Measurements of Temperature and OH Radical Concentration in Combustion Gases by Absorption Spectroscopy with a Diode Laser.

Abstract

The in-situ, quantitative profiles of temperature and OH radical concentration in a post-flame region between two-dimensional laminar counter-flow twin flames were measured by wavelength modulation spectroscopy(WMS)using a 1.5μm external cavity diode laser. The second harmonic('2f')signal was generated from absorption by two different overtone rotational-vibrational transitions of OH; the P 11.5(υ′, υ")=(2, 0)(ν0=6421.354cm-1)and the P5.5(υ′, υ")=(3, 1)(ν0=6434.613cm-1)trasitions. The absorption occurred in the post flame region between propane-air premixed twin flames stabilized in a two-dimensional laminar counter-flow burner(Tsuji burner)with a 60mm line-of-sight path length. The temperature and OH concentration profiles at different equivalence ratios(φ=0.8 and 0.9)were determined by least-square fitting of theoretical 2f lineshapes to the experimental counterparts and by calculating the ratio of the line intensities('2-line method')of the two different OH transitions. The measured temperature and OH concentration profiles were qualitatively consistent with two-dimensional numerical predictions using an augmented reduced mechanism of propane-air premixed combustion which includes OH as principal species.