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Flame behavior during propagation in small isothermal tubes characterized by different degrees of the end opening

机译：在小型等温管中传播过程中的火焰行为，其特征在于端部开口的程度不同

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摘要

In the present work, we study numerically freely propagating flame in the stoichiometric propane-air mixture. The isothermal small tubes with one end fully open and the second one characterized by different degrees of opening are examined. The degree of opening of the tubes was equal to: 0% (completely closed), 25%, 50%, 75% and 100% (fully opened) of the tube cross-sectional area. Several mechanisms, such as thermal expansion of the burned gas which can leave the tube freely (fully opened left end of the tube), frictional forces and heat losses at the tube walls, movement of the unburned mixture generated by the propagating flame, occur simultaneously during flame propagation. Only the partial opening of the right end of the tube limits the flow of the unburned gas outside this end. This results in an additional pressure gradient and a rapid increase in velocity near the right end. The heat losses to walls cause that behind the flame pressure drops up to negative values. During propagation flames change their shapes and elongates. As a result of these mechanisms, we observe that flame speed change is almost linear for greater parts of tubes. This increase depends on the right end opening and tube diameter. Our examinations show that flame speed loses its linear relationship only for the bigger tube and right end opening in the range 75-100%. It suggests that heat losses to the wall restraint a sudden flame acceleration.
机译：在目前的工作中，我们研究了化学计量的丙烷-空气混合物中火焰在数值上的自由传播。研究了等温小管，其一端完全打开，而另一根则具有不同的打开程度。管的开度等于：管横截面积的0％（完全关闭），25％，50％，75％和100％（完全打开）。同时发生几种机制，例如燃烧气体的热膨胀会自由地离开管子（管子的完全打开的左端），管壁的摩擦力和热量损失，由传播的火焰产生的未燃烧混合物的运动同时发生。在火焰传播过程中。仅管右端的部分开口限制了未燃烧气体在该端外的流动。这会导致附加的压力梯度，并且在右端附近速度会迅速增加。壁面的热损失导致火焰压力下降至负值。在传播过程中，火焰改变形状并伸长。这些机制的结果是，我们观察到较大的管件火焰速度变化几乎是线性的。这种增加取决于右端开口和管子直径。我们的检查表明，火焰速度仅在较大的管和右端开度在75-100％的范围内失去线性关系。这表明壁的热损失抑制了突然的火焰加速。

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