Experimental study on homogeneous charge compression ignition (HCCI) combustion process was carried out on a single-cylinder direct injection diesel engine fueled with dimethyl ether(DME). The influence of inert gas CO_2 on the ignition and combustion process was investigated. The research results indicate that because of the high cetane number of DME, the stable HCCI operating range is quite narrow while the engine has a high compression ratio. The HCCI operating range can be largely extended when the inert gas is inducted into the charging air. HCCI combustion of DME presents remarkable characteristic of two-stage combustion process. As the concentration of inert gas increases, the ignition timing of the first combustion stage delays, the peak heat release rate decreases, and the combustion duration extends. Inducting inert gas into charging air cannot make the combustion and heat release of DME occur at a perfect crank angle position. Therefore,to obtain HCCI operation for the fuel with high cetane number,other methods such as reducing engine compression ratio should be adopted. Emission results show that under HCCI operation, a nearly zero NO_x emission can be obtained with no smoke emissions. But the HC and CO emissions are high, and both rise with the increase of the concentration of inert gases. The study of on homogeneous charge compression ignition (HCCI) combustion process was carried out on a single-cylinder direct injection diesel engine fueled with dimethyl ether (DME). The influence of inert gas CO_2 on the ignition and combustion process was investigated. indicate that because of the high cetane number of DME, the stable HCCI operating range is quite narrow while the engine has a high compression ratio. the HCCI operating range can be largely extended when the inert gas is inducted into the charging air. DME presents remarkable characteristic of two-stage combustion process. As the concentration of inert gas increases, the ignition timing of the first combustion stage delays, the peak heat release rate decreases, and the combustion duration extends. the combustion and heat release of DME occurs at a perfect crank angle position with high cetane number, other methods such as reducing engine compression ratio should be adopted. Emission results show that under HCCI operation, a nearly zero NO_x emission can be obtained with no smoke emissions. But the HC and CO emissions are high, and both rise with the increase of the concentration of inert gases.