What can cause detonation in a reciprocating engine?

The use of a lower grade fuel than recommended can lead to detonation in a reciprocating engine due to the fuel's lower octane rating. Fuels with a lower octane rating ignite more easily under compression than those with a higher rating. In a reciprocating engine, when the fuel-air mixture is compressed to high pressures, if the fuel cannot withstand that pressure without igniting prematurely, it can lead to a situation where the combustion process turns violent, resulting in detonation. Detonation is characterized by a sudden increase in pressure and temperature, which can damage engine components and reduce overall efficiency.

Conversely, using a higher grade fuel than recommended doesn’t usually cause detonation but may lead to incomplete combustion or a loss of efficiency without triggering premature ignition. Operating at low power settings tends to reduce the risks of detonation because cylinder pressures and temperatures are lower. Keeping the mixture rich typically helps to cool the combustion process and reduce the likelihood of detonation as it alters the air-fuel mixture to a ratio that is less prone to premature ignition.