Laser-absorption-spectroscopy-based temperature and NH3-concentration time-history measurements during the oxidation processes of the shock-heated reacting NH3/H2 mixtures

Abstract

As a carbon-free fuel, NH3 has been considered as a potential and promising alternative energy carrier in the future transportation system. This study simultaneously measured the temperature and NH3-concentration time histories during the oxidation processes of the shock-heated NH3/H2 mixtures by combining laser absorption techniques. The v" = 0, P8 and v" = 1, R21 lines in the fundamental vibrational band of CO were selected for temperature time-history measurements. Nine transition lines in the v2 fundamental vibrational band of NH3 near 8.91 µm were selected for NH3-concentration time-history measurements. The temperature- and pressure-dependent NH3 absorption cross-section highly diluted in argon was measured at 1000–2200 K and 0.8–3.9 bar, respectively. The time-dependent temperature and NH3 concentration were then measured and compared with the predictions based on four mechanisms (Mathieu & Petersen, 2015; Glarborg et al., 2018; Wang et al., 2020; Shrestha et al., 2021). The four mechanisms were substantially slow in predicting the NH3-concentration time histories for the stoichiometric NH3/H2 mixtures. The Glarborg et al. mechanism and the Shrestha et al. mechanism showed very good agreements with the experiments for the fuel-rich NH3/H2 mixtures, especially in predicting the NH3-concentration time-history profiles in the burnout state. Comprehensive kinetics analyses illustrated that the NH3 addition evidently changed the mixture reactivity and formation and consumption processes of H and OH radicals. This study updated the rate coefficients of NH3 + OH = NH2 + H2O in the Glarborg et al. mechanism and the modified mechanism showed improved performances in predicting the NH3-concentration profiles.