GB639260A - Improvements relating to fuel systems for gas-turbine engines - Google Patents

Abstract

639,260. Fluid-pressure servomotor-control systems. ROLLS-ROYCE, Ltd. May 12, 1947, No. 12820. [Class 135] [Also in Group XXVI] In a fuel system for a gas-turbine engine in which a constant volume engine-driven pump 16 passes liquid through restricting means 18. variable by a speed-selecting device 20 and in which means, e.g. a piston 13, responsive to the pressure drop across the restriction 18, is operative to vary the fuel delivery to the engine, means, e.g. a capsule 37, responsive to changes in atmospheric or ambient pressure is arranged in association with the restriction 18 to vary the pressure drop across the latter, and hence to vary the fuel supply, in accordance with altitude. As shown, movement of piston 13 varies the swash-plate of a multi-plunger pump 10 supplying fuel to injection devices 12, and the capsule 37 varies a restriction 39 in parallel with the restriction 18. To prevent overfuelling by pump 10, a diaphragm valve 25 is inserted in the line between pump 16 and the inlet side of restriction 18, and the valve is loaded by a spring and, through passage 28, by the pressure on the downstream side of the restriction. This ensures that the valve will not open until a selected minimum pressure drop occurs across the restriction and, as this pressure drop is applied across piston 13, it will prevent the latter from moving too far to the left, i.e. in the increase fuel direction. Similarly, a diaphragm valve 29 byepassing restriction 18, and acting like a pressure-relief valve, prevents underfuelling. Valves 25, 29 are further loaded by an evacuated capsule 34 so that the maximum and minimum limits of fuel delivery are varied in accordance with changes in altitude. The effect of capsule 37 can be modified to give different results at varying engine speeds by providing a further restriction in series with restriction 39, and varying the former restriction by means of a piston subject to the differential pressure across a fixed throttle inserted in the fuel line between pump 10 and the injection devices 12. In a modification of this last system, the fixed throttle is inserted in the delivery line of pump 16 and the piston moves along a floating lever to which the capsule and its associated plunger are separately attached. Specifications 639,261 and 639,262 are referred to.