Patent GB-748353-A (GB)
Title: Improvements in or relating to fuel systems for gas-turbine engines
Inventor: DAVIES DAVID OMRI
IPC: F02C7/22
Filed: 1953-05-05
Abstract: 748,353. Supplying fuel to burners. ROLLSROYCE, Ltd. April 27, 1954 [May 5, 1953], No. 12529/53. Addition to 694,322. Class 75(1). [Also in Groups XXVI and XXIX] A fuel system as claimed in the parent Specification in which the fuel supply to the reheat combustion chamber is controlled so as to maintain the ratio of the absolute pressures on the upstream and downstream sides of the turbine at a constant preselected value, the pressuresensitive device comprises fluid flow means connected to a point in the engine between the compressor and turbine inlet to produce therein an auxiliary pressure source such that the ratio of the auxiliary pressure to the pressure at the point is equal to the desired ratio, a flexible diaphragm loaded on one side by the auxiliary pressure and on the other by the pressure between the turbine and the propelling nozzle and means connecting the diaphragm with the air throttle of a turbine driving the reheat fuel pump so as to maintain the pressure between the turbine and propelling nozzle equal to the auxiliary pressure. The air throttle is controlled by the rod 30 of the servomotor 27. The position of the piston 29 is controlled by the opening of a bleed valve 24. The valve 24 is mounted on a lever 18 pivoted at 32 in the wall 11 separating the chambers 12, 13. The chamber 12 is divided into two spaces by a flexible diaphragm 16. One of these spaces is connected to the engine between the turbine and propelling nozzle by a conduit 15 and the other space is connected by a conduit 14 to a conduit 21 between two restrictors 22, 23. The conduit 21 is connected at its left hand end to a point between the compressor and turbine inlet and the restrictors 22, 23 are selected so that the downstream restrictor 23 is choked in operation and the ratio of the pressure between the restrictors 22, 23 to the pressure at the inlet to the conduit 21 is equal to the pressure ratio desired across the turbine. Variations of the actual pressure ratio from the desired value will cause the diaphragm 16 to open and close the bleed valve 24 and so vary the air flow to the air turbine driving the fuel pump. This will result in a variation of the fuel flow to the reheat chamber and so vary the pressure ratio across the turbine. Flexible diaphragms 19 having arcuate slots 20 are provided to restrain the actuating rod 17 against lateral movement. In a modification, the conduit 14 is connected to the throat of a venturi located. in the conduit 21. A variable area orifice and fixed area orifice are located in the conduit 21 upstream of the venturi. - The variable area orifice enables the desired ratio to be preset. In a further modification, the conduit 14 is connected to the receiving chamber having an inlet adapted to recover as static pressure, some of the kinetic energy of an air jet supplied with air from a point between the compressor and turbine inlet. An obturator may be placed to interrupt part of the jet so that the pressure in the chamber is in the desired ratio to the pressure at the points referred to. Instead of an obturator, the relative positions of the jet and inlet to the receiving chamber may be adjustable. This may be effected by having two discs spaced apart in a tubular housing, each of the discs having a hole at the same radius from the centre of the tube and by rotating one disc relative to the other. When the holes are aligned the pressure recovery is a maximum. The space between the jet and the inlet to the receiving chamber in the first case, and the, space between the discs in the second, is vented to atmosphere. The outlet end of the conduit 21 may be connected to atmosphere or any convenient point of low pressure such that the downstream restrictor is choked in operation.