Is knock the only abnormal combustion problem?
No. Many of the abnormal combustion problems are induced by the same conditions, and so one can lead to another. Preignition occurs when the air/fuel mixture is ignited prematurely by glowing deposits or hot surfaces – such as exhaust valves and spark plugs. If it continues, it can increase in severity and become Run-away Surface Ignition (RSI) which prevents the combustion heat being converted into mechanical energy, thus rapidly melting pistons. The Ricardo method uses an electrically-heated wire in the engine to measure preignition tendency. The scale uses iso-octane as 100 and cyclohexane as 0.
