GB1377951A - Fuel control systems for gas turbine engines - Google Patents

Abstract

1377951 Gas turbine engine fuel systems JOSEPH LUCAS (INDUSTRIES) Ltd 19 Nov 1971 [19 Nov 1970] 55006/70 Heading F1G [Also in Division G3] A gas turbine engine fuel system comprises acceleration control means sensitive to a number of engine operating conditions for controlling the rate of flow of fuel to the engine during acceleration, means sensitive to an engine condition in which air passing through the engine compressor is heated by air stored in the compressor during previous running of the engine and arranged to produce an electrical output during such condition and means actuable by the output for reducing the maximum fuel flow to the engine permitted by the acceleration control means. This prevents stalling when, after a period of steady running with the throttle fully open, the throttle is closed quickly and then fully reopened quickly after a short time.(hot re-slam). The fuel flow is metered by an orifice defined by an aperture 11 in a sleeve 12 which slides within a fixed collar 13, the orifice area being dependent on the axial positions of both the sleeve and a slidable collar 14 which surrounds it. The collar 14 is movable in one direction by a lever 18 which is variably spring- loaded according to the position of a throttle linkage 31, and is urged in the opposite direction (towards the fixed collar 13) by governor weights 19, the movement being limited by adjustable stops 20, 21. The sleeve 12 is movable by a number of bellows 15 each having an evacuated left-hand portion and a right-hand portion which is subjected internally to a pressure P 2 tapped from the low-pressure side of the compressor, the bellows being subjected externally to a pressure P3p derived by an air potentiometer 16, 17 subjected at one end to the compressor delivery pressure P3 and at the other end to the pressure P 2 . The temperature T 2t immediately downstream of the compressor and T 1 immediately upstream are sensed, e.g. by thermocouples and applied as a positive and negative signal respectively to a summing amplifier 24 which produces an output proportional to the algebraic sum of its four input signals. The remaining input signals, both negative, are a signal equal to the product of a constant α and the square of the engine speed (N<SP>2</SP>) and a feedback signal from a solenoid valve 25 controlled by the amplifier. In hot re-slam conditions, the valve 25 is opened to a controlled extent to reduce the pressure applied to the exterior of the bellows 15 and thereby reduce the acceleration fuel margin. Instead of controlling a valve 25, the amplifier may control a servomotor for adjusting the stop 20. The temperature measured at the downstream end of the compressor may be the temperature of the material of the compressor rather than an air temperature. In another arrangement, the temperature of the compressor material and the temperature of the air leaving the compressor may be compared by the amplifier 24, which opens the valve 25 or moves the stop 20 when the difference between the two temperatures indicates that hot re-slam conditions exist. In a further arrangement, two temperature probes are used in the air-stream delivered by the compressor, one probe giving a rapid response while the other is lagged or located in a chamber through which there is a slow flow of air tapped in the delivery air-stream or is associated with an electronic or electro-mechanical delay arrangement, whereby a delayed response is provided. A change of temperature therefore produces a difference between the two signals, this difference effecting the control as previously.