Comparison of evaporation rate constants of a single fuel droplet entering subcritical and supercritical environments

This work compares the evaporation rate constants of a single fuel droplet under subcritical and supercritical environments by experimental visualizations (in millimeter scale) and molecular dynamics simulations (in nanometer scale). The objection is to understand the differences of fuel droplet evaporation rate constant variations under the subcritical and supercritical environments. Firstly, an experimental apparatus is designed to study the diesel droplet evaporation under subcritical and supercritical environments. The results show that the droplet evaporation obeys the D-2 law in subcritical environments, while the D-2 law is no longer strictly applicable in supercritical environments and the evaporation rate constant isn't a constant but a variable that increases with the evaporation time. Secondly, the molecular dynamics simulations are applied to investigate the evaporation of diesel surrogate n-dodecane under subcritical and supercritical environments. The results show that the droplet temperature keeps at the equilibrium temperature in subcritical environments, but keeps increasing in supercritical environments. In supercritical environments, the reason for the evaporation rate constant keeps increasing is that the droplet density keeps decreasing with the increase of droplet temperature. The droplet surface tension will rapidly vanish in supercritical environments, which implies that the formation of fuel-air mixture is no longer dominated by the surface tension, but is the turbulent diffusion in diesel trans/supercritical injection conditions. It can deduce that the evaporation rate constants of a fuel droplet in micrometer scale (that is commonly generated in engines) will follow the same trend and within the same variation scale at the same ambient pressures and temperatures. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study compares the evaporation rate constants of a single fuel droplet under subcritical and supercritical environments using experimental visualizations and molecular dynamics simulations. The results reveal that the evaporation rate constant varies in subcritical and supercritical environments, with the latter showing an increasing trend with evaporation time. Molecular dynamics simulations demonstrate that in supercritical environments, the droplet temperature keeps increasing and the droplet surface tension rapidly vanishes, indicating a shift in dominant factors affecting fuel-air mixture formation.