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 (ν0 = 6421.35 cm−1) or the Π3/2 (v′, v″) = (3, 1) P5.5f (ν0 = 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
(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)