Analysis of Wavelength Modulation Spectra for Determination of OH Radical Concentration in an Atmospheric Pressure Laminar Premixed Flames

Abstract This work is aimed at the application of wavelength modulation spectroscopy with the second harmonic detection for determination of OH radical concentration in laminar premixed flames of methane-air mixtures. Several hot water lines and two overtone OH transitions were identified in high-resolution absorption spectra measured in our experimental setup. Information on spectral line-shape parameters for selected OH transitions were extracted from the experimental data using relevant methods and approximations. An appropriate line-shape model was finally implemented into an automated least-square fitting procedure in order to quantify the local mole fraction of OH radical in an atmospheric pressure flames.