Patent GB-796203-A (GB)
Title: Afterburner fuel control for a turbojet engine
IPC: F02K3/10
Filed: 1956-03-15
Abstract: 796,203. Gas turbine jet propulsion plant. GENERAL MOTORS CORPORATION. March 15, 1956 [April 1, 1955], No. 8104/56. Class 110 (3). [Also in Group XXIX] In a fuel control for an afterburner of a gas turbine jet propulsion engine in which the fuel flow is controlled by means responsive to compressor discharge pressure, above a given compressor discharge pressure the fuel supply is also varied in response to throttle movement but below this pressure is unaffected by such movement. The afterburner fuel control, Fig. 3, is provided to control the fuel flow in accordance with the curves, Fig. 2, which show variation of fuel flow against variations in compressor discharge pressure. When the control is first put into operation the fuel flow is controlled in accordance with the curve A until a predetermined compressor discharge pressure Y is reached. From the pressure Y to the pressure Z the fuel flow is automatically controlled in accordance with the curve C. Above the pressure Z the fuel flow can be controlled by the pilot to any value between the curves A, B. The fuel flow is metered by a valve 63, the pressure drop across which is maintained constant by controlling its inlet pressure by means of a by-pass valve 62, actuated by a pressure regulator valve 77. The valve 77 comprises a fixed sleeve 281 having axiallyspaced ports 282, 283, 284 and an equal area plunger 78 having a pair of spaced hands 285, 286 which co-operate with the ports 282, 284. The upper end of the plunger is exposed to the inlet pressure of the metering valve 63 through passages 82, 81. The lower end of the plunger is loaded by a spring 80 and is exposed to the pressure in. chamber 280 which is connected to the outlet of the metering valve 63 through passages 79, 76, 74. Movements of the plunger 78 will connect the chamber 306 beneath the by-pass valve 62 either to the high-pressure fuel passage 84 or to the drain passage 287. Variations of the pressure in the chamber 306 will cause the by-pass valve 62 to open or close and thus restore the pressure drop across the metering valve 62. The metering valve 63 is actuated by a rod 100 controlled as described below. The rod 100 engages a nut 200 carried by a stud 201 slidably mounted in a sleeve piston 203 located within a stationary sleeve 204. The lower end of the sleeve 204 abuts a second stationary sleeve 208 which contains the valve element 211. The valve element 211 is biased to the closed position by a spring 216 and is connected to the sleeve piston 203 by a rod 217. A pilot valve plunger 219 contained in a bore in the sleeve piston is urged upwardly by a spring 220 so that it follows the movements of the rod 100. Movements of the rod 100 cause the plunger 219 to connect the chamber 229 either to the high-pressure fuel supply passage 234 or drain passage 232. This causes the valve 63 to move and the sleeve piston 203 to follow up the movement of the plunger 219. A solenoidoperated shut-down valve 67 which is energized when the throttle lever is moved to a predetermined position is also provided. This valve comprises a fixed sleeve 320 having a plurality of axially spaced ports 321, 322, 323, 333 and 324 and a reciprocable plunger 325 operated by the armature of a solenoid 327. When the solenoid is energized the plunger is in the position shown in which the passage 85 is uninterrupted as land 328 blocks port 321 and the annular groove 335 connects the branches of the passage 85. In addition, the passage 66 from the fuel pump discharge is connected through ports 322 and ports 323 to the passage 234 and the passage 79 is connected to the discharge passage of the metering valve 63 through ports 323, 324 and passage 74. When the solenoid is de-energized, the plunger 325 moves upwardly, passage 85 is connected to drain through passages 334 and 332, passage 66 is shut off from passage 234 and passage 79 is shut off from passage 74. Since the passage 234 supplies fluid under pressure to open the metering valve 63, the de-energization of the solenoid valve will cause the valve 63 to be closed by its spring 216. The rod 100 is operated in the following manner. A chamber 250 which contains pressure-responsive bellows 71 is subjected to compressor discharge pressure. Movements of the bellows are transmitted by a pivoted lever 274 to a pilot valve 86 which connects a chamber 261 beneath a piston 73 either to a high-pressure fuel supply port 234 or a drain passage 267. The resulting movement of the piston 73 acting on the bellows 71 through a spring 72 restores the pilot valve 86 to the neutral position. The position of the piston 73 is therefore indicative of compressor discharge pressure. The piston 73 positions a sector gear 90 connected to a splined shaft 92 through a gear train 93. The shaft 92 carries a throttle reset cam 94 and a three-dimensional compressor discharge pressure cam 95. A throttle reset cam follower 96 carried by a lever 132 is arranged to be connected under certain conditions to an input gear of the differential 89. The compressor discharge cam follower 97 is connected to a second input gear of the differential 89. The output gear of the differential is connected to a fuel flow cam 98 which positions the rod 100 through a follower 99 and pivoted lever 152. A crank 88 connected to a throttle lever positions a throttle cam 103 through a gear train 102. A lost-motion connection is provided so that movement is not imparted to the throttle cam until the throttle lever has reached a predetermined position. The throttle cam follower 104 is connected to the input arm 108 of the differential 89. When the compressor discharge pressure is below the point Z, Fig. 2, the cam 94 over-rides the cam 103 and controls the fuel flow according to the curves A and C. Above this pressure the fuel flow is dependent upon the setting of the throttle cam 103. The slope of the curve A about the origin may be initially adjusted by means of a rotatable stud 156 which adjusts the fulcrum point 153 of the lever 152. The slope of the curve A at and below a compressor discharge pressure of a valve W may be varied by adjusting the axial position of the compressor discharge pressure cam 95 by means of a stud 139. This constitutes an adjustment for altitude. A modification in which the pressure drop across the metering valve is controlled by a throttle valve in series with the metering valve is also described.