Effects of fuels with a low aromatic content on diesel engine exhaust emissions

Abstract

Tests were conducted on a Co-operative Fuel Research (CFR) diesel engine using fuels with low aromatic content. The aim of the tests was to gain a better understanding of the way in which diesel fuel components affect exhaust emissions. A set of 14 diesel fuels was used, having aromatic content between 0 and 27 per cent; three of these fuels were oxygenated using diglyme and butyl-diglyme (diethylene glycol dimethyl either and diethylene glycol dibutyl ether). The results showed that the exhaust smoke and oxides of nitrogen (NO_x) emissions correlated highly with the fuel monoaromatic content. When some of the fuel monoaromatic content was replaced by a diaromatic compound, there was a slight increase in exhaust smoke, but no clear effects on NO_x and unburned hydrocarbon emissions. Oxygenated fuels showed lower smoke and NO_x emissions. A statistical analysis of the CFR exhaust emissions suggested that the greatest influence on smoke emission was the fuel density, followed by the carbon-hydrogen mass ratio, 50 per cent distillation temperature and viscosity. A similar analysis suggested that the greatest influence on NO_x was the 5 per cent distillation temperature, followed by density, 95 per cent distillation temperature, carbon-hydrogen mass ratio, 50 per cent distillation temperature, cetane number and viscosity. Finally, a high correlation was found between the engine exhaust emissions and the laminar flame-sooting tendency of some of the fuels.