Patent GB-782653-A (GB)
Title: Improvements in or relating to gas turbine engines
Inventor: DAVIES DAVID OMRI
IPC: F02K1/16
Filed: 1953-09-14
Abstract: 782,653. Gas turbine jet-propulsion plant. ROLLS-ROYCE, Ltd. July 30, 1954 [Sept. 14, 1953], No. 25390/53. Class 110 (3). [Also in Group XXIX] A gas turbine jet-propulsion engine with a reheat combustion chamber arranged in the exhaust gases before they pass to atmosphere and a variable area propulsion nozzle has means to select the effective area of the propulsion nozzle and means to vary the flow of reheat fuel in accordance with the selected area of the nozzle together with means responsive to the compressor delivery pressure to reduce the reheat fuel flow with decrease of compressor delivery pressure. The gas turbine engine shown comprises a compressor 1 supplying air to combustion equipment 2 feeding a turbine 3 which drives the compressor. The turbine discharges through a jet cone 4, jet pipe 5 and variable area propelling nozzle 6 consisting of a pair of nozzle elements 7. The jet pipe 5 comprises an inner skin 9 and an outer skin 10 which forms therewith a cooling jacket having air inlets 11 at its upstream end. The air flow through the jacket is assisted by the ejector effect of the propulsion jet. Fuel is injected into the jet pipe by injectors 13. A lever 20 is provided for the selection of the nozzle opening and the quantity of fuel fed to the injectors 13. When it is desired to increase the area of the nozzle, the lever 20 is moved to the left. This causes the lever 22 to increase the loading of the spring 25 on the piston 26. The piston 26 moves to the right and opens the vent valve 27. The resulting flow of pressure fluid through the pipe 39 causes the pressure in the chamber 36 to fall and allows the pressure in the chamber 34 to move the piston 30 and open the nozzle elements 7. The movement of the piston 30 acts back on the piston 26 through the spring 29 and rod 28 and causes the valve 27 to be moved to the equilibrium position. The lever 20 also controls through a rod 51, arm 52, and rack and pinion 55, the valve member 53 of a needle valve 54. The needle valve forms a variable area restriction in a conduit 56 attached at its inlet end to a pipe-line 57 of large diameter connected to the compressor delivery. The conduit 57 may be connected to an intermediate stage of the compressor or to the air casing of the combustion equipment. The conduit 56 also has downstream of the needle valve a fixed area restriction 58 which is choked in operation at speeds at which reheat is to be used. Conduit 56 discharges to atmosphere or any other point of low pressure. Fuel is supplied to the injections 13 from a tank 60 by a centrifugal pump 62 driven by an air turbine 63 supplied with air from the compressor 2 by the conduit 57. The pump 62 discharges through a linear-flow valve 82 and non-return valve 68 to the injectors. The air supply to the turbine is controlled by a throttle valve 70 actuated by a piston 73. The piston 73 divides a cylinder 74 into two spaces 75, 77. The space 75 is directly connected to a source of pressure fluid, in this case the pipe-line 67 and the space 77 to the same source through a restriction 79. The space 77 is connected by a vent pipe 80 to a pressure responsive device 81 which controls the piston 73 and throttle valve 70. The device 81 has a half-ball vent valve 96 which co-operates with vent pipe 80 mounted at one end of a lever 95. The lever is loaded in the sense of opening of the valve 96 by a diaphragm 90 responsive to the pressure drop across the linear flow valve 82 and in the opposite direction by a control pressure acting on a diaphragm 100. An evacuated capsule 102 of the same area as the diaphragm 100 is provided to nullify the effects of the pressure in the chamber 103 on the diaphragm. The control system also includes a second conduit 104, connected at its upstream end to pipe line 57, which contains a pair of restrictors 105, 106. The control pressure acting on the diaphragm 100 is taken by pipes 56a, 98 from the conduit 56 between the restrictors 54, 58. A trimming control 109, which modifies the pressure in the pipe 98, comprises a half-ball valve 111 mounted on a pivoted arm 112. The arm 112 is loaded in the sense of closing the valve by a spring 113 and the load on a diaphragm 114 due to the pressure in a chamber 117 connected to the conduit 104 between the restrictors 105, 106. The diaphragm 114 is also loaded in the sense of opening the valve by the pressure in the chamber 115 which is connected by a pipe 116 to the jet pipe 5. A light spring 119 loads the diaphragm 114 to maintain contact between the rod 120 and the lever 112. Assuming that the trimming control 109 is inoperative, the pressure in the conduit 56 between the restrictors 54, 58 will be proportional to the compressor delivery pressure and the degree of opening of the needle valve 54 which corresponds to the setting of the propelling nozzle 6. Since, at constant rotational speed, the compressor delivery pressure is proportioned to atmospheric pressure, the rate of fuel flow to the reheat burners will be reduced as the altitude increases. The trimming control 109 varies the control pressure in chamber 99 so that the static pressure in the jet pipe, which depends upon the intensity of reheat combustion, is always equal to the pressure in the conduit 104 between the restrictors 105, 106 and is thus always a given proportion of the compressor delivery pressure. Opening of the nozzle 6 will cause an increase of fuel flow to the injectors 13 due to an increase in pressure in conduit 56 due to opening of the valve 54. The static pressure in the jet pipe 5 will also fall and cause a further increase in the pressure in conduit 56. When the additional fuel is ignited the pressure in the jet pipe 5 will rise and return the trimming control 109 to the equilibrium position. The throttle 70 may be replaced by a throttle valve in the fuel delivery line or by a control for varying the delivery of a variable delivery pump. The trimming control 109 may be replaced by a control responsive to the temperature of the engine working fluid upstream of the reheat combustion chamber 12. The restrictors 54, 58 and 105, 106 may be arranged as described in Specification 748,353, [Group XXIX]. The pipe 104 may discharge to atmosphere or into the jet pipe in which case the pressure between the restrictors 105, 106 will be a function of both of compressor delivery pressure of jet pipe static pressure. The chamber 115 may be subjected to jet pipe total head pressure if desired. Specifications 641,910 and 782,654 also are referred to.