The difference in the combustion rate is determined by the difference in the method by which the mixture was prepared.Corresponding with the turbulence intensity at the spark plug,the spreads of flame in the combustion chambers with pistons A and D were faster than those pistons B and C (Fig. 11). At 730 CA, the flame had nearly burned across the whole combustion chambers for pistons A and D, but a block of unburned mixture still remained in the combustion chambers with pistons B and C