Abstract:

In this work, the effects of the electric fields on the flame propagation and combustion characteristics of methane-air mixtures were experimentally investigated in a constant chamber. The loading voltages were 0,-5,-10 and -12 kV, and the excess air ratios (λ) of mixtures were 0.8, 1.0 and 1.6, respectively, representing the three mixed gas states of rich combustion, equivalence ratio and lean combustion. The experiment was performed at room temperature and atmospheric pressure. When the electric field was applied, the flame front in the electric field direction was remarkably stretched, the flame development radius and flame propagation velocity were all accelerated significantly as the loading voltage increased, and the flame shape was changed remarkably. Especial for the lean mixture, the increase of flame development was most obvious. For the mixtures of λ=0.8, 1.0 and 1.6 at -12 kV, the maximum values of flame propagation velocity were increased by 42.3%, 29.7% and 111.7%, respectively. By analyzing combustion pressure variation, it could be seen that the time of peak combustion pressure (t_p) was advanced, and the peak pressure (P_max) of lean mixture increased with the increase of loading voltage. For the mixtures of λ=0.8, 1.0 and 1.6 at -12 kV, t_p were advanced by 13.4%, 7.5% and 24.6%, P_max increased by 2.2%, 1.0% and 8.1%, respectively, compared to that when no voltage was applied. The results could be explained by the ionic wind effects produced by the electric fields and its induced flame stretch on burning methane-air mixtures.

Key words: electric field, methane, mixture, flame propagation velocity, combustion pressure, ionic wind, heat transfer, mass transfer

摘要：

利用定容燃烧弹研究了外加电场对甲烷-空气混合气燃烧特性的作用。加载电压为0、-5、-10和-12 kV，混合气的过量空气系数λ分别为0.8、1.0和1.6，代表浓燃、当量比和稀燃三种混合气状态。结果表明，电场方向上的火焰发展半径和火焰传播速度明显增加，原先近似圆球形的火焰形状发生变化。特别是稀燃混合气，电场作用下火焰的传播状况增加最为显著，火焰近似呈圆柱形。在加载电压为-12 kV时，对于λ=0.8、1.0和1.6的混合气，火焰拉伸速度最大值分别增加了42.3%、29.7%和111.7%。同时，混合气燃烧压力的发展明显加快，压力峰值出现的时间明显提前。对于浓燃和当量比浓度的混合气，压力峰值变化不大，而稀燃混合气的压力峰值增加较为明显。在-12 kV电压作用下，浓燃、当量比和稀燃三种状态下混合气的压力峰值时间提前了13.4%、7.5%和24.6%，相应的燃烧压力峰值增大了2.2%、1.0%和8.1%。本文应用外加电场对燃烧火焰产生的离子风效应及其对传播火焰形成的拉伸作用对试验结果进行了说明。

关键词: 电场, 甲烷, 混合气, 火焰传播速度, 燃烧压力, 离子风, 传热, 传质