微波辅助点火对甲烷预混球形火焰的影响

Experimental Study of CH4-Air Premixed Spherical Expanding Flames with Microwave Assisted Ignition

基于微波等离子体辅助点火可视化试验台架和分离影响因素的研究思路,试验了不同脉冲频率和峰值功率下微波辅助火花塞的放电特性,以及当量比为0.6~1.0、环境压力为0.1~0.7 MPa下的甲烷-空气预混球形火焰的着火及传播特性.干放电试验结果表明:微波脉冲频率为1 kHz时,由于第一个微波脉冲正处于放电电子密度高峰时刻,微波对火花塞放电核心膨胀的加速作用最明显,随着微波脉冲频率的增大,微波强化放电的效果减弱;随微波源的峰值功率增大,微波脉冲对放电的强化作用愈发明显.点火试验结果表明:频率为1 kHz、峰值功率为1 kW微波脉冲的馈入,使当量比为0.6、环境压力为0.1 MPa下的早期火核生长速度提升了60%,随着当量比的增加,微波对火焰发展的增强幅度减小;随着环境压力的增加,微波对点火的增强作用减弱.总之,微波对火焰发展的增强作用主要是对初始火核发展的促进;在火焰后期,燃料燃烧的热能远大于微波能量,导致微波的馈入对后期燃烧过程没有明显影响.

Effect of microwave assisted ignition on lean CH4-air spherical expanding flames was investigated based on a self-developed visual experimental apparatus and the thought of separating factors.The discharge characteristics of microwave-assisted spark plug with different pulse frequencies and peak power settings,as well as the ignition and propagation characteristics of CH4-air premixed spherical flames with equivalence ratios of 0.6-1.0 and ambient pressure of 0.1-0.7 MPa were studied experimentally.The discharge test results show that the microwave pulses exert the greatest enhancing effect on spark discharge when the pulse frequency is 1 kHz,and the first microwave pulse after breakdown is most efficient while the effects of subsequent pulses become inefficient.With the increase of the microwave pulse frequency,the enhancing effect is weakened.As the peak power of the microwave source increases,the enhancing effect of microwave pulse on spark discharge becomes even greater.The ignition tests indicate that microwave increases the development speed of early flame kernel by 60%under the condition of equivalence ratio of 0.6 and ambient pressure of 0.1 MPa.As the ambient pressure increases,the enhancement of flame kernels by microwave diminishes.In general,enhancement of microwave pulses mainly reflects in the early flame development stage.As the flame develops into the late stage,the microwave enhancement becomes unapparent because the microwave energy is negligible relative to the energy released by combustion.