Lowering NOx and PM Emissions in a Light-Duty Diesel Engine with Biodiesel-Water Emulsions

Abstract

A key barrier limiting extended utilization of biodiesel is higher NOx emissions comparedto petrodiesel fuels. The reason for this effect is unclear, but various researchers have attributed thisphenonmena to the higher liquid bulk modulus associated with biodiesel and the additional heatreleased during the breaking of C-C double bonds in the methyl ester groups. In this study waterwas incorporated into neat biodiesel (B100) as an emulsion in an attempt to lower NOx andparticulate matter (PM) emissions. When added to petroleum diesel, water has been shown toimprove fuel/air mixing, reduce peak combustion temperatures, and increase mass duringcombustion, resulting in lower NOx and PM emissions with no fuel penalty. A biodiesel emulsioncontaining 10wt% water was formulated and evaluated against an ultra-low sulfur petroleum diesel(ULSD) and neat biodiesel (B100) in a light-duty diesel engine operated at 1500RPM and 50ft-lbs.The influence of exhaust gas recirculation (EGR) was also examined. The incorporation of waterwas found to significantly lower the NOx emissions while maintaining or improving fuel efficiencywhen operating at 0 and 27% EGR, while the total PM mass was lowered dramatically for the 27%EGR condition only. Analysis of the emissions and heat release data indicate that water enhancesair-fuel premixing to maintain fuel economy and lower PM.