Effects of Cetane Number and Distillation Characteristics of Paraffinic Diesel Fuels on PM Emission from a DI Diesel Engine

Fischer-Tropsch Diesel (FTD) fuel is expected to be a promising clean diesel fuel in the future because of its characteristics of zero sulfur, zero aromatics and a high cetane number. However, the optimum fuel properties for diesel engines have not been realized. In this study, the effects of cetane number and distillation characteristics on engine-out PM emissions from a conventional direct injection diesel engine were investigated by using paraffinic fuels which were made to simulate FTD fuel. From the results of the vehicle exhaust emissions test and engine dynamometer test, it was found that the narrow distillation characteristics (which eliminates heavy hydrocarbon fraction) could reduce the soluble organic fraction (SOF) in PM emissions, and the excess high cetane number characteristic promoted the formation of insoluble organic fraction (ISOF). It is considered that shorter ignition delay due to the excessively high cetane number results in poor mixing of injected fuel and air in the combustion chamber. Future diesel engines are expected to lower the compression ratio and to require the fuels with high cetane number. However, in the case of conventional diesel, the results showed that moderate high cetane number and narrow distillation properties eliminating the heavy hydrocarbon fraction were desirable as the optimum FTD fuel.