Abstract
The in situ quantitative profiles of temperature and OH radical concentration in a postflame region of methane–air premixed counterflow flames were measured by wavelength modulation spectroscopy with a 1.5-µm external cavity diode laser. The second harmonic (2f) signal was generated from absorption by overtone vibrational–rotational transitions of OH: the Π3/2 (v′, v″) = (2, 0) P11.5e (ν 0 = 6421.35 cm-1) or the Π3/2 (v′, v″) = (3, 1) P5.5f (ν 0 = 6434.61 cm-1) transitions. The absorption occurred in the postflame region between methane–air premixed twin flames stabilized in a two-dimensional laminar counterflow burner (Tsuji burner) with a 60-mm line-of-sight path length. The temperature and OH concentration profiles at an equivalence ratio of ϕ = 0.85 were determined by least-squares fitting of theoretical 2f line shapes to the experimental counterparts and by calculation of the ratio of the line intensities of the two different OH transitions (two-line thermometry). The measured temperature and OH concentration profiles were cross checked by Rayleigh scattering thermometry, thermocouple measurements, and two-dimensional numerical prediction of premixed combustion by use of a detailed chemical kinetic mechanism. The measurements and the prediction showed reasonable agreement.
© 2001 Optical Society of America
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