A molecular dynamics study of binary-component n-alkane fuel vaporization characteristics at sub/supercritical nitrogen environments

Abstract

The emphasis of this paper is to explore the gas-liquid interface characteristics of binary-component n-alkane fuels composed of n-heptane and n-dodecane at sub/supercritical nitrogen environments, and examine the vapor-liquid equilibrium (VLE) assumption adopted in the continuum-based vaporization models using the molecular dynamics simulation. In addition, the phase transition characteristics are also revealed. The results indicate that the vaporization of the binary-component fuel follows the classical multi-component vaporization theory in subcritical environment, in which the preferential vaporization of the light-end component is obvious with distinguishing gas-liquid interface. On the contrary, in supercritical environment, the vaporization rates of light-/heavy-end components are simultaneously enhanced even in the early stage. When approaching the critical point of the heavy-end component, the solubility of the ambient gas of nitrogen in the liquid phase is greatly enhanced with the indistinguishable gas-liquid interface. The transition mechanism from VLE to non-VLE for single-component fuels is caused by the remarkable ambient gas solubility in the liquid phase and the non-ideal gas effect at high pressures. However, for binary-component fuels, it is related to the complicated interaction between the light- and heavy-end components with significant differences in the physical properties and critical points. It is also found that ambient temperature and pressure play more dominant roles in controlling the phase transition process compared to the light-end component blended ratio for the binary-component fuels.