Patent GB-1173841-A (GB)
Title: Aircraft Gas Turbine Engine Fuel System
Inventor: CROSS WALTER GEORGE
IPC: F02C9/26
Filed: 1967-01-13
Abstract: 1,173,841. Gas turbine engine fuel systems. ROLLS-ROYCE Ltd. March 21, 1967 [Jan.13, 1967], No.2075/67. Heading F1G. [Also in Division G3 ] An aircraft gas turbine engine fuel system comprises a metering device which controls the supply of fuel to engine burners, means for adjusting the metering device in dependence upon a function of the ratio of two pressures prevailing in compressor means of the engine downstream of the inlet thereof, and function adjustment means, responsive both to the setting of a pilot's throttle control and to the engine intake pressure or to a pressure functionally related thereto, for adjusting the valve of the function so that, for any given setting of the throttle control the overall pressure ratio of the compressor means is maintained substantially constant for all ambient ground temperatures below a predetermined value. A drum 80 carrying centrifugal governor fly-weights 79, 102 is rotated by an engine-driven shaft 12 through gearing 11, 10 and axially movable sleeves 6, 83. Fuel entering at 5 from a variable-delivery swashplate pump or a gear pump provided with a variable spill valve passes through an annular metering orifice formed by a fixed edge 20 and the edge 21 of an axially movable sleeve 22, and thence through triangular metering orifices 16 provided in the axially movable sleeve 6. From the interior of the sleeve 6, the fuel then passes via a passage 91 to an outlet chamber 92, from which it passes to a passage 96 leading to pilot burners and can also pass, via triangular orifices 100, to a passage 95 leading to the main burners. Flow through the orifices 100 is controlled by the axially movable sleeve 83, acted on in the opening direction by the fly-weights 102 and acted on in the closing direction by the pressure drop across the metering orifices 20, 21, 16 acting on the end wall 103 of the sleeve. An idling supply of fuel which by-passes the metering orifices 20, 21, 16 is controlled by an adjustable restrictor 94. The pressure in the passage 95 is applied through a pipe 104 to a servodevice which adjusts the delivery of the fuel pump in dependence on the pressure difference across the fuel system. The metering orifice 20, 21 is controlled by the fly-weights 79 acting on the sleeve 22 in opposition to a spring 75, for the purpose of limiting the maximum speed of the engine. The metering orifices 16 are controlled by axial movement of the sleeve 6 so as to maintain the overall compression ratio P3/P1 of the engine compressor substantially constant, for a given setting of the pilot's throttle control 68, at any forward speed and altitude and for all ambient ground temperatures below a predetermined value. For this purpose, the axial position of the sleeve 6 is controlled by a bellows stack comprising an evacuated bellows 30 and a bellows 31 whose interior is exposed via a passage 32 to the delivery pressure P2 of the L.P. compressor of the engine or a pressure functionally related thereto. The exterior of the bellows stack is exposed to a variable pressure P3" in a chamber 26. For this purpose a fuel potentiometer 36, 37 is connected between the passage 32 and a passage 40 which is open to the delivery pressure P3 of the H.P. compressor or a pressure functionally related thereto. The chamber 26 is connected via a fixed restriction 34 to the potentiometer tapping and via a variable restriction 41, 42 to a passage 45 which is open to the ambient static pressure P0 or a pressure functionally related thereto. The variable restriction 41, 42 is controlled jointly by a bellows 52 whose interior is exposed via a passage 56 to the engine intake pressure P1 or a pressure functionally related thereto, and a bellows 51 whose interior is exposed to the pressure at the tapping 61 of a fuel potentiometer 64, 65 connected between the passage 40 (pressure P3) and the passage 45 (pressure P0). Restrictor 64 of the potentiometer is controlled by the pilot's throttle control 68 while restrictor 65 is controlled by an evacuated bellows 55 exposed to the pressure P1. The pilot's throttle control 68 also varies the setting of a turbine gas temperature control (not shown). The sleeves 6, 14, 83 may be driven from the shaft 12 independently of the drum 80 and at a lower speed than the drum.