Study on the combustion character of a new HCCI combustion system fueled with dimethyl ether (DME) and compressed natural gas (CNG)

This paper reports the investigation of the combustion character of a new homogeneous charge compression ignition (HCCI) combustion system fueled with dimethyl ether (DME) with high-cetane number and compressed natural gas (CNG) with high-octane number. The experimental work was carried out on a single-cylinder, direct-injection diesel engine. The results show that the HCCI combustion process of DME/ CNG is characterized by a two-stage heat release feature. As CNG concentration is increased, the magnitude of peak cylinder pressure increases, ignition delay becomes slightly longer, and the peak heat release rate in the second stage goes up, but the burning duration almost remains unchanged. By contrast, a higher DME concentration causes an increased peak heat release rate in first stage, shorter ignition delay, higher peak cylinder pressure, and shorter primary burning duration. Both theoretical and experimental results indicate the effectiveness of using DME/CNG dual fuel to gain a wider operating range of the HCCI engine.