Experimental study on the extinction of liquid pool fire by water droplet streams and sprays

This paper provides evidence about the interaction between the water droplet stream and the flame, and explains how the interaction affects the suppression effectiveness. Two purpose-built gasoline pools were used to generate different open fires. The mono-disperse water droplet streams and water sprays were used as the flame suppressant. The first pool with a circular shape was equipped with a concentric pipe to allow the droplet stream to pass through the flame without impinging the gasoline. The second pool with a long narrow shape was equipped with expandable sides and allowed to extend the fire size. The passing ways of the droplet stream were systematically varied. The results clearly show two modes of flame inhibition; one is by blocking or interfering with the mixing of gasoline vapor and fresh air, and the other by cooling down the flames. For the stream case, the direction of the stream passing through the flame can affect the effectiveness of the suppression which increases as the angle is changed from vertical to horizontal. Also, there is an optimum distance between the stream axis and gasoline surface for flame inhibition. Moreover, the ability can be affected by the droplet size. On the same volume flow rate, the larger the droplet size, the more effective the flame suppression. For the water spray passing through the flame in the long groove pool, whenever the quantity of water vaporization reaches a critical value, the effectiveness of flame suppression by combining the obstructing and cooling effects becomes better.     

Extinction of gas and liquid pool fires with water sprays

Extinction in open space of flames from pool fires by downwardly directed water sprays has been investigated on two linear scales, one three times larger than the other. Circular pool fires were employed as fire sources, mostly in the form of gas discharge (methane) from a horizontal sand surface but also, to a limited extent, in the form of heptane pools. The results are presented in normalized plots based on scaling theory verified in a previous study. Extinction data from the methane fires are insensitive to the initial spray angle of the nozzle discharge. The data are consistent with an engineering relation showing extinction water flow rate approximately proportional to an effective nozzle diameter, and to the 0.4-power of both nozzle height and freeburn heat release rate. This result has been interpreted to indicate that spray-induced dilution of the flammable gas is a major factor in extinguishing fires from gaseous discharge. Extinction data of liquid pool fires from this study (n-heptane) and previous investigations (gasoline, JP-5) are consistent with the methane data, except for somewhat higher water rates at extinction.     

Extinction limit of a pool fire with a water mist

This work describes an experimental investigation of fire extinction limit and enhancement for a gasoline pool fire interacting with a water mist. A downward-directed nozzle produces a fine water spray over a small-scale opposed pool fire. The fire extinction limit is obtained from minimum nozzle injection pressure measured when the fire extinguish takes place. The burning rate of the fuel is also measured using a verified technique. For the conditions tested, it is shown that there are two distinct regions in the relationship between the distance from the nozzle to the fuel pan and the injection pressure, i.e. a fire extinction region and a fire enhanced region. The effective water flux is shown to be a more useful parameter than the injection pressure for the fire extinction limit. It is also revealed that the larger the spray thrust the larger the burning rate is in the fire enhanced region.     

Critical velocity and burning rate in pool fire during longitudinal ventilation

Since the prediction of ‘critical velocity’ is important to control the smoke in tunnel fires, many researches have been carried out to predict critical velocity with various fire sizes, tunnel shape, tunnel slope, and so forth. But few researches have been conducted to estimate critical ventilation velocity for varied burning rate by longitudinal ventilation, although burning rate of fuel is influenced by ventilation conditions. Therefore, there is a need to investigate the difference of upstream smoke layer (e.g., backlayering) between naturally ventilated heat release rate and varied heat release rate by longitudinal ventilation.In this study, the 1/20 reduced-scale experiments using Froude scaling are conducted to examine the difference of backlayering between naturally ventilated heat release rate and varied heat release rate by longitudinal ventilation. And the experimental results obtained are compared with numerical ones. Three-dimensional simulations of smoke flow in the tunnel fire with the measured burning rates have been carried out using Fire Dynamics Simulator; Ver. 406 code, which is developed by National Institute of Standards and Technology. They show a good degree of agreement, even if some deviation in temperature downstream of the fire is evident. Since ventilation velocity had a greater enhancing effect on the burning rate of fuel due to oxygen supply effect, the critical ventilation velocity should be calculated on the basis of varied HRR by ventilation velocity.     

