GB2041085A

GB2041085A - Fuel supply apparatus for gas turbine engine

Info

Publication number: GB2041085A
Application number: GB7937249A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1978-12-20
Filing date: 1979-10-26
Publication date: 1980-09-03
Also published as: GB2041085B

Abstract

An apparatus for controlling fuel supply to one group of burners in a gas turbine engine which includes a plurality of such groups, comprises a control valve 18 having an inlet 19 communicating with a metered fuel supply, a first, restricted outlet 20 and a second outlet 21, the outlets 20, 21 communicating with said one burner group. A control element 22 is movable in response to reduction in a servo pressure in a line 29, first to permit fuel flow to the outlet 20 and subsequently to the outlet 21. The rate of movement of the element 22 is limited by a flow restriction in the line 29. <IMAGE>

Description

SPECIFICATION Fuel supply apparatus for gas turbine engines This invention relates to apparatus for controlling the supply of fuel to the burner arrangement of gas turbine engines.

In gas turbine engines, and in particular aircraft gas turbine engines, it is knwn to provide that the fuel burners are arranged in two groups which are connected to respective manifolds, and to shut off fuel supply to one group of burners during idling of the engine, whereby the fuel/air ratio for the operative burners is increased, resulting in more efficient combustion. When such an arrangement is changed from its idling condition to a condition in which fuel is supplied to all of the burners, the manifolds of the inoperative burners are required to be primed with fuel.

The priming operation may cause the operative burners to be starved of fuel, and combustion to cease.

It is an object of the present invention to provide a fuel supply apparatus in which the aforesaid priming is controlled so as not to affect adversely the combustion at those burners which are operative during idling.

According to the invention an apparatus for controlling a supply of fuel to a gas turbine engine burner arrangement having two groups of burners comprises a delivery passage for a metered fuel supply and a valve for controlling flow from said delivery passage to one of said burner groups, said valve having an inlet communicating with said delivery passage and first and second outlets communicating with said one burner group, said first outlet providing a restricted flow path between said inlet and said one burner group, and a control element movable from a shut position of said valve first to permit fuel flow to said first outlet and subsequently to permit fuel flow to said second outlet, and means for limiting the rate of said movement of the control element.

A preferred embodiment includes a fluid pressure actuator for said control element, said limiting means comprising a flow restrictor in series with said actuator.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawing in which: Figure 1 shows diagrammatically, a gas turbine engine burner arrangement and a fuel control apparatus according to the present invention, and, Figure 2 shows details of a valve forming part of the control apparatus.

In Fig. 1 a combustion chamber of a gas turbine engine is indicated generally at 10 and includes 1 8 circumferentially arranged fuel burners 11. A metered fuel supply is delivered by way of a filter 1 2 to a circumferential delivery passage 1 3. The burners 11 are arranged in a first group 14 of nine circumferentially adjacent burners and a second group 1 5 of nine circumferentially adjacent burners. The burners 11 are arranged in sub-groups of three interconnected by respective fuel manifolds.The delivery passage 1 3 communicates with the three manifolds of the group 14 by way of respective weight-type distributors 16, the distributors 1 6 ensuring that fuel flows to the three manifolds are substantially equal.

The fuel delivery passage 1 3 communicates with the three manifolds of the groups 1 5 via respective distributors 17, identical with the distributors 16, and control valves 1 8 in series with the distributors 1 7.

One of the control valves 1 8 is shown in detail in Fig. 2 and has an inlet 1 9 for receiving fuel from the passage 13, a first, restricted outlet 20 and a second, annular outlet 21. The downstream sides of the outlets 20, 21 are commonly connected to a manifold for three of the burners 11 in the group 1 5. A valve control element 22 includes a spring-loaded self-aligning disc 23 which can engage a valve seat 24 adjacent the inlet 29. The control element 22 is movable rightwardly from the open position shown in the drawing to a position in which the annular outlet 21 is shut off from direct communication with the inlet 1 9 and in which the disc 23 engages the seat 24 to prevent flow through the outlet 20.In this rightward position of the element 22 an annular groove 25 therein allows the annular outlet 21 to communicate with a drain connection 26 the dimensions of the valve 1 8 are such that communication between the outlet 21 and the drain connection 26 does not occur until immediately before engagement of the disc 23 with the seat 24, whereby escape of fuel to drain from the supply passage 1 3 is held to a minimum.

