Experimental and kinetic investigations on diffusion flame stability of ammonia cracking combustion

As a carbon-free energy carrier, ammonia exhibits substantial potential in the context of the “dual carbon” goal and sustainable energy transition. The stability of ammonia cracking diffusion flames is critical to their efficient and safe application in power applications. In this study, a laminar diffusion flame experimental platform for ammonia cracking using oxyhydrogen gas was established. Planar laser-induced fluorescence (PLIF) was employed to measure OH radical fluorescence signals, and flame chemiluminescence was analyzed to evaluate the effects of cracked gas composition on flame stability. Additionally, Chemkin-Pro was utilized to perform sensitivity and yield analysis, identify the key elementary reactions governing radical generation and consumption, and calculate flame thickness and density ratio for assessing hydrodynamic stability. The results indicate that the volumetric flow ratio r between oxyhydrogen gas and ammonia is the core parameter governing OH radical concentration and chemical activity in the flame. Optimal flame stability is observed within the r range of 0.6-0.8, while excessively high r values result in a substantial degradation of stability. Kinetic analysis revealed that H radical formation primarily occurs via reactions R70 NH 2 + NO → NNH + OH and R4 H 2 + OH → H 2 O + H, while consumption is mainly through reactions R1 H + O 2 → O + OH and R16H + OH → O + H 2 . This study clarifies the coupling mechanism among cracked gas composition, radical kinetics, and hydrodynamic stability, providing theoretical support for the clean, low-carbon, and sustainable utilization of ammonia fuel.