Spatially resolved measurement of OH*, CH*, and C2* chemiluminescence in the reaction zone of laminar methane/air premixed flames

Spatially and spectrally resolved chemiluminescence were measured in the reaction zone of a laminar premixed methane/air flame at equivalence ratios of 0.9-1.5 in atmospheric pressure using a new Cassegrain mirror system and a spectrometer with an intensified charge-coupled device. The measurement volume of the Cassegrain optics was estimated to be 100 mum in diameter and 800 mum long. Local flame spectra of the reaction zone showed remarkably high intensity of OH*, CH*, and C-2* emission bands. The distributions of OH*, CH*, and C-2* emission intensities near the flame front were roughly revealed. The emission zone thickness of C-2* was found to be the thinnest among these radicals. The OH* emission zone had a sharp distribution within a reaction zone, but its thickness was a little wider than that of either CH* or C-2*. Highly spectrally resolved local OH*. CH*, and C-2* chemiluminescent spectra were obtained at the local flame front. It was found that the dependence of the intensity of each rotational and vibrational head of the chemiluminescence on the equivalence ratio was almost the same as that of spectrally integrated band emissions of OH*, CH*, and C-2*. It was found that the strong correlations between the peak intensity ratios of OH*/CH*, C-2*/CH* and C-2*/OH* in the reaction zone to the equivalence ratio could be used to investigate the local flame stoichiometry. OH*/CH* can be a good marker to determine the local flame stoichiometry in the reaction zone of methane/air premixed flames for a wide range of equivalence ratios.