GB598568A - Improvements in fuel supply systems for internal combustion engines - Google Patents

Abstract

598,568. Controlling fuel supply to internal-combustion engines and turbines. HOBSON. (AIRCRAFT & MOTOR) COMPONENTS,. Ltd., H. M., and GREENLAND, L. S. May 28, 1945, No. 13375. [Class 135] [Also in Groups XXVI and XXVII] In am aero-engine wherein the speed of the propeller is maintained constant at any value selected by a manually operable control, fuel is fed by a pump through a variable metering orifice, the metering pressure across which is maintained as a desired function of engine speed by a..variable radius centrifugal impeller, the effective delivery of the pump being controlled by the variations in metering pressure. The invention is described in connection with a combustion product turbine to which fuel from a variable delivery pump 10, Fig. 2, flows through a metering orifice 12 to the injectors 33 of a combustion turbine, the fluid pressure at the eye of a centrifugal impeller 14 being applied to the downstream side of orifice 12 through conduit 13 and the pressure at the effective radius of the impeller being transmitted to the upstream side by a diaphragm 17 actuating a valve 23 which controls a servopiston 26 controlling the pump delivery and thereby maintaining the desired metering pressure. The pressure of the fuel on piston 26 is balanced by a spring 28, a small flow of fuel occurring through an orifice 27 in the piston and via a conduit 44 to the suction side of the pump. A governor 37 maintains the speed of the propeller constant at speeds selected by a lever 22, and a cam 21 operated with the lever 22 rotates a valve 20 to vary the effective radius of the impeller. Movement of the lever 22 to the left increases the effective radius and sets the governor 37 to a higher speed. The resulting increase of pressure on the top of diaphragm 17 moves valve 23 down and closes orifice 24, thereby increasing the pressure on the right hand side of piston 26 and forcing it to the left to the pump output. A capsule 57 operating a valve 64 in a fuel conduit 46 returning fuel from a servomotor 65 to the suction side of the pump controls the servo piston 67 carrying a needle 56 to vary the area of the metering orifice 12 as a function of air intake pressure. A spring- closed valve 31 in conduit 11 ensures that the fuel pressure is always sufficient to operate the servomotors 25, 65, fuel for starting being supplied through a bye-pass 47 controlled by a cock 48. Normally closed spill-lines 74, 76 are opened in case of overspeeding and overheating respectively, causing piston 26 to decrease the pump output. The servomotors 25, 65, may be operated by hydraulic fluids other than the fuel supply. In Fig. 3 the fuel pump 100 is of fixed delivery type and diaphragm 17 operates a valve 123 for varying the bleed back of fuel through conduit 146 to the suction side of the pump. An overspeed corrector 81 comprises a diaphragm 82 subject to the pressure at the eye and tip of the impeller 14 and controlling a valve 83. A spring 84 normally maintains the valve closed but if the engine overspeeds the increase in pressure opens valve 83 to bleed fuel from the top of diaphragm 17 to reduce the metering pressure. It is stated that the variable radius impeller may be replaced by a fixed radius type provided with means for varying the relation between engine speed and metering pressure. Specifications 429,682, 566,323, 586,259, [all in Group XXVII], 592,769, 596,808 and 598,566 are referred to.