Patent GB-930230-A (GB)
Title: Fuel system for an aircraft engine
Inventor: JUBB ALBERT
IPC: B64D37/34
Filed: 1960-12-14
Abstract: 930,230. Gas-turbine plant. ROLLS-ROYCE Ltd. Dec. 7, 1961 [Dec. 14, 1960], No. 43126/60. Class 110 (3). [Also in Group XXIX] A fuel system for an aircraft gas-turbine engine having means for adjusting the flow of fuel through a main conduit feeding the combustion equipment of the engine, means for providing a flow of fuel to permit idling of the engine whatever the setting of the adjusting means and altitude responsive means which varies the idling flow, has automatic means for supplementing the idling flow when the aircraft is disposed above a predetermined altitude. As shown, a pair of engine-driven fuel pumps of the adjustable swash-plate type have adjusting pistons 23 controlled by the pressure in a conduit 30 and by valves 32 which are actuated by a diaphragm 36 subject to the pressure generated by a centrifugal impeller 50. The valves 32, a loading spring 37 of which is adjusted by a device 253, 252, 250 responsive to the temperature at the intake of the engine, act as a maximum speed governor. Fuel, having entered the pumps by way of a backing pump 11 and heat-exchanger 12 where it is heated by air from the engine compressors, is discharged through a conduit 60 to a further heat-exchanger 61 where it is heated by engine lubricating oil and thence through a valve 64, 65 to a conduit 120 communicating by way of a manually adjustable, rotary throttle valve 121 with a conduit 127 leading to main and pilot burners 128. The valve closure member 64 is adjusted by a piston 63 under the control of an interrupter valve 72 which is operated by a bellows 100 under the control of a bellowsactuated valve 88 subject to the pressures at the inlet to the low-pressure compressor and at the outlet of the high-pressure compressor so that the member 64 is positioned in accordance with the ratio of these pressures. A further valve 105 controlling the bellows 100 acts to limit the outlet pressure of the high pressure compressor. An interrupter valve 204 actuated by a diaphragm 213 subject to the pressure drop across the valve 64 controls the pressure in the conduit 30 to maintain the pressure drop substantially constant. The down-stream side of the throttle valve 121 is connected to a chamber 178 above a diaphragm 180 whilst the upstream side is connected through a conduit 150, passages 151, 152 controlled by hinged valves 153, 154 and a conduit 176 with a chamber 177 below the diaphragm 180. The valve 153 is actuated by a diaphragm 158 subject through a conduit 163 to the pressure generated by the impeller 50, and the valve 154 is actuated electrically in response to temperature in the jet pipe and the speed of the low-pressure compressor. The diaphragm 180 controls an orifice 182 to maintain the same pressure difference between the conduit 150 and the chamber 178 as exists across the throttle valve 121, and a flow through a passage 183, a chamber 185, and an orifice 231 in a diaphragm 227 which is proportional to the flow through the throttle valve 121. Any change in this proportional flow causes deflection of the diaphragm 227, which coacts with a needle valve, giving rise to a change in pressure difference acting on a piston 187 which, by adjusting an interrupter valve 190 varies the pressure in the conduit 30 to give a corrective adjustment of the pump control pistons 23. An evacuated bellows 194 acts to reduce the pressure in the conduit 30 to reduce fuel flow in response to increase of altitude or reduction of air speed of the aircraft. A flow of fuel for idling of the engine takes place through a passage 131, 130 by-passing the throttle valve 121, and when, at high altitude, the pressure drop across the throttle valve 121 falls to a predetermined value, a diaphragm valve 137 responsive to this pressure drop opens to supplement the idling flow. In a modification, a bellows subject externally to compressor discharge pressure and taking the place of the bellows which operates the valve 105 actuates a valve controlling application of pressure to the bellows 194. Also, the idling passages 131, 130 and valve 137 are replaced by a constant flow diaphragm valve in parallel with an adjustable idling valve. In a further modification, a valve corresponding to the valve 137 has ports arranged to impart swirling motion to the fuel to separate air therefrom.