| 摘要 |
1,194,041. Centrifugal pumps; gas turbine jet engines; ram-jet engines. DOWTY FUEL SYSTEMS Ltd. Jan. 1 1968 [Jan. 6, 1967], No.977/67. Headings F1C, F1G and F1J. Pumping apparatus for the supply of liquid fuel to supplementary burners associated with an aircraft gas turbine engine comprises a continuously driven centrifugal pump having an inlet valve interposed between a source of liquid fuel and the eye of the pump impeller, a flow selector including flow control means arranged to regulate the delivery of liquid fuel from the centrifugal pump, the flow selector at a selection of "no flow" causing the inlet valve nearly or wholly to close; an ejector pump having an inlet nozzle connectible to an independent source of liquid under pressure, a suction chamber, and an outlet diffuser passage connected to a low-pressure region of the apparatus; and a shut down valve interposed between the delivery side of the centrifugal pump and the suction chamber, the flow selector acting, upon the selection of "no flow", to open the shut-down valve. The supplementary burners may be re-heat burners in a main engine duct, burners in a by-pass duct, or the burners of auxiliary ram-jet units which are associated with the main engine. In the fuel system shown, a boost pump 2 supplies fuel to main burners 7 via a main pump 4 and a flow control unit 6 and to re-heat burners 19 via a flow control unit 11, a centrifugal pump 13 and a pressurizing valve 21. The main pump 4 may be of variable delivery type, the flow control unit 6 acting to control the delivery. The re-heat flow control unit 11 comprises a lever 37 acted on by capsules 39, 41 supplied with pressure control signals, one of which is raised by a manual reheat selector (not shown). The lever 37 co-operates with nozzles 33, 34 to vary the pressures downstream of fixed restrictors 31, 32 fed, via a pipe 29, from the main pump delivery pipe 5, these pressures being communicated to respective chambers 26, 27 at opposite sides of a piston 25 so as to control the opening of an inlet valve 17 adjacent the eye of pump impeller 14. A tapered plug 42 co-operating with an orifice 43 acts through a spring 44 to exert a force on the lever 37 which increases with flow so as to provide negative feedback. Fuel supplied through a pipe 74 passes through orifices 75 as cooling and lubricating jets directed on to a sealing ring 67 and returns through openings 76 to the interior of the impeller 14. When re-heat is not required, a lever 45 is operated to open valves 46, 56. Valve 56 vents the chamber 26 to the fuel supply pipe 1 via pipes 57, 55 to cause the inlet valve 17 to close. Valve 46 connects the discharge side of the pump 13 to the supply pipe 1 via an ejector 48 and the pipe 55, whereby a return path to the pipe 1 is provided for the cooling and lubricating flow from the orifices 75. When the fuel flow to the main burners 7 is low, a shut down valve 52 is open, allowing fuel to flow from pipe 5 to the nozzle 53 of the ejector 48 to energize the ejector whereby the latter reduces the pressure within the periphery of the centrifugal pump casing. This reduces the generation of heat in the fuel circulated through the centrifugal pump 13 and therefore limits the temperature rise of the fuel flowing through the pumps 2, 4. If the fuel flow to the main burners 7 increases, the resultant increase in the pressure in the pipe 5 eventually causes the valve 52 to close progressively to put the ejector 48 out of action. The resultant rise in the temperature of the fuel leaving the centrifugal pump 13 can be tolerated because it is absorbed by the increased flow to the main burners 7. Instead of closing completely on re-heat shut-down, the valve 17 may remain slightly open to permit a minimum flow to supplement or replace the cooling and lubricating flow. In addition to the inlet valve 17, there may be a throttle valve in the delivery which is operable by the flow control means. |
