RELATIVE IMPORTANCE OF NITRIC-OXIDE FORMATION MECHANISMS IN LAMINAR OPPOSED-FLOW DIFFUSION FLAMES

The relative importance of the Zeldovich, N2O, and Fenimore mechanisms for nitric oxide formation in stretched laminar opposed-flow diffusion flames with CH4/N2 fuel is determined using model calculations that include detailed chemical kinetics (213 reactions and 45 molecular species) and realistic multi-component transport effects. For all values of stretch, the NO formation is dominated by the Fenimore mechanism, which contributes more than two thirds of the total NO formed. The remaining NO is formed approximately equally by the Zeldovich and N2O mechanisms. The model calculations are compared with previous measurements in laminar opposed-flow CH4/N2 diffusion flames at three values of stretch (alpha = 42, 70, and 140 s-1). The model-experiment agreement (within 50 K for peak temperature and within a factor of 2 for peak NO(x) formed) supports the validity of the detailed chemical kinetic mechanism used. The Fenimore mechanism is expected to dominate NO formation in many laminar and turbulent hydrocarbon diffusion flames.