The focus of this study was an investigation for the realization of a partial homogeneous charge compression ignition (HCCI) combustion as a control mechanism for HCCI combustion. Premixed fuel was supplied using an in-cylinder early direct injection, and the second injection was made near the TDC to control the ignition and combustion rates of the premixed fuel. In order to obtain the optimal injection timing for the premixed fuel, combustion, and emission characteristics with respect to DI fuel injection timing was investigated in various operational ranges, from conventional diesel combustion to HCCI combustion. The results showed that two-stage injection was very effective in reducing NOx emissions from a DI diesel engine. Additionally, at an optimized injection timing, the ignition of premixed fuel can be controlled by the main injection without premature autoignition. Based on the experimental results, the effect of the premixed ratio and timings of the first and main injections on the combustion characteristics and exhaust emissions in a direct injection diesel engine were discussed.