Temperature measurement by two-line laser-saturated OH fluorescence in flames

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Abstract
A technique is proposed and demonstrated for measuring combustion temperatures using two-line laser-saturated fluorescence. The rotational temperature of OH is determined by saturating two different rotational transitions in the (0,0) band of the A2∑+–X2Π electronic system and detecting fluorescence emission which originates from the laser-pumped upper rotational levels. Temperature is calculated from the ratio of the fluorescence intensities for the two different excitation–emission pairs. The method is demonstrated by measuring temperature profiles in subatmospheric H2/O2/Ar flat flames. Temperatures measured by two-line saturated fluorescence are compared with temperatures measured by coated thermocouples and OH absorption and with predictions from an elementary chemical kinetics code. The temperatures measured by the two-line fluorescence technique are accurate to 3–5% and exhibit low random error.