Inhibition of counterflow methane/air diffusion flame by water mist with varying mist diameter

In the present study, the effect of fine water mist on extinguishment of a methane–air counterflow diffusion flame was investigated to understand the underlying physics of fire extinguishment of highly stretched diffusion flame by water mist. Twin-fluid atomizers were used to generate polydisperse water mist of which Sauter mean diameters were 10, 20, 40, and 60 μm. When water mist is not added, the critical stretch rate at extinguishment is 439 s⁻¹ as compared to the theoretical value of 460 s⁻¹. For the case with water mist addition, when the stretch rate is small enough, almost all the water mist evaporates within the flame zone. On the other hand, for high stretch rate case, large mist droplets pass through the flame zone and can reach the stagnation plane. However, no oscillatory motion was found around the stagnation plane. Critical stretch rate at extinguishment decreases monotonously with the mass fraction of water mist independently of the mist diameter within the range of D₃₂ from 10 μm to 60 μm. On the other hand, with increase in the surface area parameter, the critical stretch rate at extinguishment decreases rapidly and becomes less sensitive at large surface area parameter, of which tendency is qualitatively in good agreement with theoretical predictions. For a constant surface area parameter, the critical stretch rate decreases with mist diameter because the mass fraction of water mist should increase in proportion to the mist diameter to keep the surface area parameter constant. When the water mist evaporates completely in the flame zone as in the present study, the mass fraction of the water mist is the dominant factor for fire extinguishment, rather than the surface area parameter. Therefore, an appropriate combination of stretch rate and water mist mass fraction should be provided to suppress effectively a given fire with a small amount of water mist.     

Interaction of water mists with a diffusion flame in a confined space

This paper describes the study of the interaction of water mists with a diffusion flame in a confined space with proper ventilation control. Water mist was generated by a single pressure nozzle and diffusion flames were produced from ethanol and pine samples, respectively. The LDV/APV system was employed to determine the water mist characteristics. The Cone Calorimeter was used to measure the heat release rate, oxygen and carbon monoxide concentrations and other important parameters of the interaction under various conditions. The test results showed that water mist suppressed the diffusion flame in the confined space through oxygen displacement, evaporative cooling and heat radiant attenuation, and enhanced the combustion through expansion of the mixture and chain reaction as well. Suppression played the dominating role when the water mists with enough volume flux were applied to the diffusion flame in confined space. The poorer was the ventilation, the easier the suppression. The water mists had a more complex effect on the solid sample than the liquid, and affected the smoke release rate and movement.     

细水雾抑制扩散火焰的数值模拟

通过实验和数值模拟研究了细水雾抑制扩散火焰的作用过程，探讨了细水雾抑制扩散火焰的机理和规律。细水雾抑制扩散火焰主要是通过水雾的蒸发潜热吸热、热容吸热、稀释氧气等作用，达到控制和扑灭火灾的目的。在实验的基础上，进行了一维数值模拟，其模拟结果与实验数据的物理趋势基本一致，验证了实验结果的合理性。     

Extinguishing characteristics of a diffusion flame with water vapor produced from a water droplet impacting onto a heated plate

In this study, we have investigated an extinguishing method of a diffusion flame with water vapor produced from a water droplet impacting onto a headed plate, which is called as indirect fire attack. In order to clarify the extinguishing characteristics, the extinguishing experiments of a methane-air diffusion flame have been performed by using a pure water droplet with the diameter of 3.2 mm. The droplet dropped from the height of 400 mm. The wall superheat and the burner height were varied from 0 K to 330 K and from 32 mm to 102 mm, respectively. As a result, under certain wall-heat conditions, the water-vapor vortex ring is formed and visualized by the white water fog. At wall superheat of 150 K, the formation probability of the vortex ring is unity and the extinguishing probability always shows the peak values regardless of the burner height. As a result, it can be said in our study that the wall superheat of 150 K is the most effective value for the indirect extinguishing method.     

Extinction condition of counterflow spray diffusion flame with polydisperse water spray

The effect of polydisperse water droplet size distribution on the burning behavior and extinction condition of counterflow spray diffusion flame was investigated experimentally in this study. N-heptane as liquid fuel spray and nitrogen as a carrier gas were introduced from the lower duct while water spray and oxidizer consisting of oxygen and nitrogen was issued from the upper duct. The burning behavior of spray flame for different fuel droplet size with and without water spray was observed and the extinction condition of counterflow spray diffusion flame was characterized by oxygen concentration at extinction. The results show that the minimum value of oxygen concentration at extinction for counterflow spray diffusion flame with water spray is similar to the extinction condition without water spray for higher mean droplet diameter of water. The minimum value of oxygen concentration at extinction shifts to the smaller fuel droplet size when decreasing the water droplet size. For fuel droplet size higher than 48 μm, the optimum of water droplet size for suppressing counterflow spray diffusion flame was smaller than gaseous flame. The explanation of optimum water droplet size based on the coupled effect of Stokes number and vaporization Damköhler number can be used for prediction of the effectiveness of water droplet on the suppression of counterflow spray diffusion flame.     

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.     

细水雾对置障管内预混气体抑爆机理研究

为揭示细水雾对爆燃的抑制作用以及细水雾的释放位置对甲烷预混气体爆燃过程的影响,设计了4种细水雾释放位置和3种粒径(8、45、80μm)的细水雾共13种工况的实验.结果显示:8、45和80μm细水雾在位置2释放时管内压力分别降低36.59％、65.85％和31.7％.在位置3释放时管内压力分别降低34.15％、56％和3...     

