Evaluation on the Effects of Compression Ratio, CO_2 and LPG on HCCI Combustion Fueled with DME

A 2-135 C.I. engine was modified to a DME(dimethyl-ether) HCCI(homogeneous charge compression ignition) combustion. The experimental results show that DME HCCI combustion produces almost zero NO_x emission and smokeless exhaust. Within the engine load range, the emissions of CO and HC decrease with the increase of engine load. The HCCI combustion of DME displays remarkable two-stage combustion characteristic. Because the first combustion stage starts at around 28° CA BTDC,the engine can only operate at med-low load range. The method of increasing fuel input to increase engine load range is likely to lead to knock. In this paper, inorder to control ignition and combustion phase of HCCI, combustion ratio is adjusted, diluent gas CO_2 is added to the engin intake flow and LPG is added to DME fuel to extend the range of engine of operation. The experimental results show that the above methods are effective in controlling HCCI combustion and enlarging engine load range.