Shock tube study of the interaction between ammonia and nitric oxide at high temperatures using laser absorption spectroscopy

Abstract

The interaction between ammonia (NH3) and nitric oxide (NO) at high temperatures is studied in this work using a shock tube combined with laser absorption diagnostics. The system simultaneously measured the NH3 and NO time-histories during the reaction processes of the shock-heated NH3/NO/CO/Ar mixtures (NH3:NO ≈ 0.9:1.0 and 1.4:1.0). The absorption cross-sections of NH3 near 1122.10 cm–1 and NO at 1900.52 cm–1 (characterized in this study) were used for measuring NH3 and NO time-histories with the temperature measured by two CO absorption lines. The measured NH3 and NO time-histories at 1614–1968 K and 2.4–2.8 atm were compared with predictions of seven recent kinetics models. The predictions that based on different mechanisms are very different and the measured profiles are within the range of the predictions. The Glarborg, NUI Galway Syngas-NOx, and Mathieu mechanisms give the closest predictions to the measurements. Kinetics analyses indicate that the NH3 and NO consumption rates are extremely sensitive to the rate constants and branching ratio of NH2 + NO = N2 + H2O and NH2 + NO = NNH + OH, which are more reliably represented in the Glarborg and NUI Galway Syngas-NOx mechanisms. The performances of Glarborg mechanisms at lower initial temperatures can be apparently improved by revising the rate constants and branching ratio of NH2 + NO = N2 + H2O and NH2 + NO = NNH + OH. These two reactions are also the primary pathways for NO reduction and NH3 is mainly consumed via NH3 + OH = NH2 + H2O and NH3 + H = NH2 + H2. Trace amounts of NO2 and N2O impurities decompose to form O radical followed by the generation of OH radical via H-abstraction reactions, which significantly affects the predictions of NH3 and NO according to kinetics analyses.