Patent GB-687498-A (GB)
Title: Tailpipe or afterburning control for turbojet engines
IPC: F02K1/16
Filed: 1950-03-24
Abstract: 687,498. Liquid fuel supply to burners. BENDIX AVIATION CORPORATION. March 24, 1950 [April 22, 1949], No. 7484/50. Class 75(i) [Also in Groups XXVI, XXIX and XXXV] In a gas turbine jet propulsion engine in which the gases are reheated in a combustion chamber before the propulsion nozzle, the fuel supply to the reheat combustion chamber is controlled as a function of the compressor discharge pressure modified by a function of tailpipe temperature. The jet propulsion plant shown, Fig. 1, has a diffuser cone 21 leading to a tailpipe 20 having at its outlet a propulsion nozzle 22 the area of which is adjustable by means of a pair of gate valves 23, 24. The gate valves are operated by a servomotor 30 actuated by compressed air from the compressor discharge controlled by an electrically operated valve 138. The main fuel supply to the engine may be controlled by any means from a power lever 45. This lever has a lateral projection 50, movable in a slot 51, which when the lever is moved to the augmented power position, moves into an offset slot 52 and depresses a switch plunger 53. This energizes a circuit leading by wires 58, 59 and 60 to a speed-sensitive switch 62. When the switch 62 is closed the solenoid coil 71 of a magnetic clutch 72 is energized and the pump 75 then supplies fuel to the afterburning control unit 79 shown in detail in Fig. 2. A relief valve 80 controls the maximum pressure in the intake chamber 78 of the control unit. The valve 80 is connected to a diaphragm 84 which forms a movable wall between a chamber 78 and a chamber 85 in which a spring 86 is mounted and normally urges the valve 30 towards the seated position. The chamber 85 is connected to the metered fuel discharge line by a passage 87 so that the valve 80 maintains the pressure in the chamber 78 at a predetermined value over and above the metered fuel pressure. A regulator valve comprising a valve member 88, operated by temperature changes in the tail-pipe member, surrounding a valve member 91, operated by the mechanism controlling the variable area propelling nozzle, controls the fuel flow across a metering valve 94. The valve 94 is actuated by bellows 98 mounted in a chamber 100 connected to the discharge of the compressor by conduits 101, 102. The fuel flow to burners in the tail pipe is thus controlled according to the compressor discharge pressure, the exhaust nozzle area and the tail-pipe temperature. The fuel leaving the control unit 79 passes through a conduit 118, a port 119, Fig. 1, controlled by a solenoid-operated valve 155 and conduit 120 to the main afterburning manifold and discharge nozzles. The afterburning fuel system comprises one or more starting torches 121, and one or more main fuel discharge nozzles 125. Starting fuel may also flow to one or more of the main fuel nozzles 125. When the speed-responsive switch 62 is closed, the ignition device 128 is energized and the valve 155 opened. Fuel then flows to the starting torch 121 where it is ignited and this in turn ignites some of the fuel nozzles 125. When the temperature in the tail pipe rises, a thermostatic switch 133 closes and allows current to flow through the solenoid 132 of a valve 131 and the solenoid 147 of the valve 138. The valve 131 then opens and allows fuel to pass to the remainder of the nozzles 125. The valve 138 is urged to the right which allows compressed air to be passed to the right hand side of the piston 31 and the left hand side to be opened to atmosphere. The piston 31 then moves to the left and opens the gate valves 23, 24. The solenoid operated valve 155 is opened when the pilot sets the lever 45 to the augmented power position. The valve member 88 is operated by an electric motor 166 controlled by the means shown in Fig. 3. The motor has a stator winding of the two phase A.C. reversing type comprising a fixed phase field coil 162 and a variable phase coil 163. Current is supplied to the motor by an inverter 164 and the voltage on the fixed phase coil is shifted through ninety electrical degrees with respect to the supply by a series capacitor 173. The voltage on the winding 163 is supplied through a saturable reactor 174 so that if the tubes 175 and 176 are conducting the same average current, the voltage applied to the variable phase winding 163 will be zero and the motor will not run. The motor runs in one direction or the other if the plate current of one tube is greater than that of the other. A thermocouple 171 located in the tail pipe is electrically connected to a bridge circuit 172. This circuit causes .the meter arm 166 to move in one of two directions and position the valve 88 so as to maintain the tail pipe outlet temperature constant. A bias battery 177 is of such a magnitude and direction as to cause tube shut off when no current is flowing in the secondary 178<SP>1</SP> of transformer 179. When the A.C. grid voltage of either tube 175, 176 is in phase with the plate voltage between the points X, Y, the tube will conduct. The phase-splitting transformer 179 supplies voltages to the grid circuits of tubes 175, 176 which are 180 electrical degrees out of phase with one another. The primary 178 of transformer 179 is connected to the output circuit of an amplifier 181. the input of which is connected across the secondary 182<SP>1</SP> of a transformer 183, the primary 182 of which is connected across the signal circuit 184 of the bridge 172. The device 185 consist of a box of carbon graules with an overlying diaphragm 185<SP>1</SP>, which vibrates in response to changes in the magnetic field of coil 186, and functions to change the D.C. current from the bridge circuit to a pulsating current at a frequency determined by the power transformer 187. The direct current voltage on the device 185 and the primary 182 of transformer 183 is proportional to the degree of unbalance of the bridge 172 and of a polarity dependent on the direction of unbalance. The periodic variations of resistance of the device 185 produce a voltage output from the secondary 182<SP>1</SP> of the transformer 183 of a magnitude proportional to the direct current voltage on the device 185 and a phase relationship with respect to the voltage between the points X and Y dependent upon the polarity of the applied direct current voltage. A relay switch 188 connects the bridge circuit 172 with the thermocouple 171 when the afterburning system is in operation and to connect this circuit with the wiper arm 191 of a potentiometer 192 when the system is turned off. A mechanical linkage 196 connects the wiper arm 191 to the motor 160. The solenoid 193 of the switch 188 is energized when the speed operated switch 62 is closed. If when the afterburning fuel system is turned off, the wiper arm 191 is at variance with the balanced setting of the bridge, the signal output from the transformer 183 will cause the motor 160 to rotate and reduce the error until the bridge output becomes zero. A modification in which the metering valve 94 is operated by the mechanism controlling the variable area nozzle and the regulator valve is actuated by adiaphragm the pressure drop across which may be varied by a valve which is actuated by the motor 160 and bellows responsive to a function of the compressor discharge pressure. The pressure applied to the chamber enclosing the bellows is modified by a valve which is actuated by a bimetallic element responsive to the engine or compressor inlet temperature. Specifications 655,311 and 676.039, [both in Group XXVI], are referred to. Reference has been directed by the Comptroller to Specification 641,910.