材料厚度对火焰向下传播特性的影响

摘要

在常重力静止空气环境中对厚度连续变化的聚甲基丙烯酸甲酯(PMMA)平板表面火焰向下传播进行实验研究,分析了材料厚度对火焰传播特性的影响.结果表明,材料厚度增加时,火焰长度和材料热解长度单调增加,而当材料厚度减小时,材料热解长度和火焰长度先增加后减小.在这两种情况下,均存在热薄材料和热厚材料的转变厚度,其值与文献中使用均匀厚度材料得到的实验结果及理论预测一致;材料厚度小于该转变厚度时,火焰传播速度与材料厚度呈反比关系,大于该厚度时,火焰传播速度不随材料厚度变化,这分别符合热薄材料和热厚材料火焰传播速度的理论模型.%Experiments were conducted in a quiescent air environment at normal gravity to investigate downwardflame spread over a polymethylmethacrylate (PMMA)sheet whose thickness varies continuously along its length,and the effect of fuel thickness on flame spread was analysed.The experimental results show that,with increasingfuel thickness,both flame length and pyrolysis length increase monotonically,while both parameters increasefirst and then decrease when the fuel thickness decreases.The transition between thermally-thin and thermallythickfuel regime is found in both cases,and the transition thickness agrees well with both previously publishedexperimental result obtained for uniform fuel samples and theory prediction.For the fuel section whose thickness issmaller than the transition thickness,the flame spread rate is inversely proportional to sample thickness,while forthe thicker section the flame spread rate is independent of fuel thickness.The relationships between flame spreadrate and fuel thickness revealed by the present experiments agree well with the theoretical models for thermallythinfuel and thermally-thick fuel,respectively.