Decoupling the effect of viscosity and surface tension on fuel atomization characteristics

Alternative fuels are widely considered a pivotal pathway toward achieving cleaner combustion in engines. However, their widely varying viscosities and surface tensions significantly impact atomization characteristics. In this study, glycerol–(sodium fatty alcohol ether sulfate)–aqueous solutions were formulated to decouple the effects of viscosity and surface tension, enabling a quantitative and independent examination of their influence on atomization. The findings show that increasing either viscosity or surface tension reduces the population of small droplets while increasing that of large droplets. Specifically, the Sauter mean diameter increases by 11.1% and 14.8% as viscosity rises from 4.86 to 14.75 mPa s and surface tension from 25.6 to 55.6 mN/m, respectively. The radial dependence of droplet size distribution was revealed, and a mechanism analysis was also conducted. Notably, an “explosive” breakup phenomenon driven by the interplay of pressure waves and surface waves was observed in high-viscosity jets, markedly improving near-field atomization. Moreover, an empirical model for the probability density distribution of droplet size was developed based on the Lognormal distribution. This model successfully decouples the contributions of viscosity and surface tension, providing a theoretical basis for predicting the atomization performance of various alternative fuels and their blends.