The effects of the chemical composition of Diesel fuels on emissions is a critical issue for future Diesel fuels and synthetic fuels. In order to understand these effects, a series of fuels prepared from blends of pure hydrocarbons were studied in a single cylinder, DI Diesel engine. The base fuel was a 2:1 mixture by volume of iso-octane and tetradecane with a Cetane number of 40.5. The additive compounds chosen for this study were 1-methylnaphthalene, tetralin, and decalin; each additive was blended into the base fuel at several concentrations so that the effect of the chemical compound on emission trends could be determined. To minimize changes in the combustion process, as fuel composition changed, the injection timing was varied in order to adjust for Cetane number differences between fuels. Comparisons were made on the basis of performance, regulated exhaust emissions, including CO, NOx UHC, and particulates, aldehyde emissions, and soluble organic fraction.Graphic display of the particulate results indicates that addition of an aromatic compound to the base fuel increased the particulate emissions. However, a regression analysis of the measured emissions on additive concentration and a variety of combustion parameters determined that, for the 1-methylnaphthalene and tetralin blends, the emissions were mainly dependent upon combustion parameters, although particulates for the tetralin blends did exhibit a correlation with the additive concentration. Addition of decalin to the base fuel caused no significant changes in the emissions.