Patent GB-784104-A (GB)
Title: Improvements in or relating to fuel controls for gas turbine power plants
IPC: F02K3/00
Filed: 1955-06-30
Abstract: 784,104. Gas turbine plant. UNITED AIRCRAFT CORPORATION. June 30, 1955 [July 14, 1954], No. 18932/55. Class 110 (3). [Also in Group XXIX] A fuel control system for a gas turbine power plant comprises a power setting lever, first means for generating a first signal commensurate with the speed of the power plant, second means for generating a second signal commensurate with the setting of said power lever and a power plant temperature, means for receiving said first and second signals for controlling the fuel regulating mechanism, and a second means for receiving said first signal and a signal commensurate with a variable of power plant operation other than speed for further controlling said fuel regulating mechanism. As shown, fuel enters a control unit at 34 and passes through a filter 60 incorporating a relief valve 62 and then through a conduit 66 to a metering valve 92 after which it passes through conduits 106, 108 to the combustion chamber of the turbine. A relief valve 80 limits the fuel pressure in the conduit 66 and a valve 88 maintains a substantially constant pressure drop across the metering valve 92. The metering valve is adjusted in accordance with the delivery pressure of the power plant compressor by a servo-piston 164 having a control valve 160 which is actuated through a lever 156 by a bellows 152 subject internally to the compressor delivery pressure. An evacuated bellows 156 cancels the effect of variations of ambient pressure. The transmission between the servo-piston 164 and the metering valve is effected by a member 130 which is adjustable by a servo-piston 136. Under normal conditions of operation the servomotor 136 is controlled by a pilot valve 190 which is connected through a floating lever 268 and rollers 272 with levers 262, 266. The lever 262 is pivoted at 264 and engages at its upper end with a three-dimensional cam 210 which is rotated through gearing by a pilot's control lever 202 and reciprocated by a servo-piston 236 having a control valve 234 which is operated by a bellows 224 subject to the temperature of air entering the compressor. Movement of the servo-piston 236 is also transmitted through gearing 336, 333 to cause rotary adjustment of a three-dimensional cam 330, axial movement of which is effected by the supply or exhaust of oil under pressure through a conduit 360 under the control of a valve 340 which is actuated by a centrifugal governor 342 driven by the turbine. A lever 368 pivoted at 370 transmits axial motion of the cam 330 to a loading spring 348 of the governor. The lever 368 is also connected to the lever 266 which is pivoted at 300. The floating lever 268 is connected at one end to the servo-piston 136 so that the latter takes up a position, during steady running, in accordance with the position of the lever 202, the speed of the turbine, and the temperature of air entering the compressor. Should the lever 202 be actuated to demand a rapid increase in power the cam 210 causes depression of the left-hand end of the lever 268 which results in a downward movement of the valve 190 causing the chamber 140 above the servo-piston 136 to be exhausted. The selection of the higher power also causes adjustment of a cam 386 which, through a lever 388 pivoting at 390 causes movement of an underspeed pilot valve 294 to the right so as to interrupt the supply of pressure fluid through conduits 292, 296 to the pilot valve 190 so that although upward movement of the servo-piston 136 causes a corresponding movement of the valve 190 the latter is ineffective in controlling the position of the servo-piston 136. The upward movement of the servo-piston 136, however, also adjusts a floating lever 326 which is connected to a maximum limit pilot valve 322 which normally interconnects conduits 282, 284. The upward movement of the servo-piston 136 during acceleration causes the valve 322 to connect the conduit 284 with a pressure supply conduit 320 to cause pressure to be applied in the chamber 140 to limit the fuel flow. As the speed increases the cam 330 moves to the right and causes downward movement of the left-hand end of the lever 326 through a follower 328 thereby allowing the servo-piston 136 to move upwardly to increase the fuel flow as the speed increases. The increase of speed also repositions the sleeve 396 relative to the pilot valve 294 whereby fluid under pressure is again effective in the conduit 296 and the valve 190 becomes operative to position the servo-piston 136. The system also controls fuel flow during deceleration in such a manner as to prevent extinguishing of the burners. A torque limiting device for the turbine, which drives a propeller, is constituted by a bleed 438 from the bellows 152 controlled by a valve 428 acted upon by diaphragms 422, 424 subject to ambient atmospheric pressure and total head pressure at the power plant inlet. Alternatively the valve 428 may be controlled by a torque responsive device as, e.g., in Specifications 600,376, [Group XXVII], or 600,045, [Group XIX]. A fuel shutoff valve 452 is provided under the control of a pilot valve 458 which is governed by a shut-off lever 471 acting through a bell-crank lever 478 and by a solenoid 468 connected with the manual propeller feathering system. An ignition switch 490 is also controlled by the lever 471. Specification 781,961 also is referred to.