Laser Determination of Chemically Active Free Radicals in Flames

An understanding of flame chemistry is a necessary part of designing and optimizing burners to meet environmental regulations while maintaining system efficiency. We have performed quantitative, absolute concentration measurements for several free radicals to test various aspects of the predictive capabilities of GRI-Mech, the chemical mechanism for natural gas combustion. The CH, NO, OH, and HCO radicals were studied in a series of low pressure methane/02/N2 flames using the technique of laser-induced fluorescence. The results show that GRI-Mech predicts well the hydrocarbon oxidation chemistry in lean and near stoichiometric flames, but appears to have some inadequacies for rich flames. The rate coefficient for the important CH + N2 reaction in the current version of GRI-Mech appears to be too low. Finally, reburn of NO is correctly predicted for a lean flame but not a rich one