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

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.

This will be a collaborative project involving visiting researchers Professor Vladimir M. Gun'ko (Chuiko Institute of Surface Chemistry of the National Academy of Sciences of Ukraine, Kiev, Ukraine) who is an internationally recognised expert in interfacial phenomena, Dr Bing-Yang Cao (Tsinghua University, Beijing, P.R. China), whose expertise includes the development of numerical algorithms for molecular dynamics simulation and Dr Irina Shishkova (Moscow Power Engineering Institute, Russia), whose expertise is focused on the development of numerical codes for the solution of the Boltzmann equation. It will be led by Professor Sergei Sazhin, whose expertise includes the development of new physical models of fuel droplet heating and evaporation with a view of applications to modelling the processes in internal combustion engines. The Co-investigator Professor Morgan Heikal will advise the project members on the relevance of the models to automotive applications. A Research Fellow will also be included in the project. This project will build upon the currently funded EPSRC project EP/H001603/1, supporting the collaboration between the PI, Dr B-Y. Cao and Dr I. Shishkova, and previously funded EPSRC projects EP/C527089/1 and EP/E02243X/1, and a Royal Society Joint project with Russia, supporting the collaboration between the PI and Dr I. Shishkova.

It is expected that outside of the academic research community the main beneficiaries of this research will be mainly the automotive industry via the industrial partner, Ricardo Consulting Engineers Ltd. The modellers of the processes in internal combustion engines will be able to use more accurate models for droplet heating and evaporation, which will lead to more reliable predictions of the models. The project's results will be reported at 10th Euromech Fluid Mechanics Conference and the 14th International Heat Transfer Conference, which alongside academics attract many representatives from industry, including the automotive industry.
The project is expected to directly benefit the designers of fuel injection systems through an increased understanding of droplet heating and evaporation mechanisms. Importantly, further understanding of the compromise between the requirements of a direct fuel injection system, that can optimally satisfy both homogeneous and stratified charge operation, whilst simultaneously minimising engine emissions, will be incrementally advanced. It is expected that some of the results will be directly applicable to the modelling of other spray phenomena (e.g. aerosol sprays in medicine or agriculture).
The results will be disseminated to a wider audience through publication on the Sir Harry Ricardo Laboratories (SHRL) website and the University of Brighton open access repository. This will allow the general public to familiarise themselves with the state of the art developments in this field. A specific website for the project will be set up.
All three Visiting Researchers, Professor Vlad Gun'ko, Dr Bing-Yang Cao and Dr Irina Shishkova, are expected to have direct contact with Ricardo Consulting Engineers Ltd and the wider engineering and environmental community via their work at the Sir Harry Ricardo Laboratories. It is likely that their involvement in the project will contribute to the creation of links between the British, Ukrainian, Chinese and Russian academic and industrial communities. A collaboration agreement between the Sir Harry Ricardo Laboratories and the Visiting Researchers' home institutions, Chuiko Institute of Surface Chemistry, Tsinghua University and Moscow Power Engineering Institute, will be prepared in due course if the project is funded by the EPSRC.
It is expected that the Research Fellow working on this project will be primarily involved in all impact activities, with strong support from the Principal Investigator, Co-investigator and the Visiting Researchers.