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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.

Three synthetic fuels, derived from coal, were compared to a Phillips DF-2 control fuel. These fuels were tested in a single-cylinder, direct-injected, Diesel engine. Comparisons were made on the basis of performance, combustion characteristics, gas-phase emissions including aldehydes, and particulate emissions. In addition, the mutagenic activity of the soluble organic compounds from the particulates were analyzed using the Ames test. The objective of these experiments was to determine how well the synthetic fuels would perform as direct replacements for DF-2. All three synthetic fuels were manufactured from an initial batch of middle distillates produced by the Exxon Donor Solvent (EDS) process. The first fuel was a blend of the EDS middle distillate and the baseline DF-2 with a cetane number of 35.