Polynuclear aromatic hydrocarbon emissions from diesel engines

Mills, Graham Andrew (1983) Polynuclear aromatic hydrocarbon emissions from diesel engines. University of Southampton, Doctoral Thesis.

Abstract

The effect of both conventional and alternative fuels on polynuclear aromatic hydrocarbon (PAH) emissions from a direct injection naturally aspirated diesel engine has been investigated. Both particle-bound and vapour phase PAH, collected on high efficiency glass fibre filter papers and condensation trans, were extracted with cyclohexane. Following a two stage 'clean-up' involving a DMF/H,0 partition and silica-gel thin-liver chromatography compound identification and quantification was achieved by high resolution gas chromatography and/or combined gas chromatography/mass spectrometry. The technique provided a relatively quick and simple enrichment step, whilst the high separating power of the capillary column was able to resolve the many close, yet toxicologically important, isomers and substituted PAH compounds that were present. Investigations indicated the presence of a vast range of PAH species comprising both substituted and unsubstituted two-to-seven member ring systems, many of which were known carcinogens and mutagens. PAH emission levels resulting from the combustion of six specially blended fuels, having aromatic contents of 10%, 30%, 40%, 50%, 60%, 70% were assessed for nine engine speed/load combinations and compared to a conventional commercially available diesel gas oil. The PAH content of the test fuels ranged from 0.9 to 3.7% by mass and comprised mainly alkylated naphthalenes and phenanthrenes. Total measured PAH emissions were found to increase with increasing fuel aromaticity for all engine operating conditions; significant changes in PAH output were noticeable for fuels with more than 40% aromatics. The no-load, low combustion temperatures, and low soeed, full load operating conditions produced the greatest PAH exhaust concentrations. Production of the larger molecular mass, more biologically active, PAH compounds was favoured by high combustion temperature, full load engine conditions. PAS exhaust emissions from the engine operated on unmodified (sunflower, rapeseed, soyabean, coconut) and modified (ethyl-ester of sunflower) vegetable oils were compared to emissions resulting from the combustion of diesel gas oil. Three engine speed/load conditions were assessed for each fuel and emission levels for 20 PAH compounds measured. PAH emission profiles arising from the combustion of the unmodified oils were similar, but differed significantly from results obtained using diesel fuel. Increasing engine load was found to greatly increase the production of carcinogenic PAH species in the exhaust from combusted unmodified vegetable oils. Levels of alkyl substituted PAH, common in diesel exhaust emissions, were very low using these fuels. Operation of the engine on ethyl-ester of sunflower oil led to PAH emissions between those obtained using diesel gas oil and the unmodified vegetable oils.

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