Limited by the size of the modeled system, the largest PAHs detected in our MD trajectories have 9 rings. However, we do find several species that are larger than 9-ring PAH and they may be precursors of soot inception. A formation path of such a species is shown in figure . The first stage of the process involves the reactions between two 2-ring radicals to form their dimers within around 8ps. Then a larger polynuclear hydrocarbon is formed by the clustering of these two dimers. The growth process of this polynuclear hydrocarbon include both the addition of more small species and the internal formation of the aromatic rings which make the structure more stable. Finally, a large polynuclear hydrocarbon with 67 carbon atoms and 15 rings is formed. Although there are only 4,000 atoms in the simulated system, this type of species can be found several times in the trajectories, underscoring the importance of this reaction mechanism and a very likely path to soot inception. Recent experimental work also found that small PAHs serve as the main reactants for the formation of the nascent soot, which is consistent with our simulation results . In fact, aliphatic bridging is also one of the main ways to promote the rapid aggregation of PAH into soot inception .