NO(x) in methane-air jet diffusion flames

Abstract

Dynamic simulations for NOx formation in an unsteady laminar, methane jet flame are made using an axisymmetric, time-dependent CFDC code and a detailed-chemical-kinetics model. Due to the buoyancy-induced instability vortical structures developed outside the flame surface and caused the flame to wrinkle. These simulations indicate that the temperature of the flame increases locally when it is compressed by the outer vortex and decreases when it is stretched. These effects are similar to those observed in a hydrogen diffusion flame and are attributed to the local nonunity Lewis numbers. Previous studies on dynamic hydrogen flames further reveled that the concentration of NO increases significantly in the compressed flame regions where temperature increases. For understanding the flame stretching and compression effects on the production of NO in methane diffusion flames calculations are made using different NOx chemistry models. It is observed that the thermal NO increases in the compressed flame regions; however, the flame stretch effect seems to be weak on the total NO (thermal + prompt) production.