镁颗粒群非稳态着火过程数值模拟

摘要

建立了镁颗粒群着火的一维非稳态有限影响体模型，数值模拟颗粒群中镁颗粒的着火过程．研究表明，当镁颗粒表面反应加剧之后，颗粒相温度急剧上升，迅速达到着火，而其周围气相的温升速率却远小于颗粒的温升速率；在着火过程中气相温度只在颗粒表面附近升高比较明显，整体温度升高不大．分析了颗粒群内部参数和环境参数对镁颗粒群着火的影响．随颗粒浓度的增加，颗粒群变得易于着火，其着火时间变短，但颗粒浓度增大到一定程度后，继续增大该值将对颗粒群的着火起消极作用．环境压力对颗粒群着火的影响比较小，在1—5atm范围内颗粒群的着火性能基本不变．气相中氧气浓度对颗粒群的着火性能影响也不显著，但当氧气浓度过小时，对着火过程的影响将大大增强．颗粒粒径、气相／颗粒相初温、辐射源温度对颗粒群着火的影响巨大，小粒径、高温度促使颗粒群快速着火．数值模拟与文献中试验结果的变化趋势相一致．%A one-dimensional unsteady magnesium particle cloud ignition model with finite influencing sphere is established. The behavior of ignition of magnesium particle cloud is numerically simulated. The result shows that when the reaction is speeded up on the surface of magnesium particle, the temperature of the particle phase rises rapidly up to ignition temperature, while the surrounding air is much slower in temperature rising than particles; the gas temperature rising is unconspicuous in the whole sphere in the ignition process, albeit it is significant near the particle surface. The effects of the interior parameters and the environmental parameters on the ignition of the magnesium particle cloud are analyzed. With the increase of particle concentration, the particle cloud becomes easier to be ignited, and reduction in its ignition time delay can be seen. However, when the particle concentration has increased to some specific extent and its further increase will be adverse to the ignition of the particle cloud. The influence of the environmental pressure on the ignition of particle cloud is insignificant, and the ignition performance of the particle cloud almost keeps constant in a range of 1-5 arm. The oxygen concentration in the gas phase also has a weak effect on the ignition performance of particle cloud, but when the oxygen concentration is very low, the effect will significantly increase. The particle size, the initial temperature of the gas/particle and the radiant source have all great influences on the ignition performance of the particle cloud. Small particle and high temperature are helpful for speeding up the ignition process. The tendency obtained by numerical simulation coincides well with that of the experimental results from the literature.