Patent GB-753474-A (GB)
Title: Improvements in or relating to fuel systems for gas turbine engines
Inventor: DAVIES DAVID OMRI
IPC: F02C9/16
Filed: 1953-04-24
Abstract: 753,474. Gas turbine plant. ROLLSROYCE, Ltd. July 22, 1954 [April 24, 1953], No 11458/53. Class 110(3) [Also in Group XXIX] A fuel system for a gas turbine engine comprises an engine-driven centrifugal pump delivering fuel through a throttle valve to the combustion equipment of the engine, the valve being arranged so that the combined flow number of the valve and the restrictions downstream thereof including the fuel injectors, i.e.F/#PD, where F is the flow and PD the pressure difference across, the combined valve and downstream restrictions, is linear with respect to valve movement, and means to control the position of the valve in dependence on the instantaneous delivery pressure of the compressor of the engine comprising means responsive to a load dependent on that pressure and to an opposing load dependent on the position of the valve. In one embodiment, the centrifugal pump 21 delivers through a conduit 22 and throttle valve 24 to the injectors 23. The valve is actuated by a spring-loaded servopiston 25 subject on its lower face to pressure in the conduit 22 and on its upper face to a control pressure which -is governed by a vent valve 32 coacting with an opening from a conduit 29 having a restriction 30 and connected to the conduit 22 and to a chamber 28 above the servopiston. The valve 32 is mounted on a lever 42 pivoted at 41 and acted on by an evacuated bellows 43 in a chamber 38, a spring 46, and a plunger 48 having a spring connection 34 with the servo-piston. The chamber 38 has a connection 53 with the throat of a convergent orfice 52 in a duct 50 by which air at compressor delivery pressure is bled off to atmosphere or to the compressor intake, the duct also having a restriction 51 upstream of the orifice 52. The arrangement is such that up to, say, three-quarters of the maximum engine rotational speed at sea level, the pressure ratio across the orifice 52 is such that the latter is not choked and the bellows 43 is subject to substantially atmospheric pressure so that the throttle valve opening will be constant at a constant altitude. When the compressor pressure ratio is such as to choke the orifice 52 the pressure to which the bellows 43 is subject is proportional to the compressor discharge pressure, thereby increasing the opening of the valve 32 which causes an increased opening of the throttle valve 24. Fuel flow at low engine speeds may be increased by a by-pass valve in parallel with the throttle valve and loaded to open by a spring in opposition to a load proportional to engine speed, e.g. centrifugal pump pressure. The above system limits fuel flow during acceleration and therefore provides a flow which is in excess of that required for steady running, for which a trimming control is required. This may be responsive to speed or to jet pipe temperature. A speed-responsive control may consist of a centrifugal governor controlling the load on a relief valve downstream of the throttle valve and so arranged that an increase of speed permits an increased amount of fuel to be bled off. Alternatively, the trimming control, which may comprise a centrifugal pump or a mechanical governor, may control an additional vent valve from the chamber 28 or the restriction 30 or another restriction in parallel with it may be adjustable. As shown, the trimming control is effective on the pressure applied to the bellows 43 and con, sists of a vent 63 controlled by a centrifugal valve member 68 mounted on a leaf spring 69 carried by a rotor 60. Alternatively, where a variable datum speed control is required, the restriction 51 may be adjustable by speed-responsive means. Modifications of Fig. 1 consist of a convergent-divergent nozzle in place of the orifice 52, an arrangement in which the connection 53 is between the restriction 51 and orifice 52, and an alternative form in which the duct 50 connects with the chamber 38 instead of atmosphere or the compressor intake, and the vent 63 is taken from a point downstream of a single restriction in the duct.