Patent GB-1161283-A (GB)
Title: Gas Turbine Engine Fuel System
Inventor: JOHNSON CHRISTOPHER LINLEY
IPC: F02K3/068
Filed: 1968-05-03
Abstract: 1,161,283. Gas turbine fuel systems. ROLLS-ROYCE Ltd. May 3, 1968, No. 21141/68. Heading F1G. [Also in Division G3] A gas turbine engine fuel system comprises a digital computer which is supplied with digital signals representing at least the engine speed and produces a resultant signal representing the required fuel flow, and the computer is supplied with a further digital signal representing the actual fuel flow and compares this signal with that representing the required fuel flow to produce a difference signal which is used to control the fuel flow. A digital computer 26 for controlling the fuel supply to a number of vertical-lift gas turbine engines 1 is supplied, for each engine, with a digital signal representing the engine speed by means of a transducer 27 which senses the frequency of the passage past it of the blades of the engine compressor 4 or the teeth of a toothed wheel whose speed is related to the engine speed. More than one transducer 27 may be used, the speed signal being derived from the transducer which at any moment records the highest value. A digital signal representing a compressor pressure such as the compressor delivery pressure, or a ratio of compressor pressures such as the ratio of inlet to delivery pressure is also supplied to the computer 26. As shown, this signal may represent the compressor inlet pressure sensed by a transducer 22. Since the inlet pressure is substantially equal to the atmospheric pressure and, as such, the same for all engines, only one measurement of it is required for all engines, although for safety more than one transducer 22 would be used but the number of transducers can be less than the number of engines. Changes of fuel density caused by changes of temperature are allowed for by providing the computer with a digital signal representing the temperature in the fuel tank 12, sensed at 31. Additionally, the computer may be supplied with a manually set digital signal representing the density, at a given temperature, of the particular fuel used. Alternatively, the computer may be supplied with a digital signal representing the density of the fuel leaving the tank 12, as sensed by a transducer 35. The computer may also be supplied with digital signals representing atmospheric temperature at, say, the air inlet 3. Where the measurements are in analogue form, analogueto-digital converters, as at 24, 33, 37, are provided. The measurement of atmospheric temperature, fuel temperature and fuel density may be common to all the engines but for safety several measurements, which may be less in number than the number of engines, would be made. A signal representing the desired engine speed is obtained from a manual control 45. A digital signal representing the actual fuel flow is derived from a flowmeter 47 and is compared in the computer with a signal computed from the other signals and representing the desired fuel flow to provide a difference signal in the form of electrical pulses which operate an electric stepping motor 20 which adjusts a throttle valve 14 controlling the fuel supply to the engine. The computer also controls the fuel supply to the other vertical lift engines. If supplied by a sensing device 52 with a digital signal representing the aircraft attitude and by means not shown with a digital signal representing the desired attitude, the computer can increase or reduce the fuel supply to the appropriate engines to maintain the desired attitude. The computer may also be fed with digital signals representing aircraft vertical acceleration and velocity so as to aid in the stabilization of the aircraft. When necessary, the computer supplies a signal to an actuator 21 to shut an emergency shut-off cock 15.