Measurements of OH radical concentration in combustion environments by wavelength-modulation spectroscopy with a 1.55-mu m distributed-feedback diodelaser

Wavelength-modulation spectroscopy with a standard commercial 1.55-mu m dis tributed-feedback diode laser was applied to in situ quantitative measureme nts of OH radical concentration in combustion environments. The second-harm onic (2f) signal was generated from absorption by the P11.5 (v', v ") = (2, 0) overtone vibrational transition of OH at 6421.354 cm(-1). The absorptio n occurred in the postflame region of a two-dimensional laminar counterflow burner (Tsuji burner) with a 60-mm line-of-sight path length. The postflam e region lies between propane-air premixed twin flames stabilized in the Ts uji burner at various equivalence ratios (phi = 0.65-1.0). The OH concentra tions were determined by least-squares fitting of theoretical 2f line shape s to the experimental counterparts. The measured OH concentrations were in general agreement with adiabatic chemical equilibrium predictions. The lowe r limit of OH detectivity by multiline deconvolution was limited by ubiquit ous unidentified high-temperature H2O transitions. (C) 1999 Optical Society of America.