Patent GB-1022381-A (GB)
Title: Gas turbine engine fuel system
Inventor: JOHNSON CHRISTOPHER LINLEY
IPC: F02C9/30
Filed: 1964-02-04
Abstract: 1,022,381. Gas turbine engine fuel systems. ROLLS-ROYCE Ltd. Jan. 28, 1965 [Feb. 4, 1964], No. 4769/64. Heading F1G. [Also in Division G3] A gas turbine engine fuel system comprises a first fuel conduit, means for supplying the first fuel conduit with fuel the pressure of which varies in accordance with one or more engine variables, a second fuel conduit which is adapted to supply fuel to engine burners, the first fuel conduit communicating with the second fuel conduit by way of a pressurizing valve which is urged by a spring towards the closed position, there being a restricted by-pass passage which by-passes the pressurising valve and establishes a restricted communication between the first and second fuel conduits. In the embodiment shown, fuel is supplied from a backing pump (not shown) through line 12, inlet pressure regulating valve 13 and line 12a to the inlet of the centrifugal type fuel pump 23, the pump being driven by an air turbine 24 which is supplied with air under pressure from the engine compressor indicated at 22. The air passes through nozzles in the nozzle plate 25 which is secured to the engine casing 11. Air discharging from the turbine passes through the air outlet Venturi 26 the area of the throat 27 of which may be varied by the screw device 30. Fuel discharges from the pump through line 31 in which is disposed a throttle valve 32, the position of the rotary valve member being controlled in dependence on engine rotational speed by means of the governor unit 33. The governor comprises fly-weights 35 mounted on a rotary disc 34 which is driven by the engine. As engine speed increases the arm 36 of a flyweight engages arm 37 which causes lever 41 which is pivotally mounted at 40 to move anticlockwise. The lever 41 acts through linkage 42, 44, 45 against the loading of spring 43 to move the valve member 32 in a closing direction. The loading of the governor spring is varied in dependence on the position of the throttle lever 47. Fuel from line 31 downstream of the throttle valve passes through pressurizing valve 52 to the line 53 which leads by way of shut-off cock 65 to the engine burners (not shown). The pressurizing valve comprises a valve member 54 which is urged towards valve seat 55 by spring 56. A by-pass passage 60, 61, 62 by-passes the pressurising valve, the passage having a variable restrictor 63 disposed therein so that only restricted flow may pass through the by pass passage. The portion 60 of the by-pass passage communicates also with line 64 which passes by way of the shut-off cock 65 to engine starting fuel burners. The shut-off cock 65 comprises an axially-movable valve member 66 which is movable by the throttle lever 47 by means of rod 74 and rack and pinion 70, 71. In a first position of the cock, the valve member 66 closes off the line 53 to the main burners also the line 64 to the starting burners. In this first position the main burners are connected through the bore 76 in the valve member and space 76a to drain 78. In a second position of the cock, the line 53 is open to the main burners and the line 64 is open to the starting burners. In the third position shown, only the line 53 to the main burners is open. The valve member 65 may be set to a number of positions between "idle" and "maximum". An emergency governor is provided and comprises a number of projections 80 formed of magnetic material and carried by the disc 34 which move past the permanent magnet 82 which is surrounded by a coil not shown. A signal will be generated which is proportional to engine speed and this signal is passed to a frequency responsive means in the control box 48 which causes the valve member 66 of the shut-off cock to move to the closed position whenever the frequency of the signal exceeds a pre-determined value. The pressure regulating valve 13 comprises a cup-shaped valve member which has an aperture in its wall, the valve member being urged towards the closed position by spring 15. The valve member is urged towards the open position by means of bellows 16 acting through rod 18, the bellows being connected to compressor discharge pressure through line 21. The speed of the air turbine 24 and so the speed of the fuel pump and the pressure of the pump discharge are dependent on the pressure of the air which is bled from the compressor to drive the air turbine. The pressure of this air is of course dependent on engine rotational speed.