Results are presented on the effect of high temperature combustion air on the thermal and chemical behavior of propane-air diffusion flames using spectroscopic diagnostic techniques. The oxygen concentration in air was 21% by volume for both the normal and highly preheated air flames. The temperature distribution within the flames has been obtained for a burning fuel jet using normal temperature and high temperature combustion air. Spatial distribution of C2, CH and OH from within the flames in 2-D has been obtained. An ICCD (image intensified charge coupled device) camera fitted with an appropriate narrow band interference filter provided the spontaneous emission signature of the specific specie produced in the flame. The results show that the intensity level of C2 in the flame with highly preheated air is lower than the corresponding normal temperature air flames. In contrast the intensity level of CH radicals in the flame is higher than corresponding normal air temperature flames. The intensity level of OH radicals with highly preheated air is higher than corresponding normal temperature air flames. They suggest faster chemical reaction and higher heat release rate with high temperature combustion air than the corresponding normal temperature air. These findings are much different than those obtained for low oxygen concentration air flames. The Abel transformation technique was applied to obtain 3-D spatial distribution of selected radicals within the flames. Two emission peaks of C2 radical species have been observed in the visible part of the wavelength. The temperature distribution inside the flame was obtained from the ratio of these two peaks using two-color method. The effect of preheated combustion air on the flame temperature has been determined by analyzing the spectra of spontaneous emission of the C2 radicals at two discrete wavelengths.

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