Effects of Squish Area Shape on Knocking in a Four-Valve Spark Ignition Engine

Squish flow control is well known as a key technology for improving knock limit in spark ignition engines. However, to acquire a sufficient squish area in a four-valve engine is difficult. In order to achieve a maximum effect of knock suppression with a minimum squish area, we have developed, what we call, a Slant Squish Combustion Chamber for new engines. A slant squish compared with a conventional squish produces an effective reverse squish flow in the early expansion stroke, resulting in higher flow velocity and turbulence. Furthermore, flame propagation to squish area and end gas is accelerated. These improvements are considered to suppress the knock phenomenon. Consequently, with a slant squish, a high compression ratio, to achieve low fuel consumption and high engine performance is realized.