The downward flame spread over laboratory electric wire under various oxygen concentrations has been investigated experimentally to improve our knowledge of electric-wire combustion. Two kinds of electrical wire (low-density-polyethylene (LDPE)-insulated copper (Cu) and nickel-chrome (NiCr)) are used in this study. The oxygen concentration of the mixture stream (O₂ and N₂) in the test section is varied between 15 and 41 vol%. Opposed-flow velocity in the test section is fixed at 15 cm/s. For NiCr wire, the flame spread rate (V_f) and flame length (L_f) monotonically increase with oxygen concentration. For Cu wire, both V_f and L_f show non-monotonic behavior against oxygen concentration. Most interestingly, V_f decreases with oxygen concentration increase in the 25–31% range. Theoretical analysis shows two regimes of variation of V_f with oxygen concentration: the “temperature-dependent regime (TDR)” and the “negative-oxygen-dependent regime (NOR)”. The non-monotonic behavior of V_f against oxygen concentration for Cu can be explained by the controlling mechanism behind TDR and NOR. However, experimental results show one more regime above 31% oxygen concentration that cannot be explained by the theory proposed in this work, namely the “soot-generation-dependent regime (SGR)”; here, radiation from the flame and soot deposit plays a dominant role in flame spread.

实验研究了在各种氧气浓度下分布在实验室电线上的向下火焰，以提高我们对电线燃烧的了解。本研究使用两种电线（低密度聚乙烯（LDPE）绝缘的铜（Cu）和镍铬（NiCr））。在测试部分中，混合物物流（O ₂和N ₂）的氧气浓度在15和41vol％之间变化。测试部分的相对流速固定为15 cm / s。对于镍铬丝，火焰扩散率（V _f）和火焰长度（L _f）随着氧浓度的增加而单调增加。对于铜线，V _f和L _f表现出针对氧气浓度的非单调行为。最有趣的是，V _f随着氧气浓度在25-31％范围内的增加而降低。理论分析表明，V _f随着氧浓度的变化有两种变化方式：“温度依赖方式（TDR）”和“负氧依赖方式（NOR）”。V _f的非单调行为TDR和NOR背后的控制机制可以解释铜对氧浓度的不利影响。然而，实验结果表明，在氧浓度高于31％时，还有另外一种机制无法用这项工作中提出的理论来解释，即“烟灰生成依赖性机制（SGR）”。在这里，火焰和烟灰沉积物的辐射在火焰蔓延中起主要作用。