This paper introduces a new combustion system for B.I. diesel engine — CSCS system, with which a new structural pintle injector and a combustion bowl with squish lip are used and no intake swirl is needed. The injection and spray characteristics of the new injector include the uniform peripheral distribution of spray and the good atomization quality of spray as well as the higher fuel injection rate. The schlieren photograph and the DDM spray model are applied to study fuel—air mixing and combustion processes of the new combustion system, the main results are that the rates of fuel—air mixing and combustion are higher owing to homogeneous distribution and rapid evaporation of fuel. The results of test on a single-cylinder engine show the availability of the combustion system on small bore high-speed D.I. diesel and the improvements regarding fuel consumption and cold smoke.