Patent GB-693429-A (GB)
Title: Improvements in or relating to fuel systems for gas-turbine engines
Inventor: BALLANTYNE DAVID HAVELOCK
IPC: F02C7/22
Filed: 1949-11-08
Abstract: 693,429. Gas turbine plant. ROLLS-ROYCE, Ltd. Oct. 9, 1950 [Nov. 8, 1949], No. 28675/49. Class 110(iii) [Also in Group XXIX] A fuel system for gas turbine engines comprises main fuel injectors or burners fed from a main fuel pump 32, pilot fuel injectors or burners fed by an engine driven auxiliary pump 38 of the fixed-capacity positive displacement type, a flowrestricting means such as the orifice 39 through which the full flow from the auxiliary pump passes, pressure responsive means such as the diaphragm 55 subjected to the pressures on each side of the flow-restricting means and means actuated or controlled by the pressure responsive device to control the fuel delivery from the main fuel pump to the main fuel injectors. The main fuel pump which may be a centrifugal pump 32 as shown or a positive displacement pump is driven from the engine through a coupling 33 and is supplied with fuel through a pipe 30 with a coarse filter 31. The main injectors are supplied from a manifold 17 connected to a supply pipe 24. The pump delivery pipe 34 contains a control mechanism 35 and a shut-off cock 36 coupled to a similar cock 41 in the delivery pipe 25 of the auxiliary pump 38. The pump 38 is supplied through a branch pipe 30a containing a fine filter 37. The pilot injectors are supplied from the pipe 25 through a manifold 19. The pressure in the pipe 25 is maintained constant by a relief valve 43 opening into a by-pass 42. The effective area of the orifice 39 is adjusted by a valve 39a under the control of a member 40. Fig. 5 shows the control mechanism 35 in its simplest form. The pressures on opposite sides of the orifice 39 act through pipes 44, 45 on a diaphragm 55 loaded by a tension spring 56. The diaphragm 55 operates through a push rod 65 on a spring-loaded lever 61 supported by a diaphragm 66 at one end and carrying a half ball leak-off valve 60 at the other end. The diaphragm chamber 53 communicates with opposite sides of a spring-loaded piston 48 through pipes 51, 52 which are connected through a restriction 58 opposite a leak-off passage 59. The piston 48 operates a throttle valve 47 in the main fuel supply pipe 24. The throttle tends to close or open according as the engine speed increases or decreases. To compensate for changes in altitude, the throttle 47 may operate in conjunction with a further throttle actuated directly by an evacuated capsule exposed to the ambient atmospheric pressure. Fig. 7 shows a modified control mechanism in which the valve lever 61 is subject to two further controls namely a control in dependence on the absolute compressor delivery pressure or on a function of such pressure and another pressure, for instance the air intake pressure and a control in accordance with the actual fuel flow to the main injectors. Thus the lever 61 is acted on by a pull rod 69 connected at one end to an evacuated capsule 93 and at the other to a diaphragm 70 loaded by a tension spring 69a. The chamber 71 below the diaphragm is connected to the compressor delivery and the chamber 63 is connected with any convenient pressure, e.g. the compressor intake. The effective areas of the capsule 93 and the diaphragm may be equal or unequal. The lever 61 is also acted on by a push rod 74 connected to a spring-loaded diaphragm 75. The diaphragm 75 is exposed through pipes 78, 80 to the pressures upstream and downstream of a valve mechanism 79. The latter comprises two spring-closed conical lift valves 83, 86 arranged hydraulically in parallel. The shape of the valve 83 and the rating of its spring are selected so that the pressure drop across it is substantially linear with the flow through it. The valve 86 opens only after a predetermined pressure difference across the valve mechanism 79 is attained. Thereafter the pressure difference remains substantially constant whatever the rate of flow. The load exerted by the push rod 74 on the lever 61 becomes zero before the valve 86 opens. The general arrangement of the fuel system shown in Fig. 8 is similar to that shown in Fig. 4 but in this case two flow restricting orifices 100 39 are provided in the pipe 25 supplying the pilol injectors and the control mechanism 35 has twc slide valves 111, 114 controlling the main fue flow. The valve 114 is movable both axially and rotatably. The axial movement is effected by a spring-loaded diaphragm 115 movable between stops 135, 136 under the influence of the pressure drop across the orifice 39. The rotational move ment of the valve 114 is effected by an arm 123 engaging a slot 122. The arm 123 is carried on the shaft of a pinion 124 movable against the load of a torsion spring 134 by a rack 125 operated by a piston 126. The piston 126 is controlled by a leak off valve 131 actuated by an evacuated capsule 132 in a chamber 133 open to the atmosphere. The valve 111 is actuated by two diaphragms 104, 108 these being loaded in opposite senses by the pressure.drop across the orifice 100 and the pressure drop across the valve 114 respectively. The orifice 100 is varied by an element 101 adjusted by a device 102 responsive to air temperature. In a further arrangement, the pressure drop across the orifice 39 is used to control a servomotor which adjusts the obliquity of the swash-plate of a pump supplying the main injectors. Specifications 577,016, [Group XXIX], 649,287, and 651,599 are referred to. According to the Provisional Specification, the maximum opening of the slide valve 114, Fig. 8, may be limited by a stop mechanism comprising a diaphragm coaxial with the diaphragm 115 and subject to the total pressure drop across the two restricted orifices 100, 39 as described in specification 658,780. Further the compressor delivery pressure may also act selectively on either side of a diaphragm smaller than the diaphragm 70 as described in Specification 651,599.