US3444688A - Fuel flow control apparatus for gas turbine engines - Google Patents

Description

May 20, 1969 E. H. WARNEJ ETAL 3,444,633

. FUEL FLOW CONTROL APPARATUS FOR GAS TURBINE ENGINES Filed Nov. 14, 1966 United States Patent 3,444,688 FUEL FLOW CONTROL APPARATUS FOR GAS TURBINE ENGINES Eugene Harold Warne, Shirley, Solihull, and Geoffrey Albert Long, Sutton Coldfield, England, assignors to Joseph Lucas (Industries) Limited, Birmingham, England Filed Nov. 14, 1966, Ser. No. 594,210 Int. Cl. F01c 9/02; F02d 9/08; F01d 17/00 U.S. Cl. 6039.28 3 Claims ABSTRACT OF THE DISCLOSURE Apparatus for controlling the supply of fuel to a gas turbine engine comprises a throttle slidably mounted in a body to control flow of fuel through a passage in the body, a piston connected to the throttle and disposed in a cylinder in the body, a restricted passage between the upstream side of the throttle and one end of the cylinder, a plunger coaxially and slidably mounted within the piston, a manually operable control for the plunger, passage means in the plunger through which fuel can flow to drain, at a rate which is dependent upon the relative positions of the plunger and piston, and means providing a force on the piston to oppose the fuel pressure at said one end of the cylinder to enable equilibrium conditions to be obtained.

This invention relates to fuel flow control apparatus for gas trubine engines and is primarily applicable to engines in which the quantity of fuel required for acceleration in addition to that required for normal steady running of the engine at any speed is not highly critical.

The object of the invention is to provide apparatus for controlling the supply of fuel to a gas turbine engine, in a simple and convenient form.

In accordance with the present invention, apparatus for controlling the supply of fued to a gas turbine engine comprises a body, a throttle slidably mounted in the body and arranged to control the supply of fuel along a passage in the body, the body defining a cylinder containing a piston connected to the throttle for coaxial movement therewith, passage means in the body arranged to supply fuel at the pressure obtaining at the upstream side of the throttle to the cylinder at one end of the piston, a plunger which is coaxial with the piston and relatively slidable therein, a manually operable control for the plunger, further passage means in the plunger, in accordance with the relative position of the plunger and the piston to control the drain of fuel from said one end of the cylinder, and means providing a force on the piston tending to oppose that provided by pressure of the fuel in said one end of the cylinder, thus enabling equilibrium conditions of the piston to be obtained.

The invention will now be described by way of example with reference to the accompanying drawing which illustrates diagrammatically a fuel supply system for a gas turbine engine.

The system comprises a main pump 10 of the swashplate type and arranged to be driven through a shaft 11 from the engine with which the system is associated. Associated with the main pump 10 and enclosed within the same housing is a piston and cylinder type servo mechanism 12, and a governor device 13 arranged to modify the servo mechanism 12. To the pump 10 is an inlet passage 14 from a reservoir (not shown) there being, between the reservoir and the pump 10, a centrifugal boost pump 15 and a filter 16. The main pump 10 delivers fuel into a passage 17 leading to burners in an engine indicated diagrammatically at 18. The servo mechaice nism 12 is controlled primarily by the pressure difference between the inlet and the outlet of the pump 10 in known manner.

Also controlling the servo mechanism 12 is the governor 13 and a device 19 which is responsive, through passages 20, 21, to the pressures obtaining at the upstream and downstream sides of the engine compressor. This device contains a valve 22 which is arranged to control the pressure in a passage 23 leading to the servo mechanism 12. There is also a device 24 sensitive to temperature conditions in the engine and arranged also to modify the position of the valve 22 in the device 19.

Between the pump 10 and the burners in the engine 18, in the passage 17, there is provided apparatus, which forms the subject of this invention, for controlling the flow of fuel to the engine and there is also a shut off cock 25 for cutting off the supply altogether to stop the engine, with the cock 25 being manually operable by a lever 26.

This apparatus is enclosed within a body indicated by numeral 27 through which is formed a bore containing a slidable throttle rod 28 one end of which has tapering grooves 29 to enable fuel to How through an enlargement of the bore in the body 27, past an annular metering edge 30 disposed between inlet and outlet portions of the passage 17 indicated by 17a and 17b respectively. The outlet 17b communicates with the burners 18 in the englue.

The opposite end of the throttle rod 28 is formed integrally with a piston 31 slidable in a cylinder 32 formed as an enlarged extension of the bore in the body 27. Communicating with the end of the cylinder 32 nearer to the throttle rod 28 is a passage 33 containing a restrictor in the form of a pair of orifices 34, 35 in series, with this passage being subjected to the pressure of fuel at the upstream side of the metering edge 30, through a passage 36 affording a flow path from the upstream to the downstream sides of the metering edge 30. The passage 36 has two restrictors 37, 38 in series so that the main flow to the burners takes place through the portion of the passage 17 designated 17b.

This arrangement in the passage affords a liquid potentiometer, and an intermediate pressure from which is applied through a further passage 39 to the opposite end of the piston 31 in the cylinder 32. The portion 17b of the passage 17 also contains a valve 40 which is provided to ensure that flow only takes place to the burners in the engine 18 under pressure.

