The released hydrogen can be ignited even with weak ignition sources. This emphasizes the importance of the hydrogen flammability evaluation to prevent catastrophic failure in hydrogen related facilities including a nuclear power plant. Historically numerous attempts have been made to determine the flammability limit of hydrogen mixtures including several diluents. However, no analytical model has been developed to accurately predict the limit concentration for mixtures containing radiating gases. In this study, the effect of H₂O and CO₂ on flammability limit was investigated through a numerical simulation of lean limit hydrogen flames. The previous flammability limit model was improved based on the mechanistic investigation, with which the amount of indirect radiation heat loss could be estimated by the optically thin approximation. As a result, the sharp increase in limit concentration by H₂O could be explained by high thermal diffusivity and radiation rate. Despite the high radiation rate, however, CO₂ with the lower thermal diffusivity than the threshold cannot produce a noticeable increase in heat loss and ultimately limit concentration. We concluded that the proposed mechanistic analysis successfully explained the experimental results even including radiating gases. The accuracy of the improved model was verified through several flammability experiments for H₂-air-diluent.

即使使用微弱的点火源，也可以点燃释放的氢气。这强调了氢可燃性评估对于防止包括核电站在内的氢相关设施发生灾难性故障的重要性。历史上曾多次尝试确定包括几种稀释剂在内的氢气混合物的可燃性极限。然而，尚未开发出分析模型来准确预测包含辐射气体的混合物的极限浓度。在本研究中，H ₂ O 和 CO ₂通过贫极限氢火焰的数值模拟研究了可燃性极限。之前的可燃极限模型是在力学研究的基础上改进的，可以通过光学薄近似估计间接辐射热损失的量。因此，H ₂ O 引起的极限浓度急剧增加可以用高热扩散率和辐射率来解释。尽管辐射率很高，但是 CO ₂热扩散率低于阈值时，不会显着增加热损失并最终限制浓度。我们得出结论，所提出的机械分析成功地解释了实验结果，甚至包括辐射气体。改进模型的准确性通过 H ₂空气稀释剂的几个可燃性实验得到验证。