Patent GB-1352410-A (GB)
Title: Gas turbine engine fuel supply control system
IPC: F02C7/22
Filed: 1971-07-17
Abstract: 1352410 Gas turbine engine fuel systems ROLLS-ROYCE (1971) Ltd 17 July 1971 33663/71 Heading F1G [Also in Division G3] In a gas turbine engine fuel system comprising a fuel selector which is adjustable to vary the ratio of the outputs of a liquid fuel control and of a gaseous fuel control so that the ratio of the liquid and gaseous fuels supplied to the engine burners may be changed, adjustment of the fuel selector simultaneously increasing one output and reducing the other output so that the adjustment of itself causes substantially no variation in the heat input produced at the burners by the total fuel supply reaching them, an electronic governor is provided for controlling the liquid fuel supply control and the gaseous fuel supply control in accordance with one or more engine variables. The electronic governor 326, Fig. 5, comprises an exhaust gas temperature control 330 receiving signals, via an amplifier 333, of the exhaust gas temperature T 4 , e.g., from a ring of thermocouples in the jet pipe, the average signal being composed with a datum. A compressor governor 331 receives signals, via a frequency-to-voltage converter 334, proportional to the actual speed N C  of the compressor of the engine. A power turbine governor 332 having variable proportional, integral and derivative action is controlled by an actuator 335 responsive, via a frequency -to-voltage converter 336, to the actual speed N T  of the power turbine as sensed by a phonic wheel and also responsive to a reference speed signal N T  (REF) and, via an amplifier 337 and a droop adjustment device 340, to the actual compressor delivery pressure P 2 . A logic gate 327 allows the lowest of the voltages from the control 330, governor 331 and governor 332 to pass to a summing operational amplifier 325 which also receives a signal from the amplifier 337 representative of the actual delivery pressure P 2  and signals P 2  (REF) and, optionally, P 2  BALANCING from means (not shown). Any error in N C , N T , P 2  or T 4  produces an output signal from the amplifier 325 to control the torque motor of a governor servovalve (285), Fig. 3 (not shown), which controls fluid pressures acting on the servopiston 17, Fig. 2, of the swash-plate of the liquid fuel pump 14 and on the control piston 157, Fig. 4, of the gaseous fuel throttle valve 155, whereby the flow of both fuels is adjusted in the same sense. When any of the variables T 4 , N C  or N T  exceed a predetermined value, a safety monitor amplifier 341 acts via a relay 342 to close solenoid shutoff cocks 85, 175 to shut off both fuel supplies. The liquid fuel is supplied via a pipe 41 to a metering valve 45 which is axially displaceable by means of a piston 51 which is subjected on its right hand side to a pressure determined by a fuel potentiometer comprising a fixed restrictor 36 and a variable valve 59 connected between the pipe 41 and a chamber 58 which is connected to the inlet side of the liquid fuel pump 14. The valve 59 is controlled by a bellows 62 which is subjected via a line 66 to an air pressure functionally related to a compressor delivery pressure. A piston 37a subjected to the pressure drop across the metering valve 45 controls a half-ball valve 79 to influence the position of the servopiston 17 of the liquid fuel pump 14. Adjustment of the ratio of the liquid and gaseous fuel supply rates is effected by a control arm (183), Fig. 3, which acts via an arm 53 to rotate the metering valve 45 to vary the liquid fuel supply and also acts via an arm 178, Fig. 4, to rotate a valve 177 in the gaseous fuel supply line so as to vary the gaseous fuel supply in the opposite sense, the heat input produced at the burners being substantially unaffected by the adjustment. In the two extreme positions of the control arm 183, one or other of two micro-switches is actuated to cause the appropriate solenoid shutoff cock to close. The pressure in line 66 also acts via a piston 232 on a pivoted lever 223 which is also acted on via a piston 234 by the pressure downstream of the gaseous fuel throttle valve 155 and via a piston 235 by a pressure derived from the pressure P 2  by means of a potentiometer 237, 241. A half-ball valve 233 carried by the lever 223 is connected between the control line 161 of the gaseous fuel throttle valve 155 and a drain line 234 to influence the pressure acting on the control piston 157.