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Combustion
Spark plugs are used to generate the spark which ignites the compressed fuel and air mixture in the spark ignition engine. To generate the spark a high voltage of around 20, 000 Volts is applied. Low voltage current is fed through the primary winding of an inductor coil generating a magnetic field. The high voltage is generated when the low voltage supply is interrupted and the magnetic field breaks down generating a high voltage in the secondary winding which has a much larger number of coils. The low voltage supply to the coil is controlled by the distributor which also controls the spark plug that the high voltage surge is sent to. The distributor timing is critical and usually is timed mechanically from the engine. The diagram below shows the typical set-up of an ignition system for a spark ignition engine.
Compression ignition engines such as the diesel engine do not use spark plugs to ignite the fuel-air mix. When the piston reaches the top of the compression stroke the temperature and pressure in the combustion chamber is sufficient to ignite the mixture. Controlled ignition in both spark ignition and diesel engines is essential for efficient combustion and avoid uncontrolled combustion effects such as pre-ignition, auto-ignition and engine knock.
Ref: [15],[K]
The following areas of measurement are of interest during the ignition stroke:
 | Pressure analysis |
| Temperature analysis |
| Flow analysis |
| Chemical analysis |
| Flame analysis |
| Particle analysis |
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