Detonation is a common problem on highly tuned cars. What happens when detonation occurs is that a portion of the gas, usually at a corner of the combustion chamber furthest away from the spark plug self ignites but AFTER the spark plug has fired. Detonation is a far more serious problem as it is harder to cure and potentially more damaging to the engine.
The pinging noise that is heard, is the gas ignited by self ignition, colliding with the ignited gas from the spark plug. With pre ignition, the collision of the burning gasses occurs before the piston has reached the top of the bore and so not at maximum cylinder pressure, this is why it does not create so much damage. With detonation, as it occurs after the spark plus has fired and the piston is usually at TDC e.g. maximum cylinder pressure, the effect is to make the coming together of the flaming gasses that much more powerful and so damaging.
The causes of detonation can be similar to preignition, e.g., too high a compression, only causing the problem of self combustion at TDC. The favorite cause of detonation however is too weak a mixture as a weak mixture burns more easily than a rich one, hence the reason for making a lot of engines over rich as a safety measure. On supercharged and turbo charged cars, the cause is often down to inlet air too high a temperature. The results of both, but more aggravated by detonation is the flame paths colliding and hammering the combustion chamber and more importantly the piston. You can readily see the damage when you strip an engine, if it is light detonation you will see pit marks in the combustion chamber and on the piston crown in the area it has occurred, this gives you some idea as to how to rectify the problem. In many cases it is totally terminal, the piston crown collapsing with a big hole in it and usually the pieces of piston destroying the valves and cylinder head.
A few more articles that explains it further.
http://www.spearsenterprises.com/pdf/detonationPreIgnition.pdf
Detonation and Pre-Ignition
The pinging noise that is heard, is the gas ignited by self ignition, colliding with the ignited gas from the spark plug. With pre ignition, the collision of the burning gasses occurs before the piston has reached the top of the bore and so not at maximum cylinder pressure, this is why it does not create so much damage. With detonation, as it occurs after the spark plus has fired and the piston is usually at TDC e.g. maximum cylinder pressure, the effect is to make the coming together of the flaming gasses that much more powerful and so damaging.
The causes of detonation can be similar to preignition, e.g., too high a compression, only causing the problem of self combustion at TDC. The favorite cause of detonation however is too weak a mixture as a weak mixture burns more easily than a rich one, hence the reason for making a lot of engines over rich as a safety measure. On supercharged and turbo charged cars, the cause is often down to inlet air too high a temperature. The results of both, but more aggravated by detonation is the flame paths colliding and hammering the combustion chamber and more importantly the piston. You can readily see the damage when you strip an engine, if it is light detonation you will see pit marks in the combustion chamber and on the piston crown in the area it has occurred, this gives you some idea as to how to rectify the problem. In many cases it is totally terminal, the piston crown collapsing with a big hole in it and usually the pieces of piston destroying the valves and cylinder head.
A few more articles that explains it further.
http://www.spearsenterprises.com/pdf/detonationPreIgnition.pdf
Detonation and Pre-Ignition