Patent GB-729201-A (GB)
Title: Fuel control system for gas turbines
IPC: F02C9/16
Filed: 1949-07-14
Abstract: 729,201. Gas turbine plant fuel systems. BENDIX AVIATION CORPORATION. July 14, 1949 [Aug. 10, 1948], No. 18614/49. Class 110(3). [Also in Groups XXIX and XXXVIII] A gas turbine fuel system comprising a throttle valve in the fuel supply conduit to the burners operated by the pilot has means acting on the throttle valve and operable to over-ride the pilot's control which modifies the rate of fuel feed through the conduit as a function of compressor inlet temperature and engine speed, in a predetermined range of speed. The valve means, Fig. 2, comprises essentially a throttle valve 90 and a regulator valve 55 which controls the pressure drop across the valve 90. A diaphragm con-. trolled by-pass valve 37 between the discharge and suction sides of the fuel. pump 32 maintains the pressure drop across the valve means constant. For this purpose, one side of the spring-loaded diaphragm 41 is vented to chamber 34 and the other side to a chamber 45 which is connected to chambers 34 and 98 through restrictions 47, 48. The pressure in chamber 45 is thus in fixed relationship to the pressure in chambers 34 and 98. A valve 50 mounted in the by-pass valve 37 limits the maximum pressure in the valve means. The regulator valve 55 is controlled by a diaphragm 60 overlaying a chamber 61. The valve 55 and its control means form the subject-matter of Specification 729,272. A spring 62 abuts against the lower side of the diaphragm and tends to open the valve 55 against the difference in pressure in the chambers 58 and 61. The tension in the spring 62 is adjusted as a function of the compressor discharge temperature by means of rod 65 actuated by rack and pinion from the motor 70. The motor 70 is controlled by a thermocouple 71 which acts through an electronic amplifier 73 to energize one of a pair of relay coils 74 and 75 so causing the motor to rotate in one direction or the other. The potentiometer 79, which forms part of a reference voltage circuit 80, is connected to the motor 70 through a shaft 83 so as to reset the potentiometer and balance the control unit 73 at the changed setting of the regulator valve 55. A thermocouple 72 acts through an amplifier 84 to energize the relay coil 85 when the turbine inlet temperature exceeds a predetermined value. The coil 85, when energized, opens the switch 87 and closes the switch 86, which causes the circuit through the field coil 81 to be broken and a separate circuit to the field coil 82 to be closed. The motor 70 then rotates to reduce the fuel supply to the combustion chambers. The throttle valve 90 is urged towards the open position by a spring 102 and is adjusted manually by a throttle lever 103. This lever may be independent or correlated with one or more other engine controls. A speed responsive overspeed governor valve 92 is mounted in the throttle valve housing 91. The valve 92 is controlled by a diaphragm 93 which moves in response to changes of pressure between the suction and discharge of the engine-driven pump 105. The speed at which the governor opens the valve 92 is .determined by the loading of the spring 116 which may be varied manually by a lever 113. The lever 113 may be correlated with the throttle lever 103 and if the plant drives an airscrew with the airscrew blade setting lever. The end of the rod 65 is provided with a head 117 adapted to engage the end 118 of the valve stem 59 when the compressor discharge temperature is low and the pressure differential across the diaphragm 60 causes the valve 55 to approach its fully closed position. The head 117 also engages the bottom of a cup-shaped member 63 and tends to close the valve 55 in cases where an excessive compressor discharge temperature is not relieved by reducing the tension on the spring 62. To prevent the engine surging when accelerating or decelerating the opening of the throttle valve is also controlled by means operating as a function of engine speed and compressor inlet temperature. A bell-crank 120 pivoted at 121 has one arm abutting against the throttle valve 90 and the other arm abutting against the cam 122. The cam 122 is pivoted at one end to another cam 124 and at its opposite end to temperatureresponsive bellows 125 by means of a link 126, lever 127, shaft 128, lever 129 and rod 130. The bellows 125 are controlled by the element 131 located at the compressor inlet. Cam 124 is connected to a piston 133 mounted to slide in a chamber 134 against the action of a spring 135. The chamber 134 is connected to the discharge side of the pump 105 so that the position of the cam 124 is dependent on engine speed. During part throttle settings of the lever 103, the pilot has direct manual control of the throttle valve area, but at wide open settings the piston 133 positions the cams 122, 124 to limit the fuel flow. To vary the fuel supply in response to changes of density of the air entering the compressor, a by pass 140, 141; 146 is provided around the throttle valve 90. An orifice 142, the area of which is varied with changes of air inlet temperature, is provided at the entrance to the passage 140 and an orifice 144 which is varied with changes of air inlet pressure at the entrance to the passage 141. Variations of temperature, will therefore vary the pressure drop between the chambers 58 and 61 and variations of pressure between the chambers 61 and 98. Since the pressure across the throttle is the pressure difference between the chambers 58 and 98, either of these variations referred to will affect the flow through,the throttle. The density control described forms the subject-matter of Specification 729,300. A manual cut-off valve is shown at 150, which is arranged in series with a a solenoid operated cutoff valve 152. The arrangement is such that when the valve 150 is opened, the valve 152 is closed and remains closed until the engine reaches a predetermined speed. The unit indicated at 153 consisting of a diaphragm loaded by arm-adjustable spring may be used to operate one or more switches at a predetermined speed during starting.