Molecular dynamics simulation of sub/supercritical evaporation with n-butanol/n-heptane blended fuel

Sub/supercritical evaporations of single-component fuels have been developed well so far. In the last decade, dual fuels, even multiple fuels have received more attention. However, sub/supercritical evaporations of dual fuels are more complicated than that of single-component fuels, as dual fuels have uncertain critical points, and single-component fuels have exact critical points. Therefore, in this study, we focused on the functional relationship between the critical temperatures and the blending ratios (n-heptane to n-butanol) of the n-butanol/n- heptane blends by molecular dynamics simulations. A liquid film of the blends was constructed in nitrogen environment. The sub/supercritical evaporations processes of the blends were simulated in different ambient temperatures and pressures and in different blending ratios of the blends. The density profile, surface temperature, evaporation mass ratio and evaporation rate were estimated and compared under sub/supercritical states. The critical temperature of the blends was determined by the surface temperature and the surface tension. Results indicate that under ambient low supercritical condition, a transition from subcritical to supercritical state does not happen in the evaporation process of blends. The evaporation mass ratio is not always equal to the blending ratio as the way used in current evaporation model, but a function over time. A fitting formula for calculating the critical temperatures of the blends is provided.

Automated summary

The study focused on the functional relationship between the critical temperatures and the blending ratios of n-butanol/n-heptane blends, revealing complexities in the sub/supercritical evaporation processes of dual fuels. Results showed that a transition from subcritical to supercritical state does not occur in the evaporation process of blends under ambient low supercritical conditions, challenging the conventional evaporation model.