An Experimental and Kinetic Modeling Study of NO₂ Sensitization on the Autoignition of Ammonia

An experimental and kinetic modeling study was performed to investigate the influence of NO2 addition on the autoignition characteristics of NH3/O2/Ar mixtures. Ignition delay times were measured using a shock tube at temperatures of 1450–2200 K, pressures of 0.14 and 1 MPa, equivalence ratios of 0.5, 1.0, and 1.5, and NO2 concentrations from 0 to 2000 ppm. The results show that NO2 addition significantly promotes NH3 autoignition, with the enhancement strongly dependent on temperature, pressure, equivalence ratio, and NO2 concentration. The effect is particularly pronounced at intermediate temperatures (1450–1700 K) and higher pressure, and exhibits a nonlinear relationship with NO2 concentration. The updated Shrestha and Glarborg mechanisms accurately reproduced the experimental IDT data. The evolution of key species indicates that NO2 addition significantly promotes NH3 consumption, along with the formation of NO and the radicals OH and NH2. Flux analysis reveals that NO2 addition introduces a novel ammonia consumption pathway via NH3 + NO2 = NH2 + HONO, facilitating rapid NH2 radical production. HONO decomposition further accelerates OH radical formation. Reaction rate analysis confirms that NO2 promotes OH generation through NO2 + H = NO + OH, especially in the early stages of NH3 oxidation. Moreover, NO2 addition significantly alters NH2 consumption pathways, with both NO2 and NO participating in reactions with NH2, not only accelerating its consumption but also suppressing NH2 self-recombination and other radical-consuming channels.本研究开展了实验与动力学建模工作，以探究添加二氧化氮（NO₂）对氨/氧气/氩气（NH₃/O₂/Ar）混合气体自燃特性的影响。本研究采用激波管测量点火延迟时间，实验温度范围为1450~2200 K，压力分别为0.14 MPa与1 MPa，当量比设为0.5、1.0及1.5，二氧化氮浓度区间为0~2000 ppm。实验结果表明，添加二氧化氮可显著促进氨的自燃，其促进效果强烈依赖于温度、压力、当量比及二氧化氮浓度。该促进效应在中温区间（1450~1700 K）与高压条件下尤为显著，且与二氧化氮浓度呈非线性关系。更新后的Shrestha与Glarborg机理可准确复现实验测得的点火延迟时间（IDT）数据。关键组分演化分析表明，添加二氧化氮可显著促进氨的消耗，同时提升一氧化氮（NO）、羟基自由基（OH）及氨基自由基（NH₂）的生成量。通量分析显示，添加二氧化氮通过反应式NH₃ + NO₂ = NH₂ + HONO引入了一条全新的氨消耗路径，可快速促进氨基自由基的生成。亚硝酸（HONO）的分解进一步加速了羟基自由基的形成。反应速率分析证实，二氧化氮通过反应式NO₂ + H = NO + OH促进羟基自由基的生成，尤其在氨氧化的初始阶段效果显著。此外，添加二氧化氮可显著改变氨基自由基的消耗路径：二氧化氮与一氧化氮均可与氨基自由基发生反应，既加速了氨基自由基的消耗，同时抑制了氨基自由基的自复合反应与其他自由基消耗通道。