Patent GB-821057-A (GB)
Title: Control of reheat in turbojet engines
IPC: F02K1/16
Filed: 1956-05-10
Abstract: 821,057. Gas turbine jet propulsion plant. NATIONAL RESEARCH COUNCIL. May 10, 1956 [July 15, 1955], No. 14593/56. Class 110 (3). [Also in Group XI and XXIX] In a gas turbine jet propulsion engine having a reheat combustion stage in the jet pipe and a variable and a propelling nozzle, the fuel supply to the reheat stage is controlled by a main throttle and a trim throttle, the main throttle being controlled by means sensitive to the amount of propelling nozzle opening and the trim throttle by means sensitive to the ratio of the absolute pressure at the compressor and turbine discharge. The main fuel control 12 and reheat fuel control 17, Fig. 1, of a gas turbine jet propulsion engine are combined in a single control 18, Fig. 2, which comprises a quadrant 19 of operating cams actuated by a control lever 20 through a spring 21. The quadrant 19 is divided into two parts namely an unreheat region 26 and a reheat region 27. On rotating the quadrant anticlockwise, the cam 28 actuates a follower (not shown) to energize the engine igniter (not shown. If the igniter operates satisfactorily, the electromagnetically operated detent 23 is withdrawn from the recess 22 in the quadrant 19 so that the latter may follow further movement of the lever 20. In this case, the cam 29 actuates a follower (not shown) which opens the engine shut-off cock 30. Still further movement of the lever 20 and quadrant 19 will cause the cam 31 to operate the engine throttle 12. The throttle 12 has a small leak to allow fuel to pass to the engine when the shut-off cock is opened. To put reheat into operation, the lever 20 is moved further in the anti-clockwise direction. This causes a cam 32 on the quadrant 19 to close of micro-switch 33 which energizes an igniter 34 in the jet pipe 35 and a cam 37 to close a second micro-switch 38. The switch 38 completes a circuit opening the shut-off cock 39. Further movement of the lever 20 causes the cam 40 to operate the reheat throttle control 17 which allows compressed air from the engine compressor to pass to a cylinder 42 containing a piston 43 connected to a variable area propelling nozzle 44. The area of the nozzle 44 is dependent upon the opening of the throttle control 17. If the igniter 34 fails to ignite the reheat fuel, the detent 25, which is electrically operated by a detector 45 situated outside a quartz window 46<1> in the jet pipe 35, will not be retracted from the recess 24 in the quadrant 19 and prevent further movement of the quadrant. The movements of the nozzle 44 are detected by an electrical senser 46 and the resulting signal transmitted through an amplifier 48 to the servo-mechanism 49 controlling a main reheat fuel throttle 50. A trim reheat fuel throttle 56 operated by a coil 57 is provided in parallel with the throttle 50. The coil 57 is energized through an amplifier 58 by a control 59 responsive to the ratio of the pressures at the compressor outlet and turbine discharge. The throttles 50, 56 may be of the form shown, Fig. 3, in which the throttle valve 65 is attached to pistons 63, 64. The pressures in the chambers 68, 69 and therefore the movements of the pistons 63, 64 and throttle valve 65 are controlled by a leak-off flap valve 75 which regulates the flow through the leak-off nozzles 73, 74 to the drain pipe 72. The control 59 may comprise a pair of pistons of different areas connected together by a spindle which passes into a position transmitting coil. The pistons are contained in two cylinders connected respectively to the discharge of the compressor and turbine. The reheat fuel supply may also be varied with altitude. A thermocouple 77 responsive to the exhaust gas temperature and thermocouples 78 measuring the metal temperature of the jet pipe skin are connected through a discriminator 79 to the amplifier 48 so that if unsafe values of these temperatures are detected the flow of fuel through the throttle 50 is reduced. The throttles 50, 56 may be arranged in series.