The pipeline length exerts great influence on flame propagation characteristics, Realizable $k-\epsilon$ model and Premixed combustion model were used to study the influence of pipe length on propane-air explosion flame in open-ended and close-ended pipes. Using the numerical model verified by experiments, the changes of flame structure and flame propagation speed are studied. The result showed that the Realizable model was in good agreement with the experimental results. It also proved that the reflected wave produced a strong interference on the flame front, which promoted the formation of tulip flame. Besides, some obvious vortices were usually generated in the burned gas after the tulip flame formed, which will affect the flow field around the flame front and thus exert influence on the flame structure. The formation mechanism of tulip flame as well as the flame self-acceleration is different in open-ended and close-ended pipes. In close-ended pipes, the reflection wave at the pipe end and the reflection-induced countercurrent both promote the formation of tulip flame. As the flame propagates to the pipe end, the flame propagation is inhibited by the compression wave formed by the rapid expansion of combustion products under high temperature. While, in open-ended pipes, the turbulence induced by the opening at the pipe end is the main cause of tulip flame formation. The flame acceleration depends on the combustion reaction of unburned gas, so the velocity of flame propagation continues to increase. Generally, the maximum flame propagation velocity in the open-ended pipe is larger than that in the close-ended pipe.

管道长度对火焰传播特性影响较大，可实现$k-\epsilon$采用预混燃烧模型和预混燃烧模型研究了开口管和闭口管中管道长度对丙烷-空气爆炸火焰的影响。利用经过实验验证的数值模型，研究了火焰结构和火焰传播速度的变化。结果表明Realized模型与实验结果吻合较好。也证明反射波对火焰锋产生了强烈的干扰，促进了郁金香火焰的形成。此外，郁金香火焰形成后，燃烧气体中往往会产生一些明显的涡流，这些涡流会影响火焰前锋周围的流场，从而对火焰结构产生影响。郁金香火焰的形成机制以及火焰自加速在开口管和闭口管中是不同的。在闭端管道中，管端的反射波和反射引起的逆流都促进郁金香火焰的形成。当火焰传播到管端时，火焰传播受到高温下燃烧产物快速膨胀形成的压缩波的抑制。而在开口管道中，管端开口引起的湍流是郁金香火焰形成的主要原因。火焰加速取决于未燃烧气体的燃烧反应，因此火焰传播的速度不断增加。一般来说，开口管中的最大火焰传播速度大于封闭端管中的最大火焰传播速度。