One of the authors has proposed to use the decay rate of EHRR, the effective heat release rate, d2Q/dθ2 as an index for the rapid local combustion . In this study, EHRR profiles and the cylinder gas pressure oscillations of the low and high speed knock are analyzed by using this index. A delayed rapid local combustion, such as an autoignition with small burned mass fraction can be detected. In the cases of the low speed knock, it has been agreed that a rapid local combustion is an autoignition.Although whether the cylinder gas oscillation is provoked by an auto ignition in a certain cycle or not is an irregular phenomenon, the auto ignition takes place in almost all of the cycles in the knocking condition. Mixture mass fraction burned by an auto ignition is large.A small auto ignition may induce a secondary auto ignition, in many cases, mass burned by the secondary auto ignition is extremely large. On the other hand, in the cases of the high speed knock, it has not been confirmed that the rapid local combustion is an auto ignition.An intense cylinder gas pressure oscillation is provoked in most of the cycles in the knocking condition, and standing wave at the edges in combustion chamber, may induce a cylinder gas pressure oscillation even in the non-knocking cycles. A mixture mass fraction burned by a rapid local combustion seems to be small and give no influence to the EHRR profile.