A picture processing technique is applied to the analysis of flame motion in a small direct injection diesel engine. The combustion sequences were taken from the underside of the combustion chamber by the high-speed photography. Adjacent two frames of the combustion sequence, one of which was a positive picture and the other was a negative picture, were overlapped. The picture obtained by the above process showed the moved area of luminous flame at a very short period, and enabled us to investigate the direction of the flame motion in the combustion chamber. In the middle stage of combustion, the flame spouted from the inside to the outside of the piston cavity induced the radial flame motion toward the cavity in the area outside the cavity. The effect of the configuration of a nozzle hole on the flame motions inside and outside the piston cavity was discussed. Engine performance was improved by increasing the radial flame motion.
