An explosion or sudden report made by the instantaneous decomposition or combustion of unstable substances; as, the detonation of gun cotton.
This is a supersonic combustion wave. Detonations in gases propagate with velocities that range from 5 to 7 times the speed of sound in the reactants. For hydrocarbon fuels in air, the detonation velocity can be up to 1800 m/s. The ideal detonation speed, known as the Chapman-Jouguet velocity, is a function of the reactant composition, initial temperature and pressure.
Rapid and uncontrolled combustion. Detonation can occur in the cylinder of a spark ignition engine when operating on a fuel of inadequate octane rating, or with ignition timing too far advanced. It is also known as ""pinging"" or ""knocking.""