水浴保护对甲醇池火燃烧速率的影响

试验研究了水浴对不同尺寸甲醇池火燃烧速率的影响.燃烧盘与水浴盆均为正方形.结果:在水浴条件下,在稳定燃烧阶段的池火燃烧速率曲线比较平滑;在快速上升阶段,池火燃烧速率与油池尺寸及有无水浴关系不大;在下降阶段,有水浴的条件下,燃烧时间有所延长;在稳定阶段,有水浴时燃烧速率小于无水浴时,一般不超过10%.     

基于正庚烷油池火验证大尺度量热装置

针对大尺度量热计装置,在隧道量热计内开展试验对正庚烷油池火热释放速率、热释放总量进行校正。利用冷流场校正了解排烟管道气体流量的稳定性及均匀性,分别针对不同油盘个数、排列方式条件下进行正庚烷油池火校正试验。结果表明：在冷流场校正试验中,排烟管道内的烟气体积流量维持在27.9 m3/s;通过对实测热值与理论热值的误差比较分析,7组试验中有6组试验的实测热值与理论热值之间的误差低于10%。     

Burning behavior of two adjacent pool fires behind a building in a cross-wind

With the global move towards performance based fire design, fire safety assessment in and around buildings becomes increasingly important. However, key knowledge gaps still exist concerning the behavior of fire swirling, which may be generated if one or more accidental fires are in the passage of the vortices behind an adjacent tall building. The present study is focused on the experimental investigations of the burning behavior of two pool fires behind 1/50 scaled tall buildings with heights varying from 0.565 to 1.165 m in a cross-wind. The objective is to gain insight of the effect of the distance between the two fires (D2), the distance between the fires and the building (D1), wind speed (V), and the height of the scaled building (H) on the burning behavior. Important conclusions have been drawn about the influence of D1 and D2 on the fuel mass loss rate, the influence of D1 on fire swirling, the influence of D2 on the possible merging of the two fires and the effect of wind speed on the mass loss rate. The results suggested the existence of a critical velocity for the cross-wind on the initiation of fire swirling and an approximate value was identified for the conditions in the tests. The investigations also covered the effect of height of the scaled building on the fuel mass loss rate and the occurrence of fire swirling. This relationship was found to be also dependent on the wind speed. Analysis of the results has led to some important recommendations to enhance the fire protection of tall buildings.     

On wall fire interaction in a small pool fire: A large-eddy simulation study

Large-eddy simulation (LES) with stochastic fields (SF) method is used to simulate a pool fire in a compartment for different distances from the compartment sidewalls. In our previous work (Jangi et al., 2016) [24], we have formulated and validated LES-SF method for modeling pool fires. Here we use the same approach to study the wall-fire interaction. For this purpose, two cases are presented. In one case the pool is located at the center of the compartment floor far from all sidewalls, referred to as case C. In another case the pool is in the vicinity of a sidewall, referred to as case W. In both cases, it is shown that pool fires are not a fully non-premixed flame but they can involve some levels of premixed combustion, especially in the form of ignition process in fuel-lean mixtures. This is more evident in case C when the pool is far from the walls. Results in case C show that flow is mainly driven by crosswise vortices, whereas for the case W, the flow is driven by longitudinal vortices. Depending on the distance for the sidewall, two mechanisms for the fire intermittency are identified: in case C the intermittency is mainly due to quenching and re-ignition, whereas in case W, it is essentially due to the interaction between flow and the sidewall.     

双流体细水雾抑制熄灭油池火的实验研究

在3 m×3 m×3 m的受限空间内使用双流体细水雾喷头进行了灭油池火的有效性实验,实验所用的燃料试样为柴油,雾化气体为氮气.实验中使用热电偶测量火焰温度的变化,使用烟气成分分析仪测量气体组分体积分数的变化.实验结果表明:由于雾化气体的介入,双流体细水雾的灭火过程和灭火机理与单流体细水雾有所不同;双流体细水雾在一定的压力下存在最佳的灭火水流率,在此水流率下灭火时间最短.     

