Contribution of different routes forming no in lean hydrogen flames

The relative importance of different routes forming NO in premixed hydrogen flames has been analyzed by comparing experiments on the lean combustion of H-2 - O-2 - N-2 mixtures with modeling, employing sensitivity analysis. The comparison of the model predictions with [NO] measurements in these flames strongly supports the new rate constant of the reaction NNH + O = NH + NO. The sensitivity analysis shows that the relative importance of the thermal-NO and the NNH mechanism varies with the temperature, the last route being dominant below about 2000 K. Similar to the earlier analysis of the hydrogen combustion in stirred reactors, the NO formation via NNH is of major importance not only in rich flames but also in lean mixtures up to moderately high ( 1900 K) temperatures. This route therefore must be explicitly taken into account as the source of NO in hydrogen-fueled industrial installations and turbulent flames.