A Study on Effects of Spray Characteristics on Prevaporization and Premix Combustion Mechanism

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This study aims to clarify the relationship between spray characteristics, evaporation characteristics, combustion characteristics and emission characteristics, and to obtain the guide to the design of a premix and prevaporization combustor with low NOx emission. From the results of atomization experiments at room temperature, the radial profile of droplet mass flux approaches to uniform profile downstream. At the exit of the evaporation tube (495mm downstream from the nozzle), the droplet mass flux at the center is about twice of that near the tube wall. By evaporation experiments using a water at 30m/s of inlet air velocity and 550K of inlet air temperature, at 175mm far from the nozzle the droplet mass flux at the center is larger than that of the vapor. The droplet evaporation advances rapidly downstream, and at 430mm far from the nozzle the mass flux of the vapor at the center becomes larger than that of the droplet. Concerning to the radial profile of a rate of the vapor to the w … More ater component including droplets and vapor, the rate has a peak at the middle between the center and the tube wall. From the results of combustion experiments using a kerosene, the flame holding mechanism changes at 0.6 of equivalence ratio. The lower flammability limit decreases with a increase of a length of the vaporization tube, the inlet air temperature and the inlet air velocity. The NOx concentration in the exhausted gas increases exponentially with a increase of the equivalence ratio. The empirical equation of the emission index of NOx was obtained. The emission index of NOx can be reduced less than 1g (NOx) /kg (Fuel) and that of CO less than 10g (CO) /kg (Fuel) within the range of 0.54 to 0.68 of the equivalence ratio using newly designed combustor. By the numerical simulation of the spray flow and the spray evaporation without combustion under the condition of 30m/s of the inlet air velocity and 550K of the inlet air temperature, at 500mm far from the nozzle the air temperature at the center is 35K lower than that at the periphery, and the Sauter's mean diameter of the spray at the center is 30 micron smaller than that at the periphery. Less