超声速气流中乙烯点火试验与影响因素

对超声速气流中的非预混乙烯燃料扩散点火过程进行了试验研究，采用高速摄影、纹影技术获得了点火过程的火焰成功传播与失效图像和激波动态演化过程。基于点火前喷注混合流场的NPLS（纳米粒子散射）、PIV（粒子图像测速）试验数据和大涡模拟结果对影响点火结果的关键因素进行了研究，分析了点火过程的燃料分布、回流区尺寸、激波串作用、气动壅塞效应等关键流动特征对火焰传播过程和点火失效模式之间的影响关系。研究结果表明，点火过程的激波串前移过程会对燃料的分布造成影响，并进而影响凹腔内的燃料质量分数分布；凹腔角回流区是初始火焰形成的关键区域，点火能量在该区域累积建立凹腔角回流区火焰后，分别扩展形成凹腔驻留火焰，并向下游输运、掺混燃烧，建立预燃激波串，形成点火过程的正向压力反馈；凹腔内燃料分布受喷注位置、喷注压力的影响，采用凹腔内主动喷注的方法能够主动调节凹腔内的燃料分布，有助于初始火核的形成，能有效避免点火过程中由于压力反馈对燃料分布影响造成的熄火现象。 

Experiment and factors affecting ethylene ignition in supersonic flow-field

The non-premixed ethylene ignition in supersonic flow-field was experimentally conducted to obtain the events of successful/failed flame propagation and the evolution of shock wave train during ignition transient using high speed photography and schlieren method. The key flow characteristics such as fuel distribution, length of recirculation zone, effect of shock wave train and air throttling affecting flame development and the modes of flame extinguishment were analyzed with the measurement of NPLS (nano-particle-based planar laser scattering) and PIV (particle image velocimetry) technology by combing with large eddy simulation data. The results showed that the shock train was pushed forward during the process of flame initiation leading to the fuel mass fraction difference between the conditions before and after ignition. The recirculation zone trapped in the fore corner of cavity was essential to the creation of initial flame, in which the ignition energy accumulated and the flame expanded and transported downstream until cavity trapped flame and positive feedback was built up. The fuel distribution within cavity was influenced by the position and pressure of fuel injection and can be accommodated by direct injection within cavity, which was beneficial for the initial flame kernel propagation while avoiding extinguishment caused by feedback.