Patent GB-1170400-A (GB)
Title: Gas Turbine Engine
Inventor: JOHNSON CHRISTOPHER LINLEY
IPC: F02K1/16
Filed: 1968-08-30
Abstract: 1,170,400. Gas turbine jet propulsion plant. ROLLS-ROYCE Ltd. Aug.30, 1968, No.41555/68. Heading F1J. A gas turbine engine having a jet pipe with reheat combustion equipment and a variable area propulsion nozzle has a pressure responsive device controlling the nozzle area during reheat operation in functional dependence upon jet pipe pressure, a manually operable member for adjusting the quantity of fuel supplied to the reheat equipment by fuel supply control means, and biasing means, operated on adjustment of the manually operable member to select or increase reheat, for biasing the pressure responsive device so that the latter initially adjusts the nozzle area at a rate sufficient to prevent any substantial rise in the jet pipe pressure. The reheat system is shown in Figs. 2, 3 in the position corresponding to reheat inoperative and includes main and pilot burners 21, 22 to which fuel can be supplied from a control unit and pump 23. The latter is set manually by a pilot's lever 107 via a servo 185 and may be responsive to engine variables. The variable area nozzle comprises an axially slidable sleeve 32 having a downstream frustoconical portion (33, Fig. 1, not shown), forming a cam track for rollers (36) on nozzle fingers (34). Movement of the sleeve 32, and thus change in the nozzle area, is effected by rams 26 controlled during reheat operation by a master piston 82 responsive through line 90 to the jet pipe pressure, or a function thereof, and through line 86 to the high pressure compressor delivery pressure, or a function thereof. The master piston 82, when operative, controls movement of a slave piston 63 which in turn positions a spool valve 45 controlling the flow of actuating fluid to the nozzle rams 26. In the position shown, the master piston 82 is locked by a locking device 112 having a yoke 111 engaging pins 110 on a piston rod 81. Each nozzle ram 26 has an associated by-pass trip valve 55 arranged so that when the nozzle is in the fully closed position shown an arm 60 opens the valve 55 to relieve the ram of the full closing pressure of its actuating fluid. The system also includes a reheat selection valve 123 controlled by the pilot's lever 107, a device 140 for supplying priming fuel to the burners 21, 22 and to a hot streak or catalytic igniter, a reheat fuel shut-off cock 222 and an associated operating valve 235. To select reheat, the pilot moves lever 107 anti-clockwise thereby moving valve member 122 of the selection valve 123 to the right so that high pressure (H.P.) fuel pipe 69 communicates with pipes 132, 135. H.P. fuel thus flows through pipe 127 to the interior of a bellows 254 causing closure of drain valves 251, 252 associated with the burners 21, 22. At the same time H.P. fuel flows through pipe 127, non-return valve 126 and pipe 120 to the master piston locking device 112, causing release of the lock by movement of a piston carrying yoke 111 to the right. The movement of lever 107 also causes movement of a lever 102 which pivots a lever 97 to open a half-ball leak-off valve 95,96 at the end of a pipe 93 leading from the space 84 at the left side of master piston 82, i.e. the side subjected to compressor pressure. The pressure in space 84 therefore rapidly falls causing the piston 82 to be biased to the left and the nozzle to open before the jet pipe pressure has increased, thus preventing an appreciable rise when reheat ignition occurs. At the same time, H.P. fuel in pipe 132, providing a speed responsive valve 136 is open, will be applied to the left hand end of a valve member 142 in the priming device 140 causing the valve member 142 to move to the right and permitting H.P. fuel to flow through pipe 149, passages in member 142, and pipes 171, 176 to prime the main and pilot burners 21, 22. With further rightward movement of member 142, H.P. fuel is supplied sequentially to pipe 167 and to pipe 170 leading to the igniters. Pipe 167 supplies fuel to pipe 153 and via the now open valve 235 and pipe 234 to space 230 to move piston 226 of cock 222 to the right so that L.P. fuel can flow from passage 79 through cock 222 to the fuel supply control unit and pump 23. The movement of the pilot's lever 107 also causes corresponding rightward movement of piston 190 and rod 192 of servo 185 to start to adjust the reheat fuel supply and control unit 23. Fuel is thus supplied to the burners 21, 22 and, on ignition, the burning of this fuel will in turn increase the jet pipe pressure and hence further adjust the master piston 82 to increase the nozzle opening. After the piston 190 and rod 192 have moved a small distance to the right a bleed valve 213 will be opened by a lever 217 pivoted to rod 192 to equalize the pressures in spaces 186, 187 on either side of piston 190 and temporarily prevent further rightward movement of piston 190. The reheat fuel supply cannot therefore increase further until a cam type nozzle area sensing mechanism 267, which limits the maximum fuel flow for any given nozzle opening, moves lever 217 clockwise causing bleed valve, 213 to move in a closing direction, whereby producing further rightward movement of piston 190 and hence an increased fuel supply. When the latter has reached the value set by pilot's lever 107 and the nozzle has opened to the required extent, a feedback through link 104 pivots lever 97 to close the leak-off valve 95, 96 to remove the bias from master piston 82.