In the HCCI Engine, the in homogeneity exists in fuel distribution and temperature in the premixture microscopically, and has the possibility of affecting the ignition and combustion process. In this study, the effect of the in homogeneity in DME/n-Butane Air mixture in the combustion chamber on the HCCl combustion was investigated by chemiluminescence method in order to understand the spatial distribution of the combustion. DME and n-Butane were used as a test fuel because those of combustion characteristics are different. First, in the 4-stroke optically accessible engine, after clarifying the relation between the heat release and the chemiluminescence from DME/nButane-Air mixture HCCl combustion, the effects of the inhomogeneity in fuel distribution in the pre-mixture on the heat release, flame structure and exhaust gas composition were evaluated. Next, HCCI combustion without the hot residual gas was realized in the 4stroke engine and the rapid compression machine, and the effect of the in homogeneity in temperature and gas composition due to the hot residual gas on the heat release and flame structure was evaluated.