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

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 A(2)Sigma(+)-X(2)II 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 H(2)/O(2)/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.