GB1205553A - Fuel systems for gas turbine engines - Google Patents

Abstract

1,205,553. Gas turbine engine fuel systems; elastic fluid turbines. JOSEPH LUCAS (INDUSTRIES) Ltd. Sept.21, 1967 [June 23, 1966], No.28145/66. Headings F1G and F1T. A fuel system for a gas turbine engine comprises pumping apparatus for delivering fuel to the engine and including a pump driven by an air turbine, a manually operable throttle disposed between the pumping apparatus and the engine, and a further servo-operated throttle between the manually operable throttle and the engine, the further throttle being responsive to changes in a number of variables and also serving as a shut-off cock for the system, and means responsive to a function of the pressure drop created by the flow through the throttles to control the volume of air reaching the air turbine. As shown, fuel is delivered to a burner manifold 11 by way of an engine-driven pump 12, a pump 13 driven by an air turbine 17, a manually operable throttle 27, a servo-operated throttle 28, a shut-down valve 29 and pressurizing valves 61, 62. The throttle 27 comprises a fixed sleeve containing holes 38 which are variably obturated by a movable sleeve 34 under the control of a manual lever 35 to throttle the flow from passage 26 to passage 32. Additional holes 39, also variably obturated by the sleeve 34, form a variable restrictor which in conjunction with a fixed restrictor 70 forms a variable potentiometer connected, via a non-return valve 43 and a passage 71, between the inlet passage 26 and outlet passage 32 of the throttle 27. The variable function of the total pressure drop across the throttle 27 appearing across the lower link of the potentiometer is applied to a valve spool 66 to control the position of the valve spool. The valve spool 66 forms, in conjunction with a fixed restrictor 74, a variable potentiometer connected between the passage 71 and a drain passage 78, the pressure at the tapping of the potentiometer being applied via a passage 75, a valve 76 and a fixed restrictor 77 to the piston 46 of throttle 28 in opposition to a spring 47. The throttle 28 is thereby controlled so as to maintain a constant pressure drop across the subsidiary holes 39 of the throttle 27. The throttle 28 is also controlled in accordance with engine speed by governors 64, 65 respectively driven by the two shafts of the engine (or a single governor in the case of a single-shaft engine), each governor controlling a valve 79 or 80 connected in series with a restrictor 89 or 90 between the passage 26 and the drain passage 78, the junction between the valve and the restrictor being connected via a non-return valve 93 or 94 and a passage 95 to the junction between the restrictor 77 and the throttle 28. The air supply to the turbine 17 is . controlled by a throttle 24 operated by a servo device 25 subjected, on its opposite sides via respective passages 96, 98 to the pressure at the tapping of the potentiometer 70, 39 and the pressure down-stream of the throttle 28. The fuel supply can be shut down by closing the valve 76 to cut off the supply of fuel under pressure to the piston 46 of throttle 28, which consequently closes. Additionally , a valve 55 is also closed to cut off the supply of fuel under pressure to the piston of a dump valve 59, which consequently opens to allow fuel to escape via a passage 60. Valve 76 is actuated by a piston 105 which is actuated by fuel under pressure under the control of solenoid valves 103, 104. During starting, igniter burners 112 are supplied by an electrically driven fuel pump 111. Since the centrifugal pumps 12, 13 do not develop sufficient pressure during starting to open the throttle 28, the pump 111 is connected for this purpose to the passage 71 via a passage 115.