High-Temperature Measurements of NH2 and NH3 for Resolving Ammonia Kinetics

Ammonia is an important molecule for aeronautical and power generation applications. Ammonia has the potential to replace methane as a climate-friendly alternative, however ammonia chemical kinetics are not well known. Current models are mostly tuned to laminar flame speeds, ignition delay times, and speciation data. Intermediate species such as NH2 have not been investigated thoroughly, with only one major study reporting NH2 concentrations during ammonia pyrolysis. To contribute to resolving ammonia kinetics, a new NH2 laser diagnostic was developed at 597.375 nm and is used in parallel with an NH3 laser diagnostic stationed at 10440.17 nm. Both systems were used between 1993 and 2671 K to obtain an absorption coefficient for NH2 of kv = 9.6989 × 1010/T3 – 4.7499 × 107/T2 + 9.1168 × 103/T (atm−1cm−1), which agrees with that suggested by Mertens et al. (1991) and Clees et al. (2024). This absorption coefficient is estimated to have an uncertainty of ± 15%. Future uses of this new diagnostic include measuring NH2 during ammonia oxidation and ammonia/hydrogen mixtures.