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Related to preignition: Spark knock
The ignition of fuel in an internal-combustion engine before the spark passes through the fuel, resulting from a hot spot in the cylinder or from too great a compression ratio for the fuel.
pre•ig•ni•tion(ˌpri ɪgˈnɪʃ ən)
ignition of the charge in an internal-combustion engine earlier in the cycle than is compatible with proper operation.