Rapid laser-wavelength modulation spectroscopy used as a fast temperature measurement technique in hydrocarbon combustion

A fast temperature measurement technique is described which is suitable for use in dynamic reacting gases, particularly in situations which involve hydrocarbon-air combustion. Temperature is determined from the relative intensity of a pair of fully resolved absorption lines probed with a rapid-tuning single-frequency laser. Demonstration of the technique using 300-micros scans across the R(1) (7) and R(1)(11) lines in the (0, 0) band of the A(2)Sigma(+) ? X(2)II system of OH present in the postflame gases above a CH(4)-air flat-flame burner is reported. Fluorescence monitoring of the absorption spectra was used to provide improved spatial resolution. Temperatures inferred from simultaneous absorption and fluorescence measurements showed good agreement with radiation-corrected thermocouple scans.