It is the burning of a fuel and air mixture charge in the combustion chamber.
The burn should be complete with no remaining fuel-air mixture. The remaining fuel in the end gas simply lacks sufficient octane rating to withstand this combination of heat and pressure.
The engine becomes more mechanically efficient. The good thing is, most engines will live with a fairly high level of detonation for some period of time. We are talking some 160-180 degrees of bum being compressed that would normally be relatively cool. Sometimes a knock sensor will react to sounds other than those produced by detonation.
There is going to be a point where the power is the greatest. If switching to a higher octane fuel fails to eliminate a persistent detonation problem, it probably means something else is amiss. Carbon deposits form a heat barrier and can be a contributing factor to preignition. Engine Basics: A static compression ratio of 9: However, under extreme conditions the shock wave from the detonation spike can cause that boundary layer to breakdown which then lets a lot of heat transfer into those surfaces.
Damage attributed to both detonation and pre-ignition would be evident. The wrong heat range plug can cause detonation as well as preignition.
This behavior has fooled a lot of people because they will watch the EGT and think that it is in a low enough range to be safe, the only reason it is low is because the engine is detonating. Remember, the spark plug ignites the mixture and a sharp pressure spike occurs after that, when the detonation occurs.
It does this by "leaking" recirculating small amounts of exhaust into the intake manifold through the EGR valve. Detonation is one phenomenon that is abnormal combustion. Others use an "idle stop solenoid" that closes the throttle completely to shut of the engine's air supply.
Thus, those engines, as a result of the chamber design, required a tremendous amount of spark advance, about 40-45 degrees. Sometimes you hear mistaken terms like "pre-detonation". An unmuffled engine running straight pipes or a propeller turning can easily mask the characteristic ping. Written by Allen W.