What is Knock/Detonation?
Knock is a condition caused by abnormal combustion of the air/fuel mixture and can result in damage to an engine. The three factors that result in engine knock are: 1) knock resistance characteristics (knock limit) of the engine, 2) ambient air conditions, and 3) octane rating of the fuel being used. • Since every engine is vastly different when it comes to knock resistance, there is no single answer to “how much.” Design features such as combustion chamber shape, spark plug location, bore size and compression ratio affects the knock characteristics of an engine. In addition, engine calibration of fuel and spark plays an enormous role in dictating knock behavior. • For the turbocharger application, both ambient air conditions and engine inlet conditions affect maximum boost. Hot air and high cylinder pressure increases the tendency of an engine to knock. When an engine is boosted, the intake air temperature increases thus increasing the tendency to knock. Charge air cooling (e.g. an in
