Patent GB-843535-A (GB)
Title: Tailpipe afterburner control for gas turbine jet propulsion engines
IPC: F02K1/16
Filed: 1956-07-03
Abstract: 843,535. Gas turbine jet propulsion plant. BENDIX AVIATION CORPORATION. July 3, 1956 [July 8, 1955], No. 20621/56. Class 110 (3). [Also in Group XXIX] A gas turbine jet propulsion engine in which fuel is burnt in the tailpipe has the fuel flow to the tailpipe controlled by a valve regulated by means responsive to a pressure derived from the compressor which defines maximum and minimum fuel flows for each value of the compressor pressure and manually operated means to select the fuel flow between these limits. Fuel is supplied to the main combustion equipment 12, Fig. 1, of a gas turbine jet propulsion engine by a pump 32 through a control device 30 responsive to the compressor inlet temperature, compressor discharge pressure, engine speed, and to the position of the pilot's control lever 52. The fuel supply to the reheat burners 68 from the pump 67 is controlled by a fuel control 64 responsive to the compressor discharge pressure and pilot's control lever position. The area of the propelling nozzle is controlled by a bullet 78  which is positioned as a function of the pilot's control lever position or tailpipe temperature or both. Movement of the pilot's control lever 52 over the quadrant sector A in a counterclockwise direction will increase the speed setting of an all-speed governor in the fuel control 30 and decrease the area of nozzle 22 to increase the thrust. Movement of the lever over the sector B will not affect appreciably the speed setting of the governor but will further decrease the area of the nozzle 22. Further movement of the lever 52 over the sector C will cause fuel to be supplied to the reheat burners 68 as a function of compressor discharge pressure and pilot's control lever position. The temperature control 92 can override the pilot's control of the area of the nozzle 22 when the pilot's control lever 52 is in the sectors A and B. When the lever 52 is in the sector C, the control 92 operates continuously to maintain a predetermined constant tailpipe temperature. The temperature control 92 may be connected to the reheat fuel control 64 by a switch 100 operated by the bullet 78 in its wide-open position so that the fuel flow is reduced when a predetermined temperature in the tailpipe is exceeded. The reheat burner fuel control 64, Fig. 2, comprises a balanced regulator valve 110, a metering valve 122 and a shut-off valve 130. The regulator valve 110 is spring loaded in the opening direction by a spring 132 and urged in the closing direction by the difference in the pressures at the inlet and outlet of the metering valve 122 acting on a diaphragm 138 so that the pressure difference is maintained substantially constant. The metering valve 122 is attached to piston 148 contained in a chamber 146 the pressure in which is varied by means of half-ball servo valve 152 carried by a lever 160 which is moved by evacuated bellows 154 in response to the pressure changes in the chamber 156. The chamber 156 is connected to a passage 182 in turn connected through a restriction 170 to the compressor discharge pressure conduit 46 and through a chamber 172 vented to atmosphere through an opening 174, the area of which is controlled by a needle valve 176. The needle valve 176 is positioned by the pilot's control lever so that the pressure in the chamber 156 is dependent upon this lever position and the com pressor discharge pressure. If a predetermined temperature in the tailpipe is exceeded, when the switch 100 is closed by the bullet 78, the solenoid 190 is energized to open the valve 188 and vent the chamber 156 to atmosphere. This causes a reduction in the reheat fuel supply. A manually adjustable piston 194 in a chamber 196 connected to the passage 182 is provided to control the time rate of the change of pressure in the passage 182 following rapid opening or closing of the valve 176. The valve 176 is actuated by a piston 234 the position of which is controlled by a leak-off valve 250 actuated by a piston 216 through a pivoted lever 246. The piston 216 is moved and positioned against the spring loading on the lever 246 by the pressures in the chambers 200, 214 which are determined by the throttle lever position 52. As the lever 52 is moved to increase the power output, the rack 220 is raised by pinion 222 to increase the tension of the spring 226 which acts through the flexible diaphragm on a halfball valve 218 to increase the pressure in the chamber 208 until the pressure difference across the diaphragm 224 balances the higher spring loading. The pressure in the chamber 198 is controlled by a valve 204 so as to maintain a constant pressure difference between the passage 202 and the chamber. A control 280 is provided to limit the minimum quantity of fuel that can flow to the reheat burners at any given compressor discharge pressure. A half-ball valve 282 is carried by one arm of a bell-crank 284 which is spring loaded to urge a roller 290 carried by the other arm against a cam 292. The cam element 292 is actuated by evacuated bellows 298 in response to changes in compressor discharge pressure. When valve 122 moves so far closed that the contact of the roller 290 on the cam 292 causes the half-ball valve 282 to be unseated so the pressure differential across the piston 148 is increased and prevents further closing movement of the valve 122. A fuel flow cut-off valve 130 contains ports 307 connecting conduit 126 to a chamber 308 and a passage 310 controlled by a pilot valve 312 connecting chamber 308 with the discharge conduit 70. The pilot valve 312 is urged in the closing direction by an adjustable spring 316 and in the opening direction by the pressure differences across the. diaphragms 318, 323. The pressure drop across the diaphragm 323 is proportional to the throttle lever position. The pressure drop across the diaphragm 318 is proportional to engine speed obtained from an engine-driven impeller 327. At a predetermined engine speed the valve 329 moves and the pressure drop across the impeller 327 is applied to the diaphragm 318. The loading of the spring 316 is such that the valve 312 does not move in the opening direction until a predetermined speed and a given throttle lever position has been attained. When valve 312 opens the passage 310, the pressure in chamber 308 falls and the cut-off valve 130 is opened. In a modification the valve 176 is operated by a three-dimensional cam rotated by the throttle lever and axially movable by evacuated bellows in response to changes in compressor discharge pressure. In another modification, Fig. 3 (not shown), the metering valve is spring loaded in the closing direction and the amount of movement in this direction is limited by a roller which contacts an inclined plane member. The angle of incline of this member is determined by two cams which are rotated by means responsive to compressor discharge pressure. The position of the roller on the plane is determined by the throttle lever position.