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.