NH and OH Concentration Profiles in a Stoichiometric CH4/N2O Flame by Laser Excited Fluorescence and Absorption Techniques

摘要

The concentration profiles of NH and OH were measured in an atmospheric pressure premixed laminar Ch4/N2O flame over a porous plug flat flame burner. Relative profiles were obtained by laser excited fluorescence for both compounds and normalized by laser absorption at a single point for NH. The OH concentration was high enough to allow absorption measurements at several points for comparison with fluorescence results. The steeply rising portions of the profiles occur at about the same height above the burner but the NH is confined to the primary reaction zone while the OH decay extends into the burnt gases. The apparent OH decay was found, using a simple analysis, to be consistent with second order kinetics as observed by previous workers on other flames. However, it should be noted that diffusion of OH is at least partially responsible for the apparent shape of the profile resulting in the second order decay kinetics found using the simple analysis. The decay rate is smaller than that observed by previous workers for CH4/air flames. Qualitative reasons for the different decay rates found in the studies are discussed in detail. A strong dependence of OH decay rate on final flame temperature, and hence the cooling rate peculiar to the burner concentration in CH4/air, CH4/NO, and H2/N2O flames were made in order to elucidate the flame chemistry. (Author)