少量聚氨酯泡沫样品从阴燃到有焰燃烧的变化研究

试验主要观察处于阴燃状态的少量聚氨酯泡沫样品的流速、氧气浓度和辐射热通量对气／固界面的影响。因为此试验研究对象是少量聚氨酯汽沫，所以阴燃蔓延以厦转化到有焰燃烧时必须借助于降低热损失并同时增加其氧气浓度。试验中，我们把呈平行六面体的样品竖向放置在风道中。样品的其中三个侧边处在高温状态，第四边暴露在上升气流和辐射中。结果发现，随着气流流速的降低以度氧气浓度的增加，或者增加辐射通量，都会加快其变成有焰燃烧的过程，减少这种变化的延误时间。试验结果表明，炭化部位内部的有焰变化因阴燃作用而出现滞后，这已经通过超声波穿透样品内部得到了证实。笔者这里给出了简化了的分析，证明这种变化可以作为一个气相燃烧程序进行处理。

Transition from forward smoldering to flaming in small polyurethane foam samples

Experimental observations are presented of the effect of the flow velocity and oxygen concentration, and of a thermal radiant flux, on the transition from smoldering to flaming in forward smoldering of small samples of polyurethane foam with a gas/solid interface. Because small polyurethane foam samples were studied, the smolder propagation and the transition to flaming had to be assisted by reducing the heat losses to the surroundings and increasing the oxygen concentration. The experiments are conducted with small parallelepiped samples vertically placed in a wind tunnel. Three of the sample lateral-sides are maintained at elevated temperature and the fourth side is exposed to an upward flow and to a radiant flux. It is found that decreasing the flow velocity and increasing its oxygen concentration, and/or increasing the radiant flux enhances the transition to flaming, and reduces the delay time to transition. Limiting external ambient conditions for the transition to flaming are reported for the present experimental set-up. The results indicate that transition to flaming occurs in the char left behind by the smolder reaction, as evidenced by ultrasound probing of the sample interior, and it has the characteristics of a gas-phase ignition induced by the smolder reaction. A simplified scale analysis is presented, which shows that the transition can be treated as a gas-phase ignition process.