Study on Stabilization of Supersonic Combustion Using Ram Accelerator

本研究的主要目的是寻找可燃气体混合物在超声速流动中持焰稳定性的特性，并证明冲压加速器是研究超声速燃烧的有力装置。我们在广岛大学开发的冲压加速器被设计为一种工具，用于对燃烧与激波、边界层等相互作用进行基础研究，因此管具有矩形截面，其中平行的玻璃窗安装在光学观测中。在此基础上，得到了超声速流动中火焰的图像，明确了不同条件下的燃烧流场。研究了不同楔形角、不同侧体形状以及边界层厚度对弹体持焰性能的影响。研究还表明，弹丸的后壁是作为火焰保持器的最重要部分。激波总是在先导火焰前面形成，这意味着火焰只存在于亚音速区域。超声速燃烧的流场非常复杂，因此对超声速燃烧进行数值模拟是必要的。并编制了CH_4-O_2-CO_2混合物全动力学反应的计算机程序，与实验结果相吻合。由于实际需要，采用CH_4-O_2-N_2混合体系进行实验和数值模拟。冲压加速器工作在弹丸的亚爆速，虽然超爆模式也很重要。作为一种新型推进装置，脉冲爆震发动机的爆震特性也是近年来研究的热点。

The main objects of the present research are to find the properties on the stability of the flame holding in supersonic flows of the combustible gas mixtures, as well as to show that the ram accelerator works as a powerful device to study the supersonic combustion. The ram accelerator we have developed in Hiroshima University is designed as a tool to make fundamental studies on the interactions of combustion with the shock waves, the boundary layer, and so on, so that tube has a rectangular cross section where parallel glass windows are mounted for optical observations. Then, we have got pictures of the flames in the supersonic flows, and the burning flow fields are made clear for various conditions. Flame holding properties are investigated for the different wedge angles and shapes of the side bodies of the projectile, or for the effects of boundary layer thickness. It is also shown that the back-step of the projectile is the most important part as a flame holder. A shock wave is always formed in front of the leading flame, which means the flame exists only in the subsonic region. The flow fields are so complicated that the numerical simulations are necessary to study the supersonic combustion. The computer program is also developed including full kinetic reactions of the CH_4-O_2-CO_2 mixtures, comparable to the experimental observations. Because of the practical necessary, CH_4-O_2-N_2 mixture system is to be used in experiments and the numerical simulations. The ram accelerator is working with the sub-detonative speed of the projectile, though super-detonative mode is also important. The properties of the detonations are also recently studied as a new propulsive device as a pulse detonation engine.