Study on the combustion mechanism in SCRAMJET

超燃冲压发动机是近年来因“空天飞机”概念而受到关注的一种新型发动机。然而，在其发展之前，有几个重要问题需要解决。本文首先研究了在低密度、低温气氛下，硅烷作为氢氧燃烧点火助剂的点火问题。NASA的一个小组利用机械燃烧机理的相似性，开发了一种硅烷/氧/氢/氮点火机理。对SiH_4/O_2/H_2/N_2混合气体点火延迟的数值模拟与800-1000 K的实验结果吻合较好。但由于硅烷及其相关化合物的热力学数据不真实，模型不能反映1000-1700 K高温下的点火延迟。他们使用了通过近似甲烷数据获得的数据。正确的热力学数据的理论开发使用RRKM理论。从实验结果可以看出，SiH 4/O2/H2/N2混合物的反应机理在1000 K附近发生了变化，硅烷的加入有利于在低于1000 K的温度下增强氢的点火。除了点火问题外，本文还通过数值模拟氦气垂直注入超音速气流来研究混合问题。数值计算结果表明，由于注入的氦气和主气流之间的相互作用和几个循环，其中占主导地位的流场的物理高频振荡。

Scramjet has been recently paid attention concerning with the "space plane" concept. There are, however, several important problems to be solved before its development. They are the mixing, ignition, combustion, and so on. First of all, the ignition problem is studied by looking at silane as an ignition aid of oxyhydrogen combustion unfer the low density and low temperature atmosphere. A group of NASA developed a silane/oxygen/hydrogen/nitrigen ignition mechanism by using a similarity in the mechanism of mechane combustion. Their numerical modeling in the ignition delay of the SiH4/O2/H2/N2 mixture simulated well their experimental results at the temperature of 800-1000 K. However their modeling could not show the ignition delay at the high temperature of 1000-1700 K because the thermodynamic data of silane and its related compounds were not true. They used their data obtained by approximating the methane data. The correct thermodynamic data are developed theoratically using RRKM theory. It can be said from our experimental results that the reaction mechanism of SiH4/O2/H2/N2 mixture is changed at the border of 1000 K and the silane additivity works for enhancing the hydrogen ignition at the lower temperature than 1000 K.Besides the ignition problem, the mixing problem is studied by numerically simulating the helium injection vertically into the supersonic air flow. The numerical results show the high frequency oscillation due to the interaction between the injected helium and the main air flow and several circulations which dominate the physics of the flow field.