What is pre-ignition and what can cause it?

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Multiple Choice

What is pre-ignition and what can cause it?

Pre-ignition is ignition of the air-fuel mixture before the spark plug fires. It happens when heat in the combustion chamber raises the mixture to its ignition temperature before the timed spark, so the flame starts ahead of the intended moment. Common causes include hot spots in the chamber (like carbon deposits on the piston or chamber walls), overheating of components (high cylinder head temperature, hot valves, or a piston that’s excessively hot), and a spark plug with a heat range that’s too hot or timing that’s too far advance. When pre-ignition occurs, the result is abnormal, advancing combustion that can cause high pressures and potential engine damage. The other descriptions don’t fit: ignition after the spark describes normal post-spark combustion rather than pre-ignition; claiming it only happens when the engine is cold is not accurate; and saying pre-ignition is the same as detonation confuses two different phenomena—detonation is auto-ignition caused by pressure and heat after the spark, not before.

Pre-ignition is ignition of the air-fuel mixture before the spark plug fires. It happens when heat in the combustion chamber raises the mixture to its ignition temperature before the timed spark, so the flame starts ahead of the intended moment. Common causes include hot spots in the chamber (like carbon deposits on the piston or chamber walls), overheating of components (high cylinder head temperature, hot valves, or a piston that’s excessively hot), and a spark plug with a heat range that’s too hot or timing that’s too far advance. When pre-ignition occurs, the result is abnormal, advancing combustion that can cause high pressures and potential engine damage.

The other descriptions don’t fit: ignition after the spark describes normal post-spark combustion rather than pre-ignition; claiming it only happens when the engine is cold is not accurate; and saying pre-ignition is the same as detonation confuses two different phenomena—detonation is auto-ignition caused by pressure and heat after the spark, not before.

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