GB684244A - Improvements in or relating to gas-turbine engine fuel systems - Google Patents

Abstract

684,244. Supplying fuel to burners. ROLLS-ROYCE, Ltd,. Oct. 16. 1950 [Nov. 14, 1949], No. 29142/49. Class 75(i) [Also in Groups XXVI and XXIX] A gas turbine reheat fuel system comprising a plurality of main burners and a pilot burner to which fuel is supplied continuously while fuel is supplied to the main burners has the fuel supply to the pilot burner controlled so as to maintain the fuel-air ratio at the pilot burner substantially constant. The turbine exhaust gases are reheated in the jet pipe 14 by means of a main fuel injector 17 comprising a plurality of nozzles 17a which are ignited by a pilot injector 16 having a pair of nozzles 16a. Fuel is supplied to the injectors 16, 17 by means of two pumps 20, 21. The discharge of the pump 21 contains a shut-off cock 24 downstream of which the flow is divided into two branches 25, 26. The branch 25 leads to the injector 16 and the branch 26 through a main burner fuel cock 27 and throttle valve 29 to the injector 17. The shut-off cocks 24, 27 are electrically controlled solenoid valves. Each comprises a disc 30 carried by a flexible diaphragm 31 separating the inlet chamber 32 of the valve from a chamber 33 which is connected with the chamber 32 by a restriction 34 and with the outlet of the valve by a passage controlled by a valve 38 and a duct 35. The disc 30 is spring loaded on to a seat 30a. When the solenoid 39 is energized, the valve 38 is lifted off its seat, fluid flows from the chamber 33 and the valve opened by the action of the pump discharge pressure. The fuel pump 21 is driven by means of an air turbine 40 supplied with air from the engine compressor 11. The air supply is controlled by a throttle valve 43 operated by a piston 44 and biased to the open position by a spring 45. A conduit 46 from the main engine fuel pump supplies pressure fluid directly to the cylinder 44a of the piston 44 and through a restriction 47 to the cylinder on. the other side of the piston. A solenoid operated valve 48 controls the flow through the restriction 47. When the solenoid is de-energized the valve 48 closes the restriction so that the pressure fluid cannot reach the spring-loaded side of piston 44 and the latter moves to the right and closes the throttle 45. When the solenoid is energized pressure fluid can reach the spring-loaded side of piston 44 which can then control the throttle 43 according to the pressure on this side of the piston which is determined bv, the amount of fluids passing through the pipe 51 and bleed valve 52. The valve 52 is mounted on one end of a lever 53 carried by a flexible diaphragm 53a. A flexible diaphragm 55 forming a chamber 56 connected to the compressor discharge and an evacuated capsule 57 are connected to the other end of the lever. A further flexible diaphragm 59 responsive to the pressure drop across the valve 60 in the fuel supply line to the pilot injector also acts on the lever. The valve 60 is so arranged that the pressure drop across it is proportional to the flow and is known as a linear flow valve. The arrangement is such that an increase of the compressor discharge presures alone results in an increase in the output of the pump 21 and an increase of the pressure drop across the valve 60 alone results in a decrease in the output of the pump and the lever 53 is balanced when the pressure drop is in fixed proportion to the compressor discharge pressure. A branch conduit 70 from the supply conduit 28 downstream of the shut-off cock 27 leads to the fuel supply conduit 25 of the pilot fuel injector 16 through a second linear flow valve 71 so that when the shut-off cock 27 is opened a second supply of fuel is led to the pilot fuel injector 16. This additional flow will also be proportional to the compressor discharge pressure as the pressure drop across the valve 71 is the same as that across the valve 60. A pressure operated electric switch 72 operated by a diaphragm 73 subjected to the pressure between the pumps 20, 21 operates the solenoids 39, 49 so that on failure of the fuel supply, the system is put out of operation. A restrictor 74 is provided to facilitate adjustment of the pressure-flow characteristics of the pilot burner 16. If desired the pumps 20, 21 may be driven by separate air turbines. Specification 667,394 is referred to.