Patent GB-721173-A (GB)
Title: Improvements in or relating to systems for controlling the rate of fuel feed to gas turbine engines
IPC: F02C9/16
Filed: 1952-05-26
Abstract: 721,173. Gas turbine plant. BENDIX AVIATION CORPORATION. May 26, 1952 [June 14, 1951], No. 13326/52. Class 110 (3). [Also in Group XXIX] In a gas turbine fuel control system the fuel is metered as a function of the product of the square root of the compressor pressure rise and a function of compressor inlet pressure modified by the compressor inlet temperature. The fuel supply system shown comprises three main portions, a metering head regulator section 21, a governor section 22 and a surge modulator section 23. Fuel from a pump 25 passes through a regulator valve 27 to a chamber 28 from which it passes through orifices 49, 50, a metering orifice 52 controlled by a governor valve 53 and a conduit 17 to the engine. The regulator valve 27 is preferably of the balanced type and is controlled by a pair of diaphragms 29, 30. The diaphragm 29 is subject to the pressures in the chamber 28 and the metered fuel pressure in the conduit 17. The diaphragm 30 is responsive to the pressure in the chambers 32, 33, which are connected through conduits 35, 37 to the pressures at the inlet and discharge of the compressor 10 respectively. The pressure in the chamber 33 is modified by a contoured needle valve 39 controlled by bellows 40 responsive to the pressure at the intake of the compressor. The pressure difference across the diaphragm 30 is also modified by a contoured needle valve 44 controlled by bellows 45 responsive to the temperature at the inlet of the compressor. The position of the valve 27 and hence the metering head between the chamber 28 and conduit 17 is thus determined by the pressure rise across the compressor and the temperature and pressure at the compressor intake. The fuel flow is controlled so as to be proportional to the product of the square root-of the compressor rise and the square root of the inlet pressure divided by the inlet temperature. The fuel flow across the metering valve 53 is controlled by an all-speed governor consisting of a governor 58 the spring 56 of which is variably loaded by a lever 57 connected to the pilots control lever. The maximnm amounts of opening and closing of the valve 53 are determined by adjustable stops 64, 64<SP>1</SP>. When the pilot desires to accelerate to the maximum governed speed from a low powered setting the valve 53 is opened to the position determined by the stop 64, but the rate of fuel feed at each point of transition is determined by the regulator valve 27 as a function of compressor pressure rise and the pressure and temperature at the compressor intake. To prevent surging of the compressor the fuel flow is also controlled in the mid-speed range by the surge modulator 23. The modulator 23 comprises a variable orifice 49 controlled by a contoured valve 70 which is positioned as a function of engine speed by centrifugal weights 71<SP>1</SP> loaded by spring 81, the loading of which is adjustable by a screw 82. A contoured valve 85, which regulates the area of the orifice 50 and is externally adjustable by a screw 86, is provided to enable the control to be used on engines of the same design having slightly different operating characteristics. At a point determined by the setting of the spring 81 and the contour of the valve 70, the valve 70 restricts the area of the orifice 49 and reduces the metering head across the governor valve 53. The shape of the valve 70 is such that at the upper and lower ends of the speed range it offers no appreciable restriction to the fuel flow through the orifice 49. To modify the effect of the temperature control in the midspeed range, a further temperature control 87, Fig. 3A, may be provided. The area of the orifice 88 which is in parallel with the orifice 49, is controlled by a valve 89 actuated by bellows 91 responsive to the temperature in the compressor intake. The control 87 may be substituted for the valve 85.