Transition of Combustion Mode in Scramjet

超燃冲压发动机通过将燃烧从亚音速模式切换到超音速模式，在较宽的马赫数范围内保持高性能。这种模式转变是混合、燃烧和拟激波相互作用的复杂过程，其具体机理尚不清楚。本研究旨在通过分离相互作用中的每一种现象并独立控制每一种现象来研究其对其他现象的影响来阐明过渡机制。作为研究的第一步，在吸气式风洞产生的超音速流动中注入氦。拟冲击波的产生由安装在试验段出口的背压阀控制。准激波强烈地促进了氦的混合。准激波上游越远，增强作用越强，从试段底壁注入的氦气射流通常由伪单脉冲…沿横向扩散。第二步，去掉背压阀，装上等离子体炬作为注射器。火炬的原料是氮气或氢/氮混合物。准冲击波是通过增加火炬的输入功率和/或原料中氢的分数来产生的。研究发现，当出口段满足广义堵塞条件时，就会产生拟激波，当拟激波的锋面从喷口向上游约4倍于管道高度时，沿流向壁面压力分布在靠近喷口附近有一峰值，沿下游方向逐渐减小。只有在喷口上游才能看到准激波中的激波序列，燃料被注入到等离子体炬的上游。这些结果表明，燃烧模式从超音速转变为亚音速。在出口段测得的放热量小于准一维理论中热堵塞所需的数值。燃烧方式的改变增加了喷射剂的穿透能力，但氢的分布和燃烧效率没有明显变化。较少

Scramjet engines keep high performance in a wide Mach number range by shifling the combustion from the subsonic mode to the supersonic mode. This mode transition is a complicated interaction among mixing, combustion and pseudo-shock wave, and its detailed mechanism has not been clarified. This research project intends to clarify the transition mechanism by separating each phenomenon in the interaction and by controlling each phenomenon independently to investigate its influence to others.As the first step of the research, helium was injected into a supersonic flow produced by a suction-type wind tunnel. The pseudo-shock wave was produced and controlled by a back-pressure valve installed at the exit of the test section. The pseudo-shock wave strongly enhanced mixing of helium. The more upstream the pseudo-shock wave went, the stronger the enhancement effect became, The helium jet injected from the bottom wall of the test section usually spread in the lateral direction by the pseudo-shoc … More k wave, but the helium was diffused in the transverse direction depending on the location of the front of the pseudo-shock wave.In the second step, the back-pressure valve was removed and a plasma torch was attached as an injector. The feedstock of the torch was nitrogen or hydrogen/nitrogen mixture. The pseudo-shock wave was produced by increasing the input power to the torch and/or the fraction of hydrogen in the feedstock. It was found that the pseudo-shock wave was established when the generalized choking condition was satisfied at the exit section.When the front of the pseudo-shock wave went upstream about four times of the duct height from the injection port, the streamwise wall pressure distribution had a peak near the injection prot and decreased in the downstream direction. The shock train in the pseudo-shock wave was seen only upstream of the injection port fuel was injected upstream the plasma torch. These result indicated that the combustion mode shifted from supersonic to subsonic. The amount of heat release measured at the exit section was less than the value required for the thermal choking in the quasi-one-dimensional theory. The transition of the combustion mode resulted increase of the penetration of the injectant, but no significant change was observed in the hydrogen distribution and the combustiorn efficiency. Less