Effects of Compression Ratio on Performance, Combustion, and Emission Characteristics of an HCCI Engine

The effects of the dimethyl ether (DME) homogeneous charge compression ignition (HCCI) engine compression ratio on its performance, combustion, and emission characteristics were studied experimentally on a modified single-cylinder diesel engine. Three kinds of compression ratio, 8, 10.7, and 14, were designed by separately enlarging the volume of the combustion chamber on the piston head. The experimental results indicate that the HCCI engine has a wider stable working region and higher effective thermal efficiency at ε = 10.7. It was also found that an increased compression ratio produces advanced ignition and increased energy release rates. The variety of compression ratio has no effect on NO x and smoke emission and the DME HCCI engine achieves smokeless combustion and zero NO x emission with all the designed compression ratio; CO emission is reduced with an increase of compression ratio at comparable working conditions; HC emission presents a dramatic result, the highest at ε = 10.7 and the lowest at ε = 14.