Experimental study on effects of gas flow rate on soot characteristics in diffusion flames coupled with plasma

This study examined the evolution of morphology and nanostructure of soot particles from the plasma-flame interaction for various gas flow rates. The current study used both optical diagnostic and sampling methods to explore the soot production and combustion characteristics. Soot particles were characterized at the same positions downstream from the flame zone by thermophoretic sampling and transmission electron microscopy. Moreover, X-ray diffraction analysis, and thermogravimetric analysis were performed to study the nanostructure and oxidation reactivity of soot. A reduction in soot concentration was found with the plasma addition, which illustrated an inhibition effect of plasma on soot emission. The increased gas flow rate promoted soot concentration since a growing number of carbons participated in the combustion process. Depending on the gas flow rate (carbon content) variation and plasma activation, either liquid-like soot material with irregularly shaped protrusions or chain-like structure, or a mixture of both, were generated from the diffusion flames. The soot produced by plasma-flame interaction also demonstrated a high correlation between nanostructure and reactivity. The soot from lower carbon content with plasma activation had a shorter fringe length and larger fringe tortuosity related to higher oxidation reactivity. On the contrary, soot from the highest carbon content without plasma-flame interaction exhibited prevalent fullerene-like nanostructures with evident large or small shells and also had a higher carbonization degree resulting in lower oxidation reactivity