Patent GB-1426281-A (GB)
Title: Devices for the metered supply of liquid fuel to combustion engines especially to aircraft gas-turbine engines
IPC: F02C9/26
Filed: 1973-02-15
Abstract: 1426281 Gas turbine engine fuel systems PLESSEY CO Ltd 23 Jan 1974 [15 Feb 1973] 7469/73 Heading F1G In a fuel system for combustion engines, of the kind in which liquid fuel is supplied to an engine through one or more injection nozzles in a rapid sequence of short, uniformly time-spaced pulses and the rate of fuel supply is controlled by varying the mark/space ratio of the pulses, there is provided a flow-control device which is responsive to a pressure difference substantially equal to the pressure drop in the ignition nozzles or the sum of that pressure drop and the pressure drop in an adjustable throttle valve connected in series with the nozzles, the flow-device being operative, in response to variations of the pressure difference, to neutralize the effect upon the pressure difference of variations of the rate, or of the pressure, of the fuel supply. A centrifugal pump 2 supplies fuel to injection nozzles 5 of a gas turbine engine via a line 3 containing a pressure-regulating valve 13 and a throttle-and-shut-off valve 6. The valve 13 is actuated by a diaphragm 16 subjected on one side to the pressure upstream of the throttle valve 6 and on the other side, via a restrictor 18 to the engine compressor delivery pressure P3, which is the pressure downstream of the injection nozzles 5, the valve 13 therefore acting to maintain the total pressure drop across the throttle valve 6 and the injection nozzles at a constant value determined by the adjustable preloading of a spring 15. Correction for altitude is provided by an evacuated capsule 21 subjected to the ambient pressure P1 and acting on the valve 13 via levers 24, 27. The injection nozzles 5 are open only when energized via electric lines 28, the energization being in the form of a rapid succession of pulses supplied by a digital controller 10. The mark/ space ratio of the pulse output of the controller, and therefore the fuel flow through the nozzles 5, is determined by inputs from a pilot's speed-select lever 8, the speeds N G  and N F  of the gas-generator turbine and power output turbine and the gas temperature TET at the entrance to the turbines. A pilots engine-condition lever connected to a link 9a acts via a spring box 11 and a lever 9 to adjust the settings of both the controller 10 and the throttle valve 6. An emergency governor valve 29 driven by the gas-generator-turbine opens in the event of that turbine overspeeding to vent the chamber 17 to atmosphere and thereby reduce the opening of valve 13. Similarly, the chamber 17 can be vented via a connection 30 by means of an overspeed trip associated with the power output turbine. In the event of failure of the controller 10, the mark/space ratio of the energization of the nozzles 5 automatically reverts to the maximum value, and control can then be effected manually by operating the throttle valve 6, by means of the pilot's engine-condition lever. In an emergency the fuel supply can be shut off by means of a pilot's manual reversion lever, acting through a link 12. The centrifugal pump 2 may be replaced by a gear-pump, in which case the valve 13 is replaced by a by-pass valve which returns fuel to the pump inlet. The emergency governor 29 similarly acts to return fuel to the pump inlet.