The traditional line reversal method for measuring flame temperatures has been modified to eliminate balancing of the background radiation source and facilitate real-time measurement. Two closely spaced emission lines of a Group IA element are simultaneously monitored and compared to the emission of a known source. The new technique uses optical filtering to reduce the apparent temperature of the source at the wavelength corresponding to one of the transitions. The ratio of the absorption/emission intensities of the two lines is directly related to the flame temperature. Flames as hot as 2800 K can readily be probed using the new technique. Experimental data for cool flat flames compare well with thermocouple measurements.

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