Abstract The concept of an edge flame structure has been adopted to explain the laminar lifted flames in a non-premixed jet. Two similarity solutions of velocity and fuel concentration have been used to explain flame stability. Recently, it was shown that the experimental results from studies of jet velocities and lift-off heights could be converted to a relationship between the edge flame speed and the fuel concentration gradient. However, this was not sufficient to explain actual structures and behaviors of lifted flames. In this study, related theories and their similarity solutions were improved to get more realistic results through an efficient process. Experiments were conducted with various parameters such as jet velocity, fuel type, tube diameter, air-premixing ratio, and fuel dilution. Effective mass diffusivities and effective Schmidt numbers were estimated based on the experimental results. Using these values, the theoretical basis for a new relationship between the edge flame speed and the fuel concentration gradient was obtained. It was conclusively found that non-monotonic variation in the edge flame speed occurs. From this, flame structures were classified into three regimes based on flame structures and heights: ordinary edge flame in a lower-regime, merged edge flame in a middle-regime, and premixed flame in a higher-regime. Flame speeds of the ordinary edge flames in the lower-regime were selected for comparison with the results of previous studies. From this work, the relationship between the similarity solutions and the experimental results can now be understood in greater detail, and the deviations due to the flame structure can be distinguished.

中文翻译：

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非预混射流层流火焰的结构及其与相似解的关系

摘要 采用边缘火焰结构的概念来解释非预混射流中的层流火焰。速度和燃料浓度的两个相似解已被用于解释火焰稳定性。最近，研究表明射流速度和升空高度的实验结果可以转化为边缘火焰速度和燃料浓度梯度之间的关系。然而，这不足以解释升起火焰的实际结构和行为。在这项研究中，相关理论及其相似性解决方案得到了改进，以通过有效的过程获得更现实的结果。使用各种参数进行实验，例如射流速度、燃料类型、管径、空气预混合比和燃料稀释。基于实验结果估计有效质量扩散率和有效施密特数。使用这些值，获得了边缘火焰速度和燃料浓度梯度之间新关系的理论基础。最终发现边缘火焰速度发生非单调变化。由此，基于火焰结构和高度将火焰结构分为三种状态：低级的普通边缘火焰，中间的合并边缘火焰和高级的预混火焰。选择较低区域中普通边缘火焰的火焰速度与先前研究的结果进行比较。从这项工作中，现在可以更详细地了解相似性解与实验结果之间的关系，