Effects of oxygenated additives on soot and PAH in a diesel engine and premixed flame.

摘要

An experimental study using a diesel engine along with a modeling study using detailed kinetic mechanisms was conducted in an attempt to clarify how addition of oxygenated compounds into fuel can change production of soot. As the first part of the present study, experiments were performed in an optically-accessible DI diesel engine to investigate the effects of the addition of oxygenated compounds to diesel fuel. Two oxygenated additives (dimethyl carbonate and dimethoxy methane), one cetane improver (2-ethylhexyl nitrate), and one pure hydrocarbon (2,2-dimethyl butane) were used as blending compounds to obtain information on the influence of fuel oxygen content, boiling point and combustion characteristics such as ignition delay and heat release pattern on emissions. Each oxygenate was blended into the baseline diesel fuel to obtain 2% and 4% oxygen by fuel mass. For each fuel blend, pressure traces were recorded and analyzed to obtain information on ignition delay and rate of heat release. Laser light extinction was used to measure soot variation during combustion as well as exhaust soot levels. NOx, CO2 and CO concentrations in the engine exhaust were also measured using gas analyzers. Heat release analysis showed that modifications of the combustion characteristics from those of the baseline diesel fuel were significant, with increases of up to 1.7° of crank angle in ignition delay and increases in the fraction of premixed burn. The addition of each compound decreased the peak level of soot during combustion as well as the exhaust soot levels. For the equivalent level of oxygen addition, DMM (dimethoxy methane) was more effective than DMC (dimethyl carbonate) in reducing soot at the same level of oxygen content. Reductions in NOx of 4 to 15% were also observed; no changes in CO levels were observed. (Abstract shortened by UMI.)