Combustion and Emission Characteristics of Biodiesel Fuels in a Common-Rail Diesel Engine

A single cylinder DI (direct injection) diesel engine equipped with common-rail injection system was used to investigate the combustion and emission characteristics of biodiesel fuels. Tested fuels were conventional diesel and biodiesels obtained from unpolished rice oil and soybean oil. The volumetric blending ratios of biodiesel with diesel fuel are set at 0, 10, 20 and 40%. Experimental results show that the peak injection rate is reduced as the mixing ratio increased. The effect of the mixing ratio on the injection delay of biodiesel is not significant at the equal injection pressure. The peak combustion pressure was increased with the increase of the mixing ratio at an injection pressure of 100MPa. The ignition delay became shorter with the increase of the mixing ratio due to a higher cetane number of the biodiesel. HC and CO emissions are decreased at a high injection pressure. However, NO_x emissions are increased at higher mixing ratios.