镁粉与二氧化碳动态点火燃烧特性数值研究

Numerical Study on Dynamic Ignition and Combustion Characteristics of Magnesium Powder and Carbon Dioxide

关键词:  Mg/CO₂  点火燃烧  颗粒粒径  雷诺数  氧燃比

Key words:  Mg/CO₂  Ignition and combustion  Particle size  Reynolds number  Oxygen-fuel ratio

摘要:

Mg粉/CO₂粉末发动机是火星探测中较为理想的原位资源利用方案，为了掌握Mg/CO₂粉末发动机稳定点火燃烧特性，在考虑氧化层厚度对Mg颗粒熄火影响的基础上，基于涡耗散/有限速率模型建立了点火燃烧模型，并应用数值计算方法研究了Mg粉颗粒粒径（5μm， 10μm， 15μm， 20μm和25μm）、入口预混气流雷诺数（1500， 2000， 2500， 3000和3500）和CO₂/Mg氧燃比（0.5， 1， 1.5， 2和2.5）对Mg粉/CO₂动态点火燃烧的影响。计算结果表明：雷诺数和氧燃比恒定时，随着粒径从5μm增加到10μm，平均温度升高，平均点火时间延长，燃烧效率增加；随着粒径从10μm增加到25μm，平均温度降低，平均点火时间延长，燃烧效率减少。粒径和氧燃比恒定时，平均温度随雷诺数增加而下降；平均点火时间和燃烧效率随雷诺数增加基本不变。粒径和雷诺数恒定，随着氧燃比从0.5增大到1.5，平均温度升高；随着氧燃比从1.5增大到2.5，平均温度下降；平均点火时间和燃烧效率随氧燃比增大基本不变。

Abstract:

Mg powder/CO₂ powder engine is an ideal in-situ resource utilization scheme in Mars exploration. In order to master the stable ignition and combustion characteristics of Mg/CO₂ powder engine， considering the flameout of Mg particles affected by the thickness of the oxide layer， the ignition and combustion model was established based on eddy dissipation / finite rate model. The effects of Mg particle size， Reynolds number of premixed flow and CO₂/Mg oxygen-fuel ratio on dynamic ignition and combustion of Mg powder/CO₂ were calculated by using the ignition combustion model， and the particle size of Mg powder was 5μm， 10μm， 15μm， 20μm and 25μm， the Reynolds number of inlet premixed gas was 1500， 2000， 2500， 3000 and 3500， and the CO₂/Mg oxygen-fuel ratio was 0.5， 1， 1.5， 2 and 2.5. The numerical results show that at constant Reynolds number and oxygen-fuel ratio， with the increase of particle size from 5μm to 10μm， the average temperature increases， the average ignition time prolongs and the combustion efficiency increases. With the increase of particle size from 10μm to 25μm， the average temperature decreases， the average ignition time prolongs and the combustion efficiency decreases. At constant particle size and oxygen-fuel ratio， the average temperature decreases with the increase of Reynolds number， while the average ignition time and combustion efficiency remain unchanged with the increase of Reynolds number. At constant particle size and Reynolds number， with the increase of oxygen-fuel ratio from 0.5 to 1.5， the average temperature increases. With the increase of oxygen-fuel ratio from 1.5 to 2.5， the average temperature decreases. The average ignition time and combustion efficiency basically remain unchanged with the increase of oxygen-fuel ratio.