Abstract
The effect of highly preheated combustion air on the combustion characteristics of propane flames is presented. Data have been obtained on the spatial distribution of emission intensity from selected radicals, fluctuations of emission intensity, and flame temperature using several diagnostic techniques. Several propane and high-temperature air flames, produced with the crossflow diffusion of gas into highly preheated combustion air (obtained by a regenerative combustion facility) having normal oxygen content and reduced oxygen content (<21% by volume) have been examined. The diagnostics used include a UV-charge coupled device (CCD) camera integrated with an interference filter, a high-speed video camera, array of thermocouples, and gas analyzers for NO x and O 2 . The UV-CCD camera fitted with the desired optical interference filter provided the spontaneous emission signature of the flames produced. Fast Fourier transform applied to the video camera recorded image provided information on the two-dimensional distribution of emission intensity fluctuation. The emission results show that the intensity level of OH and C 2 radicals in the flame with highly preheated and lower oxygen concentration air is much lower than the corresponding normal air flames. The fluctuations of emission intensity with highly preheated combustion air are significantly lower in the high-temperature combustion region of the flame. The temperature measured from the ratio of the emission intensities had much higher spatial resolution than those obtained with the conventional thermocouple array. The results indicate that preheated air drastically reduces both the temperature gradient and temperature fluctuations in the flames. NO x measurements were made in the exhaust gas using a chemiluminescence analyzer. The results showed that reducing the oxygen concentration in the high temperature combustion air reduces NO x emission levels in the exhaust gas.
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