Insight into the Carbon–Nitrogen Coupling Mechanism during CH4/NH3 Cofiring

Abstract CH4/NH3 cofiring represents an effective technical approach to overcome the inferior combustion characteristics of NH3. The combustion characteristics and pollutant formation mechanism during the cofiring constitute important research directions. Hence, it is of considerable significance to gain a comprehensive understanding of the CH4/NH3 cofiring and its mutual influence mechanism. This paper first demonstrates that the general “atmospheric type” blending model in the existing literature may lead to extreme hypoxia during the simulation, thereby overestimating the pollutant formation characteristics. Compared with the “fuel-type” blending model proposed in this paper, it is believed that the new model can precisely analyze the cofiring and reaction mechanism of multiple fuels. Subsequently, the “fuel-type” blending model was used to systematically study the effects of temperature, ammonia blending ratio (ENH3), and equivalence ratio (φ) on the cocombustion. Third, by sorting out the reaction network, it was discovered that under the stoichiometric condition, CH4 and NH3 react independently of each other, which is distinct from the phenomenon in the “atmospheric type” blending model. Contrarily, in the fuel-rich scenario, a coupling mechanism occurred between CH4 and NH3. NO can react with the excess CHi groups in the system through NO + CHi → CHiNO → CHiN → HCN/CN, then decouple to generate CO and N/NH, and then further reduce to N2. Finally, the C–N coupling mechanism was investigated to correct the Okafor mechanism and improve the prediction effect of NO and HCN. These findings not only provide a reference for the subsequent ReaxFF MD study of multiple fuels to construct reaction systems in reality but also provide solutions for reducing NO emissions from CH4/NH3 in actual industry.