Molecular dynamics study of condensation/evaporation and velocity distribution of Diesel fuel at liquid-vapour phase equilibria

Some recent results of molecular dynamics simulations of the condensation/evaporation and velocity distribution of n-dodecane (C12H26), theclosest approximation to Diesel fuel, at a liquid-vapour interface in equilibriumstate are briefly described. It is shown that molecules at the liquid surface need togain relatively large translational energy to evaporate. Vapour molecules with largetranslational energy can easily penetrate deep into the transition layer and condensein the liquid phase. The evaporation/condensation coefficient is shown to becontrolled mainly by the translational energy. The properties of the velocitydistribution functions of molecules at the liquid, interface and vapour regions are summarised. It has been shown that the distribution functions of evaporated andreflected molecules for the velocity component normal to the surface deviate considerably from the Maxwellian, while the distribution function for all moleculesleaving this surface (evaporated and reflected) is close to Maxwellian. Theevaporation coefficient has been shown to increase with increasing molecularenergy in the direction perpendicular to the surface. These properties have been recommended to be taken into account when formulating boundary conditions for kinetic modelling