Effect of oxygen contents on morphology, nanostructure, and its formation of soot in laminar coflow ethylene-ammonia diffusion flames

Abstract

Oxygen content plays a crucial role in influencing the characteristics and formation processes of soot particles. This study explores the effects of varying oxygen levels on the morphology, nanostructure, and formation of soot particles in laminar coflow ethylene-ammonia diffusion flames using a combination of experimental analysis, model development, and numerical simulation. Initially, the impact of oxygen concentration on morphology and nanostructure of particles is examined experimentally. Subsequently, a novel C₂H₄-NH₃-PAHs kinetic model, incorporating cross-reactions between C3\A1-A3 and HCN, is developed and validated through parameters such as ignition delay, laminar flame speed, and species concentrations. The new model is then used to analyze the effects of different oxygen concentrations on soot formation and nitrogen-containing PAHs in ethylene-ammonia flames. The findings show that a decrease in oxygen concentration results in an increase in the average diameter of primary particles, a reduction in fringe separation distance and fringe length, and an increase in fringe tortuosity. Additionally, lower oxygen concentrations are found to slightly reduce PAH formation and significantly decrease the surface growth rate via the HACA mechanism, leading to reduced soot formation. Furthermore, the primary nitrogen-containing PAHs identified are 2-benzonitrile and 2-naphthonitrile, followed by pyrrolyl and cyanophenanthrene, with lower oxygen concentrations diminishing the formation of these nitrogen-containing PAHs.