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为了研究火箭/冲压喷气的二次燃烧机理,试制了将二次燃烧的局部燃烧现象模型化的燃烧实验装置,进行了甲烷-空气的基础实验。本实验中的燃烧现象是在具有浓度梯度的可燃混合气体中的火焰传播。浓度梯度最初是由静止状态的甲烷气体与空气的扩散现象形成。火焰传播现象是通过高速旋转切口板把火焰波形随时间的变化拍摄在静止照片上进行观察。本实验研究证明,由于扩散时间比较短的气体之间的扩散,对任何气体组成都容易形成具有浓度梯度的可燃混合气体,同时还明确了以下问题:火焰在与浓度梯度垂直的方向传播时,燃烧速度与预混火焰的燃烧速度相比明显下降,而且随着燃烧距离的增加而减速。另外,具有浓度梯度的可燃混合气体在气体中有熄火情况,点火能量、当量比及浓度梯度可以作为熄火条件的参数考虑。
In order to study the secondary combustion mechanism of rocket / ramjet, a combustion experiment device modeling the local combustion of secondary combustion was developed and a methane-air basic experiment was carried out. The phenomenon of combustion in this experiment is the flame propagation in a combustible gas mixture with a concentration gradient. The concentration gradient is initially formed by the diffusion of quiescent methane gas and air. The phenomenon of flame propagation was observed by photographing still photos with changes in flame waveforms over time by rotating the incision plate at a high speed. The experimental study proves that due to the diffusion between gas with a relatively short diffusion time, it is easy to form a combustible gas mixture with a concentration gradient for any gas composition. Meanwhile, the following problems are also clarified: when the flame propagates perpendicularly to the concentration gradient, The combustion rate is significantly lower than the combustion speed of the premixed flame and decelerates as the combustion distance increases. In addition, flammable gas mixtures with concentration gradient have flameout in gas, ignition energy, equivalence ratio and concentration gradient can be considered as parameters of flameout conditions.