Patent GB-1002816-A (GB)
Title: Gas turbine engine fuel ssystems
Inventor: LEWIS GEOFFREY ARTHUR
IPC: F02C9/16
Filed: 1962-05-21
Abstract: 1,002,816. Gas turbine engines. JOSEPH LUCAS (INDUSTRIES) Ltd. May 21, 1963 [May 21, 1962], No. 19403/62. Heading F1G. The invention relates to a fuel system for a gas turbine engine of the kind which incorporates a pair of metering orifices through which fuel must flow in series from a source to the burner or burners, the size of each orifice being determined in part at least by the speed of the engine. In accordance with the invention, a single centrifugally operable device is provided for controlling two movable parts associated with the two orifices respectively, means being provided for applying to one of the movable parts a force dependent on the density of the fuel whereby the size of one of the orifices will be dependent on fuel density whilst the size of the other orifice will be substantially independent of fuel density. In Fig. 1 the fuel control unit comprises a body part 3 in which is formed a pair of aligned bores 4, 5, a hollow cylindrical sleeve member 6 being disposed within the two bores. A cylindrical sleeve 17 is disposed around the sleeve 6 between the ends of the bores 4 and 5, the adjacent edges of the bore 5 and sleeve 17 forming an annular opening which co-operates with a triangular-shaped aperture formed in the sleeve 6 to form a variable metering orifice 18. Fuel is supplied to the unit through an inlet 7 and passes into the sleeve 6 and thence through the orifice 18 into the space 19. A further bore 20 is provided in the casing 3, a piston member 21 being disposed within the bore and having formed in its skirt portion a triangular-shaped aperture which co-operates with an annular recess 23 in the wall of the bore to provide a second variable metering orifice 22 through which fuel flows from the space 19 to the outlet 24. The sleeve 6 and the piston 21 are arranged to be rotatably driven by means of gearing 25, 26. The piston 21 carries at its upper end a pair of centrifugal weights 29 which act against a collar 30 slidably disposed on a shaft 27, the collar having a knife-edge 32 which abuts against a lever 33 pivotally mounted at one end in the casing 3, the opposite end of the lever bearing against the sleeve 17 in opposition to the loading of the governor spring 34, the loading of the spring being adjustable by means of a speed control lever 36. With increase in speed, the centrifugal weights will tend to move the sleeve in a direction to reduce the area of the orifice 18 and at the same time move the piston 21 downwardly against the loading of the inlet fuel pressure acting upwardly on the piston, so as to increase the area of the orifice 22. The density of the centrifugal weights is so chosen that they will be sensitive to and compensate for changes in the density of the fuel. The shaft 27 which rotates with the piston 21 carries a centrifugal pump member 28 at its upper end, the pump taking its suction from the chamber 19 through the duct 41 in the shaft 27 and discharging into a bore in the wall of the casing 3. Fuel from within the sleeve member 6 is also supplied to the bore by means of an opening 38 in the wall of the sleeve and an annular recess 39, the bore having a restriction 40 therein. The fuel pressure within the bore at the pump side of the restriction gives a measure of the fuel density and this pressure is applied to a diaphragm 37 forming one wall of a chamber 42. The diaphragm carries an abutment which bears against the free end of the pivoted lever 33 whereby the forces opposing the governor spring 34 are substantially unaffected by fuel density. The axial position of the sleeve member 6 is controlled in dependence on pressure by means of a pivoted lever 9 which is connected to a capsule assembly comprising an evacuated capsule 10 connected to a capsule 16 which is connected to compressor intake pressure in line 14 by means of a line 15. The chamber 11 within which the capsule assembly is disposed is connected by line 12 to a point in the line 14 between a pair of restrictions 13, the line 14 being connected at its lower end to compressor intake pressure and at its upper end to compressor discharge pressure. In a second embodiment, Fig. 2, the centrifugal weights 29 act directly on the sleeve 17 in opposition to the loading of the governor spring 34 and react against a knife-edge 45 on a lever 46 pivotally mounted at its left-hand end in the casing 3, the opposite end of the lever acting on a bearing device 48 to control the axial position of the piston 21. The pressure derived from the pump 28 which is a measure of fuel density is applied to the lever 46 by means of the diaphragm 37 as before but in this case it acts to oppose the centrifugal loading of the weights 29 which is applied to the lever to control the axial position of the piston 21. In this embodiment the centrifugal weights are of sufficient density so as to be substantially unaffected by variations in the fuel density.