Comparison of Engine Performance between Nano- and Microemulsions of Solketal Droplets Dispersed in Diesel Assisted by Microwave Irradiation

As a derivative product of bio-glycerol, this study first uses solketal as a combustion improver for enhancing diesel engine characteristics. The emulsions of nanometer- and micrometer-sized droplets of solketal, which disperse evenly in the ultra-low sulfur diesel (ULSD), are formed by the effects of microwave irradiation. The performance of diesel engine fueled with the nanoemulsion of ULSD with scattered solketal droplets is analyzed and compared to that with the microemulsion. The experimental results show that the nanoemulsions can form when over 15 wt. % surfactant mixtures of Span 80 and Tween 80 and less than 5 wt. % solketal are mixed and emulsified with the remaining ULSD content, which acts as the continuous phase of the emulsions. The nanoemulsions are observed to have significantly lower brake-specific fuel consumption (bsfc) and higher fuel conversion efficiency and exhaust gas temperature than those of the microemulsions and the neat ULSD. However, the bsfc of the nanoemulsions increases with greater engine speed and gradually approaches those of the latter two test fuels. In addition, the dispersed solketal droplet sizes are mostly concentrated around 127 nm with peak intensity of 12.65% in the nanoemulsions. The microwave-assisted formation used in this study is found to successfully produce the nanoemulsions in which all of the dispersed droplet sizes are much smaller than 1000 nm.