Surface growth rate of soot by reactive Molecular Dynamics

Isothermal surface growth of incipient soot nanoparticles is investigated by reactive molecular dynamics (MD) simulations at 1350-1800 K. The mass increase of soot nanoparticles, having initial diameter of 3-4.5 nm, is tracked as a function of time during surface reactions with hydrocarbon molecules and radicals produced by acetylene pyrolysis. Soot growth accelerates with increasing initial acetylene concentration and flame temperature. This temporal evolution of the soot mass growth allows for the direct derivation of a "lumped" surface growth rate constant, based on the hydrogen-abstraction acetylene addition (HACA) reaction model, however, without relying on explicit information or assumptions about the soot surface reactivity. The proposed MD-derived surface growth rate equation that follows an Arrhenius dependence with process temperature is employed into a monodisperse particle dynamics model, nicely predicting soot volume fraction measurements in various burners. The presented MD methodology can be applied in material synthesis to determine the surface reaction rate of a range of nanomaterials, where surface reactions are typically oversimplified by being lumped with gas phase reactions into an overall reaction rate.