Most previous work concentrated on the one-sided upward flame spread under limited conditions. However, few investigations have studied the effects of limited distance between wall and fuel surface on two-sided upward flame spreading. In this paper, a series of upward flame spread experiments were conducted using 0.65 mm thick, 130 cm tall and 4.0 cm wide flax fabric sheets with various limited distance of 1.0 cm–3.5 cm. The flame shape, flame length, flame standoff distance, pyrolysis spread rate and surface temperature were measured and analyzed. An unexpected but interesting behavior of one-sided flame blow off was observed in upward flame spread. When limited distance is no more than 1.5 cm, the one-sided flame blow off behavior occurs on unlimited side, whereas this behavior occurs on limited side for 2.0 cm–3.5 cm limited distance. This result could be qualitatively explained by Damkohler number Da, which could be characterized by two parameters of induced flow velocity and heat flux received by virgin surface. Moreover, the maximum flame length, steady flame length, maximum spread rate and steady spread rate first increase and then decrease as the limited distance. This non-monotonicity trend is determined by heat flux profiles in the preheating zone, which is due to the combined limited distance effects of restricting oxygen supply, chimney effect and wall radiation. The surface temperature profile ahead of pyrolysis front is used to qualitatively describe the heat flux received by virgin surface. The results in this paper are essential for better understanding of self induced flame blow off mechanism and upward flame spread under limited distance conditions.

中文翻译：

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有限距离对薄织物燃料上火焰向上蔓延的自感吹散和传热影响的实验分析

以前的大部分工作都集中在有限条件下的单侧向上火焰蔓延。然而，很少有研究研究壁与燃料表面之间的有限距离对两侧向上火焰蔓延的影响。在本文中，使用 0.65 毫米厚、130 厘米高和 4.0 厘米宽的亚麻织物片进行了一系列向上火焰蔓延实验，这些亚麻织物片具有 1.0 厘米-3.5 厘米的各种有限距离。对火焰形状、火焰长度、火焰间隔距离、热解扩散速率和表面温度进行了测量和分析。在向上的火焰蔓延中观察到了一种出乎意料但有趣的单侧火焰吹灭行为。当有限距离不超过1.5 cm时，无限侧发生单侧火焰吹灭行为，而2.0 cm-3.5 cm有限距离发生在有限侧。这个结果可以用 Damkohler 数 Da 定性解释，它可以用诱导流速和原始表面接收的热通量两个参数来表征。此外，最大火焰长度、稳定火焰长度、最大蔓延速度和稳定蔓延速度随着有限距离先增加后减小。这种非单调性趋势是由预热区的热通量分布决定的，这是由于限制氧气供应、烟囱效应和壁面辐射的综合有限距离效应。热解前沿之前的表面温度分布用于定性描述原始表面接收的热通量。本文的结果对于更好地理解有限距离条件下自诱导火焰吹灭机制和向上火焰蔓延至关重要。