OH rotational temperature from two-line laser-excited fluorescence.

A two-line laser-excited fluorescence technique has been developed to measure the rotational temperature of the OH molecule. This technique eliminates problems encountered in the application of other laser fluorescence methods for measuring the OH temperature in combustion environments, such as fluorescence trapping, nonequilibrium excited state population, spectral bandwidth sensitivity, and quenching. The technique consists of exciting a specific rotational level of the OH molecule in the A(2)Sigma (upsilon' = 0) excited state from two different rotational levels in the X(2)Pi(upsilon'' = 0) ground state using a tunable dye laser and monitoring the broadband fluorescence. An example of the implementation of this technique in an atmospheric pressure methane-air flat flame is included. The possible application of this technique in turbulent combustion is also evaluated.