Search for the Optimizing Control Method of Compound Charge Compression Ignition (CCCI) Combustion in an Engine Fueled with Dimethyl Ether

Abstract

Taking advantage of HCCI combustion and in-cylinder direct-injection combustion for an engine fueled with dimethyl ether (DME), a new concept combustion system, namely, a compound charge compression ignition (CCCI) combustion system by port aspiration and direct injection of DME, is proposed. A diesel engine was modified to carry out this test. Combustion and emission characteristics were investigated in different premixed fuel ratios and fuel delivery advance angles. To further optimize the emissions and improve the DME fuel consumption in a CCCI engine, port fuel design concept and port aspiration of CO2 were employed. The experimental results show that the CCCI combustion process comprises HCCI combustion, premixing combustion, and diffusion combustion. The combustion characteristic is mainly decided by a premixed fuel ratio and CO2 concentration in air charge. In comparison to a homogeneous charge compression ignition (HCCI) combustion mode, CCCI combustion can extend the operating range with low NOx, hydrocarbon (HC), and CO emissions. To control the ignition and combustion phase of HCCI, the effect of liquid petroleum gas (LPG) added to DME fuel was evaluated. As a result, NOx emissions decreased and thermal efficiency was improved with the mix of LPG. It is of interesting to note that HCCI−MK (modulated kinetics) combustion for CCCI combustion engines was observed at a 14°CA before top dead center (BTDC) fuel delivery advance angle with an appropriate CO2 concentration in air charge, and NOx emissions could be lowered to near-zero levels.