Abstract: In order to reduce the soot content in the exhaust gas from diesel engine model 6120, experiments and research work are done on a 1120 singlecylinder test set designed by the authors, including design of the combustion chamber and the intake-port as well as choice of the fuel system. The results indicate that the new a -combustion system used in the diesel engine model 6120 is very effective in reducing the soot content of the exhaust gas.