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Although whether the cylinder gas oscillation is provoked by end-gas autoignition in a certain cycle or not is a irregular phenomenon, autoignition itself takes place in almost all of the cycles in the knocking condition. Detection of the autoignition makes it possible to realize a knock anticipating strategy. Using the decay rate of the effective heat release rate as the index, delayed autoignition with small auto-ignited mass fraction can be detected. Applying this index for the analysis of the autoignition in the acceleration process, it was clarified that heavy autoignition immediately after the acceleration caused by the selective induction of the low boiling point gasoline components into the cylinder is followed by the period where the low combustion chamber wall temperature reduces the autoignited mass fraction and suppresses the cylinder gas oscillation.

To execute the computational fluid dynamics coupling with fuel chemistry in internal combustion engines, simplified chemical kinetic models which capture the low-temperature oxidation kinetics would be required. A steady-state analysis was applied to see the complicated reaction mechanism of alkylperoxy radicals by assuming the steady state for hydroperoxyalkyl (QOOH) and hydroperoxyalkylperoxy (OOQOOH) radicals. This analysis clearly shows the systematic trend of the reaction rate for the chain-branching and non-branching process of alkylperoxy (ROO) radicals as a function of the chain length and the carbon class. These trends make it possible to classify alkylperoxy radicals by their chemical structures, and suggest a reduced low-temperature oxidation chemistry.