Molecular dynamics simulation of complex molecules using quantum-chemical potentials: application to modelling fuel droplets

Sazhin, Sergei (2015) Molecular dynamics simulation of complex molecules using quantum-chemical potentials: application to modelling fuel droplets. [Data Collection]

Project Description

This proposal is concerned with the development of a new hybrid quantum mechanics/ molecular dynamics (QM/MD) model for the simulation of complex hydrocarbon molecules and the application of this model to the simulation of n-dodecane and a mixture of n-dodecane and dipropylbenzene molecules in Diesel engine-like conditions. The solution of the time independent Schrodinger equation will allow us to obtain the equilibrium geometry of a molecule or an ensemble of molecules, and to calculate the potential energy for any position of atoms and electrons in the system. This approach will give us the potential energy of interacting molecules as a function of their geometry. Comparison of this energy for interacting individual C and H atoms and molecules with the interaction energy calculated by the conventional MD approach (taking into account the internal degrees of freedom of molecules, used in our current EPSRC project EP/H001603/1) for the same inter-atomic distances will allow us to analyse the differences in the QM and classical potentials. It is anticipated that our results will be used to calculate the corrections for the potentials used in the classical MD calculations. The new hybrid model will be used for the analysis of the dynamics of n-dodecane molecules in liquid and gas phases and at the liquid/gas interface, using techniques developed during the work on EPSRC project EP/H001603/1. It is anticipated that at this stage we will be able to establish the range of applicability of the conventional MD approach. A new approximate method of taking into account the QM corrections to the classical results will be developed. Also, the previously developed kinetic model, taking into account the presence of two components (fuel vapour and air) in the kinetic region will be generalised to take into account the presence of the three components (two species of fuel and one of air) there. These new models will be applied to the analysis of Diesel fuel droplet heating and evaporation in realistic engine conditions. In contrast to the previously developed models, the kinetic effects will be taken into account alongside the effects of temperature gradient and recirculation inside droplets and the effects of the moving boundary during the evaporation process. We are not aware of any previous research in this area.