Effect of air turbulence and fuel composition on bi-component droplet evaporation

Abstract

Understanding the influence of fuel composition and air turbulence on evaporation of bi-component fuel droplet is the aim of the current investigation. Experiments were carried out with a single fuel droplet (a mixture of n-heptane and ethanol) suspended using the cross-wire technique within a box of turbulence facility that is capable of generating near zero-mean homogeneous and isotropic turbulence at its center. The fuel composition (i.e. the volume fraction of ethanol) as well as turbulent intensity within the chamber were varied over a wide range. The images of the evaporating droplet were recorded using back-light illumination. The initial droplet size was about 30–40 times smaller than the integral length scale of air turbulence, while it was about 10 times larger than the Kolmogorov length scale. For each fuel composition, five different turbulent conditions were considered. While the effect of turbulence was found to enhance droplet evaporation rate for all cases, the extent of its influence depends on fuel vapor mass diffusivity in air, and, in addition, on the initial fuel composition of the binary mixtures. The evaporation constant for the first stage of evaporation is sensitive to both air turbulence level and composition, while that for the second stage of evaporation shows a specific trend with fuel composition for all cases of turbulent intensity. Finally, an experimental correlation for normalized evaporation constant is presented.