LIF MEASUREMENTS IN METHANE AIR FLAMES OF RADICALS IMPORTANT IN PROMPT-NO FORMATION

Laser-induced fluorescence measurements have been made of the OH, CH, and NO radicals in slightly rich methane/air flames burning at 30, 70, and 120 torr. Absolute NO and OH concentrations were determined using separate calibration experiments. Temperature profiles were deduced from OH rotational excitation scans, and fluorescence quenching rates for NO and CH were determined. Predicted profiles of the concentrations of these radical species as a function of height above the burner were obtained from a computer model of the flame, and comparison made with experiment. Good agreement is achieved for the relative concentration profiles, the absolute NO concentration, and concentration ratios between 30 and 70 torr, although slight disagreement with the CH profile indicates there remain some unknown aspects of the flame chemistry.