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

The interaction between ammonia (NH 3) 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 NH 3 and NO time-histories during the reaction processes of the shock-heated NH 3 /NO/CO/Ar mixtures (NH 3 :NO ≈ 0.9:1.0 and 1.4:1.0). The absorption cross-sections of NH 3 near 1122.10 cm^–1 and NO at 1900.52 cm^–1 (characterized in this study) were used for measuring NH 3 and NO time-histories with the temperature measured by two CO absorption lines. The measured NH 3 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-NO x , and Mathieu mechanisms give the closest predictions to the measurements. Kinetics analyses indicate that the NH 3 and NO consumption rates are extremely sensitive to the rate constants and branching ratio of NH 2 + NO = N 2 + H 2 O and NH 2 + NO = NNH + OH, which are more reliably represented in the Glarborg and NUI Galway Syngas-NO x mechanisms. The performances of Glarborg mechanisms at lower initial temperatures can be apparently improved by revising the rate constants and branching ratio of NH 2 + NO = N 2 + H 2 O and NH 2 + NO = NNH + OH. These two reactions are also the primary pathways for NO reduction and NH 3 is mainly consumed via NH 3 + OH = NH 2 + H 2 O and NH 3 + H = NH 2 + H 2. Trace amounts of NO 2 and N 2 O impurities decompose to form O radical followed by the generation of OH radical via H-abstraction reactions, which significantly affects the predictions of NH 3 and NO according to kinetics analyses. [ABSTRACT FROM AUTHOR]