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.