Effects of HCN and NH2 on the formation of nitrogen-containing PAHs during ammonia-hydrocarbon blended combustion: a ReaxFF molecular dynamics study

YZ Gao and SW Wang and YZ Duan and HY Zhao and H Jiang and YP Li, PROGRESS IN REACTION KINETICS AND MECHANISM, 50, e024 (2025).

DOI: 10.48130/prkm-0025-0022

During ammonia-hydrocarbon blended combustion, nitrogen-containing polycyclic aromatic hydrocarbons (NPAHs) such as pyrrole and pyridine emerge as critical pollutants due to their high toxicity and potent carcinogenicity. C4H6, an important pyrolysis intermediate in the co- combustion of ammonia and hydrocarbons, readily participates in reactions with HCN and NH2 to form NPAHs. However, the mechanisms through which HCN and NH2 interact with C4H6 to form the incipient nitrogen-containing aromatic rings, as well as the effects of carbon- nitrogen (C-N) interactions on the selectivity of reaction pathways, remain poorly understood. The current limitations in understanding the formation mechanisms of NPAHs hinder the advancement of clean ammonia combustion technologies. In this study, ReaxFF molecular dynamics simulations were employed to investigate the competitive roles of HCN and NH2 in NPAH formation. Systems with varying concentrations of HCN and NH2, and mixtures containing both species, were systematically examined. The results indicate that HCN is more favorable for the formation of NPAHs compared to NH2 and exhibits a strong tendency to form pyridine. In contrast, NH2 preferentially participates in side reactions that generate abundant other substances, thereby limiting its contribution to pyrrole formation. Carbon-nitrogen interactions play a crucial role not only in the formation of NPAHs but also in the generation of soot precursors. These insights provide theoretical guidance for the targeted reduction of nitrogen content in ammonia- blended fuels.

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