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Behaviors of shock waves in knocking phenomena were observed in detail and influences of low temperature reaction on the flame and spontaneous ignition of end gas were investigated through experiments using high-speed direct and schlieren photography. As a result, it was found that light emission of shock waves, that is an indicator of pressure, rose when the shock waves collided with the cylinder wall and that pressure waves arose by low temperature reaction before knocking occurrence. Flame oscillation was caused by pressure waves. It is presumed that pressure waves influence spontaneous ignition.

The influence of the eddy scale of initial turbulence in RCM on the pressure rise rate after spontaneous ignition of end gas was investigated. The combustion time of the end gas after spontaneous ignition was observed by using high-speed direct photography. As a result, the large scale eddy reduced the pressure rise rate after spontaneous ignition. The temperature inhomogeneity of end gas was higher with the large scale eddy. The combustion time of end gas after spontaneous ignition was prolonged by variation in local ignition delay due to inhomogeneity. The large scale eddy may prevented the knocking occurrence.