Laser absorption spectroscopy for high temperature H₂O time-history measurement at 2.55 μm during oxidation of hydrogen

Concentration time-histories of H₂O were measured behind reflected shock waves during hydrogen combustion. Experiments were conducted at temperatures of 1117-1282 K, the equivalence ratios of 0.5 and 0.25, and a pressure at 2 atm using a mixture of H₂/O₂ highly diluted with argon. H₂O was monitored using tunable mid-infrared diode laser absorption at 2.55 μm (3920.09 cm^-1). These time-histories provide kinetic targets to test and refine reaction mechanisms for hydrogen. Comparisons were made with the predictions of four detailed kinetic mechanisms published in the last four years. Such comparisons of H₂O concentration profiles indicate that the AramcoMech 2.0 mechanism yields the best agreement with the experimental data, while CRECK, San Diego, and HP-Mech mechanisms show significantly poor predictions. Reaction pathway analysis for hydrogen oxidation indicates that the reaction H+OH+M=H₂O+M is the key reaction for controlling the H₂O formation by hydrogen oxidation. It is inferred that the discrepancy of the conversion percentage from H to H₂O among these four mechanisms induces the difference of performance on H₂O time-history predictions. This work demonstrates the potential of time-history measurement for validation of large reaction mechanisms.