NH2 Measurements during the Pyrolysis and Oxidation of Ammonia/Propane Mixtures in a Shock Tube

Ammonia/propane pyrolysis and oxidation mixtures were studied using NH2 laser spectroscopy to obtain NH2 time histories in a shock tube. An NH3 diagnostic based on a quantum cascade laser was used to verify the initial ammonia concentrations, while a 597.375-nm laser diagnostic measured NH2 in the post-reflected shock region. A 75/25% (by volume) ammonia/propane pyrolysis mixture, diluted in 99% argon, was tested between 1682 and 2926 K at near-atmospheric pressure. Three elementary reactions─C3H8 ⇆ C3H7 + H, NH3 + H ⇆ NH2 + H2, and NH2 + H ⇆ NH + H2─were identified as influential for accurately modeling NH2. Additionally, mixtures composed of 75/25% ammonia/propane with O2 in 99% argon were tested at equivalence ratios of 0.5, 1.0, and 2.0 between 1318 and 2404 K. Four key reactions, namely C3H8 + M ⇆ C2H5 + CH3 + M; NH3 + H ⇆ NH2 + H2; NH3 + OH ⇆ NH2 + H2O; and O2 + H ⇆ O + OH, heavily influenced the production of NH2 at early time scales, with CH4 + M ⇆ CH3 + H + M and H2 + O ⇆ H + OH being responsible for the delayed destruction of NH2. The data presented in this study are available in the supplementary material for chemical kinetics modeling validation.