Abstract A series of experiments were carried out to investigate the effect of ullage height, i.e. the distance between fuel surface and the pool upper rim, on flame characteristics of heptane and ethanol pool fires. The pool diameters included 10 cm, 15 cm, and 20 cm. For each pool, ullage height was increased from zero to the value that the flame self-extinguished. During each test, the ullage height was kept constant by a fuel level maintaining device. Results show that ullage height has a significant effect on flame characteristics. When the ullage height equals zero, there is a stable conical structure near the pool upper rim, above which the unstable plume develops. Under lower ullage height conditions, plume puffing happens. The unstable plume begins to initiate around the pool upper rim, then rolling and expanding upward. At the same time, its beneath flame is stretched thinner and thinner and eventually breaks from the bulk. When the ullage height further increases, plume puffing becomes less evident. While for the mass loss rate, it generally decreases with the increase of h/D. It was proved in literature that the previous flame height model is inapplicable to pool fires with large ullage height. In this paper, to consider the effect of ullage height on plume flow structures, an equivalent hydraulic diameter, Deq., is proposed to establish one new flame height correlation. By comparing previous model predictions with the current experimental data, it is found that conventional flame oscillation models are unsuitable to pool fires with large ullage height. Based on Deq., two new dimensional and dimensionless flame oscillation models were proposed according to the current experimental data. The correlated flame height model and proposed flame oscillation models were validated and agreed well with reference data.

中文翻译：

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空余高度对水池火灾火焰特性影响的实验研究

摘要 开展了一系列实验，研究了燃料表面与水池上缘之间的空缺高度对庚烷和乙醇水池火灾火焰特性的影响。水池直径包括 10 厘米、15 厘米和 20 厘米。对于每个池，空缺高度从零增加到火焰自熄的值。在每次测试期间，油位高度保持装置使油量高度保持恒定。结果表明，空量高度对火焰特性有显着影响。当空量高度为零时，池上缘附近有一个稳定的锥形结构，不稳定的羽流在其上方发展。在较低的空缺高度条件下，会发生羽状喷发。不稳定的羽流开始围绕水池上缘开始，然后向上滚动和扩展。同时，它下面的火焰被拉得越来越薄，最终从大块中断裂。当空量高度进一步增加时，羽流膨化变得不那么明显。而质量损失率一般随着h/D的增加而降低。文献证明，以往的火焰高度模型不适用于大空缺高度的水池火灾。在本文中，为了考虑空量高度对羽流结构的影响，建议使用等效水力直径 Deq. 来建立一种新的火焰高度相关性。通过将之前的模型预测与当前的实验数据进行比较，发现传统的火焰振荡模型不适用于大缺损高度的水池火灾。基于 Deq., 根据目前的实验数据，提出了两种新的维数和无量纲火焰振荡模型。相关的火焰高度模型和提出的火焰振荡模型经过验证并与参考数据一致。