This paper describes knocking improvement by achieving a high heat release pattern at late stage combustion using a reverse squish flow. The gas flow in a cylinder flow (tumble and squish flow) flame propagation, and the combustion pattern were measured with a real SI engine. A flow-direction relationship between the tumble and squish flows and the influence of a tumble ratio were examined for each of various combustion chamber shapes. This examination clearly shows the reverse squish flow becomes intense at a high tumble ratio when the tumble and reverse squish flows are in the same direction, while it becomes intense at a low tumble ratio when in a conflicting direction, and a relatively low tumble ratio makes the reverse squish flow the maximum when the tumble and reverse squish flows are in the conflicting direction compared to that in the same direction. Increasing the reverse squish flow rate can enlarge the heat release pattern at the late stage combustion, thus achieving a high effect of knock improvement.
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