H2O time histories in the H2-NO2 system for validation of NOx hydrocarbon kinetics mechanisms

The development and refinement of NOx chemical kinetic mechanisms have been instrumental in understanding and reducing NOx formation. However, relatively little work has been performed with NOx species as the oxidizer, and such experiments can provide unique insights into NOx kinetics. Furthermore, speciation data can often provide useful information that complements global measurements such as ignition delay times in facilitating mechanism refinement. To provide such speciation data in the H-2-NO2 system, H2O measurements were performed using a fixed-wavelength, direct absorption laser diagnostic near 1.39 mu m behind reflected shock waves in fuel-lean, near-stoichiometric, and fuel-rich mixtures of H-2 and NO2 highly diluted in argon. Experiments were performed between 917 and 1782 K near atmospheric pressure. The H2O profiles obtained herein are markedly different from those using O-2 as the oxidizer obtained in a previous study. The GRI 3.0 mechanism was found to greatly underestimate the H2O formation, whereas two modern mechanisms were found to predict the H2O formation quite accurately except at colder temperatures for fuel-rich conditions. Explanations for the differences between these mechanisms are given and discussed, with the conclusion that older mechanisms such as GRI 3.0 should not be used to model hydrocarbon/NOx combustion chemistry as they are lacking several key reactions and species, namely NO3 and HONO. The discrepancy between models and data at lower temperatures could not be reconciled even when modifying two of the most-sensitive reaction rates. To the best of the authors' knowledge, this study presents the first shock-tube speciation study in the H-2-NO2 system.