Engine performance and emission characteristics of three-phase diesel emulsions prepared by an ultrasonic emulsification method

The emulsification method is a potential technique for reducing pollutant emissions from combustion equipment primarily due to occurrence of micro-explosion to enhance burning. In this study, an ultrasonic emulsification method was applied to prepare two-phase water-in-oil (W/O) and three-phase oil-in-water-in-oil (O/W/O) emulsions. The engine performance and the pollutant emission characteristics of a diesel engine were measured and analyzed. A rather violent ultrasonic wave may result in the phenomena of cavitations and hot spots, which in turn promotes fast chemical and physical reactions. Various kinds of liquid, which are immiscible with each other, may thus become highly mixed so that an emulsion is formed. This study first used an ultrasonic oscillating bath to produce ultrasonic waves by which two- and three-phase emulsions were prepared. The experimental results show that the emulsions prepared by the ultrasonic vibrating method have much finer and better-distributed droplets. The use of these emulsions as an engine fuel produced lower NO emission, lower soot concentration and lower black smoke opacity, while creating a larger brake specific fuel consumption (bsfc) and a larger CO emission compared with that of an engine using neat diesel fuel. However, the variations in the concentrations of CO2 and O2 emissions between the emulsions and neat diesel fuel were not significant. In a comparison with the characteristics of the two-phase W/O emulsion, the three-phase O/W/O emulsion was found to have a larger CO emission, larger soot particles and larger bsfc while producing a lower brake thermal efficiency and a lower black smoke opacity.