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Ignition system

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Ignition system of reciprocating and turbine engine aircrafts

Publié dans : Ingénierie
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Ignition system

  1. 1. Aircraft Ignition System
  2. 2. Basics • Wherever there is an electric field there is an accompanying magnetic field • Electromagnetic induction • Transformer action
  3. 3. Ignition system-piston engine • It must deliver high tension spark at each cylinder at the correct firing order at predetermined timing. Battery ignition Magneto ignition
  4. 4. Battery Ignition System • Similar to the ignition system of automobiles • A cam rotated by the engine disrupts the flow of current in the primary circuit. This collapsing magnetic field inducers a high voltage at the ignition coil . • This voltage is directed to the spark plug
  5. 5. Magneto Ignition System A magneto is an engine driven AC generator It works on the principle of mutual induction Engine rotates a permanent magnet surrounded by an electric coil. This rotation induces an electric current in the coil windings.  At correct time the current is stopped & magnetic field collapses in the secondary winding and the resultant induced current is carried to the spark plug. The spark Jumps the electrodes starting ignition.
  6. 6. Magneto Ignition System • High tension magneto • Low tension magneto
  7. 7. High Tension Magneto Magnetic circuit Primary electrical circuit Secondary electrical circuit
  8. 8. Magnetic circuit permanent multi-pole rotating magnet, a soft iron core, and pole shoes
  9. 9. Magnetic density  It is subjected to an increasing and decreasing magnetic field  A change in polarity each 90° of magnet travel
  10. 10. Primary electrical circuit consists of a set of breaker contact points, a condenser, and an insulated coil. Coil consists of few turns of copper wire Capacitor is wired parallel to breaker points Primary circuit is completed when breaker points are in contact Condenser is to avoid arcing when opening circuit
  11. 11. Breaker contact points breaker points with condenser opens to interrupt the flow of current in the primary coil, causing an extremely rapid change in flux linkages. The resultant high-voltage in the secondary winding discharges across the gap in the spark plug. They automatically open & close the primary circuit at correct time in relation to piston position.
  12. 12. Secondary Electrical Circuit • They contains the secondary windings of the coil, distributor rotor, distributor cap, ignition lead, and spark plug. • secondary coil is made up of a winding containing approximately 13,000 turns of fine, insulated wire • distributor numbers represent the magneto sparking order
  13. 13. Magneto inherent problems • Moisture is a good conductor of electricity • If absorbed by the no conducting material in the magneto, such as distributor blocks, distributor fingers, and coil cases can create an electrical circuit. • The high-voltage current that normally arcs across the air gaps of the distributor can flash across a wet insulating surface to ground or misfire the spark plug called flash over and causes misfiring of the cylinder. • This causes pre-ignition, to prevent this coils ,condensers, distributors are waxed. • This causes carbon tracking
  14. 14. Ignition harness • The ignition harness consists of several ignition leads. Ignition leads are insulated wires that that carries the electrical energy from the magneto to the spark plug. • It provides an electrical path to spark plug as well it shields the system from external magnetic fields.
  15. 15. Low Tension Magneto In early years, it was difficult to provide insulators that could contain the high-voltage all weather and radio- equipped aircraft have ignition wires enclosed in shielding to prevent radio noise due to high-voltages.  Low voltage is generated in magneto  This low voltage is increased by transformer action of secondary coil.  Ignition lead will have short length  Distributor uses brush type contact so flash over is avoided  high-voltage is present only in short leads between the transformer and spark plug
  16. 16. Spark plug Its function is to create a spark that will ignite the fuel air mixture Spark plugs operate at extreme temperatures, electrical pressures, and very high cylinder pressures.
  17. 17. Different types of Spark plug  Hot plugs have a long insulator nose that creates a long heat transfer path  Cold plugs have a relatively short insulator to provide a rapid transfer of heat to the cylinder head.  High compression engine will have cold spark plug  Low compression engine will have hot spark plug
  18. 18. Problems associated with spark plug • Lead fouling • Carbon fouling • Electrode erosion • Graphite Fouling of Spark Plugs
  19. 19. Turbine engine Ignition system Capacitor-type , Consists of 2 independent ignition units operating from low voltage DC power(aircraft battery/permanent magnet generator) Fan air is ducted to the exciter box flows around the igniter lead and goes to nacelle. Typical ignition system includes two exciter units, two transformers, two intermediate ignition leads, and two high tension leads
  20. 20. Turbine engine Ignition system There is no timing of ignition Once engine is started the ignition system is switched off However continues ignition is used in critical flight modes such as take off and landing, emergency situations. A continuous series of sparks is produced until the engine starts
  21. 21.  filter that prevents noise voltage from being induced into the aircraft electrical system  DC Motor driving the multilobe cam and single lobe cam are operated by this low V  When the breaker opens, the flow of current stops, and the collapse of the field induces a voltage in the secondary of the transformer  When capacitor is charged, contactor is closed by lobe mechanical action  A portion of the charge flows through the primary of the triggering transformer and the capacitor  This current induces a high-voltage in the secondary, which ionizes the gap at the spark igniter
  22. 22. Thank you

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