Effects of Co-Combustion Ratio on Rapid Combustion, Cyclical Variation, and Emissions of a Heavy-Duty Diesel Engine Fueled with Diesel-Methanol Dual-Fuel

摘要

Diesel-methanol dual-fuel (DMDF) combustion was achieved on a 6-cylinder, heavy-duty, turbocharged and common-rail diesel engine. In DMDF mode, the coal-produced methanol is induced to the upstream of the intake manifold and premixed with the fresh air to form a homogeneous methanol-air mixture and then ignited by direct-injected pilot diesel in cylinder. The purpose of this study is to investigate the effects of co-combustion ratio (CCR) on the rapid combustion, cyclical variation and emissions of the DMDF engine. The experimental results show that CCR affect the rapid combustion (α) and knock tendency (β) greatly. With CCR increasing, both α and β increase significantly. The β exhibits an obviously large value under heavy load although CCR and a are small. At larger CCR, DMDF mode may generate a seriously cyclical variation and the coefficient of variation for indicated mean effective pressure (COV_(IMEP)) exhibits a relatively large value. However, with engine load increasing, the cyclical variation can be obviously decreased. It is also shown that both NOx and smoke emissions in DMDF mode present an obviously decrease trend, while CO and HC emissions exhibits an increase trend. A further reduction of NOx and smoke emissions can be obtained by increasing CCR, but CO and HC emissions are increased in this case.