NOx formation in flat, laminar, opposed jet methane diffusion flames

It is shown that the detailed structure of a flat laminar opposed jet diffusion flame can be modeled, by properly coupling the momentum and energy conservation equatins and by using detailed finite rate combustion kinetics. Such a flame is one dimensional (for a given stretching rate) provided that the proper velocity boundary conditions, which are a result of the model are employed. A laboratory CH 4 /N 2 /O 2 opposed jet diffusion flame was realized and gave good agreement with predictions with respect to both, one dimensinality and the temperature and species profiles within the reaction zone. However, the actual location of the reaction zone was displaced by a small distance. The theoretical/experimental tool developed was utilized to test kinetic mechanisms of NO formation from fuel nitrogen. In this case, anhydrous ammonia was introduced first with the fuel and then with the oxidizer. The formation of NO was well predicted, using a detailed kinetic mechanism developed by others, when ammonia was introduced with the fuel, but agreement was poor when ammonia was injected in the air side. This indicates that there are some deficiencies in the ammonia pyrolysis kinetic mechanism when it is utilized in the absence of hydrocarbon fragments. The qualitative dependence of the NO profile on flame stretching was correctly predicted by the model. This also allowed the prediction of reaction zone thickness and the rate of formation of NO as a function of stretching rate and these results can be related to NO formation in strained laminar diffusion flamelets as they occur in turbulent diffusion flames.