Effect of Hydrocarbon Molecular Structure on Diesel Exhaust Emissions Part 1: Comparison of Combustion and Exhaust Emission Characteristics among Representative Diesel Fuels

Combustion and exhaust emission characteristics were compared among three representative diesel fuels called “Base (corresponding to a Japanese market fuel)”, “Improved” and Swedish “Class-1” using both a modern small and an optically accessible single-cylinder DI diesel engines. In these tests, the relative amount of PM collected in the exhaust was “Base” >“Class-1” >“Improved” at almost all of the operating conditions. This means that “Class-1” generated more PM than “Improved”, even though “Class-1” has significantly lower distillation temperatures, aromatic content, sulfur, and density compared with “Improved”. There was little difference in combustion characteristics such as heat release rate pattern, mixture formation and flame development processes between these two fuels. However, it was found that “Class-1” contained more branches in the paraffin fraction and more naphthenes. From these results, there is a possibility that branched structures in the paraffin fraction and naphthenes in diesel fuels can influence the PM emissions, especially in the case of low aromatic content fuels.