The control element 22 includes an actuator piston 27 which is biased leftwards by a high pressure signal in a line 28. The piston 27 can be urged against this biasing pressure by a servo pressure signal in a line 29. As seen in Fig. 1 the line 29 includes a flow restrictor 29a by means of which the rate of movement of the control element 22 may be limited. The lines 26, 28, 29 from the valves 18 communicate, as shown in Fig. 1, with respective common connections 30, 31, 32. The o.- nection 32 communicates by way of a flow restrictor 33 with a low pressure return line 34. A high pressure supply line 35 communicates with the connection 31 and also, by way of a solenoid valve 36 with the connection 32 between the restrictor 33 and the valve 1 8. The connection 30 communicates with a drain line 37 by way of a further solenoid valve 38.

The line 28 is maintained at the high pres sure in line 35. When neither of the solenoid valves 36, 38 is energised the pressure in line 29 is the low return pressure in line 34. The control element 22 is thus moved lettward to open the valve 1 8 and to admit fuel to the burners of the group 1 5. All the burners will thereby be in operation. The solenoid valves 36, 38 are operated in unison and when this occurs the pressure in the connection 32 is at a value intermediate that in the lines 35, 34.

This intermediate servo pressure is applied via the line 29 to the piston 27. The differential area of the piston 27 causes the latter to be moved rightwardly, urging the control element 22 to shut the valve. As previously described at its rightward extremity of movement the outlet 20, 21, are shut off from direct communication with the inlet 19, and fuel within the associated manifold escapes to drain via the connections 26, 30, valve 38 and line 37. In this condition only the burners of the group 14 are supplied with fuel and the engine is in its idling state.

When the engine is accelerated from its idling state both solenoid valves 36, 38 are simultaneously shut, causing the control element 22 to move leftward. This leftward movement first causes the disc 23 to move away from the seat 24, and the end of the element 22 to move away from the vicinity of the outlet 20. Fuel thus flows from the inlet 1 9 through the restricted outlet 20 to the associated manifold of the group 1 5. Leftward movement of the control element 22 is controlled by the restrictor 29a, and this leftward movement is sufficiently slow as to ensure that all the manifolds of the group 1 5 are primed through their respective valves 1 8 before the outlets 21 open.The flow restrictions of the outlet 20 prevent fuel being drawn from the passage 1 3 at a rate sufficient to adversely affect combustion at the burners of the group 14. When the manifolds of the group 1 5 are fully prime flow to both groups of burners is equal. The delivery passage 1 3 may include a balancing restrictor 30 to compensate for the restriction provided by the valves 18.

As shown in Fig. 2 each valve 1 8 includes a tension spring 40 to maintain the valve open in the absence of a high pressure signal on line 35. Additionally, each valve 18 includes an electrical switch 41 which closes when the control element is other than in its fully open position, the switches 41 being connected in parallel to an indicating device 42.

Each valve 18 also includes a by-pass 43 between the inlet 1 9 and annular outlet 21.

The by-pass 43 being closed by a spring loaded plate 44. Should a valve 1 8 fail with its control element 22 in the shut (idling) position, an increased fuel pressure in the supply passage 1 3 when the engine is accelerated from its idling position, will be sufficient to lift the plate 44 and provide a fuel supply to the associated burner manifold.

Claims

1. An apparatus for controlling a supply of fuel to a gas turbine engine burner arrangement having two groups of burners comprises a delivery passage for a metered fuel supply and a valve for controlling flow from said delivery pasage to one of said burner groups, said valve having an inlet communicating with said delivery passage and first and second outlets communicating with said one burner group, said first outlet providing a restricted flow path between said inlet and said one burner group, and a control element movable from a shut position of said valve first to permit fuel flow to said first outlet and subsequently to permit fuel flow to said second outlet, and means for limiting the rate of said movement of the control element.

2. An apparatus as claimed in claim 1 which includes means for biasing said control element towards an open position of said valve, and means for applying a servo pressure to said control element, to urge the latter against said biasing means.

3. An apparatus as claimed in claim 2 in which said biasing means includes means for applying a fluid pressure to a face of said control element.

4. An apparatus as claimed in claim 2 or claim 3 in which said biasing means includes a spring.

5. An apparatus as claimed in any preceding claim in which said means for limiting the rate of movement of said control element comprises a flow restriction in a passage through which fluid is displaced as a result of said movement.

6. An apparatus as claimed in any preceding claim in which said valve includes a drain outlet, said control element being operable to interconnect said drain outlet and said second outlet when communication between said inlet and said second outlet is shut off.

7. An apparatus as claimed in any preceding claim in which said apparatus comprises a plurality of said valves for controlling fuel supply to respective ones of a plurality of subgroups of burners, said sub-groups providing said burner group.

8. An apparatus for controlling a supply of fuel to a gas turbine engine, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.