GB1171312A - Fuel Systems for Gas Turbine Engines - Google Patents

Abstract

1,171,312. Gas turbine engine fuel systems. JOSEPH LUCAS (INDUSTRIES) Ltd. March 2, 1967 [March 15, 1966], No.11328/66. Heading F1G. [Also in Division G3] A gas turbine engine fuel system particularly applicable to a vertical lift engine comprises a manually controlled throttle valve in a main line between a pump and the burners, the throttle valve being by-passed by a by-pass line containing two variable flow-restricting orifices one of which is controlled in accordance with a pressure related to that in the engine intake while the other is controlled in accordance with a further pressure obtained from the engine, and a speed-responsive device is also arranged to control the flow of fuel through the main line in accordance with engine speed. The fuel system shown in Fig. 2 comprises a pump 10 delivering fuel to the burners via a main line 11 containing a throttle valve 12, an engine overspeed control 14, 15 with an adjusting cam 16, a manually operated throttle valve 17 and a shutoff cock 18. A line 22 connected to the main line 11 to by-pass the valves 15, 17 contains variable orifices 23, 24 and a valve 25 linked to the throttle valve 17. A knife edge 35 for controlling the orifice 24 is controlled by the engine air intake pressure acting via a passage 37 on a capsule 36. A knife edge 27 for controlling the orifice 23 is controlled by e. g., the engine compressor discharge pressure acting via a passage 41 on a capsule 31. It may in addition be controlled by a diaphragm 38, one side of the diaphragm being exposed to the engine air intake pressure acting via a passage 40, the other side being exposed to the compressor discharge pressure. The diaphragm 38 is connected to the capsule 31 through a rod 39, a spring 42 and a sleeve 43. A rise in the compressor discharge pressure initially collapses the capsule 31, the diaphragm 38 being held against stops 44 by the action of the spring 42. The resultant opening of orifice 23 increases the fuel supply, the maximum opening being reached when the head of the rod 39 abuts a shoulder 45 on the sleeve 43. Further increase of the compressor discharge pressure cannot further open the orifice 23. However, at some predetermined higher value of this pressure, the diaphragm 38 is moved away from the stops 44 and carries the capsule 31 with it, thereby reducing the opening of the orifice 23. Decrease of engine air intake pressure (which in the case of a vertical lift engine not subjected to ram effect is substantially atmospheric pressure and therefore dependent on altitude) reduces the opening of orifice 24. The throttle valve 12 is acted on in the closing direction by the pressure upstream of the line 22 acting on one side of a diaphragm 13, and is acted on in the opening direction by a spring 30 and the pressure downstream of the orifice 23 acting via a passage 29 on the other side of the diaphragm 13. Since the last mentioned pressure is dependent on the relative openings of the orifices 23, 24, which form a potentiometer in parallel with the throttle valve 17, the opening of the throttle valve 12 is dependent on the engine air intake pressure and the compressor discharge pressure. A throttle valve 20 in line 19 supplying starter burners is linked to the throttle valve 17 so that the latter is opened as the former is closed. Shut-off cocks 18 and 21 are linked so as to close simultaneously.