GB888328A - Improvements in fuel systems for aircraft gas turbine engines - Google Patents

Abstract

888,328. Gas-turbine plant. DOWTY FUEL SYSTEMS Ltd. Oct. 1, 1958 [July 3, 1957], No. 21070/57. Class 110 (3). [Also in Group XXIX] A fuel supply system for a gas-turbine engine comprises an adjustable aperture through which fuel flow to the engine passes, means to control this aperture either partly or entirely in accordance with compressor outlet pressure or a function thereof and means to adjust fuel flow passing through the aperture to the engine to maintain a predetermined ratio between an engine speed signal and a signal proportional to pressure drop across the adjustable aperture. As shown, a variable displacement pump 1 delivers fuel to a line 13 connected to a casing 16 housing an adjustable throttle valve 19 controlling ports 17 leading to a line 21 supplying fuel to the burners. The valve 19 is adjustably positioned by a servo piston 22 slidable in a cylinder 23 to which pressure fuel is fed from the line 13 through a restriction 24 and allowed to escape through a vent valve 25 under the control of concentric bellows 27, 28 fed respectively with compressor inlet pressure and compressor outlet pressure, an evacuated bellows 29 of the same diameter as the bellows 27 and a spring 31. On, e.g. a reduction in compressor inlet and/or outlet pressure the vent valve 25 will open to reduce the pressure below the piston 22 so that the valve 19 moves towards closure to reduce the loading on the spring 31 and allow the vent valve 25 to reach a predetermined equilibrium position in which a lower pressure is established on the lower surface of the piston 22 as compared with that on its smaller upper surface effectively reduced by the valve 19. The position of the valve 19 and hence fuel flow is thus determined by compressor inlet and/or outlet pressure. The casing 16 also houses a centrifugal governor 32 rotatably driven by the engine and cooperable with a lever 38 mounting a vent valve 15 controlling leakage from a cylinder 8 fed with fuel from the line 13 through a restriction 14 and slidably mounting a piston 7 connected by a rod 9 and spigot 11 to regulate the eccentricity of a track ring 4 to regulate the output of the pump 1. The lever 38 is also loaded by an adjustable spring 44 and a piston 39, 41 subjected on opposite faces to the pressure upstream and downstream of the throttle valve 19 so that pump output is dependent both on engine speed and the pressure differential across the throttle valve which is in turn dependent upon compressor inlet and/or outlet pressure. An increase in speed tends to open the vent valve 15 and whilst an increase in pressure differential tends to close it. The force exerted by the governor 32 on the lever 38 is prevented from falling below a predetermined minimum value by a stop 42. To control engine speed at a desired constant value a by-pass valve 49 is fitted. This valve is under the control of a servo piston 51 slidable in a cylinder 52 to which pressure fuel is fed from the line 13 through a restriction 53 and exhausted therefrom by means of a vent valve (not shown) under the control of an all-speed governor. Specification 879,982 is referred to.