The temperature dependence of laser-induced NO A2Σ+–X2Π fluorescence in the hot gases of natural gas–air flames, seeded with known quantities of NO, has been determined experimentally by means of a difference method. The flame temperature at three fixed equivalence ratios was changed when the mixture velocity was varied through a water-cooled, flat-flame burner and was measured by coherent anti-Stokes Raman spectroscopy. When the possible reburning of part of the seeded NO is allowed for, the results in the range 1700–2150 K are best described by the temperature dependence obtained from a model in which quenching corrections are neglected, as in the case of a saturated two-level system, when millijoule pulse energies are used. Measurements of the fluorescence intensity at constant seed concentration as a function of equivalence ratio between 0.75 and 1.3 also indicate that quenching corrections are unnecessary under these excitation conditions. Using the measured intensities of the seeded flame as a calibration factor, we determined the absolute NO concentrations as functions of the equivalence ratio at 1 cm above the burner. The results indicate that, with the calibration method presented here, a relative accuracy of 5% should be obtainable.
© 1997 Optical Society of America
A. V. Mokhov, H. B. Levinsky, and C. E. van der Meij, "Temperature dependence of laser-induced fluorescence of nitric oxide in laminar premixed atmospheric-pressure flames," Appl. Opt. 36, 3233-3243 (1997)