Distinguishing the Effects of Aromatic Content and Ignitability of Fuels in Diesel Combustion and Emissions

The influence of aromatic content in fuels on the soot and NOx emissions from a diesel engine was analyzed under controlled ignition lags with spark-assisted operation. Monocyclic aromatic hydrocarbons and n-hexane mixtures were used as fuels, and the aromatic content was varied from 0 to 75 v-%.

The experiments showed that, at the same equivalence ratio and regardless of the molecular structure of the fuel, the soot concentration in the exhaust gas could be described by a linear-combination function with two variables representing the ignition lag and C/H atom-ratio of the fuels. For unchanged ignition lags, the soot emissions increased linearly with increased C/H atom-ratios, which are controlled by the aromatic content. The degree of increase in soot emissions with increasing C/H atom-ratio decreased with decreasing equivalence ratios. The NOx emission increased slightly with increases in the C/H atom-ratio and ignition lag.