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

研究目的在于阐明喷雾特性、蒸发特性、燃烧特性和排放特性之间的关系，为低NOx排放预混预蒸发燃烧室的设计提供指导。从室温雾化实验结果来看，液滴质量流量的径向分布在下游趋于均匀分布。在蒸发管出口处（喷嘴下游495 mm处），中心处的液滴质量通量约为管壁处的两倍。在进口风速为30 m/s、进口温度为550 K的条件下进行了水的蒸发实验，在距喷嘴175 mm处，中心处的液滴质量通量大于水蒸气的质量通量。液滴的蒸发向下游迅速推进，在距喷嘴430 mm处，中心蒸汽的质量流量大于液滴的质量流量。关于蒸汽对水蒸气的速率的径向分布， ...更多信息 对于液滴和水蒸气组成的水组分，在中心和管壁之间的中间处，速率有一个峰值。从燃烧实验的结果，使用煤油，火焰稳定机制的变化在0.6当量比。可燃性下限随汽化管长度、进气温度和进气速度的增加而减小。排气中的NOx浓度随着当量比的增加而指数地增加。得到了NOx排放指数的经验公式。在当量比为0.54 ~ 0.68的范围内，采用新设计的燃烧室，NOx排放指标可降低到1g（NOx）/kg（燃料）以下，CO排放指标可降低到10 g（CO）/kg（燃料）以下。通过对进口空气速度为30 m/s、进口空气温度为550 K条件下无燃烧喷雾流动和喷雾蒸发过程的数值模拟，发现在距喷嘴500 mm处，中心空气温度比周边空气温度低35 K，中心喷雾Sauter平均直径比周边小30 μ m。少

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