Patent GB-769504-A (GB)
Title: Fuel feed and power control system for gas turbine engines
IPC: F02C9/32
Filed: 1954-09-20
Abstract: 769,504. Gas-turbine plant. BENDIX AVIATION CORPORATION. Sept. 20, 1954 [Oct. 26, 1953], No. 27191/54. Class 110 (3). [Also in Group XXIX] A fuel control system for a gas turbine engine comprises means for producing a fluid pressure as a function of the pressure ratio across the compressor, and means responsive to that pressure for controlling the flow of fuel so as to prevent over-fuelling during acceleration. In the embodiment described fuel is fed by a pump 22 having a constant pressure valve 24 to a valve 44 and thence through a metering valve 68, all-speed governor 40, e.g. as described in Specifications 716,415 or 745,146, and conduit 42 to the burners 16. The valve 44 is actuated by a diaphragm 48 subject to the pressure drop across the valve 68 and by a centrifugal governor 62 so as to maintain a pressure difference across the valve 68 proportional to the square of the engine speed. The valve 68 is actuated by a bellows 82 which is subject, through a conduit 92, to the pressure that is a function of the compressor pressure ratio. The total pressure at the compressor delivery passes by way of a conduit 98 to parallel restrictions 122, 124, conduits 106, 108 and orifices 116, 118 controlled by valves 126, 128 to a chamber 114 which connects through a conduit 120 with a point 104 for detecting total or ram pressure at the intake of the compressor. The valves 126, 128 are mounted on a rod 130 and actuated by a servo-piston 132 controlled by a valve 142 which is actuated by a lever 182 pivoted at 184 and operable by bellows 162, 164, 166, 168 of which 162 and 168 are responsive to the pressures in the conduits 108 and 120 respectively and 164 and 166 are evacuated and cancel out the effect of atmospheric pressure variations on the bellows 162, 168. Thus the valve 128 is adjusted to maintain a constant pressure ratio Px/Pr across the orifice 116 in consequence of which the displacement of the valves 126, 128 is always a predetermined function of the compressor pressure ratio Pc/Pr, and the pressure Pm which acts on the bellows 82 and is controlled by the valve 126 is also, therefore, a function of the pressure ratio Pc/Pr. The pressure Pm is also a function of altitude, which may be expressed in terms of compressor inlet or discharge pressures, due to the connection of the orifice 118 with the conduit 120. The system therefore controls fuel flow during acceleration (Pc) according to the expression Pr.N. f <SP>1</SP>- or (Pr) (Pc) Pc.N. f<SP>2</SP>- where f<SP>1</SP> and f<SP>2</SP> are predetermined (Pr) functions and N represents the rotational speed of the engine, this term being introduced by the valve 44. The following modifications are referred to. Two pressures within the compressor may be utilized instead of the inlet and discharge pressures. The servo mechanism including the bellows 162 ... 168 for actuating the valve may be replaced by a diaphragm or bellows. A servo system may replace the bellows 82. The adjustable orifices 116, 118 may be upstream of the restrictions 124, 122. For controlling fuel flow during deceleration the orifice 122 may be adjustable or the pressure Pm could be vented to the region at pressure Pr. Altitude compensation, e.g. as described in Specification 655,311, may be utilized with the valve 44 so as to control the pressure difference across the valve 68 in accordance with altitude as well as speed. The valve 68 could be connected directly or through servo means to the valve 128 and the means for obtaining the pressure Pm could be eliminated.