Diesel odor and the formation of aromatic hydrocarbons during the heterogeneous combustion of pure cetane in a single-cylinder diesel engine

Abstract

Experimental facilities and methods, based on combined gas-chromatographic and mass-spectrometric techniques, which can be employed for the qualitative analysis of odoriferous and carcinogenic compounds formed during the heterogeneous combustion of pure hydrocarbon fuels are described. Exhaust-gas samples from a lightly loaded, CFR diesel engine operating on a lean, pure cetane-air mixture at a compression ratio of 14 to 1 have been collected and analyzed. A number of species including saturated and unsaturated aldehydes, alcohols and acids, both homo- and heterocyclic compounds and aromatic compounds have been qualitatively identified. The significance of these results are discussed in conjunction with both the diesel-odor problem and the possible biological activity of diesel exhaust. Since commercial lubricating oil contains significant quantities of cyclic compounds, the pyrolysis and partial oxidation of any oil blow-by was investigated as a possible source of the aromatics. Additional engine experiments showed that aromatics were still present in the exhaust when the commercial oil was replaced by an oil that did not contain any cyclic compounds. The combustion products of pure cetane-air mixtures burning at atmospheric pressure, in an air-aspiring spray burner, were also found to contain aromatic hydrocarbons. Based on these experiments, it can be concluded that a large number of aromatic hydrocarbons are synthesized during the heterogeneous combustion of pure cetane-air mixtures, and that any blow-by of lubricating oil that occurs in a diesel engine enhances the production of aromatic hydrocarbons.