Using UV Absorption Spectroscopy to Measure the Time History of the Hydroxyl Radical in a Shock Tube

摘要

The hydroxyl radical (OH) is an important intermediate species in any hydrogen- or hydrocarbon-based flame. Despite its importance, few direct measurements of OH at elevated temperatures and pressures have been made behind reflected shock waves. Described in this work is a relatively inexpensive yet surprisingly little-used diagnostic for measuring OH within a shock tube using UV absorption spectroscopy utilizing light from a UV xenon arc lamp passed through a spectrometer. OH absorption was performed over a narrow range of widely-studied wavelengths around 309.5 nm. A calibration mixture of stoichiometric H_2/O_2 diluted in 98% argon by volume was tested and compared with a well-known hydrogen-based kinetics mechanism to generate an absorption coefficient correlation. This correlation was used across the temperature range of 1182 to 2017 K and at two pressures of 2 and 13 atm. Using these correlations, OH time histories were found to show good agreement with mechanism predictions. The spectrometer-based approach is shown to provide rather good signal-to-noise ratios during elevated-pressure experiments, up to 34 atm in the present study.