乙烯/空气在激波管中自点火流场显示研究

为认识不同压力（p₅）和温度（T₅）的乙烯/空气自点火和火焰传播特征，在矩形激波管中，采用火焰自发光信号触发高速ICCD相机拍摄了反射激波后流场，得到了不同工况下乙烯/空气自点火流场序列图像。结果表明:对p₅=106kPa，当T₅=1210K，点火首先发生在激波管反射端面附近，向上游（右侧）传播并形成近似平面火焰。火焰面随时间推进趋于垂直激波管轴线，火焰在传播过程中厚度近似保持不变，且内部存在漩涡结构。当降低T₅，自点火位置逐渐远离反射端面，初始火焰厚度增大且光强变弱，由单个平面火焰演变为多个离散的不规则火焰。当T₅=1077K，初始火焰首先出现在观察窗右侧（远离反射端面）并向上下游传播。当增大p₅，火焰光强增大且漩涡尺寸减小，不同p₅对应的火焰产生和传播规律类似。当p₅=265和419kPa，火焰内部产生局部爆炸现象，多个局部爆炸区在传播过程中不断融合，最终形成向上游传播的近似平面火焰。

Flow field visualization for ethylene/air auto-ignition at different pressures and temperatures in a rectangular shock tube

Flow field visualization for the auto-ignition of the ethylene/air mixture is key important in understanding properties and characteristics of the flame generation and propagation. High-speed photography was used in experiments and ICCD camera was triggered by the flame signal located at the test section. The series of images for the auto-ignition flow field were obtained at different temperatures (T₅) and pressures (p₅) in a rectangular shock tube. In the case of p₅ being 106kPa, auto-ignition occurs and the initial flame is close to the tube end of shock reflection when T₅ is 1210K. Then, the flame propagates upstream (right side) and evolves as a planar one. The vortex-lets are obviously embedded in the flame surface. The flame front gradually evolves to be vertical to the tube axis as it propagates upstream. In contrast to decreasing T₅, the initial flame becomes thicker and moves away from the tube end of shock reflection. More-over, the flame emission becomes weaker corresponding to the lower reaction rate. Also, the flame decays from a planar front into several irregular zones. When T₅ is 1077K, the auto-ignition occurs far away from the tube end of shock reflection, and then propagates upstream and downstream. With increasing p₅, the flames emit strongly and the vortex-lets almost disappear on flame surfaces. When p₅ are 265 and 419kPa, respectively, the local explosions take place frequently. These local explosions merge into an approximately planar front and propagate upstream with time going by.