Six-stroke diesel engine proposed here has six processes in one cycle and by the direct EGR in the 2nd combustion process, NO emission is expected to decrease. However, weak mixing in 2nd combustion process produced much soot. To improve 2nd combustion process, changing valve timing and supercharging is introduced. The result showed that supercharging was effective in soot reduction. In CASE1 (exhaust valve was opened and shut after 1st combustion process) and CASE2 (the exhaust and intake valves were opened and shut after 1st combustion process) the improvement was not accomplished because the decrease of combustion gas containing oxygen in the 2nd combustion. In CASE3 (the timing of exhaust valve opening was advanced), a fresh air could be introduced into the 2nd combustion due to the pressure drop in the cylinder after the 1st combustion. As the result, NO and Soot in the 2nd combustion process decreased.
