Patent GB-1381100-A (GB)
Title: Fuel control apparatus for gas turbine engine
IPC: F02K3/10
Filed: 1971-04-13
Abstract: 1381100 Gas turbine engines reheat fuel system JOSEPH LUCAS (INDUSTRIES) Ltd 24 March 1972 [13 April 1971] 9270/71 Heading F1J The invention relates to fuel control apparatus for reheat combustion equipment of a gas turbine engine, the combustion equipment comprising first, second and third reheat burners. The apparatus comprises a reheat fuel pump 10 of the vapour core type which supplies fuel to inlet 14 of the metering apparatus 13 which comprises three metering devices 15, 16, 17, the first device 15 comprising a spool 19 disposed within a ported sleeve 18 for axial and angular movement. Fuel from the inlet passage 14 passes through ports 20 in sleeve 18 and then through port 21 into the annular space 22, the flow being dependent on the size of the variable metering orifice defined by the spool and the sleeve and hence by the axial position of the spool. Fuel from the space 22 flows through a throttle defined by an orifice 43 and an axially movable piston 44 to an annular space 42 and thence to the first reheat burner. Fuel from the space 22 also flows through orifice 37 to outlet 38 and thence at pressure DP1 to chamber 39 Fig. 2 for control purposes. The axial position of the spool valve 19 is controlled by pressures applied at either side of piston 24, the space above the piston being connected to fuel inlet passage 14 through orifice 28 and the space below the piston through orifice 26; the pressures are controlled by a pivotally mounted lever 3 1 which controls the leakage through orifices 25, 27. The position of the lever is controlled by bellows 32 which is subject to pressure P 1  P derived from compressor discharge pressure P 2  and compressor inlet pressure P 1 . The lever 31 is loaded by springs 33, 34, the spring 33 also acting against the lower end of the spool 19. The spool carries at its upper end a three-dimensional cam 57 and is rotated by means of a motor 23 in dependence on engine air intake temperature. The spool also carries an edge cam 60 the angular position of which is dependent on the position of the engine throttle lever. The throttle piston 44 is acted on at its lower face by spring 45 also by servo pressure S supplied through line 46. The metering apparatus 13 comprises also a second metering device 16 comprising a piston member 49 mounted within sleeve 47, the piston and sleeve having apertures 50, 48 which co-operate to define a variable metering orifice through which fuel flows from inlet 14, through a throttle controlled orifice 64 and outlet 68 to a second reheat burner; the orifice 64 is controlled by a piston member 65 acted on at its lower surface by spring 66 and by servo pressure S2 supplied through inlet 67. The metering piston 49 is movable axially and rotationally, axially by means of a lever 58 which acts on the stem 53 and is movable by the cam 57, and rotationally by the lever 62 which is secured to the stem 53 and which engages with the edge cam 60 which is movable in dependence on engine throttle position. Fuel also passes from inlet 14 through orifice 52 to the upper side of piston 49 and thence through bore 54 under control of ball valve 56 which is acted on by lever 58 under control of spring 59 and cam 57. Fuel downstream of the metering orifice 50, 48 passes through orifice 69 and line 70 to provide a control pressure DP2. The metering apparatus 13 comprises also a third metering device 17 similar to the device 16, which supplies fuel through outlet 76 to a third reheat burner. The throttle piston is acted on by servo pressure S3, and a control pressure DP3 is supplied through orifice 74 and -  outlet 75. The control unit 40 is shown in Fig. 2, the valve member 11 of the reheat fuel pump 10 being acted on at one side by pressure Pp at fuel pump outlet and at the other side by a servo pressure derived from spool device 82 and communicated through outlet 85 and duct 12. The spool 82 is acted on at one side by fuel pump discharge pressure and at the other side by control pressure DPI in chamber 39 also by centrifugal governor device 81 responsive to engine speed. The control unit 40 comprises also a spool valve 86a which is acted on at its left-hand side by control pressure DP2 and at its right-hand side by control pressure DPI within chamber 39. Fuel pump pressure PP is supplied to inlet 87 and servo-pressure S2 is derived at outlet 90; servo-pressure S1 also is derived at outlet 89. It is arranged that DP 1  and DP 2  are equal. A further spool valve 92 is provided, similar to spool valve 86, the valve 92 being acted on at its left-hand side by control pressure DP3 and providing servo-pressure S3 at its outlet, also servopressure S1.