Patent GB-790052-A (GB)
Title: Improvements in or relating to apparatus for metering the fuel supplied to a prime mover
Inventor: CHAMBERLIN REGINALD HENRY DOUG
IPC: G01F1/00
Filed: 1954-12-14
Abstract: 790,052. Gas-turbine plant. NAPIER & SON, Ltd., D. Nov. 11, 1955 [Dec. 14, 1954], No. 36172/54. Class 110 (3). [Also in Group XXIX] In apparatus for metering the fuel supplied to a gas-turbine engine, the turbine of which drives the engine compressor and a propeller having its pitch adjustable by a speed governor, comprising a metering orifice 11 incorporating two relatively movable members 12, 13, the former being adjustable manually by a main control 23, and member 13 being controlled by an element 19 responsive to the compressor inlet temperature, the main control 23 regulating the governor setting, a member 33 responsive to pressure in the compressor inlet 'and controlling the pressure drop across the orifice 11, the fuel flow is dependent upon engine speed for datum conditions of compressor inlet pressure and temperature and variations, any variations of the inlet pressure automatically resulting in a variation of fuel flow whilst any deviations from the datum inlet temperature cause a corrected fuel flow which is a function of a variable operating condition of the engine, e.g. speed. The pump 1 with a variable delivery draws filtered fuel from a passage 6 and delivers it through a pressurizing valve 9 into a casing 10 wherein is the orifice 11 formed by a tapering slot in an outer sleeve 12 which co-operates with the adjacent ends of inner sleeves 13 and 14. Fuel leaving the metering orifice 11 passes to the fuel burner, not shown, via a pipe 15 in which is disposed a dump valve 64 to cut-off the fuel supply to the burners and discharge to atmosphere the fuel in the pipes leading to the burners. The sleeve 13 is operated by a piston 18 the control valve of which is actuated by the element 19 having its bulb 20 in the compressor inlet whilst the outer sleeve 12 is coupled to a lever 21 on a shaft 22 that is operated by the main control lever 23. The datum setting of the orifice is effected by manner setting of the sleeve 14. Across the orifice 11 is a diaphragm 24 which acts upon a relief valve 26 controlling the escape of fuel that flows through a restriction 27 from one end to the other of a cylinder in which is a piston 4 that effects variation of the fuel pump capacity in such a manner as to maintain a desired pressure drop across the orifice, the position of the piston 4 is also depedent upon speed-responsive devices 66, 67. The valve 26 is acted upon by a spring having an abutment 29 connected to a piston 30 via a variable fulcrum lever 31 and controlled by a valve 32 actuated by a bellows aneroid device 33 to control the pressure drop across the orifice 11 so that it is proportional to the square of the compressor inlet pressure, whilst fuel flow through the orifice 11 is controlled linearly with this pressure; the fulcrum of the liner 31 may be adjustable to enable a relationship other than linear to apply to the control of the fuel through the orifice. The control of the governor is effected from the levers 21 and 23 by a device comprising a valve 34 connected to the lever 21 while a piston 35 is attached to the governor control 37 through a rod 36 and a temperature compensated linkage, not shown; the rod 36 acts through a lever 38 and a rod 39 on a sleeve 40 for the valve 34 so that the piston 35 always moves into a position corresponding to that of the valve 34 and hence lever 23. The piston 35 also acts via a cam 35a on a lever 35b to move a slide 35c on which is pivoted a lever 17 so that the relationship between piston 18 and sleeve 13 is varied with changes in the position of the piston 35 whereby the percentage variation in fuel flow effected by the element 19 varies with engine speed according to a law determined by the form of cam 35a. The rate of movement of the rod 36 on any change in position of lever 23 is controlled by a device comprising a lever 41 connected to the rod 36 and a sleeve valve 42 associated with one or more ports 43 through which fuel can flow from the servo device 35, 34 which is exhausted during acceleration, and fixed and variable orifices 44 and 45, respectively, in series with one another but in parallel with the port or ports 43 by which such flow can also take place. During deceleration the exhaust from the device 34, 35 traverses a further orifice 46; the flow resistance offered by orifices 45 and 46 is determined by a camactuated flap, the cam 47 being operated by the bellows 33 so that the rate of movement of the piston 35 during acceleration is fixed by the range of movement of lever 23 and the compressor inlet pressure; on deceleration the rate of movement of the piston 35 is set solely by the latter pressure. A manual over-ride 48 is provided to enable an increased speed to be obtained independently of the lever 23. Associated with the lever 23 and rod 36 is a element 49 responsive to turbine inlet temperature and acting on a lever 50 that controls a valve 51a which when opened reduces the pump delivery. The lever 50 is pivoted to another lever 53 by a rod 51 which lever 53 is acted upon by cams 54, 55 operated by levers 21 and 38 so that when control lever 23 is moved to effect acceleration the element 49 is influenced to permit an excessive temperature until subsequent movement of the cam 55 and piston 35 moves the rod 36, so altering the setting of the element 49 at which it will reduce fuel only if the maximum turbine inlet temperature appropriate to the new setting is exceeded whereby the element 49 functions solely as a safety device. The cams 54 and 55 may be formed so that movement of the lever 23 only produces a part of the temperature datum increase or decrease, the follow-up movement of the piston 35 and rod 36 completing the remainder or the required increase or decrease. A torque limiting device 56 subject to differential pressures from a torque responsive apparatus, not shown, controls a valve 60 whereby the supply of fuel from the pump 1 is reduced or cut-off if a given torque in the propeller shaft is exceeded; the differential pressures are also applied to a device 61 to alter the propeller pitch should a negative torque or a given low positive torque occur. A piston 65 may also be provided to control the angle of the guide names in the compressor inlet in response to engine speed. Specifications 625,055, [Group XXIX], 743,418, [Group XIX], and 783,880 are referred to.