CH, NH, and NH₂ concentration profiles in methane/air flames doped with N₂O

Intracavity Laser Absorption Spectroscopy (ICLAS) and Cavity Ring-Down Spectroscopy (CRDS) were used to measure concentration profiles of the CH, NH, and NH₂ radicals in a low-pressure (30 Torr) stoichiometric methane/oxygen/ nitrogen flat flame doped with a small amount of nitrous oxide (1.7%). Concentration profiles of the CH and NH radicals were measured by CRDS, whereas the NH, radical profile was measured by ICLAS. Temperature profiles were obtained using measured CRDS spectra of the OH radical. The radical absorption spectra were recorded with good signal-to-noise ratio. For the first time, absolute concentrations of NH and NH₂ were measured in flames of this kind. The obtained experimental profiles and peak amounts agree well with model predictions based on GRI-Mech 2.11 (Gas Research Institute Mechanism). The mechanism also describes well the observed decreasing CH concentration with addition of N₂O.