Influence of the H2 proportion on NH3/H2/air combustion in hot and low-oxygen coflows

• Published in: International journal of hydrogen energy Vol. 63; pp. 480 - 490
• Main Authors: Wang, Guochang, Liu, Xiangtao, Li, Pengfei, Shi, Guodong, Si, Jicang, Liu, Zhaohui, Mi, Jianchun
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 18.04.2024
• Subjects: H2 proportion; MILD combustion; NH3/H2 blends; NOx generation; Reaction characteristics; H2 proportion; NH3/H2 blends; MILD combustion; Reaction characteristics; NOx generation
• ISSN: 0360-3199
• DOI: 10.1016/j.ijhydene.2024.03.212

This study investigated the effect of the H2 fraction on reaction dynamics and NOx formation in a premixed NH3/H2/air jet flame within a hot coflow (JHC) through numerical simulations. We found that even a small mole fraction of H2 (e.g., XH2, F = 5%) significantly enhances the ignition of the premixed NH3/air flame. However, the presence of H2 markedly intensifies the main combustion reactions only when XH2, F ≥ 30%, resulting in a sharp increase in temperature and heat release rate. Moreover, as XH2, F increases, the NOx emission first increases until XH2, F = 75% and then decreases. Without any H2 addition, a high emission of unburned NH3 occurs in the pure NH3 JHC flame. On the other hand, when XH2, F ≥ 50%, the emissions of unburned H2 and OH increase rapidly due to extremely high temperatures. Notably, maintaining XH2, F between 5% and 20% minimizes the emissions of NOx, NH3, H2, and OH. Furthermore, the preferential diffusion of H2 plays a key role in enhancing the production of active radicals (OH, O, and H), thereby significantly boosting the initiation and combustion reactions of NH3/H2 blended fuel. [Display omitted] •Effect of H2 addition on the premixed NH3/H2/air jet flames is investigated.•A small amount of H2 (5%) in the fuel notably enhances the ignition of NH3 flame.•H2 significantly boosts major combustion reactions only when its proportion ≥30%.•Optimal H2 proportion is 5%–20% to reduce emissions of NOx, unburned NH3 and H2.•Preferential diffusion of H2 greatly enhances the ignition and combustion reactions.