Patent GB-703700-A (GB)
Title: Fuel supply means for a gas turbine engine
Inventor: JAGGER JAMES HARTLE
IPC: F02C9/16
Filed: 1951-01-26
Abstract: 703,700. Gas turbine plant. ARMSTRONG SIDDELEY MOTORS, Ltd. Jan. 10, 1952 [Jan. 26, 1951], No. 2014/51. Class 110 (3). [Also in Group XXIX] In a liquid fuel supply system for a gas-turbine engine and of the kind in which the effective delivery of an engine-driven fuel pump is controlled by a pressure-responsive plunger actuating a spill valve of a fixed-displacement pump or an adjustable swashplate of a variable displacement pump and subject on one face to the pump delivery pressure and on the opposite face to pressure in a chamber having communication through a restriction with the pump delivery and a connection to a control passage in which the pressure may be regulated in dependence upon operating conditions, the effective delivery of the pump is passed through an air-fuel ratio device which prevents over-fuelling during acceleration of the engine and comprises a variable choke actuated in response to a function of the output pressure of the compressor of the engine, and in series through a flow control device also having a variable choke which is actuated by barometric control means. The pressure difference across each choke controls an associated valve for the control passage of the pump, that valve controlled by the choke of the flow control device also being subject to a throttle control. As shown, the pump is of constant displacement type and consists of a rotor 11, Fig. 2, rotatable on a fixed boss 14 by a shaft 12 and having radial cylinders 16 with pistons 17 carrying slippers 18 which coact with an eccentric bore 20 of the pump body. The boss has inlet and outlet passages 23, 24 and the effective delivery is determined by a plunger 30 constituting a spill valve for interconnecting the inlet and outlet passages and subject, on an upper annulus 29, to pump delivery pressure communicated through a spring- loaded valve 27 and on its lower surface to a control pressure in a passage 100. This passage has connection through a restriction 32 with the pump outlet passage 24. An overspeed governor is provided by an impeller 72 connected across a diaphragm 83 associated with a spring-closed leak-off valve 89 which, when opened, vents the passage 100 to increase the opening of the spill valve. The output from the pump passes to a chamber 36 in the air-fuel ratio device, through a choke constituted by an orifice 38 and a plunger 39 and thence to an outlet passage 37. The plunger 39 is fast with a piston 43 whose upper face is exposed to the pressure in the chamber 36 and which has a restricted connection 46 with a chamber 44 the pressure in which is controlled by a valve 61 actuated, through a lever 42, by a capsule 59 subject externally to compressor output pressure. The pressures before and after the choke are applied to a piston 51 which actuates a leak-off valve 65 connected to the passage 100. When the engine throttle control, situated in the passage 37, is opened the consequent increase in compressor output causes an opening movement of the valve 61 resulting in an opening movement of the plunger 39 which increases the tension of a spring 41 loading the valve 61 in the closing direction. The reduction in pressure drop across the choke due to the opening movement of the plunger 39 results in a closing movement of the valve 65 to reduce the opening of the spill valve 30. Thus the fuel flow increases in dependence upon the compressor pressure until the original pressure drop across the choke is restored. Owing to the fact that the above arrangement limits engine speed at high altitudes a modification is described. which takes account of the compression ratio of the compressor. In this modification, the intake and delivery pressures of the compressor are applied to a differential bellows assembly which actuates a valve controlling the passage of air from the compressor through a Venturi the pressure at the throat of which is applied to the capsule 59. At low compression ratios the valve is open and the capsule 59 is subject to the static pressure at the throat of the Venturi, whereas at higher compression ratios the valve is closed and the pressure at the throat of the Venturi rises to the full compressor pressure. The flow control device is connected to the passage 37 and includes a choke 201, Fig. 6, through which fuel flows to an outlet 200 of the burners. The pressures before and after the choke are conveyed by ducts 204, 205 to either side of a diaphragm 206 by which is operated a leak-off valve 224 for the spill valve 30. The effective size of the choke is adjusted by an extension 231 of a piston 230 which is positioned according to the adjustment given to a needle valve 233 by a capsule containing air at a predetermined pressure and subject externally to barometric or compressor intake pressure. The change in pressure drop across the choke consequent upon movement of the piston 230 causes the valve 224 to be operated to adjust the spill valve 30 to restore the pressure drop to its original value. To ensure efficient operation of the valve 224 at low values of pressure difference across the choke a spring-loaded valve 203 is employed to exaggerate the pressure difference. The throttle control of the engine is effected by a lever 210 which, through a servo device, varies the compression of a spring 218 loading the diaphragm 206, and thereby causes adjustment of the spill 'valve 30 to alter the pressure drop across the'choke 201 to balance the spring force. A rack-operated shut-off valve 238, when in a po'sition closing the outlet 200, connects the down stream side of the choke 201 with the pump intake line 21. Specification 703,701 is referred to.