Slidably mounted within the piston 31 and throttle rod 28 is a coaxial plunger 41 in a closed ended bore 42 extending from the end at which the piston 31 is disposed, with the wall of the throttle rod 28 being pierced by a hole 43 normally opening into the end of the cylinder 32 at the side of the piston 31 at which the throttle rod 28 is provided. The plunger 41 has an annular groove 44 and a central passage 45, with the latter communicating with the closed end of the bore 42 which, in turn, has a radial passage 46 leading, through a passage 47, to the inlet passage 14 of the pump 10 or other low pressure part of the system.

Connected to the plunger 41 to enable its position to be controlled by an operator, is a rod 48. Between the plunger 41 and the piston 31 is a compression string 49 which, in the event of a failure in the normal control apparatus in the fuel system, causes movement of the plunger 41 to move the throttle to its fully open position.

In this event, emergency fuel supply to the engine would be controlled by the shut off cock 26 in the system.

In use, steady running conditions are maintained by positioning the piston 31 by a balance of the pressures 3 at its opposite sides. This is achieved by allowing a drain through the orifice 43, the annular groove 44, the passage 45 to the bore 42 and thence out through the passage 46 to the passage 47.

If it is desired to accelerate the engine to a new steady running speed it is not only necessary to open the throttle but it is also necessary to provide additional fuel for acceleration purposes. To achieve this, the rod 48 is first moved manually to a position which, when equilibrium conditions are again established, will correspond to the required throttle opening for the new steady running conditions. Movement of the rod 48 causes the plunger 41 to move (to the right in the drawing) to cut off communication between the orifice 43 and the annular groove 44. Pressure therefore builds up in this end of the cylinder 32 to move the piston 31 until such communication is again possible whereupon equilibrium will become reestablished. The rate of movement of the piston 31 will be dependent upon the size of the orifices 34, 35 in the passage 33. Such movement of the piston 31 will result in an additional quantity of fuel, which would normally be drained through the orifice 43, being delivered to the engine through the throttle. In the opposite end of the cylinder 32 there is also a less significant displacement of fuel through the passage 39 and into the passage to the burners 18 through the orifice 38, which is larger than the orifice 37, with the additional quantity supplied by these means being the required amount for acceleration, and this additional fuel supply ceases when the piston 31 stops upon commencement of the drain through the orifice 43 to reestablish equilibrium conditions.

If it is desired to decelerate the engine, the rod 48 is moved in the opposite direction by the desired amount. This results in movement of the plunger 41 in the same direction, (to the left in the drawing). The orifice 43 now communicates fully with the annular groove 44 thus substantially increasing the drain from the cylinder 32 and reducing the fuel quantity delivered to the engine by creating a greater demand at the cylinder 32, to be drained through the orifice 43. The pressure at this end of the cylinder 32 will fall to permit the piston to move under the influence of pressure acting from the passage 39. This will thus reduce the throttle opening until equilibrium conditions are again established.

The characteristics of the acceleration and deceleration is governed by the additional flow in the case of acceleration and the reverse in the case of deceleration. These flows are, in turn governed by the size of the orifices 34, 35 in acceleration conditions, and by the sizes of the orifices 37, 38 in the deceleration conditions.

Having thus described our invention what we claim as new and desire to secure by Letters Patent is:

1. Apparatus for controlling the supply of fuel to a gas turbine engine, comprising a body, a throttle slidably mounted in the body for controlling the supply of fuel along a passage in the body, the body defining a cylinder, a piston in the cylinder connected to the throttle for coaxial movement therewith, passage means in the body arranged to supply fuel from the upstream side of the throttle to the cylinder at one end of the piston, said passage means having restrictors therein, a plunger coaxial with the piston and relatively slidable therein, a manually operable control for the plunger, further passage means in the plunger arranged, in accordance with the relative postions of the plunger and the piston, to control the drain of fuel from said one end of the cylinder, and means providing a force on the piston tending to oppose that provided by the pressure of the fuel in said one end of the cylinder, thus enabling equilibrium conditions of the piston to be obtained.

2. The apparatus as claimed in claim 1 including spring means located between the plunger and piston to cause movement of the plunger to move the throttle to its fully open position in the event of a failure in the normal control apparatus by the establishment of equilibrium conditions therein.

3. A fuel supply system for a gas turbine engine having burners comprising a pump arranged to obtain a supply of fuel from a reservoir, means defining a fuel passage between the pump and the burners in the engine, and apparatus for controlling the supply of fuel along said passage, said apparatus comprising a body, a throttle slidable mounted in the body for controlling the supply of fuel along a passage in the body, the body defining a cylinder, a piston in the cylinder connected to the throttle for coaxial movement therewith, passage means in the body arranged to supply fuel from the upstream side of the throttle to the cylinder at one end of the piston, said passage means having restrictors therein, a plunger coaxial with the piston and relatively slidable therein, a manually operable control for the plunger, further passage means in the plunger arranged, in accordance with the relative positions of the plunger and the piston, to control the drain of fuel from said one end of the cylinder and means providing a force on the piston tending to oppose that provided by the pressure of the fuel in said one end of the cylinder, thus enabling equilibrium conditions of the piston to be obtained.

References Cited UNITED STATES PATENTS 908,224- 12/1908 Eckland 251-38 XR 3,139,892 7/1964 McRoberts 39.28 XR JULIUS E. WEST, Primary Examiner.

US. Cl. X.R. 13718;25l---38

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