Patent GB-843976-A (GB)
Title: Afterburner fuel control system
IPC: F02C9/16
Filed: 1958-01-08
Abstract: 843,976. Gas turbine jet propulsion engines. UNITED AIRCRAFT CORPORATION. Jan. 8, 1958 [Jan. 15, 1957], No. 821/58. Class 110 (3). A reheat fuel system for a gas turbine power plant comprises a shut-off valve in the fuel supply conduit which is held in the closed position by pressure responsive means, fluid-operated means controlling the effect of the pressureresponsive means on the valve and means for introducing a fluid under pressure to the fluid operated means when the required power plant output exceeds a predetermined level, the fluid operated means including a first pilot valve controlling the admission of fluid to a separate pilot valve which modifies the effect of the pressure responsive means on the shut-off valve. Fuel for the afterburner 24 is supplied by a pump 50, driven by the engine, to the fuel control 54. In the control, the fuel dasses through a metering valve 56 responsive to compressor discharge pressure and a shut-off valve 58, the pressure drop across the valve 56 being maintained constant by a valve 59. The fuel flows from the control through conduit 60 to an annular manifold 62. The shutoff valve 58 is urged to the closed position by a spring 68 and the pressure in the chamber 70. The chamber 70 is connected on the one hand to the supply conduit 52 through a passage 72 and restriction 74 and on the other by a passage 76 to a pilot valve 80. When the pilot valve 80 is raised the passage 76 is connected to the drain 150. The resulting pressure drop in the chamber 70 allows the pressure of the metered fuel to open the valve 58. The pilot valve 80 may be raised by operating manually and motor actuated means as described below. The throttle or power lever 86 controls the fuel supply to the main combustion equipment 18 through a control 44 and also a valve 88. When the power lever has been advanced beyond a certain point, fuel under pressure is passed from the control 44 to the shut-off valve controlling portion of the after burner fuel control 54. This fuel passes through orifice 92 and passage 94 to chamber 96 between lands 98, 100 on an electric motor actuated pilot valve 102 (shown in the " OFF " position). Fuel is also admitted to passages 104, 106 extending between passage 94 and pilot valve 108. The downstream end of passage 104 is blocked by land 110 on the pilot valve 108 while the fluid in passage 106 is admitted to chamber 112 defined between lands 110, 114 on the pilot valve. The pilot valve 108 normally is maintained in the position shown by a spring 118. The fluid in chamber 96 of the pilot valve 102 passes through passage 120 and restriction 122 to chamber 124. This moves the pilot valve 108 upwards against the action of the spring 118. In this position of the pilot valve fluid in passage 104 is admitted to chamber 124 thus short-circuiting chamber 96 of the pilot valve 102. Upward movement of land 114 permits fluid to pass from chamber 112 through passage 128 to chamber 130. The switch 136 is now closed and the motor 139 raises the pilot valve 102. The movement of the land 134 connects the passage 140 to the chamber 130 so that pressure fluid is supplied to the chamber 142 and the pilot valve 80 raised. It is necessary to first move the lever 86 beyond a certain point and then to close the switch 136 before the shut-off valve 58 can be opened. The arrangement is such that if either of these operations is omitted or the lever 86 and switch 136 operated in the wrong sequence, fuel cannot be supplied to the afterburner.