Soot reduction through plasma-flame interaction: A comparison of diluting gases

Abstract

This study systematically investigates plasma-flame synergistic effects on soot reduction through comparative experiments in nitrogen (N₂), argon (Ar), and helium (He) dilution atmospheres. By integrating optical diagnostics with multiscale sampling analysis, we reveal three pivotal advancements: High-resolution TEM demonstrates plasma-induced amorphous nanostructures (reduced fringe length) with enhanced oxidation reactivity, particularly in N₂-diluted flames showing 0.15 nm shorter fringe lengths. Plasma coupling with N₂ achieves maximum soot suppression (33 % concentration reduction versus 13 % in He), attributed to N₂ vibrational excitation enhancing soot oxidation pathways. The optical measurements consistently indicated lower temperatures in helium diluted flames, which may be explained by the higher thermal diffusivity than that of nitrogen and argon. The incorporation of plasma led to a reduced soot concentration, suggesting that plasma addition exerts a suppressive influence on soot emissions. Crucially, we establish quantitative correlations between soot’s reactivity and nanostructure. The soot characteristic parameters provided valuable information regarding the sensitivity to plasma activation under identical excitation conditions. With plasma coupled with nitrogen, the average soot concentration, soot microcrystalline parameters and soot reactivity have higher relative change rate. These findings underscore the significant correlations between soot characteristics and the coupling of plasma with dilution gases, highlighting the potential for reducing emissions.