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An experimental investigation was conducted to evaluate the effect of three different oxygenated compounds, diglyme, diethyl maleate and dibutyl maleate, on emissions from a Volkswagen 1.9 litre, turbocharged, direct injection diesel engine. Sampling was performed using a mini-dilution tunnel technique to obtain particulate matter and a Fourier transform infrared (FTIR) spectrometer for gaseous emissions. The particulate samples were analysed using thermal analysis and Soxhlet extraction to determine the fraction of volatile and soluble organic material respectively. All three oxygenated compounds were found to be effective at reducing particulate emissions, with the maleate compounds being more effective overall than the diglyme. Analysis of the relative contributions of changes in the soot and soluble organic fraction (SOF) to the reduction of particulate matter indicated that, for diethyl maleate and diglyme, reductions in soot were the dominant effect. No consistent trends in NO x emissions were observed, although the diethyl maleate, which was most effective at reducing the particulate matter, increased the NO x slightly at most of the test conditions. Differences in the combustion chemistry of the additives are discussed as a possible explanation of the greater effectiveness of the maleate compounds in reducing soot, as well as for the difference in the effectiveness of diethyl and dibutyl maleate.
Litzinger et al. (Tue,) studied this question.