纤维质燃料正向阴燃传播的数值分析

Numerical Simulation Analysis of Forward Smoldering Propagation of Cellulosic Materials

根据多孔固体燃料3步反应动力学机理,建立了2D非稳态纤维质材料水平填充床正向阴燃的数学模型。阴燃的化学动力过程包括燃料吸热热解、燃料放热氧化及焦炭的放热氧化3个过程。该模型既考虑了固-气之间的热交换,也考虑到了气体在多孔介质内的扩散系数的变化。辐射换热采用扩散近似的方式在模型中予以考虑。应用该模型,数值模拟了来流速度对阴燃速度及平均最高温度的影响,结果表明:阴燃传播速度与来流速度基本上呈线性关系,来流速度对阴燃最高温度影响不大。同时也模拟了燃料阴燃温度分布、燃烧过程中气体组分(O2,CO,CO2,H2O)及固体成分(燃料、焦炭和灰分)的变化过程。数值计算阴燃速度与实验速度基本吻合。

Based on a three-step kinetic mechanism, a two-dimensional and time-dependent numerical model is presented for the forward smoldering propagation in a horizontally packed bed of cellulosic material. The kinetic processes include pyrolysis and oxidation degradation of fuel and oxidation of coke. In this model, heat transfer between solid and gas is taken into account as well as the diffusion coefficient varies with the temperature. Radiative transfer is also included by using the diffusion approximation. The effects of airflow velocity are numerically simulated on smoldering velocity and average maximum temperature of fuel. The results indicate that the smoldering velocity linearly varies with increase of airflow velocity, and there is only a bit of effect on the maximum temperature. Simultaneously, the profiles of solid temperature are examined. The evolutions of gas components （including O2, CO, CO2 and H2O） and solid components （ including fuel, coke and ash） are presented along the packed bed. The computational smoldering velocities basically agree with the experimental measurements.