Many recent works have dealt with the influence of fuel composition on regulated and specific pollutant emissions from spark ignition engines. While many qualitative correlations have been already proposed, only a few quantitative ones are known (benzene remains an exception). This paper describes qualitative and quantitative correlations between fuel composition and specific pollutant emissions (individual hydrocarbons, aldehydes, ketones, alcohols, and organic acids) of a spark ignition engine. The aim of this work was to find the precursors of the main specific pollutants. Then, for each of them, a multilinear equation has been calculated, illustrating the correlation between its concentration in exhaust gases and its content in the fuel. The results of these calculations point out which initial compound favors the formation of a determined pollutant. As lean conditions are probably going to be used in future commercial engines, the fuel effect has been studied for a broad range of equivalence ratios (from 0.8 to 1.2). Two fuel matrixes were designed. The first one was obtained by introducing eight pure hydrocarbons (nC(6), nC(8), isoC(8), 1-hexene, cyclohexane, toluene, o-xylene, and ethylbenzene) in an alkylate base. The second one was formulated to test the behavior of four oxygenated compounds (methanol, ethanol, isopropanol, and methyl tertio-butyl ether [MTBE]). Individual unburned hydrocarbons, aldehydes, alcohols, and organic acids were analyzed according to accurate methods developed in our laboratory. Results show that benzene exhaust is mainly emitted from benzene fuel, the substituted aromatics, and, to a lesser degree, from cyclohexane; 1,3-butadiene is produced from l-hexene or cyclohexane; and isobutene is a product of isooctane and MTBE. Exhaust toluene comes mainly from toluene fuel, but also from o-xylene and ethylbenzene fuels. Isopropylbenzene exhaust seems to be produced only from ethylbenzene fuel. Exhaust concentrations of acetaldehyde and acetone showed a strong correlation with, respectively, ethanol and isopropanol fuel contents. Methacroleine exhaust concentration was strongly correlated with the fuel's isooctane content. Benzaldehyde was produced by the aromatic fuels, Methanol was found in the exhaust gases of all the oxygenated fuels. High quantities of hexane or isooctane in fuels seem also to favor methane formation. Ethanol and isopropanol were found in the exhaust gases only when these components are added to the fuel. Propionic acid was produced by the aromatic fuels, while butyric acid came from o-xylene. Based on these results, this paper proposes the probable intermediate paths for formation of some of these pollutants. Finally, the ozone-forming potential of the exhaust gas of each fuel was calculated. Toluene and the oxygenated components of the fuel were shown to decrease this potential.
