Patent GB-1344341-A (GB)
Title: Afterburner ignition fuel metering unit for a turbojet engine
IPC: F02C7/22
Filed: 1971-04-19
Abstract: 1344341 Gas turbine engines - re-heat fuel control MOTOREN-UND TURBINENUNION MœNCHEN GmbH 19 April 1971 [9 April 1970] 26690/71 Heading F1J The invention relates to an after-burner ignition fuel metering unit for a gas turbine jet engine, the ignition fuel being injected into the main combustion chambers 20, 21 of the engine through injectors 57, 58, the resulting ignition flame passing through the turbine 23 to the after-burner section 24. After-burner fuel is supplied to the burners 26 through line 33 by pump 34 from tank 28. Fuel is supplied to the burners 27 in the main combustion equipment from tank 28 by pump 38 through line 37. Fuel is supplied to the after-burner ignition fuel control unit 1 from tank 28 by pump 31 and line 42 to inlet 43, this being high pressure fuel, and by pump 32 and lines 46, 47, 48, this being low pressure fuel. The control unit comprises a cylinder 1 providing two chambers 2, 5 in which are disposed a first control piston 3 and a second control piston 6 respectively, the first piston being acted on by control spring 4 so that it bears against a stop formed in the cylinder; the piston 6 is acted on by control spring 7 so that it bears against a stop member 45. A cylinder 11 is mounted on the end wall 8 of the cylinder 1 and contains a piston 12 which is loaded to the right by spring 17, the piston having a projection 13 which extends through an opening 14 in the cylinder end wall 8 and carries a stop member 15 which engages the inside of the piston 3. A filling valve member 9 is also mounted on the end wall 8 being connected to the low pressure fuel line 47. The low pressure fuel line 48 is connected through opening 49 to the cylinder space 5 in which is disposed the control piston 6, this piston being formed with an annular recess 50 and passages 51, 52. A solenoid 60 is disposed around the cylinder 5 and when energized acts to hold the piston 6 to the right so that the piston 6 is acting to compress the spring 7. When re-heat is selected, the high pressure fuel in line 42  passes through opening 43 to act on the right hand face of piston 3 whereby the piston is moved to the left against the action of the spring 4, so forcing fuel contained within the cylinder 2 out through opening 53 and lines 54, 55, 56 to the after-burner ignition injectors 57, 58. When the inside surface of the piston 3 contacts the stop member 15 the electrical circuit is broken and the second control piston 6 is moved to the left under the action of the control spring 7 so that the opening 43 is closed off and the opening 49 is aligned with the annulus 50 in the piston 6. The piston 3 is now urged to the right under the action of spring 4, the filling valve 9 opens and the cylinder 2 is re-filled through line 47 and the open valve 9 ready for the next ignition. The position of the stop member 15 and thus the amount of ignition fuel injected is dependent on the piston 12 which in turn is controlled by the spring 17 and the pressure of the fuel in cylinder 2 acting on the face 12' of the extension 13. The piston 12 may be loaded alternatively by the pressure in the engine intake, which pressure is communicated through line 62, or by compressor discharge pressure. In Fig. 2, the piston 65 is disposed in cylinder 83 being urged to the right by spring 66. A filling valve 92 is connected to low pressure fuel line 89 and a discharge orifice 84 is connected to line 86 and ignition injectors. The second control piston 79 is disposed in cylinder 80 and is urged to the right by spring 81. A diaphragm 76' is connected to a stem 78 which bears against the piston 79. When re-heat is selected, pressure is applied to the diaphragm 76' as indicated at 77 urging the piston 79 to the left whereby the port 94 is opened and high pressure fuel from line 87 can pass through port 94, through passage 95 in the piston 79 to the cylinder space 80, the high pressure fuel thus acting through opening 82 on the right hand side of piston 65 which thus moves to the left against the action of the spring 66 and discharging fuel from the cylinder 83 through opening 84 and line 86 to the ignition injectors. As the piston 79 moved to the left it closed off the opening 93 connected to the low pressure fuel line 90. In the wall 64 of the cylinder 83 are three openings 67, 68, 69 each connected through lines containing pressure relief valves 73, 74, 75, to fuel return 76 to tank 28, the valves being responsive to different pressures whereby the amount of ignition fuel injected varies in dependence on the ambient pressure. In a third embodiment the first control piston is formed with a stem which moves within an electric coil, current to which is controlled by a device in response to ambient pressure.