中文摘要：

利用高速纹影摄像等技术探讨了密闭管道内不同当量比的甲烷／空气预混气体火焰的传播特征。结果表明，当甲烷含量接近当量值时，预混气体火焰传播中会发生火焰阵面由向未燃区弯曲到向已燃区弯曲的转折过程，逐渐由层流燃烧转变成湍流燃烧，并形成Tulip火焰结构；当甲烷含量偏离当量值一定程度时．预混火焰呈现出典型的层流燃烧特征。不会发生火焰阵面由向未燃区弯曲到向已燃区弯曲的转折过程。Tulip火焰结构形成于火焰传播速度迅速降低的区间里，且只有当减速阶段的最大加速度的绝对值大于某一数值时才能形成；Tulip火焰结构是预混火焰由层流燃烧向湍流燃烧转变的一个中间过程。

英文摘要：

The techniques of the high-speed schlieren photography, etc. were used to investigate the characteristics of the premixed methane-air flames with different equivalence ratios propagating through a closed tube. Based on the experimental results, the combustion behaviors and characteristics of the premixed flames were analyzed. Analyzed results show as follows： （1） the transformation process of the flame front bending to the unburned zone turning into bending to the burned zone during the flame propagation happens while the equivalence ratio volume approaches to 1, thus the typical tulip flame structure forms during the transformation; （2） the transformation process of the flame front does not happen while the equivalence ratio volume deviates from 1 to a certain extent, and the premixed flame shows the typical laminar combustion. （3） the tulip-flame structure forms in the period of the flame propagation velocity decreasing greatly and it can form only while the maximum deceleration is larger than a certain quantity; （4） the tulip-flame structure is a middle stage during the transformation of the premixed flame from the laminar combustion to the turbulent combustion.