Patent GB-1041212-A (GB)
Title: Improvements in or relating to fuel control systems for gas turbines
Inventor: MATTHEWS ROBERT BARRY
IPC: F02C9/16
Filed: 1962-03-06
Abstract: 1,041,212. Gas turbine engine fuel systems. PLESSEY CO. Ltd. March 6, 1963 [March 6, 1962], No. 8494/62. Heading F1G. [Also in Division G3] A fuel supply system for a gas turbine engine comprises fuel control means so constructed as to make the fuel flow to the engine proportional to the product of the engine speed and of a pressure difference obtained from the engine compressor. The fuel control unit shown in Fig. 1 comprises a booster pump 2 which takes in fuel through inlet 1 and delivers it through filter 3 to the gear pump 4, the pump 4 delivering to a chamber 6. The fuel passes from the chamber 6 to chamber 9 by way of profiled ports 8 in a valve member 7, and from the chamber 9 to the outlet 10 by way of two paths in parallel, one through the orifice 11 in the governor-controlled valve 12 and the other through the fixed orifice 15. A differential link valve 16 is disposed between the valves 7 and 12 and is formed with an orifice 17 by which fuel in the chamber 9 may be passed back to the suction side of the pump 4. The valve 16 is urged downwardly so as to tend to increase the opening of the orifice 17 by the pressure difference across the orifice 11, the pressure 'downstream of the orifice 11 being communicated through a duct to the lower side of the valve 16. The valve 16 is urged upwardly by the pressure difference across the orifice 8, the pressure upstream of the orifice 8 being communicated through a duct to the lower side of the valve 16. The link valve 16 acts to maintain the pressure difference across the orifice 11 equal to that across the orifice 8. The axial position of the valve 7 is controlled by means of a diaphragm 19, the space 20 above the diaphragm being subject to compressor discharge pressure P 2  and the space 21 below the diaphragm being subject to compressor intake pressure P 1 . The valve member 7 thus takes up a position dependent on P 2 -P 1  and the effective area of the orifice 8 is arranged to be inversely proportional to P 2 -P 1 . When the engine speed is below a value determined by the position of the throttle lever 13, the orifice 11 will be a fixed value, while the orifice 8 will have a value inversely proportional to P 2 -P 1 . Flow through the orifice 8 is proportional to engine speed N (due to the volumetric action of the gear pump 4) so that pressure drop across the orifice 8 will be proportional to N<SP>2</SP>(P 2 -P 1 )<SP>2</SP>. The pressure drop across the orifice 11 is kept at the same value by means of the differential link valve 16 so that the flow through the orifice 11 at low engine speeds, that is to say under acceleration conditions, will be proportional to the square root of this pressure drop, that is, proportional to N(P 2 -P 1 ). Since the pressure drop across the fixed orifice 15 is the same as that across the fixed orifice 11 it follows that the total flow Q e  to the engine will, up to the speed at which the governor 12 responds, be proportional to N(P 2 -P 1 ). In a second embodiment, Fig. 2, an isochronous governor is provided in place of the all-speed governor 12 of Fig. 1.