GB888243A - Improvements relating to jet propulsion engine fuel systems - Google Patents

Abstract

888,243. Jet-propulsion plant; centrifugal compressors. GENERAL MOTORS CORPORATION. Sept. 9, 1960 [Sept. 11, 1959], No. 31119/60. Classes 110 (1) and 110 (3). [Also in Group XXIX] A jet-propulsion engine fuel system has a fuel tank, a pump to deliver liquid fuel from the tank to the engine, a separate pump to deliver vapour or gas from the tank to the engine which is responsive to the pressure of the vapour or gas and a fuel-metering valve which reduces the amount of liquid fuel supplied to the engine as the amount of fuel vapour or gas increases. Fuel from a tank or tanks 28 is supplied to the main and reheat combustion chambers of a gas-turbine jet-propulsion engine E. The fuel tank 28 contains a quantity of liquid fuel 29 above which is fuel vapour 31. A boost pump 32 supplies liquid fuel to the main fuel pump 34 and to the reheat fuel pump 37. The pump 34 discharges through a main fuel control 40 which is responsive to the setting of the pilot's power lever 41, engine speed through shaft 44 and inlet air temperature from the bulb 46, to the manifold 18. The main fuel control also controls the supply of vapour fuel to the manifold 19. Liquid fuel is supplied by a centrifugal pump 37 through a control 55 to the manifold 21. The control 55 also regulates the supply of vapour to the manifold 22. The control 55 is regulated by the pilot through lever 41 and by a control 58 responsive to the pressure ratio across the turbine. The area of the propulsion nozzle is controlled by means 70 responsive to the air inlet temperature 46 and the position of the pilot's lever 41. The reheat fuel control 55 also controls a valve 63 supplying air to a turbine 66 driving the reheat fuel pump 37. The vapour pump system 75, comprises vapour compressing or pump means, controls therefor, and means for cooling by-passed vapour. The system 75 is shown in detail in Fig. 2 and comprises a pair of centrifugal pumps 82, 83 driven by the engine through a variable speed hydraulic coupling 84. A scoop tube 91 which controls the hydraulic coupling is positioned by a servomotor 93 controlled by means 99 responsive to the vapour pressure in the tank 28 and the actual pump speed 98. Any change in pump speed causes fluid to be supplied to or extracted from the chamber 111 to move piston 108 to re-centre the pilot valve 106. The position of piston 108 and rod 112 is thus indicative of pump speed. Increase in fuel pressure or decrease in compressor speed will control the scoop tube 91 so that the pump speed is increased. Decrease in vapour pressure and increase in speed controls the tube 91 to decrease the pump speed. The arrangement is such that pump speed is governed to a value determined by vapour pressure. To prevent surging of the pump 82, 83, a by-pass valve 126 is provided. The valve 126 is controlled by a servomotor 129 regulated by a control valve 133. The valve 133 is connected to a lever 148 connected to bellows 141, 138 responsive to the pressures before and after the pumps 82, 83. Bellows 144, 147 are evacuated compensating bellows. The lever 148 rocks on a fulcrum 151 the position of which is determined by a cam 154 so that it is related to engine speed. When the relationship of compression ratio to speed is such that surging is likely to occur, the valve 126 is opened by the control 137 to allow vapour to pass back to the suction of the pump. This vapour is cooled in a cooler 127 into which liquid fuel is injected through a valve 160 controlled by a thermostatic device 163. The arrangement operates as follows. Assuming that the engine has been operating on liquid fuel and highspeed flight has caused vapour to form in the tank 28. The pressure of this vapour causes coupling 84 to energize the vapour pumps. During acceleration of the pump, the valve 126 opens to prevent surging. When the pressure in line 79 reaches a predetermined value vapour is supplied to the reheat burners through line 81. Valve 126 then closes. If the vapour pressure rises further, vapour is then supplied to the main burners through line 80. The fuel valve arrangement 165, Fig. 3, for the main fuel control 40 comprises a liquid fuel valve 166 and a vapour fuel valve 167. The liquid fuel valve 166 comprises a valve member 169 which is reciprocable and rotatable. Fuel passes from the line 38 through rectangular port 171 and is discharged through line 176. The stem 174 is rotated by means responsive to engine inlet temperature and is reciprocated by rod 177 regulated by a governor device responsive to the difference between actual engine speed and the speed called for by the pilot's lever 41. The rod 177 also controls the vapour fuel valve 167. The valve 167 comprises a piston 183 which controls a port 187 through which vapour is supplied from line 80. A spring 188 biases the valve 167 in the opening direction. Valve 167 therefore remains open until the valve member 169 of valve 166 has been moved against a stop 189. Further movement of the rod 177 then closes the vapour fuel port 187. To prevent coking of the burners a minimum flow of liquid fuel is always supplied through valve 166. The reheat fuel control valve 55 may be of similar construction except that the valve 174 will be responsive to turbine pressure ratio only.