Hydrocarbons in a diesel fuel, the backend fraction, exhaust gas, and the particulate ( PM ) were analyzed. It was found that hydrocarbons in exhaust gas corresponded to those in the fuel and that the hydrocarbons in PM corresponded to those in the backend fraction. That is, the high boiling point fraction of unburnt fuel was found to correspond to the hydrocarbons in PM or SOF.

Using a set of emission data from a D.I. diesel engine supplied with 9 fuels, the changes in ISF or SOF with changes in engine conditions were determined. SOF, whose main components stemmed from the high boiling point fraction of unburnt fuel, was found to be in a trade-off relation with ISF, formed by carbonization of fuel.

An indicator estimating PM : R₃₁₀�~(C/H)₃₁₀, which was found from the above results and the analytical results of a diesel fuel ( cf. Part 1 ), showed high determination coefficients against PM emissions obtained under low- and medium-load conditions. Here, R310 is the backend fraction at a distillation temperature of 310C, and (C/H)₃₁₀ is the C/H ratio of the fraction.

Linear regression analyses using R₃₁₀ and (C/H)₃₁₀ or (C/H)_Total, which shows the C/H ratio of the whole fuel, were performed. Regression formulas with (C/H)_Totalwere found to show higher correlation coefficients for the particulate emissions obtained under various engine conditions than the formula with (C/H)₃₁₀.