The present study investigates experimentally flame lengths in the two directions underneath a horizontal ceiling (x-direction: parallel to the longer side of the burner; y-direction: perpendicular to the longer side of the burner) produced by line-source fire. It is noted that the previous classical equations are limited for axi-symmetrical sources where only one-dimensional radial flame length is considered. They are non-applicable for the two-dimensional impinged ceiling flow induced by non-axi-symmetrical line-source in despite that it is also a basic source condition in fire science essentially and practically. Experiments are conducted employing a line-source gas burner using propane as fuel. The flame lengths due to impingement upon the ceiling in the two directions are measured, and their difference are quantified, at various heat release rates and ceiling heights. Experimental results show that the flame length in x-direction is shorter than that in y-direction. Their difference decreases with increasing of ceiling height, meanwhile increases with increasing of heat release rate. A new global formula is derived to describe the flame lengths underneath the ceiling based on the analysis of un-symmetrically distributed un-burnt fuel mass flows after impingement in the two directions reflected by their characteristic lengths, which are proposed to be the fire plume impinging zone characteristic dimensions in the two directions determined by the initial source dimensions, ceiling height and air entrainment. The proposed new function well represents the flame lengths globally in both directions. It provides for the first time a general model for describing the flame lengths underneath a ceiling of line-source fire plume impingement.

本研究实验性地研究了水平天花板下方两个方向上的火焰长度（x方向：平行于燃烧器的较长边；y-方向：垂直于燃烧器的长边）由线源火产生。注意，先前的经典方程式仅在考虑一维径向火焰长度的轴对称源中受到限制。尽管它们在本质上和实践上也是消防科学中的基本信源条件，但它们不适用于由非轴对称线源引起的二维冲击顶流。使用使用丙烷作为燃料的线源气体燃烧器进行实验。在两个不同的放热速率和天花板高度下，测量了在两个方向上撞击天花板引起的火焰长度，并量化了它们的差异。实验结果表明，x方向的火焰长度比y方向的火焰长度短。-方向。它们的差异随着天花板高度的增加而减小，同时随着放热率的增加而增大。在分析了两个方向上的不对称分布未燃烧燃料流后，得出了一个新的全局公式来描述顶棚下的火焰长度。在两个方向上的区域特征尺寸由初始源尺寸，天花板高度和空气夹带确定。拟议的新功能很好地代表了双向火焰的整体长度。它首次提供了一个通用模型，用于描述线源火羽撞击天花板下的火焰长度。