Accurate thermometry using NO and OH laser-induced fluorescence in an atmospheric pressure flame (Checked by narrow-band N-2 coherent anti-stokes Raman scattering)

Planar laser-induced fluorescence (PLIF) using OH and NO facilitates noncon tact two-dimensional temperature measurements, and is therefore expected to be an effective technique for combustion thermometry. However, the accurac y of the measurement has not been clarified. The relaxation in the upper ro tational levels of the tracer molecule is not easy to be predicted, and the rotational dependence of the molecular constants, such as absorption and e mission coefficient, has not been fully clarified. Furthermore, it is not c onfirmed whether the rotational distribution of the tracer molecule maintai ns the quasi-equilibrium states or not. In this study, we investigated the accuracy of thermometry by means of laser-induced fluorescence (LIF) using NO : A - X (0, 0) and OH : A - X (3, 0) excitation far a premixed methane - air laminar flame in atmospheric pressure as a measuring target. These were checked by narrow-band N-2 CARS with high spectral resolution, which is be lieved to be the most reliable temperature standard in flames. NO LIF tempe rature showed several % lower temperature than N-2 CARS one, and OH LIF tem perature 30% lower. Both methods were calibrated under exponential dependen ce assumption of molecular constants, and the calibrated temperature of NO and OH LIF agreed well with N-2 CARS one. Furthermore, two-dimensional ther mometry in a flame cross section using calibrated NO PLIF was demonstrated.