Effect of fuel aromatic content and structure on direct-injection diesel engine pollutant emissions

An experimental investigation is conducted to examine the effect of fuel aromatic fraction and type on DI diesel engine performance, gaseous and particulate emissions. Various diesel fuels with total aromatics between 0 and 27% were tested in a naturally aspirated single-cylinder DI diesel engine. The experimental results reveal a strong relationship between measured pollutant emissions and both total and monoaromatic content, whereas only a small effect is found on other aspects of engine performance. An abrupt increase in exhaust smoke is observed when the aromatic content is increased from 0 to 15%, whereas, for higher aromatic contents, tailpipe soot remains almost constant. Nitrogen oxide and carbon monoxide emissions increase with the increase in total aromatics, whereas unburned hydrocarbons decrease slightly with total aromatics. The substitution of monoaromatics by diaromatics results in an improvement of the bsfc/NOx trade-off and in an increase in CO and HC emissions, whereas it has a rather detrimental effect on soot/NOx trade-off. To examine the sensitivity of exhaust smoke to fuel parameters, a multivariate statistical analysis was carried out. The results of the regression analysis reveal that soot is affected by C/H mass ratio, fuel volatility (end-fuel boiling point), flammability (cetane number) and fuel aromatic percentage and type (monoaromatics and total aromatics).