As shown in Fig. , the reactants used in this part of the simulation are the 5 products produced in the part A plus acetylene. The acetylene was added because it is the most abundant hydrocarbon molecule in combustion flames and is important to the formation of soot. All six reactants are mixed with equal ratio (150 molecules per species) with a density of 0.25 g/cm 3 . A total of 5ns reactive MD simulations were performed (500ps per trajectory with a total of 10 trajectories). To accelerate the reaction, the simulation temperature was slightly increased to 2000K. The evolution of the products as the function of simulation time is shown in Figs. . Fig. shows three reaction paths leading to the formation of three-ring structures that are discovered in the trajectories. As can be seen, these three-ring species are produced from tworing species. The path 6 describes the formation of an acenaphthene by acetylene addition to the fusing site adjacent to the bay region in the 1-naphthyl, which leads to the closure of a 5-membered ring. This path can be completed in just over 30ps and is a typical HACA-like growth mechanism that has been verified both experimentally and theoretically . Path 7 shows another way to form 3-ring PAH, the (E)-1-(buta-1,3-dien-1-yl) naphthalene radical can be produced by adding an acetylene to the bay carbon atom of 1-naphthyl followed by a second acetylene addition. Then a 1-methylacenaphthylene radical is formed by adding an H atom while drop a CH group. And finally, a phenalene radical was formed by losing an H atom and rearrangement of carbon atoms. This is a new HACA-like mechanism , to our knowledge, has not been previously reported. The phenalene can also be produced by the reaction of 2indenylidene with 2-naphthyl flowing the drop of a C6H4 group (path 8). As the molecular size of PAH increase, the number of possible reaction paths leading to their formation increase. In Fig. , typical PAH growth paths that appear frequently in trajectories and thus have certain statistical significance are shown. Path 9 shows the formation of a 4-ring PAH from the addition of a phenyl at the fusing site of a naphthalene radical. This is the well-known PAC mechanism that has been discovered by experiment . A formation path for a 5-ring PAH is shown in path 10, which is also a PAC reaction mechanism. In addition, there are two efficient ways to form 4-ring PAH by the polymerization of 2-ring aromatic species, such as path 13 and 14. Similar mechanisms are also found in the formation of 5-ring and 6-ring PAHs (path 11, 12, and 15). It is important to note that in path 12 and 15, the participation of acetylene is critical. In addition, it is found that reactions involving either indenyl or naphthyl as reactant(s) can lead to the formation of larger PAHs, such as 7-ring and 9-ring PANs. In fact, it worth to mention that many reaction paths in Fig. follow the recently proposed CHRCR theory. Small resonant stabilized radicals (RSRs) such as 2-naphthyl can invoke chain reactions of RSR species, and a more stable (larger) RSR can be produced every step in this sequence. The energy barrier of such reactions is very small and therefore the reaction is fast.