Flame-Spread over Thin PMMA under Micro-Gravity Condition

在正常重力和微重力条件下，研究了PMMA薄膜上的火焰传播。通过尺度分析表明，在自然对流条件下，火焰传播是由气相中的热传导驱动的。另一方面，在静止条件下或在存在轻度对流的情况下，辐射损失变得显着，它可以影响火焰传播速率。在第一年中，我们测量了正常重力下PMMA薄膜的向下扩展率，并证实了尺度分析的结果与实验结果一致。在第二年，滴实验进行了不同的对向流速，我们发现，蔓延率有最小值时，相对流速较低。这意味着辐射损失降低了扩散率，这是由尺度分析预测。在第三年，我们测量了火焰附近的温度场。结果很好地支持了由尺度分析预测的现象。当对流速度减小时，预热区的规模增大。在这种情况下，辐射热传递与传导热传递的比率增加。辐射损失随燃料厚度的增加、氧含量的降低和相对于火焰的流速的降低而增加。当热损失超过一定值时，固体预热区稳定的热平衡就会被打破，从而发生熄灭。

Flame spread over thin PMMA films was investigated under normal gravity and micro-gravity conditions. A scale analysis was preformed and the result states that the flame spread is driven by the heat conduction in gas phase when there is free convection. On the other hand, under quiescent condition or in the presence of mildly convective flow, the radiation loss becomes significant and it can affect flame spread rate. In the first year, we measured downward spread rates over thin PMMA films under normal gravity, and confirmed that the result of the scale analysis agrees with the experimental results. In the second year, drop experiments were carried out with varying opposed-flow velocity, and we found that the spread rate had minimal value when the relative flow velocity was small. It implies that radiation loss decreases the spread rate, which was predicted by the scale analysis. In the third year, we measured the temperature field near the flame. The results well supported the phenomena that were predicted by the scale analysis. When the opposed-flow velocity decreases, the scale of the preheat zone increases. In such situation, the ratio of radiative heat transfer to the conductive heat transfer increases. The radiation loss increases with the increase in fuel thickness, with the decrease in oxygen level, and with the decrease in the flow velocity relative to the flame. When the heat loss excesses over a certain value, the steady heat balance in the solid preheat zone breaks, then the extinction occurs.