The <i>in situ</i> 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 (2<i>f</i>) signal was generated from absorption by overtone vibrational–rotational transitions of OH: the Π<sub>3/2</sub> (<i>v</i>′, <i>v</i>″) = (2, 0) <i>P</i>11.5<i>e</i> (ν<sub>0</sub> = 6421.35 cm<sup>−1</sup>) or the Π<sub>3/2</sub> (<i>v</i>′, <i>v</i>″) = (3, 1) <i>P</i>5.5<i>f</i> (ν<sub>0</sub> = 6434.61 cm<sup>−1</sup>) 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 2<i>f</i> 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
(120.1740) Instrumentation, measurement, and metrology : Combustion diagnostics
(300.1030) Spectroscopy : Absorption
(300.6260) Spectroscopy : Spectroscopy, diode lasers
(300.6380) Spectroscopy : Spectroscopy, modulation
Tetsuya Aizawa, "Diode-Laser Wavelength-Modulation Absorption Spectroscopy for Quantitative in situ Measurements of Temperature and OH Radical Concentration in Combustion Gases," Appl. Opt. 40, 4894-4903 (2001)