Conformerisation Phenomena in Fuel Droplet Hydrocarbon

Accurate prediction of thermal evaporation and condensation coefficients (tECCs) has long been debated using molecular dynamics simulation techniques based on the non-reactive force fields in which chemical bonds were modelled as rigid or harmonic. Here, molecular dynamics simulation with reactive force field ReaxFF is presented in parallel with the quantum chemical calculations to determine bond energies and Gibbs free energy of internal molecular dynamics of n-dodecane conformers and analysis of the collisions of individual molecules with the nanodroplet in order to show the reliability of ReaxFF for this study. The effects of temperature jump at liquid-vapour interface on the tECCs have been studied by performing transient non-equilibrium molecular dynamics simulations for estimation of partial tECCs. Quantum continuum solvent model calculations analytically and numerically revealed a role of driving forces of conformerisation phenomena in evaporation of n-dodecane. These findings form the basis for kinetic modelling applicable to evaporation of highly flexible molecules. In our approach to the estimate of the tECCs a transient non-equilibrium molecular dynamics method was applied using the ReaxFF. The nano-droplet was minimized and subsequently pre-equilibrated to desired temperature of 400 K. The Berendsen’s thermostat controlled the kinetic energy of the system and a Velocity-Verlet algorithm was used to integrate the equations of motion. The time step used was 0.25 fs. After equilibrating the systems, the interfacial layers were strongly coupled with thermostat (τT = 1 fs) while the rest of the system was weakly coupled (τT = 100 ps) in which gas phase had temperatures higher than liquid one. The time constants, by which systems are allowed to reach the quasi-equilibrium state in microcanonical conditions (NVE), clarified the thermal tECCs, for which energy and mass transformations were coupled via the interface in a non-steady way and exchanged suddenly. This method allowed us to study gradient of temperature during the evaporation/condensation process over the boundaries.