重力对层流扩散火焰烟黑生成特性影响

SOOT FORMATION OF LAMINAR COFLOW DIFFUSION FLAMES IN DIFFERENT GRAVITY CONDITIONS

本文采用数值模拟方法研究了重力对甲烷/空气同轴射流层流扩散火焰烟黑生成特性的影响,数值分析中将详细的气相化学反应机理、复杂的热物性和输运特性关系、半经验的双方程烟黑生成模型和非灰体辐射模型耦合到燃烧场的计算中。同时考虑烟黑经O_2、OH和O的氧化途径。热辐射计算采用与统计窄波段调K(SNBCK)模型相耦合的离散坐标法求解。烟黑的谱带吸收系数根据小颗粒的Rayleigh理论计算。结果表明,随着重力水平的降低,火焰峰值温度降低,微重力下烟黑浓度的最大值约为正常重力下相应火焰的两倍。这一计算结果与已有的试验数据符合较好。计算结果还表明,重力也影响烟黑成核和表面生长的位置和强度。

Simulations of a laminar coflow methane/air diffusion flame are conducted to investigate the effects of gravity on soot formation.The detailed gas-phase chemistry,complex thermal and transport properties coupled with a semiempirical two-equation soot model and a nongray radiation model are used in the calculations.Soot oxidation by O2,OH and O was considered.Thermal radiation was calculated using the discrete ordinate method coupled with a statistical narrow-band correlated-K（SNBCK） model.The spectral absorption coefficient of soot was obtained by Rayleigh＇s theory for small particles.The results show that the peak temperature decreases with the decrease of the gravity level.The peak soot volume fraction in microgravity is about twice of that in normal gravity under the present conditions.The numerical results agree very well with available experimental results.The predicted results also show that gravity affects the location and intensity for soot nucleation and surface growth.