GB1112481A - Fuel supply systems for jet propulsion engines - Google Patents

Abstract

1,112,481. Gas turbine jet engine reheat fuel systems; rotary meters; centrifugal pumps. DOWTY FUEL SYSTEMS Ltd. Oct.12, 1965 [Oct. 20, 1964], No. 42762/64. Headings F1C, F1F and F1J. [Also in Division G3] The invention relates to fuel supply systems for jet propulsion engines and provides means for regulating the supply of fuel to each of a number of sets of burners in a reheat system of a gas turbine engine. In the system shown the reheat system comprises three fuel manifolds 11, 12, 13 to which fuel is supplied by a centrifugal pump 14 having a control valve 26 at the inlet to the impeller. Fuel from the pump discharges through line 15 by way of a flow metering device 57 and a main valve 84 to three lines 16, 17, 18 to the manifolds 11, 12, 13, rotary positive displacement metering devices 21, 22, 23 being disposed in the lines 16, 17, 18 respectively. A tapping is taken from line 15 through non-return valve 35 to a servofluid line 34, the line 34 being also connected through a non- return valve 36 to the main fuel pump 37. The position of the inlet valve 26 of the pump 14 is controlled by a servopiston 29 integral therewith, the piston 29 having an orifice 32 therethrough, leakage of servofluid from the chamber at the right-hand side of the piston 29 being controlled by a half-ball valve 82 which in turn is controlled by the diaphragm 77 of a pump flow control device 76. The diaphragm 77 is controlled in dependence on fuel flow through the flow-metering device 57 by means of the pressure difference existing in the chambers 66, 67 of the metering device 57, which pressures are communicated through lines 75, 78 to the chambers at the sides of the diaphragm 77. With increased fuel flow the pressure difference increases and the diaphragm 77 moves to cause the half-ball valve 82 to open the vent 33 whereupon the piston 29 acts to close the valve 26 at the inlet to the pump impeller. The flow through the metering device 57 is controlled by the position of the spool 63 which is controlled by a servopiston 68 integral therewith, also by the lever 58 which is pivotally mounted at 59, the lever being acted upon at its left-hand side by opposed bellows 55, 56. The reheat control lever 41 acts through cam 38 on a plunger 42 which has a tapered portion 48 movable in an orifice 47. Air at compressor discharge pressure is supplied through line 46 and passes through the orifices 47 and 49 to the vent 50 also through the orifices 51 and 52 to the vent 50, the pressures intermediate the orifices 47, 49 and 51, 52 being passed through lines 44, 45 to the bellows 55, 56 respectively. Thus with increasing demand for reheat, the pressure in bellows 55 increases so that the lever 58 moves to allow the half-ball valve 74 to open the orifice 73 whereupon the servopiston 68 moves downwardly causing the spool 63 to increase the opening of the annular chamber 66. The movement of the plunger 42 to the right also acts to close first the switch 53, then the switch 54. Fuel from the metering valve 57 passes through the main valve 84 which is controlled by a servovalve unit 115 in response to fuel flow through the branch line 16 leading to the manifold 11, the fuel pressures upstream and downstream of the flow metering valve 85 in the line 16 being taken through lines 113, 114 to the unit 115. Compressor discharge pressure is also supplied to the bellows 117 of the unit 115. The main valve 84 comprises a spool 121 which is acted upon at its upper and lower ends by servopressure or vent pressure supplied through lines 119, 118 under control of the valve spool 116 of the unit 115. When the spool 121 moves downwardly it acts to restrict fuel flow to the manifolds 11, 12, 13 by closing off the port 122 and at the same time opens port 123 leading to vent pipe 40. The unit 115 compares the fuel flow in the line 16 with the air mass flow as signalled to the bellows 117 and adjusts the spool 121 accordingly. In each of the lines 16, 17, 18 leading to the manifolds 11, 12, 13 is a rotary positive displacement metering device 21, 22, 23 respectively, the devices being interconnected by means of a shaft 19 the displacements of the devices being determined so as to maintain a fixed proportionality of fluid displacement to the respective manifolds. Shut-off valves 92, 93 are disposed in the lines 17, 18 leading to the manifolds 12, 13 so that when the first position 41A of the reheat control lever is selected, fuel passes only through the line 16 and positive displacement device 21 to the manifold 11. A valve controlled duct is provided across the device 21. When the second position 41B of the control lever is selected, the plunger 42 acts to close the switch 53 which causes solenoid valve 98 to open and so servovalve 94 moves to open the shut-off valve 92 so that reheat fuel now passes also to manifold 12. Similarly movement of the lever to the third position 41C acts to close switch 54 causing solenoid valve 105 to open shut-off valve 93, whereupon fuel flows additionally to manifold 13. Valve controlled return ducts 88, 91 are provided across the positive displacement devices 22, 23.