Abstract View
A Reactive Molecular Dynamics-based Exploration of Soot Inception Pathways in Combustion
Khaled Mosharraf Mukut, Akaash Sharma, Eirini Goudeli, SOMESH ROY, Marquette University
Abstract Number: 660
Working Group: Combustion
Abstract
Accurate prediction of the formation of soot in combustion systems is important for many reasons – from better combustion efficiency to combat climate change. Yet, the fundamental physico-chemical processes behind the formation of soot are still not completely understood. In this study, the mechanism of incipient soot formation is investigated in silico by reactive molecular dynamics (MD) simulation using the reactive force field (reaxFF) potentials without making any a priori assumption about the inception pathways or characteristics of incipient soot. Acetylene molecules are allowed to collide at 1500 K to form new species leading to incipient soot. The temporal evolution of precursor species is tracked to understand the pathways to soot and to identify and isolate the key soot precursors. The evolving mixture composition contains small molecules (up to molecular weight, MW < 240 kg/kmol) in the very early stages of nucleation. Later, the gradual formation of distinct clusters of larger molecules and incipient soot (MW > 1000 kg/kmol) are observed. The molecular population can be differentiated into active, abundant small molecules and rare, transitionary large molecules, providing insight into the transition boundary between gaseous precursor molecules and incipient soot. Additionally, the internal structure of the formed soot clusters is quantified based on the aliphatic/aromatic carbon ratio and by the number of 5-, 6- and 7-member rings. The incipient soot shows an aromatic core with a shell made of aliphatic carbons. It is also observed that the aliphatic molecules play a significant role during coalescence. The soot growth rates are found to be closely linked to the chemical structure of obtained incipient soot. The soot clusters that are rich in aliphatic carbon chains are softer and, thus, more prone to coalesce with each other, in contrast to larger clusters that are rich in aromatic rings.