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Abstract
Two types of OH radicals exist in a mixture of CH4–H2 fueled flame, which are produced respectively from CH4-air and H2-air combustion reactions. We have devised a new diagnostics tool for planar laser-induced fluorescence (PLIF) spectroscopy using isotope shift (herein called IS/PLIF spectroscopy). This diagnostics was applied to separately visualize two-dimensional (2-D) distributions of net (not absolute) OH radical fluorescence intensities produced from CH4–O2-air and H2–O2-air combustion reactions in a CH4–H2–O2-air premixed flame. In result, the OH radical produced from H2–O2-air combustion reaction appeared on upstream side of the inner flame as compared to that produced from CH4–O2-air combustion reaction. Since OH radical is one of chain carriers in combustion reactions, this indicates that H2 tends to react at more upstream location than CH4 in the CH4–H2 mixture flame. This tendency is attributable to the fact that H2 differs from CH4 in the high burning velocity and extended flammability limit.