Evaporation of acoustically levitated stable microemulsion droplets

Emulsified fuels have attracted significant interest due to their distinct combustion characteristics and have the potential to reduce harmful emissions in gas turbines and combustion engines. In this study, the evaporation characteristics of thermodynamically stable microemulsions with long stability have been explored. The influence of the water-to-surfactant molar ratio and volume fraction of the dispersed phase on the evaporation behavior of emulsions with different oils (decane, dodecane, and xylene) is discussed. The microemulsion droplets were introduced into a contactless environment using an ultrasonic acoustic levitator and then heated using an infrared continuous laser at different laser irradiation intensities. High-speed shadowgraphy and infrared thermography are employed to study the dynamics of the stable emulsion droplets. The droplets undergo three distinct stages of evaporation in their lifetime. We report that increasing the number density and size of water sub-droplets reduces the evaporation rate, while increasing the irradiation intensity results in faster evaporation. The residual structures obtained post-evaporation were analyzed using SEM imaging. In addition, a theoretical model has been proposed to predict the evaporation rate of the emulsion droplets.