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Show the results suggest that the central recirculation zone nearly disappeared for low-swirl flame, but apparantly existed in cases of higher swirl flames. The measured values of temperature and C02, CO,HC concentrations around the region of center line for low-swirl flame are much lower than those of higher swirl flames, but the 02 concentrations are much higher. It is evident that hollow reaction zone for 5=0.3 swirl flame is the result of dilution and quenching effect of the cold, high velocity air stream on center line. The penetration distance of fuel spray is reduced with increasing swirl level and therefore the flame zone reduces and shifts to near-wall region. The high temperature burnt gases forming the central recirculation zone enhance the evaporation of fuel spray and complete combustion. 5.CONCLU5IONS 1. Most of the fuel reacts outside the recirculation for higher swirl strength (S > 0.8). 2. The process of fuel air mixing starts to happen at the upstream zone near tip of the atomizer. 3. The structure of the flame formed around a fuel spray is largely influenced by the extent of the interaction between the fuel spray and surrounding, swirling combustion air. The high turbulent mixing rate for higher swirl level enhance the evaporation of fuel droplets and consequently speed the chemical reaction process. 4. There is no central recirculation zone for low-swirl flame ,but evidently exist for higher-swirl flames. The results obtained for the flames with S=0.3, S=0.8 and S=1.2 swirl level indicate that the flame zone is shorter wider as as the increase of the swirl level. ACKNOWLEDGEMENTS This study was supported by National Science Council of the Republic of China (C577-0210-D006-16) and National Cheng Kung University. - 7 - |