Patent GB-697953-A (GB)
Title: Improvements in or relating to electrical ignition systems of gas turbine engines
Inventor: WEST HAROLD EDWARD WILLIAM
IPC: F02C7/266
Filed: 1949-12-30
Abstract: 697,953. Gas turbine plant. ROLLS-ROYCE, Ltd. Dec. 11, 1950 [Dec. 30, 1949], No. 33444/49. Class 110(iii) [Also in Group XXVII] A gas turbine engine having a plurality of combustion chambers has an electrical ignition system comprising a plurality of electrical igniter devices in the combustion chambers of the engine, a source of electrical energy at high potential and distributer means actuated by electrical operation of an igniter device or devices to disconnect the igniter device or devices from the source and to connect the source to a succeeding igniter device or devices. The gas turbine engine 10 has a plurality of combustion chambers 11 each fitted with a spark type igniter device 12. The devices 12 are supplied with energy. by a booster coil 13, the primary coil 13a of. which is connected through make and break contacts 14. across a low tension supply 15. One terminal of the secondary winding 13b is connected to a rectifier 16 and the other terminal is connected to the earthed side of an accumulator condenser 17 having a capacitance of about 6 microfarads. The other side of. the accumulator condenser is joined to the rectifier 16. A lead 18 from the connection between the rectifier 16 and accumulator condenser 17 is connected to one electrode of a spark gap 19. The other electrode of the spark gap is jointed to a distributer 20 which consists of a rotatable ratchet wheel 21 carrying a contact arm 22, contact points 23 and a pawl 24 operated by a servo-mechanism 25. The contact points 23 are connected by leads 26 to the spark igniters 12. The servo-mechanism 25 comprises a circuit, arranged in parallel with the accumulator condenser 17 after the rectifier 16, having in series a high resistance 27 of approximately 250,000 ohms.; an auxiliary condenser 28 of 0.5 microfarad capacity and the operating coil 29 of a relay. When switch contacts 30 are closed by the energization of the coil 29 the solenoid 31 is energized and the armature 32 moves downwards. This causes the pawl 24 to rotate the ratchet wheel 21 one division. In operation, the booster coil 13 charges up the accumulator condenser 17 and auxiliary condenser 28 via the rectifier 16. The spark gap 19 prevents discharge of the two condensers 17, 28 until the voltage reaches that of the breakdown of the spark gap. On discharge of the accumulator condenser 17 current flows through the distributer 20 to that igniter device 12 connected to the condenser through contact 23 and contact arm 22 and initiates ignition in the associated combustion chamber. When the condenser 17 has been substantially fully discharged, the auxiliary condenser 28 discharges either across the spark gap 19 or into the accumulator condenser 17. This causes a flow of current sufficient to energize the relay coil 29 to close the switch contacts 30 and energizes the solenoid 31 which then rotates the ratchet wheel 20. The resistance 27 and auxiliary condenser 28 are arranged to give a definite time of operation of the relay 29, 30 and with the values given above, this time is one-tenth of a second. The relay 29, 30 is adjusted to close the contacts 30 when a current of 2¢ milliamps flows through the coil but not to operate them with a current of 1¢ milliamps.