Patent GB-776672-A (GB)
Title: Improvements in or relating to gas-turbine engine fuel systems
Inventor: BASFORD KENNETH ARNOLD
IPC: F02C7/22
Filed: 1954-06-28
Abstract: 776,672. Gas turbine plant; centrifugal pumps. ROLLS-ROYCE, Ltd. May 24, 1955 [June 28, 1954], No. 18940/54. Addition to 684,244. Classes 110 (1) and 110 (3). [Also in Groups XI and XXIX] A reheat fuel system as claimed in the parent Specification which comprises a plurality of main burners and a pilot burner to which fuel is supplied continuously while fuel is supplied to the main burners and in which means are provided to supply fuel to the pilot burner so as to maintain substantially constant the fuel to air ratio at the pilot burner by means adapted to maintain the fuel flow to the pilot burner for operational to the absolute compressor delivery pressure has means to provide a liquid pressure load which is proportional to the compressor delivery pressure, a fuel pump to supply fuel to the pilot burner through restrictor means and control means to maintain the pressure difference across the restrictor means as a function of the liquid pressure load. Fuel is supplied to the reheat combustion equipment in the jet pipe 15 by two sets of injectors, namely, primary injectors 23 and secondary injectors 24. Fuel from the tank 27 is supplied by a booster pump 28 and an air turbine driven centrifugal pump 30 to a delivery line 31 leading to a control unit 32 which is connected to the injectors 23, 24 by pipelines 25, 26. The air turbine 34 is supplied with air from the discharge of the gas turbine compressor 10 and the rate of air flow is controlled by the servomotor operated throttle valve 36. The valve 36 is connected to a piston 37 working in a cylinder 38. Fuel from the discharge of the main fuel pump 20 is supplied direct to one side 38a of the piston and through an orifice 41 to the other side 38b. The side 38b has a vent pipe 42 the discharge through which is controlled by a half-ball valve 43. The halfball valve 43 is carried by a pivoted lever 44 which is subject to opposing loads depending on the rate of fuel supplied to the primary ejectors 23 and to the compressor delivery pressure. The right-hand end of the lever is connected to a flexible diaphragm 48 which is responsive to the pressure drop across a linear flow valve consisting of an orifice 49 and co-operating spring-loaded valve element 50. The shape of the head 50 and rate of the spring 51 is such that the pressure drop across the orifice 49 is directly proportional to the fuel flow through the orifice. The diaphragm 48 is connected to the lever 44 so that the load on the diaphragm tends to lift the half-ball valve 43 off its seat. The other end of the lever 44 is loaded by a spring 58 and is connected to a diaphragm 55 which is responsive to the pressure drop across a fixed area restriction 64 which is made directly proportional to the absolute compressor delivery pressure in the following manner. Fuel from the delivery of the main fuel pump 20 is passed through an inlet controlled by a half-ball valve 62 into a chamber 60 and then passes through the fixed area restrictions 64, 65 to a chamber 66 which is connected to the fuel tank 27 by a pipe 67. The half-ball valve 62 is carried on an arm 69 projecting from a rod 70 secured at its ends to a pair of flexible diaphragms 71, 72. The chamber 73 having one wall formed by the diaphragm is connected to the compressor discharge through a conduit 74 and the chamber 75 having one wall formed by the diaphragm 72 is evacuated. The load on the diaphragms 71, 72 which are of equal area is therefore proportional to the absolute delivery pressure of the compressor 10. This load is balanced by the difference of pressures in the chambers 60, 66 due to the action of the half-ball valve 62. The pressure drop across the restrictors 64, 65 and thus the restrictor 64 is also proportional to the absolute compressor delivery pressure. An increase in this pressure causes the half-ball valve 43 to close and thus cause the throttle valve 36 to open and increase the fuel delivery of the pump 30. This increase in fuel delivery increases the pressure drop across the orifice 49 which causes the diaphragm 48 to re-open the valve 43 until a new position of balance is reached corresponding to the absolute compressor delivery pressure. The control unit 32 also includes a shut-off cock which is so arranged that when the reheat is inoperative there. is a flow of fuel through the unit 32 for cooling purposes. The shut-off cock comprises a flexible diaphragm 76 separating a pair of chambers 77, 78 and carrying the valve element 50 of the linear flow valve leading to the primary fuel injectors 23. The chamber 77 is connected to the chamber 79 upstream of the linear valve through a fixed area restrictor 80 and to an outflow duct 82 through a flow restrictor 83. The chamber 78 is connected to the chamber 79 through an orifice 81. When the valve 84 in the duct 82 is closed the pressures on each side of the diaphragm 76 are equal so that the diaphragm has no effect on the linear flow valve. When the valve 84 is opened fuel flows through the duct 82 and the pressure in the chamber 77 falls below that in chamber 78 and the valve head 50 is moved and closes the orifice 49. Since there is no flow to the primary ejectors 23 and the throttle 33 is closed the half-ball valve 43 will be opened fully, the air throttle 36 fully closed and the pump 30 stopped. Cooling fuel may however flow from the discharge of the main fuel pump 20 through the pipe 40, restrictor 41, chamber 38b, pipe 42 and vent valve 43 into the chamber 79 whence it is returned to the fuel tank 27 through restrictor 80, chamber 77, restrictor 83 pipe 82 and valve 84. Specification 667,394 is referred to.