镁颗粒群着火和燃烧过程数值模拟

建立了一维非稳态球形镁颗粒群的着火燃烧模型, 数值模拟镁颗粒群的着火和燃烧过程, 研究表明, 颗粒群着火首先发生在颗粒群边界, 随后初始的燃烧火焰会分离为两个, 一个向颗粒群内部传播, 一个向外部传播, 最终内部火焰消失, 外部火焰维持并控制着整个颗粒群的燃烧; 内火焰向颗粒群内部传播过程中, 传播速度会逐渐加快, 且火焰温度值呈逐渐降低趋势. 分析了颗粒群内部参数和环境参数对镁颗粒群着火燃烧的影响. 随颗粒浓度的增大, 颗粒群着火时间略有增长, 但火焰传播速度更快, 燃烧稳定时火焰球尺寸也更大. 颗粒群初温越高, 则颗粒群着火时间越短, 火焰传播速度也会加快, 但燃烧稳定时火焰球尺寸基本不变. 环境温度对颗粒群着火燃烧的影响较复杂, 环境温度越高, 颗粒群着火时间越短, 但火焰传播速度却越慢, 燃烧稳定时火焰球尺寸变化很小. 颗粒粒径和辐射源温度对颗粒群着火燃烧的影响较显著, 颗粒粒径越小或辐射源温度越高, 则颗粒群着火时间越短, 火焰传播速度越快, 燃烧稳定时火焰球尺寸也越大. 数值模拟结果与文献中试验结果相一致. 关键词： 粉末燃料冲压发动机 镁着火燃烧 颗粒群

Numerical studies of ignition and combustion of pulverized magnesium particle cloud

A one-dimensional unsteady ignition and combustion model is established for the pulverized magnesium particles in a spherical cloud. The behavior of ignition and combustion of magnesium particle cloud is numerically simulated. The result shows that the ignition of particle cloud occurs at the boundary of particle cloud first, then the initial of which bifurcates into two flames, one of which propagates into the particle cloud, and the other moves away from it. Finally, the inner flame disappears because of O₂ depletion, and only the outer flame, which maintains and controls the combustion of magnesium particle cloud, exists at the outside of it. The flame propagation velocity accelerates, while the flame temperature decreases during the process of the inner flame going into the magnesium particle cloud. The effects of the interior and the environmental parameters on the ignition and combustion of the magnesium particle cloud were analyzed. With the increase in the particle concentration, the ignition delay time increases slightly, but the propagation velocity of the inner flame becomes faster, and the steady particle cloud flame sphere is enlarging. With increasing initial temperature of the particle cloud, the ignition delay time canbe reduced significantly, the propagation of inner flame speeds up, but the size of steady particle cloud flame sphere keeps almost constant. The effect of ambient temperature on ignition and combustion of particle cloud is complicated. The higher the ambient temperature, the shorter the ignition delay time, however, the propagation velocity of inner flame becomes slower, and the size of the steady particle cloud flame sphere changes very insignificantly. Both the size of particle and the temperature of radiation source have great influences on the ignition and combustion of particle cloud. The smaller the particle size or the higher the temperature of radiation source, the shorter the ignition delay time of particle cloud, the faster the propagation velocity of inner flame, and the bigger the size of steady flame sphere. The results of numerical simulation are in good agreement with experimental data published in the literature.