Type Effect of Fuel Properties on Unburned HC and Particulate Matter Emissions in a Small DI Diesel Engine

Fuel properties are a very important factor to reduce particulate matter (PM) and other emissions with diesel engines. Especially the effect of aromatic contents has been discussed, though details of the influence differ in different reports. In this study the mechanism of PM formation was investigated in a small direct injection diesel engine. The fuels tested were paraffinic hydrocarbons (C₇∼C₁₂) with different boiling points (98∼216 °C), and the blending of aromatic hydrocarbons (1∼4 rings) with paraffinic and olefinic hydrocarbons. The effect of the structure of fuels with the same carbon numbers (dodecane and dodecene) was also investigated. The results showed that the amount of SOF decreases to about one tenth of that of diesel oil when using low boiling point paraffinic hydrocarbons like heptane. However, the total amount of unburned hydrocarbon increases due to over-leaning of the mixture due to the early evaporation. Even when carbon numbers are the same, dodecene with a double bond olefinic structure and blended with aromatic hydrocarbons result in higher SOF than dodecane with its ordinary paraffinic structure. Blending of aromatic hydrocarbons with dodecane causes increases in dry soot emissions while SOF emissions are almost unchanged.