氧浓度对同轴乙烯层流扩散火焰中碳烟形貌及粒径演变的影响研究

Effects of Oxygen Volume Fraction on Morphologyand Particle Size Evolution of Soot in Laminar Coflow Ethylene Diffusion Flames

关键词:  层流扩散火焰  碳烟  氧体积分数  沉积形态  温度

Key words:  Laminar diffusion flame  Soot  Oxygen volume fraction  Deposit morphology  Temperature

摘要:

为探究氧体积分数对乙烯同轴射流扩散火焰中碳烟颗粒生成及演变过程的影响，采用SiC纤维沉积法和热泳探针采样法，对层流扩散火焰中不同径向和轴向位置处的碳烟生成特性进行了研究。研究表明，氧体积分数增加，使火焰同一位置温度升高。在氧体积分数低于31%、火焰高度低于30mm时，SiC纤维上碳烟沉积物形态由火焰中心位置处的表面光滑的类液态演变为粗糙的凹凸块状，随温度升高及氧化作用加强，渐渐被氧化为疏松的团簇状、絮状，最终过渡为致密的团簇状和纤维网状。相同氧体积分数下，碳烟颗粒平均粒径随火焰高度增加呈现先增大后减小的趋势。在氧体积分数21%、火焰高度30mm处初生粒子直径达到最大值，为41.8nm。在火焰根部，碳烟颗粒平均粒径随氧浓度升高而增大，而火焰较高位置处则呈现了相反趋势。

Abstract:

In order to study the effects of oxygen volume fraction on the formation and evolution of soot particles in laminar coflow diffusion flames of ethylene， SiC fiber deposition and thermophoresis probe sampling methods were used to investigate the soot characteristics at different radial and axial positions in laminar diffusion flame. The results demonstrate that the temperature increases with increasing the oxygen volume fraction at the same location. When the oxygen volume fraction is less than 31% and the flame height is lower than 30mm， the morphology of the soot deposits on the SiC fiber evolves gradually from smooth droplet-like at the centerline to uneven clusters at larger radical locations. With increasing temperature and enhanced role of oxidation， the morphology of soot deposits on the SiC fiber is gradually oxidized into loose cluster-like， flocculent， and final transition to dense clusters and fiber mesh. Under the constant oxygen volume fraction， the average particle size of soot particles increases first and then decreases with the increase of flame height. The diameter of primary particles reached the maximum at 21% oxygen volume fraction and flame height 30mm， which was 41.8nm. At the base of the flame， the average soot particle size increased with the increase of oxygen concentration， the opposite trend was observed at higher flame heights.