Patent GB-1120808-A (GB)
Title: Improvements in and relating to ignition in jet engine afterburners
IPC: F02C7/26
Filed: 1966-04-29
Abstract: 1,120,808. Gas-turbine jet-propulsion plant. UNITED AIRCRAFT CORPORATION. April 29, 1966 [April 30, 1965], No. 18995/66. Heading F1J. [Also in Division G3] An apparatus for igniting a fuel mixture supplied by a spray injector to the reheat burner of a jet engine having a combustion chamber located upstream of a turbine section comprises a main injector device for injecting a predetermined amount of igniting fuel into the combustion chamber, an auxiliary injector device for controlling a flow of igniting fuel to the reheat burner between the combustion chamber and the spray injector, conduit means for actuating the auxiliary injector device, and an arming valve connected to the main injector device to provide for its actuation after the spray injector has started to supply fuel. When it is desired to use the reheat equipment of a jetpropulsion engine, a valve 306, Fig.2, is opened to direct fuel from a reheat fuel control 302 via a conduit 308 to a spray ring 20 in the jet pipe. An accompanying increase in the pressure communicated via conduits 314, 226 to a cylinder 170 of the auxiliary injector device 32 moves a piston 172 to the left to allow fuel at high-pressure to flow via conduits 316, 232, an annular groove 176 and conduit 258 to open an auxiliary injector valve 38 and thence flow via a conduit 272 into the jet pipe just aft of the turbine blading. The fuel pressure at the spray ring 20 is communicated via conduits 276, 246 to the underside of a diaphragm 60, the upper side of which is exposed via conduits 242, 274 to the pressure in the jet pipe immediately downstream of the spray ring 20. The resultant upward movement of the diaphragm 60 causes a valve 46 to move downward, thereby opening a port 42 and closing a port 44. The increased pressure in conduit 226 is then communicated via port 42 and conduit 260 to chamber 84 of the arming valve 28 to move a piston 82 to the right to allow fuel at high-pressure to pass via conduits 316, 232, annular groove 100, conduit 250 and a variable or exchangeable restriction to move a piston 142 of the main injector device 30 to the right whereby the piston 142 forces fuel from cylinder 140 via conduit 254, annular groove 103 and conduit 256 to open a main injector valve 36 and thence flow via conduit 270 to one of the combustion chambers of the engine. This injection of a shot of additional fuel into one of the combustion chambers produces a flame which reaches through the turbine blading to ignite the fuel being injected through the conduit 272. This extends the flame further downstream to ignite the fuel being injected through the spray ring 20. When the piston 142 reaches the end of its stroke, fuel from the space to the left of the piston passes via longitudinal passages 160, annular passage 162 and further longitudinal passages 164 to openings 166 which now align with an annular groove 158 and thence passes via a conduit 262 and a variable or exchangeable restriction to move a piston 189 downwards to close an opening 192 and align an opening 197 with an opening 196. This disconnects a conduit 264 from a low-pressure source (conduits 312, 220 leading from an intermediate stage of a fuel pump 300) and connects it instead to the conduit 262, whereby high-pressure fuel enters the lefthand end of the cylinder 170 to return the piston 172 to the position shown to shut-off the fuel supply to the conduit 272. The high-pressure fuel leaks around the piston to an annular groove 184 and thence to conduit 220, the leakage flow providing cooling. When the valve 306 is closed to cut-off the fuel supply to the spray ring 20, the fuel pressure in conduits 314, 226 reduces to its normal value, and the resultant drop in pressure in chamber 84 allows spring 90 to return the piston 82 to the position shown. Conduit 250 now communicates via an annular groove 102 with a drain line 238, allowing spring 146 to return the piston 142 to the position shown. Since conduit 254 now communicates via the annular groove 103 with the conduit 220, the cylinder 140 becomes recharged with fuel ready for the next use of the reheat equipment. The pressure in the spray ring 20 and therefore in the conduits 276, 246 is now equal to that in the jet pipe as sensed through conduits 242, 274; this equalizes the pressure on the opposite sides of the diaphragm, and the valve 46 consequently returns to the position shown.