It was shown in our previous study that the air-jet in the late combustion period reduces the diesel exhaust soot effectively. However, the plunger-pump type air-jet generator used in our previous study has a big power-loss. In this paper, the reduction of soot emission with a newly designed air-accumulation type air-jet generator is investigated using an experimental single cylinder engine. The optimum design parameters, such as the spring constant and the air outlet diameter, are examined experimentally. The effectiveness of the air-accumulation type air-jet generator for the reduction of soot and NOx emission is about a half of that of the plunger-pump type. It is confirmed that the disappearing speed of the luminous flame region accelerates with the increase of the heat-release in the late combustion period.