Aircraft Ignition System
16AE206 Aircraft system and instruments prepared by 3/9/2020 1 R.Vijayakumar AP/Aero Basics
• Wherever there is an electric field there is an accompanying magnetic field • Electromagnetic induction • Transformer action
16AE206 Aircraft system and instruments prepared by 3/9/2020 2 R.Vijayakumar AP/Aero 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
16AE206 Aircraft system and instruments prepared by 3/9/2020 3 R.Vijayakumar AP/Aero 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
16AE206 Aircraft system and instruments prepared by 3/9/2020 4 R.Vijayakumar AP/Aero 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.
16AE206 Aircraft system and instruments prepared by 3/9/2020 5 R.Vijayakumar AP/Aero Magneto Ignition System
• High tension magneto
• Low tension magneto
16AE206 Aircraft system and instruments prepared by 3/9/2020 6 R.Vijayakumar AP/Aero High Tension Magneto
Magnetic circuit Primary electrical circuit
Secondary electrical circuit
16AE206 Aircraft system and instruments prepared by 3/9/2020 7 R.Vijayakumar AP/Aero Magnetic circuit
permanent multi-pole rotating magnet, a soft iron core, and pole shoes
16AE206 Aircraft system and instruments prepared by 3/9/2020 8 R.Vijayakumar AP/Aero Magnetic density
It is subjected to an increasing and decreasing magnetic field A change in polarity each 90° of magnet travel
16AE206 Aircraft system and instruments prepared by 3/9/2020 9 R.Vijayakumar AP/Aero 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
16AE206 Aircraft system and instruments prepared by 3/9/2020 10 R.Vijayakumar AP/Aero 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.
16AE206 Aircraft system and instruments prepared by 3/9/2020 11 R.Vijayakumar AP/Aero 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
16AE206 Aircraft system and instruments prepared by 3/9/2020 12 R.Vijayakumar AP/Aero 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
16AE206 Aircraft system and instruments prepared by 3/9/2020 13 R.Vijayakumar AP/Aero 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.
16AE206 Aircraft system and instruments prepared by 3/9/2020 14 R.Vijayakumar AP/Aero Low Tension Magneto
In early years, it was difficult Low voltage is generated in magneto to provide insulators that This low voltage is increased by could contain the high-voltage transformer action of secondary coil. all weather and radio- Ignition lead will have short length equipped aircraft have ignition Distributor uses brush type contact wires enclosed in shielding to so flash over is avoided high-voltage is present only in short prevent radio noise due to leads between the transformer and high-voltages. spark plug
16AE206 Aircraft system and instruments prepared by 3/9/2020 15 R.Vijayakumar AP/Aero 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.
16AE206 Aircraft system and instruments prepared by 3/9/2020 16 R.Vijayakumar AP/Aero 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 cylinderhead. High compression engine will have cold spark plug Low compression engine will have hot spark plug
16AE206 Aircraft system and instruments prepared by 3/9/2020 17 R.Vijayakumar AP/Aero Problems associated with spark plug
• Lead fouling • Carbon fouling • Electrode erosion • Graphite Fouling of Spark Plugs
16AE206 Aircraft system and instruments prepared by 3/9/2020 18 R.Vijayakumar AP/Aero 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
16AE206 Aircraft system and instruments prepared by 3/9/2020 19 R.Vijayakumar AP/Aero 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 isproduced until the engine starts
16AE206 Aircraft system and instruments prepared by 3/9/2020 20 R.Vijayakumar AP/Aero 16AE206 Aircraft system and instruments prepared by 3/9/2020 21 R.Vijayakumar AP/Aero 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
16AE206 Aircraft system and instruments prepared by 3/9/2020 22 R.Vijayakumar AP/Aero