GB845269A - Improvements in fuel flow control apparatus for gas turbine engines - Google Patents

Abstract

845,269. Gas turbine engine fuel systems. DOWTY FUEL SYSTEMS Ltd. Dec. 20, 1956 [Dec. 21, 1955], No. 36676/55. Class 110 (3). [Also in Group XXIX] An aircraft gas turbine engine has means continuously computing a non- dimensional fuel flow and maintaining the parameter constant or controlling rate of increase in the fuel flow parameter according to non-dimensional engine speed to prevent stall. As shown the ratio of the absolute compressor discharge to intake pressure is taken as the non-dimensional engine speed parameter and these pressures are applied respectively to diaphragms 17, 22, opposed by evacuated bellows 21, 25 in a unit 1 operating only during acceleration to position a leak-off valve 27 and a piston 28 rotating a fuel flow control valve 58, follow-up between the piston and leak-off valve taking place through a cam 38 moving a lever 16 carrying the fulcrum 15 for the hinged valve 27. A pilot's speed-selection lever 53 acts through a cam 51 and spring 49 loading a second leak-off valve 54 for the piston 28, follow-up between the piston and the hinged valve 54 taking place through spring 48. In a modification (Fig. 3, not shown) the travel of the piston 28 is made proportional to the non-dimensional engine speed parameter N/#T1, the engine speed being detected by a tacho-generator and the compressor inlet temperature T1 is detected by a thermocouple, and both signals fed into an electrical system which energizes a solenoid actuating the hinged valve 27. The fuel flow is also controlled in response to a non-dimensional fuel flow parameter by means of the by-pass valve 5 of the fuel pump 3 and a plunger valve 65 controlling the orifice through the rotary valve 58. The valve 65 is actuated by a piston 66 positioned by a leak-off valve 76 seating on the end of the hollow piston rod 71 and actuated by a bellows 75 responsive to compressor inlet pressure in a unit 2 operating under steady state conditions. The piston 66, through a link and lever 95, 96 positions a stop 94 for the adjustable abutment 93 whereby the minimum fuel flow for a speed selected by the pilot's lever is in accordance with the altitude of the aircraft. The by-pass valve is actuated by a piston 8 under the control of a hinged leak-off valve 86 positioned by a thermal element 85 responsive to compressor inlet temperature and by pistons 81, 82 responsive to the pressures upstream and downstream of the valve 65. The non-dimensional fuel flow parameter is represented by Q/P1#T1, where Q is the fuel flow rate, and P1 and T1 are the compressor inlet pressure and temperature respectively. If the fuel flow parameter has the engine speed N substituted for square root of T1, then an engine-driven governor exerting a force proportional to N squared is substituted for the element 85. The bellows 75 may control the piston 66 through a hinged leak-off valve. The armature of a solenoid 88 acts on the valve 86 to reduce the fuel flow to the engine when a maximum speed is reached. An inner rotary valve 59 is provided as an emergency manual override control or for operation by a variable jet nozzle device. The Provisional Specification describes piston 28 connected to a piston valve in a branch from pump 3 and positioned by a hinged servo valve responsive to compressor inlet temperature and the pressure drop across the valve, the flow through the valve being determined by a series servo diaphragm valve positioned by pressure drops across an engine-driven centrifugal pump and an orifice between the piston and diaphragm valves respectively via a pair of opposed diaphragms controlling a hinged valve. An arcuated bellows opposing a bellows responsive to compressor inlet pressure and correcting for the Reynolds Number may act on valve 86 or on a valve in series with valve 54, the latter also having a spring connection with piston 28.