Nonequilibrium Molecular Dynamics Modeling Of A Fuel Nanojet In Sub/supercritical Environments: Chamber Pressure Effects On Characteristics Of The Gas–liquid Interface

Abstract

ABSTRACTMolecular dynamics simulation is conducted to microscopically study the effects of environmental pressure on the injection process of a fuel nanojet. The united-atom force field and Lennard-Jones 12-6 potential are applied, which is validated by a single liquid droplet evaporation model against experiments. A gas–liquid–gas model represented by a simulation box for single droplet evaporation and an n-heptane nanojet injected into vacuum, lowly supercritical, and highly supercritical environments are investigated. Results indicate that at lowly supercritical conditions, the gas–liquid interface has been widened, and the interface tension still exists and the phase interface is detected. Only at highly supercritical conditions does the interface becomes sufficiently wide and a continuous phase transition without a distinct phase interface prevails. The most interesting conclusion from the molecular dynamics (MD) results is that the transition of a fluid from subcritical to supercritical states does not occur instantaneously when it goes across the critical point but is a gradual process that can be completed only when the temperature and pressure are sufficiently higher than the critical values. This microscopic analysis is well in accordance with the macroscopic measurements and observations in the literature.