GB716254A - Improvements in or relating to gas-turbine engine fuel systems having fluid-pressureoperated automatic control mechanisms - Google Patents

Abstract

716,254. Gas turbine plant. ROLLS-ROYCE, Ltd. Aug. 14, 1952 [Aug 28, 1951], No. 20287/51. Class 110(3) [Also in Group XXIX] The supply of fuel to a gas turbine engine is controlled as a function of an engine operating variable e.g.' speed, by the relative movement between an obturator and a unit providing a nozzle and a fluid receiving chamber between which the obturator is adapted to move, the movement of one of the parts, say the obturator, being effected by changes in the engine operating variable and the movement of the other part i.e. the nozzle and receiving chamber being effected through pressure-responsive means by changes in the control pressure in the receiving chamber and being in the same sense as the movements of the first part so that the movements of the second part follow up the movements of the first part. In this way, the fuel supply is regulated to maintain the engine operating variable constant or to maintain a correct relation between the fuel supply and the engine operating variable. Fig. 2 shows the invention applied to the speed control of an aircraft gas turbine engine, the control mechanism being mounted beneath a nacelle 21 in engine air intake 22. The control mechanism comprises a nozzle 26 formed in the flanged head 25 of a rotary fuel throttle valve 20, a receiving chamber 28 formed in a flange 29 on the throttle valve and having an inlet 27, and an obturator formed as a rotatable steel cup 32 co-axial with the head 25 and flange 29 and having an axial slot 33. The engine is supplied with fuel through a conduit 18 leading to a centrifugal pump 16 driven from the engine through the compressor 10. The fuel delivered by the pump passes along a conduit 19 controlled by the throttle 20 to the burners. The throttle 20 is formed as a hollow rotary plug with constantly open inlet ports 23 and an outlet port 24. A by-pass 23b is also provided. The receiving chamber 28 communicates with the inner free end of a spiral Bourdon tube 30 the other end of which is attached to a housing 31 formed with chambers 40, 41. The cup 32 is carried by a spindle 34 loaded by spiral springs 35, 36 which grow in the same direction as the Bourdon tube 30, the outer ends of the springs 35, 36 being anchored to the housing 31 and the flange 29 respectively. The shaft 34 carries a bronze or a copper lined steel cup 37 the skirt of which is arranged between a soft iron stator 38 and a rotating magnet 39 on an extension 16b of the pump shaft. The skirt '37 is thus subject to. a magnetic drag which increases with engine speed so that the obturator 32 is deflected against the springs 35, 36 an amount dependent on the change of speed and the consequent change of pressure in the Bourdon tube 30 adjusts the throttle 20 so as to restore the engine speed to its datum value. The obturator and the inlet 27 may be arranged so that the throttle does not start to close the port 24 until a quarter of the jet has been blanked off and so that the port 24 is completely closed when three quarters of the jet has been blanked off. Alternatively the slot 33 may be arranged so that the jet is obturated less as the engine speed increases, the direction of growth of the Bourdon tube being reversed in this case. The nozzle may be directed radially inwards, the receiving chamber being formed in the head of the throttle valve 20. The Bourdon tube may be at the opposite end of the throttle 20 to the receiving chamber, the two being connected by a co-axial tube in the throttle valve. The springs 35, 36 may be adjustable. Thus the spring 35 may be anchored to a pinion adjusted by a worm. Fig. 3 shows a reciprocating arrangement of the control mechanism in which the fuel delivery pressure in the pipe 19 is regulated by adjusting the obliquity of the swash-plate 54 of a multicylinder pump 50 driven by the engine. The swashplate 54 is carried on the inclined part 56a of a spindle 56 movable axially by a servo-piston 57 one side 58 of which is constantly subject to pump delivery pressure through conduits 60 and the other side 59 being connected with the first side 58 through a jet 61 and an opposed inlet 62 separated by a bore 63 in which operates an axially movable obturator 64. The obturator 64 is actuated through a rod 65 by a diaphragm 69 subject to pump inlet pressure on one side and to pump delivery pressure on the other. The pump delivery pressure is also regulated in accordance with the ambient atmospheric pressure which has access to a chamber 73 containing an evacuated capsule 72 connected to the rod 65. Specification 716,255 is referred to.