Experimental study on the dynamics characteristics of biodiesel/ethanol droplets impacting upon the heated wall

The dynamics characteristics of two-component mixed liquid droplets impacting on a heated wall is experimentally conducted. In the experiments, the two-component mixture consists of biodiesel and ethanol, with ethanol concentrations ranging from 0 % to 40 %. The Weber numbers (We) ranges from 40 to 230 while the wall temperatures (Tw) changes from 25 degrees C to 350 degrees C. Through quantitative analysis of high-speed images captured during the experiments, the effect of the Tw and the We on the spread diameter of the droplet is examined. The introduction of ethanol additives is found to significantly enhance droplet atomization and breakup. The model for predicting the maximum spreading coefficient is revised for two component mixture droplets. It is found that the maximum spreading coefficient (/3max) exhibits a power law dependence on We with a scaling exponent of 0.19. The scaling coefficient is found to be correlated with the droplet's viscosity. To consider the effect of wall temperature on predicting the maximum spreading coefficient of the droplet after impacting on the heated wall, based on the experimental data of this study and literatures, a new empirical model incorporating a dimensionless temperature term is proposed and the relative error is less than 6.5 %.