Patent GB-693428-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: 693,428. Gas turbine plant; centrifugal compressors. ROLLS-ROYCE, Ltd. Oct. 9, 1950 [Nov. 8, 1949], No. 28568/49. Classes 110(i) and 110(iii) [Also in Groups XI and XXIX] A gas turbine fuel system comprises an engine driven centrifugal pump and an engine driven positive displacement pump connected to deliver fuel to the gas turbine in parallel with one another. In the arrangement shown, fuel from a supply tank, filtered in a coarse filter 31. is divided into two parts, one part flows through an engine driven centrifugal pump 32, conduit 24, manifold 17 and conduits 18 to main fuel injectors in the combustion chamber of the engine and the other part flows through an engine driven positive displacement pump 38, conduit 25, manifold 19 and pipes 20 to pilot fuel injectors also arranged in the combustion chamber. A relief valve 41 maintains the discharge pressure of the pump 38 constant. A fine filter 37 is provided to prevent choking of the fine clearances in the pump 38 which may be of the eccentric vane, piston and cylinder or gear type. Shut off valves 36, 39 operated by a common link 42 are also provided. The output of the centrifugal pump 32 is controlled by the mechanism 35. The mechanism 35 comprises a throttle valve 50 and variable orifice 52 arranged hydraulically in series. The area of the orifice 52 is varied by a weir element 53 carried by a piston 54 which is controlled by a spring 56 and the fluid pressure difference across it. Fuel at constant pressure from the discharge of the pump 38 is fed direct to the top of the cylinder and to the lower end of the cylinder through a restricted orifice 58. A bleed pipe 59 controlled by a valve 60 leads from the lower end of the cylinder. The position of the weir element 53 is thus determined by the leak-off through the pipe 59. The valve 60 is mounted on a lever 61 which is loaded at one end by an adjustable spring 69, at the other end by a barometric capsule 67 and intermediately by a tappet 74 operated by a diaphragm 73 responsive to the pressure drop across the throttle valve 50. Variations of the pressure drop across the throttle valve 50 due to variations in fuel flow will cause the element 53 to open or close and restore the fuel flow to its present value. Changes in barometric pressure also operate the element 53, and the apparatus is designed so that a given setting of the valve 50 corresponds to a given engine rotational speed irrespective of altitude. In a modification the output of the positive displacement pump is passed through a variable area orifice and pressure sensitive means responsive to the pressure drop across the orifice used to control the output of the centrifugal pump. An arrangement in which the positive displacement pump 38 discharges into the conduit 24 through a non-return valve and a non- return valve is placed between the discharge of the pump 32 and the connection to the conduit 24 is also described. In this arrangement, the pilot and main fuel supplies are injected into the combustion chamber through a common injector. An arrangement in which a single injector has passages for both the pilot and main fuel supplies is also described. A further modification has three sets of injectors, one set of pilot injectors and two sets of main injectors. The pilot injectors and one set of the main injectors are fed with fuel as described above. The second set of main injectors are fed from the conduit 24 through a pressurising valve and are used only at high loads. Specification 693,429 is referred to.