Absolute concentration measurements of chemically-important flame radicals

A fundamental understanding of flame chemistry is a necessary part of desig ning and optimizing combustors to meet environmental regulations while main taining system efficiency. We have performed quantitative, absolute concent ration measurements for several free radicals to test various aspects of th e predictive capabilities of the natural gas combustion chemistry mechanism , GRI-Mech 2.11, the chemical mechanism for methane combustion. The CH, NO, OH, and HCO radicals were studied in a series of low-pressure methane/O-2/ N-2 flames using the technique of laser-induced fluorescence. The results s how that GRI-Mech 2.11 predicts well the hydrocarbon oxidation chemistry in lean and near stoichiometric flames, but appears to possess some inadequac ies for rich flames. Of special importance is the finding that the rate coe fficient for the important CH + N-2 reaction in the current version of GRI- Mech appears to be too low. Also, reburn of NO is correctly predicted in a lean flame but not a rich one.