GB826125A - Improvements in or relating to gas-turbine engine fuel systems - Google Patents

Abstract

826,125. Jet propulsion gas turbine plant. ROLLS-ROYCE Ltd. March 27, 1956 [April 6, 1955], No. 10158/55. Class 110 (3). [Also in Group XXIX] This invention relates to a gas turbine jet propulsion engine with a variable area propelling nozzle and a reheat fuel control system having a reheat burner fuel supply conduit comprising a variable area flow restrictor, the area of which is varied as a function of and in the same sense as changes in the absolute compressor delivery pressure and a throttle valve in series with the restrictor which is loaded in the closing sense by a load which varies directly as the pressure drop across the restrictor and in the opening sense by a second load which varies in the same sense as the effective area of the propelling nozzle so that the pressure drop is controlled in accordance with the nozzle area. Fuel is supplied to the main burners 16 and a pilot burner 17 arranged in the jet pipe 13 from a tank 18 by means of a booster pump 19 and an air-turbine driven centrifugal pump 20. The fuel supply to the main burners is controlled by an orifice 25 the area of which is varied by a tapered plug valve 26 and a throttle valve 32. The valve 26 has a portion 26b formed as a piston which works in a cylinder 27. The position of the piston in the cylinder and therefor the valve 26 is determined by a leak-off valve 44 which controls the flow through the cylinder space 27a. The valve 44 is carried by a pivoted lever 45 loaded by the bellows 48, 49 and a spring 46. The bellows 48 are evacuated and the bellows 49 contain air at a pressure dependent upon the delivery pressure of the compressor. This pressure is taken from a conduit 51 connected to the compressor discharge between two fixed area orifices 52, 53. A third variable area orifice 55 controlled by a needle valve 55a is provided so as to vary the relationship between the pressure in the capsule 49 and the compressor delivery pressure. The arrangement is such that the area of the orifice 25 is determined by the absolute compressor delivery pressure. The valve 55a is actuated by an electric motor 59 controlled by temperature or pressure responsive means in the jet pipe upstream of the reheat combustion equipment and is provided to keep this temperature or pressure at a selected value. The orifice 25 leads to a fuel chamber 29 which is connected to main burner fuel line 30 through the throttle valve 32. The valve 32 is loaded in the closing sense by a capsule 33 connected to the fuel conduit 21 upstream of the valve 25 and in the opening sense by the pressure in the chamber 29 and the loading of a spring 36. The loading of the spring 36 is varied by a cam 38 connected to the propelling nozzle area adjusting elements 15 so that the loading is increased as the nozzle area is increased. This arrangement ensures that the pressure drop across the orifice is directly proportional to the square of the increase of the effective area of the propulsion nozzle 14. A solenoid-operated valve 71 is provided to shut down the reheat system. When the valve 71 is open the valve 25 is closed. The pilot burner 17 is connected to the chamber 29 so that the fuel is supplied to the burner on energization of the valve 71. A valve 62 is provided to shut off the reheat system when the pump 20 is inoperative. This valve has a bleed hole 62a through which fuel may flow via conduits 35, 41, space 27a, pipe 43 and chambers 50, 40 for cooling purposes. A pressure-operated switch 64 is provided to permit operation of the variable area propulsion nozzle only when the pressure in pipeline 21 rises to a preselected value. In a modification the throttle valve 32 forms part of a piston loaded on one side in the sense of opening by the pressure in chamber 29 and on the other side by a spring and a servopressure. The servo-pressure is obtained from the conduit 21 by means of a branch conduit from the conduit 35 which contains a needle valve and leads to the servo-space. The outlet from the servo-space passes through a restrictor to drain. The needle valve is controlled by a diaphragm responsive to the pressure drop across the orifice 25 and to the loading of the spring 36 so that opening of the propulsion nozzle 14 closes the needle valve which decreases the servo pressure and thus causes the valve 32 to open. The tapered plug valve 26 may be replaced by a valve in which a number of ports are uncovered by a cylindrical valve member. In another modification the vent valve 44 is carried by a body supported by three circular flexible metal diaphragms mounted in a casing so as to divide it into four chambers. The outermost chambers are connected in the fuel tank through drain pipes. The chamber above the lowermost diaphragm is evacuated and the chamber below the uppermost diaphragm is connected to the conduit 54. In a further modification, the electric motor 59 is replaced by an arrangement comprising an orifice in the conduit 51 which is arranged upstream of a variable area orifice formed by a half-ball valve. The branch 54 is taken from between the orifices. The half-ball valve is carried by a body supported by three circular flexible metal diaphragms mounted in a casing to divide it into four chambers. One end chamber which contains the half-ball valve is subjected to the jet pipe pressure and the other end chamber is subjected to the pressure between a pair of fixed-area orifices in a conduit branched off from the conduit 51. The two central chambers are separated by a smaller-area diaphragm and are interconnected through an orifice. These chambers are filled with a liquid to damp the movements of the diaphragm assembly. The arrangement is such that the conduit 54 receives a pressure equal to the compressor delivery pressure when the half-ball valve is completely closed and which is less than this pressure when the valve is open by an amount which is a fraction of the difference between the compressor delivery pressure and the jet pipe static pressure, the fraction being determined by the position of the half-ball valve and thus by whether the jet pipe static pressure is greater or less than the pressure between the restrictors in the conduit branched off from conduit 51.