intermediate line 150 passes inside the valve member 160. In this example, a chamber 161 is defined between the valve member 160 and the sheath 164. The chamber 161 may be generally cylindrical in shape, as shown in FIG. 3. In the vicinity of the chamber 161, two dynamic seals 166 are incorporated that are capable of withstanding the back and forth movements of the slide so as to isolate the chamber 161 when the FRV is open, and thus force the fuel towards the tank 110 by making it pass through the regulators 123, 133, and then through a space (not shown in FIG. 3) that lies between the front end of the valve member 160 and the opening 165, and then via the opening 165.

(21) Thus, during operating stages of the turbine engine in which the FRV is open, the hydraulic connection between the hot and cold lines 130, 120 is interrupted and the fuel passes through each of the filters 125, 135 in its normal flow direction, such that the fuel is cleared or cleaned of its impurities (i.e. impurities of sizes deemed to be too great are captured by said filters) prior to reaching the FRV. In this way, the FRV is protected against pollution and the proper operation of the FRV is preserved throughout its entire lifetime.

(22) Conversely, during operating stages of the turbine engine in which the FRV is closed, the hydraulic connection between the hot and cold lines 130, 120 is established, and the fuel passes through one or the other of the filters 125, 135 in a direction opposite to the normal flow direction, such that the impurities that have been captured by the filter 125 or 135 become detached therefrom under the effect of the reverse flow of the fuel. These impurities are returned to the main circuit 102, which circuit is designed to be capable of accepting particles of this size. The filter 125 or 135 is thus cleaned.

(23) A pressure difference naturally exists between the cold and hot lines 120, 130. This difference is due to the head loss between the two tapping points where fuel is taken from the main circuit 102. The greater the head loss, the greater the flow rate of the generated backwashing. The head loss between the two tapping points is conventionally at least a few bars, depending on the circuit under consideration, and it may reach 5 bars, for example. In the example shown, it should be observed that the head loss is generally associated with a high flow rate of injected fuel and with a fuel temperature that is relatively cold, since otherwise the valve FRV would be open.

(24) This pressure difference between the hot and cold lines 120, 130 creates a flow of fuel from the cold line 120 towards the hot line 130 that enables the filter 135 to be backwashed. This flow also depends on the constriction created by the clogged filter 135, which depends on the extent to which it is clogged. Generally, the clogging level of the filter 135 is not too great, since it is backwashed on each flight of the airplane. The flow rate generated is therefore not excessively diminished by the clogging level of the filter 135.

(25) Furthermore, when the jet pump 119 is activated, it causes the pressure in the hot line 130 to be greater than that in the cold line 120, thereby creating a flow of fuel from the hot line 130 towards the cold line 120, thus enabling the filter 125 to be backwashed. Thus, the filter 125 is backwashed at certain stages of flight in which the FRV is closed and the jet pump 119 is activated. It should be observed that the pressure difference generated by the jet pump 119 may be very large, for example it may be as much as 35 bars. As a result, the backwashing flow rate of the filter 125 may also be very large. However, the greater the backwashing flow rate of the filter 125, the shorter the time required to perform backwashing. Also, the fact that the above-mentioned conditions are satisfied on a few occasions and/or for little time during a flight cycle, does not raise any difficulty. In any event, these conditions are satisfied at least once per flight.

(26) It should be observed that the first filter 125 is subjected to more clogging than the filter 135, since the filter 125 generally passes fuel that has not yet been filtered. The filter 135 also generally passes fuel that has not been filtered, but this fuel is diluted in a larger volume corresponding to the volume of fuel in the recirculation loop 115. Conventionally, the flow rate in the recirculation loop 115 is at least five times greater than the flow rate in the injection line. The concentration of impurities in the fuel reaching the filter 135 is therefore often at least five times smaller than that of the fuel reaching the filter 125.

(27) Downstream from the connection points 151, 152 of the intermediate line 150, the hot and cold lines 120, 130 also include respectively the first and second pressure regulators 123, 133, and first and second constrictions 124, 134 (see FIG. 3). The two regulators 123, 133 shown in detail in FIG. 3 operate only when the FRV is in the open position, and they send fuel to the tank 110 via the return line 109.

(28) Finally, in order to control the flow rate of fuel in the intermediate line 150, an adjustable constriction 140 is provided in this intermediate line, as shown in FIG. 3. In this example, the constriction 140 is situated between the connection point 151 and the FRV. Thus, depending on the systems and on the backwashing requirements of the filters 125 and 135, the constriction 140 is adjusted to modify the flow rate of fuel between the cold and hot lines 120, 130 when the FRV is closed.

(29) The embodiments or examples described in the present description are given by way of non-limiting illustration, and in the light of this description, a person skilled in the art can easily modify these embodiments or examples, or can envisage others, while remaining within the scope of the invention.

(30) Furthermore, the various characteristics of these embodiments or examples may be used on their own or they may be used in combination. When they are used in combination, the characteristics may be as described above or they may be different, the invention not being limited to the specific combinations described in the present description. In particular, unless specified to the contrary, a characteristic described by way of example with reference to one particular embodiment, may be applied in analogous manner to any other embodiment or example.