微波对超声速燃烧火焰结构的影响

超声速中等离子辅助燃烧是一种具有潜力的助燃方式。通过将低功率微波馈入超燃冲压发动机燃烧室的方式，研究了微波对火焰结构的影响。实验来流马赫数为2.5，常温乙烯燃料从壁面横向射流，以单级凹腔作为火焰稳定器，分别加入500 W和700 W连续2.45 GHz的微波，利用高速相机拍摄火焰CH^*发光图像。研究表明微波的加入使超声速火焰稳定结构发生改变，火焰的起始和稳定位置从凹腔剪切层向射流出口转移，表明微波对火焰传播速度或者燃烧反应速率有增强作用。同时利用火焰边界提取和分形几何的方法，发现微波能够增大火焰边界分形维度，分析认为火焰传播速度由于微波的加入而增加，证明小功率的微波对超声速燃烧有促进作用。

Influence of microwave on structure of supersonic combustion flame

Plasma assisted combustion in supersonic flow is a promising method. The effect of microwave on the flame structure is studied by feeding low-power microwave into the combustor of the scramjet. The combustor inlet flow Mach number is 2.5. Room temperature ethylene is injected perpendicular to the combustor wall. Single stage cavity is used as flame stabilizer, and 500 W and 700 W continuous 2.45 GHz microwave are added into the combustor. A high-speed camera is used to capture flame CH^* illuminating images. After the addition of microwave, the stable position of the flame changes from cavity shear layer flame to jet flame, which indicates that the microwave has an effect on the flame propagation speed or the combustion reaction rate. Using the method of flame boundary extraction and fractal geometry, this paper finds that microwave can increase the fractal dimension of flame boundary, indicating that the propagation rate of flame increases due to the addition of microwave. The paper concludes that a low power of microwave can assist supersonic combustion.