Combined cavity ringdown absorption and laser-induced fluorescence imagingmeasurements of CN(B-X) and CH(B-X) in low-pressure CH4-O-2-N-2 and CH4-NO-O-2-N-2 flames

A combined cavity ringdown absorption spectroscopy and laser-induced fluore scence imaging method is used to study CN and CH absolute concentration pro files in low pressure premixed flames featuring prompt NO and reburn chemis try. For methane-air flames with and without seeded NO, the absolute concen trations and the shapes and peak positions of CN and CH above the burner co mpare favorably to model predictions and validate the chemical mechanism. C avity ringdown absorption of CN provides part-per-billion detection sensiti vity. The CH results agree with previous laser-induced fluorescence measure ments calibrated with Rayleigh scattering, after correcting cavity ringdown for laser linewidth effects and accounting for the spatial inhomogeneities of the CH distribution in the flame. (C) 2001 by The Combustion Institute.