微重力下层流扩散火焰碳烟生成过程

根据详细的燃料氧化机理和多环芳烃生成机理，对乙烯同轴射流火焰在重力变化下碳烟生成情况进行计算.认为碳烟的初始成核是由两个较大的多环芳烃（PAH）二聚而成，碳烟的表面生长机理为HACA，凝结过程主要考虑PAH与碳烟的碰撞吸附，碳烟生长和氧化过程耦合在分节气溶胶模型中.计算结果表明，微重力条件下乙烯同轴射流火焰峰值温度下降230K，碳烟浓度显著增加，且浓度峰值在微重力条件下更加偏离中心线.分析重力变化对碳烟前驱体乙炔和多环芳烃的分布、初始成核速率、表面生长速率及凝结速率的影响.结果表明碳烟在中心轴线上主要是通过凝结过程生成的，且微重力条件下PAH在碳烟表面的凝结更加重要.由于微重力条件下停留时间更长，导致碳烟直径更大. 

Soot Formation in Laminar Diffusion Flame under Microgravityormalsize

The soot formation in a coflow ethylene/air laminar flame at 1g/0g (normal gravity and zero gravity) has been studied using particular fuel oxidation and PAH mechanism. The nucleation process is regarded as the dimerization of two large PAH, and HACA mechanism is used to describe the surface growth process. The collision of soot and PAH is mainly taken into account for the condensation process in soot surface. The initial nucleation, soot surface growth, condensation and oxidation are simulated with a discrete sectional aerosol model to capture the different size soot with different mass. The calculating results show that the peak temperature of the flame at 0g decrease by 230K, whereas the peak soot volume fraction is nearly twice larger than that of the 1g condition. This paper also studied the distribution of precursors (C₂H₂ and PAH), nucleation rate, surface growth rate, and condensation rate under microgravity. It is indicated that the condensation is the major process of soot formation in the centerline of flame for both 1g and 0g conditions, and it plays a more important role under microgravity. The average diameter of soot is lager due to long residence time under microgravity.