GB925483A - Fuel supply apparatus for gas turbine engines - Google Patents

Abstract

925,483. Gas turbine plant. D. NAPIER & SON Ltd. Aug. 8, 1961 [Aug. 12, 1960], No. 28062/60. Class 110 (3). [Also in Group XXIX] A gas turbine engine of the kind in which at least part of the useful output is in the form of a mechanical drive, e.g. an engine having a compressorturbine 11, 14 and a free power turbine 15 driving a helicopter rotor 21, is supplied with fuel by a variable delivery pump controlled, at speed settings above a predetermined value, in response to power turbine speed to maintain that speed at a set value, whilst at speeds below the predetermined value fuel flow is controlled by a metering orifice the pressure difference across which is maintained constant by means operative on the fuel pump. As shown, a variable swashplate fuel pump 23 driven by the compressor turbine delivers fuel through a conduit 29 to the interior of a fixed sleeve 49 from which the fuel through a metering orifice 53 and conduit 41 to the burners 13. The orifice 53, which consists of a triangular port in a tube 46 slidable on the fixed sleeve 49, is adjustable by a speed control lever 54 which moves the tube 46 axially and by a sleeve 50 which is movable by means 52 responsive to the temperature at the inlet to the compressor. The swashplate of the fuel pump is adjusted by a servopiston 30 under the control of valves 60, 62 in series and the arrangement is such that at low speed settings a speed setting lever 69 is positioned so that the valve 62 is relieved of pressure of a spring 67 whereby it remains fully open and does not influence the servopiston 30 which is then controlled solely by the valve 60. This valve, which is actuated by a diaphragm 56 subject to the pressure drop across the metering orifice and may be influenced also by ambient pressure, therefore governs the servo piston to keep the metering pressure drop constant. At higher selected speeds, due to the action of the spring 67, the valve 62 comes into action to increase the pump displacement so that the pressure drop across the metering orifice becomes such as to hold the valve 60 fully open and to cause a spring-loaded valve 42 to open to allow fuel to by-pass the metering orifice. Speed control is then effected by the action of diaphragms 66, 71 opposing the spring 67. The diaphragm 66 is subject to a pressure differential generated by a speedresponsive device 18 on the output shaft 16 of the power turbine, whilst the diaphragm 71 is subject to the pressure differential generated centrifugally by a drilling 35 in the fuel pump rotor and is therefore a function of compressorturbine speed. An inertia governor, as described in Specification 925,482, opens a fuel dump valve 73 to stop the engine in the event of excessive acceleration. In a modification the two valves 60, 62 are replaced by a single valve acted upon, through a lever, by the diaphragms 56, 66, 71.