[-YYZ-]

Ah, but taking it one step further, why does too hot result in detonation?

[HOTTIEBOY]

A combustion chamber that is coated with carbon deposits starts to glow if it gets too hot. That produces enough heat to fire the mixture before it is ready. The same principle applies to dieseling whereas glowing carbon deposits in a combustion chamber act as spark to keep the engine going after the key is switched off. Ever hear that? Notice it has a distinct knock and ping to it? That knock is the sound of a mixture being fired too soon. That is detonation.