Estimating large pool fire burning rates

Data for estimating the burning rate and heat output of large pool fires (diameter ≳ 0.2 m) are compiled and computational equations presented. Since a large scatter in the reported data is noted, attention is also focused on areas where further research is most needed in order to improve predictability.     

流淌火与油池火燃烧特性对比实验研究

建立流淌火燃烧特性实验研究平台,采用93#汽油进行油池火与流淌火的对比燃烧实验,研究在不同斜面角度条件下流淌火与油池火灾在质量损失速率、火焰温度、火焰热辐射等特性参数上的差异,并分析其原因.结果表明,流淌火的火焰高度较低而且非对称分布,火焰波动较大,质量损失速率较小,温度较低,热辐射值较小.可为建立与完善流淌火燃烧理论模型和热辐射危害模型提供参考依据,同时对大型油罐区消防安全设计及灭火救援也具有重要意义.     

池火灾数值模拟研究进展

介绍了池火灾的数值模拟研究现状,并指出今后池火灾模拟的研究发展方向。     

Measurements of gas velocities and temperatures in a large open pool fire

A number of measurements were made to help define the thermal and flow conditions in a 9 × 18 meter pool fire that was used to simulate a transportation accident. Temperatures were measured at twenty-eight locations throughout the continuous flame region. Velocities were measured at four vertical stations near the centerline of the pool. Heat fluxes were estimated from thermal measurements on and near vertical steel plates. As is often the case in fires of this size, the effects of mild, ambient winds on the measurements were pronounced. Attempts have been made to mitigate these effects by the application of conditional sampling. Temperatures and velocities are compared with other experimental results as well as results of modeling efforts.     

小尺度变压器油池火灾燃烧特性的实验研究

开展了直径20～50 cm 的圆形变压器油池火实验,分别测量并研究了火焰形态、燃烧速率、火焰轴心温度等燃烧特性。结果表明：在变压器油燃烧的3 个阶段中,稳定燃烧阶段持续时间最长,而衰减熄灭阶段要明显短于起始燃烧阶段。在燃烧速率方面,油池的直径越大,变压器油燃烧速率越快,燃烧时间越短,变压器油的液位下降速度也越快。变压器油的单位面积燃烧速率与经典辐射模型具有良好的一致性,单位面积燃烧速率与油池直径呈现幂函数形式。在火焰温度方面,油池中心线温度呈现距离液面的垂直高度越大其火焰温度越低的趋势,液面上方火焰温度最高可达700～800 ℃,同时油池火尺度对火焰最高温度的影响不大。     

浅谈住宅小区集中消防水池的设计

结合工程实践,从合理设置集中消防水池及消防水池取水口等方面进行了论述,达到了既能防止和减少建筑物火灾危害,保护人身和财产安全,又能节省大量的设备基建投资及日后的维护管理费用的效果。     

自由燃烧下油池火灾的燃烧特性研究

通过对93#汽油、0#柴油和95％的乙醇的自由燃烧试验,得出了3种燃料的燃烧特性,包括液层温度、质量损失速率、燃烧速度、密度、热释放速率、火焰温度等,并结合理论公式拟合热释放速率随油盘直径变化的曲线.质量损失速率与火焰高度汽油＞柴油＞乙醇;汽油、柴油、乙醇燃烧时的液面温度分别为125、310、80℃;3种燃料都在2 min以后达到稳定燃烧状态.     

依托单位消防水池建设公共消防取水口研究

针对部分市、县不能保证市政供水管网24 h 供水,停水期间,消防水鹤、市政消火栓均无法使用,现有规范标准不便于使用且防冻效果不好、建设成本较高等问题,提出了依托消防水池建设公共消防取水口的技术措施,并就建设公共取水口的水池选择、建设形式和建设要求进行了研究,表明该措施具有建设周期短、建设成本低、防寒、取水方便等特点,可有效解决部分城区公共消防供水能力不足的问题。     

隧道火灾下不同沥青路面结构的燃烧情况分析

对隧道火灾下不同沥青路面结构的燃烧情况进行了分析,通过计算估计了隧道内发生火灾时人员的撤出时间,分析了在有燃烧油料的情况下,两种路面结构的排除能力,并对不同路面的燃烧情况从温度变化、燃烧面积及燃烧沥青量三个方面进行了分析。