GB1293672A - Improvements in fuel supply systems for aircraft gas turbine jet engines - Google Patents

Abstract

1293672 Gas turbine jet engines - re-heat fuel systems H M HOBSON Ltd 19 April 1971 [5 March 1970] 10647/70 Heading F1J The invention relates to a re-heat fuel control system for an aircraft gas turbine engine in which re-heat fuel is supplied to three manifolds - the primary, gutter and colander manifolds, through respective control valves, the valves being controlled by means of a three-dimensional cam so as to maintain fuel flow in the three manifolds as desired functions of engine conditions, there being means for controlling the pressure difference across the primary flow control valve as a function of engine speed. The fuel pump 10 has an inlet control valve 17 and receives fuel through inlet line 8 in which is an inlet valve 21, the pump discharging through line 9 through the primary, gutter and colander control valves 14,15,16 to the lines 11,12,13 and so to the primary, gutter and colander manifolds, not shown. Purge valves 22,23,24 are associated with the manifolds and are closed by the pneumatic actuator 82 when re-heat is selected, the opening of the inlet valve 21 being co-ordinated with the closing of the purge valves. A by-pass passage 25 leads from the pump discharge line 9 to by-pass the control valves 14,15, 16 so that when re-heat is selected, re-heat fuel passes through lines 9,25 through the priming line shut-off valve 26 which is open at this phase, through the non-return valves 89, 90, 91 to the respective manifolds for priming thereof. The pump inlet valve 17 is controlled by a servo-piston 35 and is normally held in the open-position by the loading of a spring 38, the space below the piston being connected to pump discharge pressure through line 37 and the space above the piston being connected to a modified pump discharge pressure which is supplied through lines 53, 51 under control of a variable orifice 50, also a fixed orifice 40 in line 39 connected to the pump inlet. The variable orifice 50 is controlled by a flap valve 7 in dependence on pressures in chambers 54, 52 above and below diaphragm 41, the position of the diaphragm being also controlled in dependence on engine speed by means of governor device 42 and in dependence on inlet total temperature by the device 61 acting to control valve 58 in the outlet line 57 from the chamber 54. The governor 42 is only driven when re-heat is selected, the clutch member 44 normally being held open by the spring 45 but being moved into the operative position by fuel under pressure supplied through line 49 to the piston 46, the line 49 being connected to pump discharge line 9, 25 through a pressure regulating valve 48. The three-dimensional cam 29 is movable rotationally and axially, rotationally by actuator 28 upon selection of re-heat, and axially by means of a piston 64 which is urged downwardly by spring 67, and which is formed with an orifice 68. The axial position of the piston and so of the cam 29 is controlled by compressor discharge pressure Pt2 supplied to a chamber in which is disposed capsule 65, the capsule controlling a pivoted flap valve 66 which controls leakage from chamber 70 through nozzle 69 back to the pump inlet. The primary control valve 14 is controlled by the axial position of the cam 29 whereas the gutter and colander control valves 15,16 are controlled by the axial and rotational positions of the cam. A device 71 comprising a diaphragm 72 and valve members 18,19 senses the pressures downstream of the primary and gutter control valves 14,15 and acts to equalise these pressures. Fuel flow to the colander manifold through line 13 is controlled by device 73 which comprises a diaphragm 80 and a valve member 20, the diaphragm being subject at one side to the pressure downstream of the control valve 16, and at the other side to pressure from a potentiometer comprising line 74, fixed orifice 75 and variable orifice 76, the variable needle 76 of the orifice being controlled by the temperature sensing device 61 acting through cam 81. The hot streak ignition device shown in Fig.2 is connected to the regulated pressure fuel line 49 through line 119 and in the position shown with the spool valves 111 ,112 disposed to the right by force of springs 117, fuel passes to the chambers 107, 108 forcing the pistons 109,110 to the left against the loading of springs 123, 124. Upon selection of re-heat the piston 27 is urged to the left by fuel pressure in line 128, causing the yoke member 114 and so the two spool valves 111,112 to move to the left. The pressure fluid in line 119 now acts at the left hand sides of the pistons 109,110 forcing the pistons to the right and discharging the fuel from the chambers 107, 108 through lines 120,121 to No.2 and No.1 ignition jets respectively. The spool valves 111,112 are rotated continuously in operation but the yoke member 114 is constrained against rotation by means of rollers 116. The fuel in line 128 is taken from line 49 through line 98 under control of valve 93 which is controlled by pressure Pt5, the pressure in the jet pipe, the arrangement being such that the hot shot is not released until the priming by-pass line 25 has been shut off by valve 26.