GB785305A - Improvements relating to fuel systems of gas turbine engines - Google Patents

Abstract

785,305. Gas-turbine plant. ROLLS-ROYCE, Ltd. July 27, 1955 [July 27, 1954], No. 21984/54. Class 110 (3). [Also in Group XXIX] In the fuel system of a gas-turbine engine including a speed governor comprising a fixedcapacity engine-driven pump 18, Fig. 1, passing liquid through an orifice 20, the area of which is adjustable in accordance with the temperature of the air entering the engine compressor, the pressure difference across the orifice 20 is applied to a diaphragm 24 that controls the delivery of fuel to the engine so that a given value of N/#T is not exceeded, where N is the engine speed and T the compressor inlet temperature. The stroke of an engine-driven swashplate fuel pump 53 is controlled by a piston 60, one side 64a of which is directly acted upon by the pump delivery pressure whilst the other side 64b is subjected to the pressure of a spring 61a and is in communication with the pump delivery duct 59 via a restriction 66; fuel is bled from side 64b by way of a pipe 10 and a half-ball valve 11. The pump rotor 56 embodies a bore 67 connected with the fuel tank by a duct 15 and a booster pump 51, which bore 67 opens into radial passages 68 so that a pressure proportional to engine speed is generated in the pump casing, this pressure being conveyed to one side of a diaphragm 13 having its other side in communication with the pump inlet through duct 15; the diaphragm is adjustably loaded by a spring 16, attached to a differential piston 17, and formed with a rod 75 by which the valve 11 is actuated. The gear pump 18 which draws fuel from the duct 15 has the orifice 20 connected across it the degree of opening of the orifice being determined by a temperature bulb 21 in the compressor inlet 20a and a Bourdon tube 21a carrying a needle valve 21b. The diaphragm 24 subjected to the pressure across the orifice supports a spring-loaded half-ball valve 25 controlling the flow from a duct 26 containing a restriction 27 and opening into the duct 59; a connection 28 from the duct 26 incorporates a restriction 30 and opens into a space 29 on the larger face of the piston 17 whilst a further connection 31 upstream of the restriction 27 leads to a space 31a on the smaller face of the piston 17. When the valve 25 gradually closes the piston 17 moves to the left to decrease the load on the diaphragm 13; when the valve 25 is open the load of spring 16 and hence the diaphragm is increased. In a modification, the outlet from pipe 10, Fig. 2, is controlled by a half-ball valve 92 on a spring-loaded lever 89a in a casing 90 comprising two chambers 93 and 97, the chamber 93 incorporating a drain connection 95 to the fuel tank 50 and a piston 96 which tends to open the valve 92. Chamber 97 is open to atmosphere and contains a capsule 98 that acts on the lever 89 in a direction to open the valve 92 with a decrease in atmospheric pressure. The diaphragm 81 which is subjected to the pressure across the orifice 20 supports a normally open half-ball valve 84 controlling the flow of fuel from a duct 88, containing a restriction 89 connected to the delivery 59 of the pump 53; the duct 88 downstream of the restriction 89 opens to the piston 96. When the valve 84 is opened the fuel from pump 53 traverses duct 88, pipe 83 and duct 15 but when the valve begins to close a pressure is built up on piston 96 which then opens valve 92 to reduce the delivery of the pump 53.