Auto
Ignition:
- A mixture of fuel and air can react spontaneously and produce heat by chemical reaction in the absence of flame to initiate the combustion or self-ignition.
- This type of self- ignition in the absence of flame is known as Auto-Ignition.
- The temperature at which the self-ignition takes place is known as self- igniting.
Pre
Ignition:
- Pre-ignition is the ignition of the homogeneous mixture of charge as it comes in contact with hot surfaces, without spark.
- Auto ignition may overheat the spark plug and exhaust valve. So that its temperature is sufficient to ignite the charge in next cycle during the compression stroke before spark occurs and this causes the pre-ignition of the charge.
- Pre-ignition is initiated by some overheated projecting part such as the sparking plug electrodes, exhaust valve head, metal corners in the combustion chamber, and carbon deposits.