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Pre-ignition and 'super-knock' in turbocharged spark-ignition engines

Pre-ignition of reactants becomes prevalent as engine pressures increase due to turbo-charging. Critical hot spot sizes for the observed gas phase pre-ignitions are calculated to assess this probability over ranges of fuel/air mixtures and engine conditions. Although spasmodic, it is sometimes followed by end gas auto-ignition at “hot-spots” followed by engine-damaging “super-knock.” Computations for these conditions suggest the observed “super-knocks” are not commensurate with the fuel and observed engine conditions. This is an important area of uncertainty and it is suggested that the auto-ignition might arise from small droplets of long-chain lubricants. Awarded the SAGE Best Paper Prize 2012.