Molecular dynamics simulation of soot formation during diesel combustion with oxygenated fuel addition

This study investigates the soot formation process of diesel combustion using molecular dynamics simulations with reactive force fields by examining the effects of five oxygenated additives on diesel soot reduction. The newly improved ReaxFF CHO2016 parameters are employed due to their feasibility in modelling the kinetics of large hydrocarbon fuels and describing the chemistry of carbon condensed phases. The detailed pathways of soot formation examined include the thermal decomposition of fuels, the formation of aromatic rings, the mechanism of nucleation, and the mass growth of nascent soot. The morphological developments of the soot formation are obtained, together with quantities indicating the physical and chemical properties, such as mass, size, C : H ratio and aliphatic-to-aromatic C : H ratio. The role of aliphatic-substituted aromatics in nascent soot coalescence and the appearance of aliphatic side chains in soot structures are identified. The concentrations of C-atoms in nascent soot particles contributed from oxygenates blended with diesel are quantified and visualized for the first time. The effects of the molecular structure of the oxygenated additives, i.e. the existence of esters, alcohols, carbonyl groups and ethers, on soot precursor mitigation are elucidated by evaluating the early formation of CO and CO2 quantitatively during the thermal decomposition.