Patent GB-694322-A (GB)
Title: Improvements in or relating to gas-turbine engine fuel systems
Inventor: DAVIES DAVID OMRI
IPC: F02K3/10
Filed: 1950-07-20
Abstract: 694,322. Gas turbine jet propulsion plant; centrifugal pumps. ROLLS-ROYCE, Ltd. July 19, 1951 [July 20, 1950], No. 18192/50. Classes 110(i) and 110(iii) [Also in Groups XI and XXIX] In a gas turbine jet propulsion plant with re' heating in the turbine exhaust, the fuel is supplied to the reheat combustion stage by a pump driven by an air turbine the air supply to which is regulated by a throttle controlled by a pressure responsive device sensitive to the ratio of a pressure at a point between the compressor delivery and turbine inlet to a pressure at a point between the turbine and the propelling nozzle. The gas turbine jet propulsion engine shown. Fig. I, has a variable area propelling nozzle 16 and means as described in Specification 667,394 for burning extra fuel in the jet pipe. The pilot fuel injector 17 of the extra fuel burning means is supplied with fuel from the fuel supply system of the main combustion equipment through a shut-off cock 30 and a non-return valve 31. The cock 30 may be electrically operated as shown in Fig. 2 and opened by energisation of a solenoid 30a which acts against the action of a spring 30e. The fuel supply to the second pilot fuel injector 19 and main fuel injectors 20 comprises a centrifugal pump 40 drawing fuel from the tank 21 and discharging it through a shutoff cock 42 and non-return valve 43. The shut-off cock 42 may be of any type but is shown as electrically controlled and consists of a valve element 42a carried by a flexible diaphragm 42b and loaded by a spring 42c to bear against a seat 42d. The diaphragm separates an inlet chamber 42e from a chamber 42f which are interconnected through a restrictor 42g. When the solenoid 47 is energised, valve 46 is lifted and fuel flows from the chamber 42e, through restrictor 42g and chamber 42f. This causes a pressure difference between chambers 42e, 42f, and the valve element 42a is lifted off its seat 42d. The pump 40 is driven by an air turbine 48 fed with air from the discharge of the compressor 11 through a throttle valve 50. The throttle valve 50 is actuated by a piston 51 working in a cylinder against the action of a spring 54. Fuel from the discharge of the main fuel pump 22 is passed through the space 52, and a restrictor 59 to the space 53 which has a bleed port 65 controlled by a valve element 66. The position of the piston 51 is thus determined by the flow through the port 65. A port 60 controlled by an electrically operated valve element 62 may also be provided. The valve element 66 is supported by a carrier 67 connected at one end to an evacuated capsule 70 and at its opposite end to two flexible diaphragms 72, 73. The effective area of the diaphragm 72 is less than that of the diaphragm 73. A chamber 75 between the diaphragms 72, 73 is connected to the air supply conduit 49 to the turbine 40 upstream of the throttle valve 50. The chamber 77 is connected by a conduit 78 with a point in the exhaust assembly downstream of the turbine 13. The conduit 78 contains a flow restrictor 79 and is connected with the conduit 76 by a conduit 80 containing a flow restrictor 81. The pressure in chamber 77 is therefore proportional to and greater than the pressure in the conduit 78. The flow restrictors 79, 81 allow the ratio to which the pressure responsive device regulates to be adjusted. The arrangement is such that the pressure ratio to which the pressure responsive device regulates is equal to the ratio of the areas of the diaphragms 72, 73. The capsule 70 has an effective area equal to the area of the diaphragm 72 and the resilient load is balanced by a spring 83. In a modification, the bleed port 65 is controlled by movements of a lever mounted in a flexible diaphragm. The valve element 66 is mounted on one end of the lever on which the spring 83 acts whilst the diaphragms 72, 73 and capsule 70 act on the other end of the lever. In this construction, the valve element 62 controls the flow from the space 52 to the space 53 and when closed causes the throttle valve 50 to be closed. A temperature sensitive element located on the downstream side of the turbine may be used to energise a solenoid 85 and thus open the port 65 when a preselected temperature is exceeded or may be used to modify the control by the diaphragms 72, 73 so that a given temperature is maintained. The temperature sensitive element may be of the type described in Specification 641,910. The stop valve 30 may be of similar construction to the valve 42 described above. The valve ,at which the ratio is maintained when the reheat combustion chamber is operating is preferably that which exists at the maximum rotational speed when this combustion chamber is inoperative and this may be effected by opening the variable area propelling nozzle when the reheat combustion chamber is put into operation.