GB681473A - Improvements in or relating to fuel systems for gas-turbine engines - Google Patents

Abstract

681,473. Gas turbine plant. ROLLS-ROYCE, Ltd., Aug. 3, 1950 [Aug. 18, 1949] No. 21552/49. Class 110(iii) [Also in Group XXIX] In a fuel system for gasturbine engines of the kind in which a pressure-responsive means 51 subject to atmospheric pressure or a pressure related thereto is operative to maintain a predetermined fuel pressure difference across a selectively variable fuel flow metering device 19 of the orifice type, such pressure difference being substantially proportional to the atmospheric or other pressure acting on the pressure responsive means, a selectively variable orifice 70 the pressure drop across which for a given effective area is substantially proportional to the square of the flow therethrough is arranged hydraulically in series with a further orifice 74 the pressure drop across which is substantially proportional to the flow therethrough so that the controlled fuel pressure difference is the aggregate of the pressure drops across the two orifices. The orifice 70 is selectively variable by a plunger 71 operable by a hand lever 73. The other orifice 74 is automatically controlled by a conically shaped valve 75 loaded by a spring 76 to reduce the area of the orifice 74. A "linear fuel flow valve" 77 similar to that formed by the orifice 74 and valve 75 is arranged hydraulically in parallel with the orifice 70 as described in Specification 681,474 so that during idling the whole of or most of the fuel passes through the valve 77. Fuel is supplied to the fuel injection devices 14 through a pipe 18 past the metering device 19 and a shut-off valve 20. The pipe 18 is supplied with fuel by an engine-driven variable delivery swash-plate pump 16. The inclination of the swash-plate mechanism 26 is adjusted by a servomotor 27 under the control of a fluid pressure actuated leak-off valve 45 as described in Specification 577,016, [Group XXIX]. The leak-off valve 45 forms part of a barometric flow control unit 21 and is carried by a lever 46 pivotally supported by a diaphragm 47 which divides the unit into two chambers 48, 49. The chamber 48 is connected to the pump suction conduit 17. The chamber 49 contains an evacuated expansible capsule 51 which acts on one end of the lever 46. The chamber 49 is connected through a pipe 52 to a point subject to the static ambient atmospheric pressure or to the ambient atmospheric pressure as modified by the flight of an aircraft or by the conditions prevailing in the compressor air intake. The lever 46 is also loaded in a similar sense by the total pressure drop across the metering device 19 such pressure drop acting on a diaphragm 53 acting on the lever 46 through a tappet 54. These two loads are balanced by the load due to an adjustable spring 57. An overspeed control is provided by a further leak-off valve 33 which controls a vent passage 32 from the servo-motor 27 and is actuated through a lever 36 by a spring-loaded diaphragm 39 subject to the pressure in a chamber 42 generated centrifugally due to radial passages 43a in the pump rotor 23.