一种防误喷细水雾灭火系统

由于意外情况,细水雾灭火系统可能发生“误喷”。一旦发生误喷,将可能造成严重的后果。为此,本文介绍了一种有效防止系统误喷的细水雾灭火系统。通过实体试验可知,其灭火性能与普通细水雾系统相当,同时还具有提高系统可靠性、降低灭火用水量、减少水渍损失等优点。     

Spectral radiation intensities of a turbulent buoyant ethylene flame: CFD-aided tomographic inversion

Radiation heat transfer has been found to dominate fire spread in large-scale fires. The radiation heat loss of buoyant turbulent fires is coupled with fluid mechanics, combustion processes, and soot/gas concentrations. Deconvolution of these combined phenomena can facilitate the development of combustion and radiation models for use in predictive fire modeling. Therefore, in this work, line-of-sight spectral radiation intensities have been measured from a buoyant turbulent pool-fire-like ethylene diffusion flame. In an attempt to be representative of practical turbulent fires, a burner of 15.2 cm in diameter was used. Temporal measurements of radiation intensity were obtained with a fast (400 Hz) mid-infrared spectrometer at a horizontal plane located at half a burner diameter above the burner. Measurement statistics, including mean, root mean square (RMS), probability density function (PDF) of line of sight intensity, and intermittency are reported herein for wavelengths dominated by soot and CO₂ radiation. The data show that radiation is affected by large-scale vortical motions, resulting in varying flame intermittency in the radial direction. Radial distributions of local scalar properties (temperature and soot volume fraction) were calculated through tomographic inversion, using measured data at multiple soot radiation wavelengths. The inversion technique was coupled with the results of a computational fluid dynamics (CFD) fire simulation code. CFD results were used to construct PDFs and spatial correlations for the scalars of interest. The estimated scalars are shown to be consistent with values from the literature, and mean and RMS radiation intensities computed from these scalars are in good agreement with measurements.     

细水雾作用下原木楞堆燃烧温度场研究

进行落叶松原木楞堆细水雾灭火试验,分析原木楞堆燃烧过程中各测点温度场的变化规律。结果表明:细水雾能够有效控制原木楞堆燃烧;细水雾作用时受风向的影响,使上、下风向的温度场变化速率产生差异,下风向的温度场变化速率高于上风向的温度场变化速率;楞堆顶层、中层、底层的温度场呈现不同的变化规律,且下一层的温度场是在上一层明火熄灭后开始下降的。     

超细水雾影响小型火焰在固体可燃物上蔓延的数值模型

开发了CFD模型，用来预测细水雾中火焰沿固体燃料蔓延的特性。采用气体和固体燃料作为对比试验，利用不稳定两维保守公式描述自持性火焰蔓延情况。因为的分析重点主要放在火焰前锋火焰的熄灭机理（火焰前锋完全暴露在细水雾中），所以考虑了有限率（finite—rate）化学反应。火焰基本传播数据也可虑了用于细水雾和蒸气质量的公式，这包括水蒸发造成的能量消耗。还对在细水雾喷洒下聚合材料做成的厚燃料床上火焰的水平传播进行了试验。结果显示，火焰热释放区内自持性能量守恒对外部能量消耗非常敏感。在本试验中，主要是水滴蒸发造成的能量消耗。因此，在火焰前锋，火焰在细水雾的喷洒下挣扎着，要么按几乎相同的速度（没有水喷雾情况下）继续传播，要么被完全熄灭。本文还研究了水滴直径大于30μm细水雾的灭火特性。本文获得了在不同条件下火焰蔓延情况下，灭火需要的细水雾质量分率的关键浓度。     

细水雾对有限空间火灾的研究分析

对细水雾的灭火机理和消烟理论,进行了较为系统全面的阐述。同时结合实际,进行了细水雾扑灭有限空间火灾的试验,并对试验过程中,60～90s出现的＂飘忽不定＂现象进行了解释。通过细水雾的消烟实验发现,细水雾对降低烟尘颗粒有很好的效果。     

水喷雾应用探讨

提出了移动式水喷雾灭火系统的概念 ,建议将其应用在火电厂或变电站 ,扑救可能产生的带电火灾的消火栓系统上。     

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.     

含添加剂细水雾灭火模型及其应用

通过对细水雾的一维瞬间模型进行修改，建立了含添加剂细水雾灭火模型，并论述了该模型的实际应用，结合已有的实验条件对模型进行了验证。主要在于通过含添加剂细水雾灭火模型，提出了细水雾中添加剂灭火有效性的评价指标K，该模型还可对已安装的细水雾灭火系统的灭火有效性进行评价，因而具有较大的实际应用意义。     

障碍物作用下细水雾熄灭油火数值模拟

建立FDS数值模型模拟障碍物作用下细水雾抑制熄灭受限空间油池火的过程和机理,分析开启细水雾后障碍物周围的温度、火焰、水蒸气等的变化情况,讨论障碍物作用下细水雾抑制油火燃烧的有效性。结果表明,在障碍物处火焰膨胀并产生很多大的气流漩涡,这是细水雾与热烟气及障碍物相互作用的结果;细水雾受热蒸发得到的水蒸气易于达到较高浓度从而抑制熄灭障碍物下的残存油火。     

Major fire spread in a tunnel with water mist: A theoretical model

A model of the effect of water mist on major fire spread in a tunnel is described. It employs the concepts of non-linear dynamical systems theory and identifies the onset of instability with major fire spread in a tunnel. The purpose is to identify the thermo-physical and geometrical conditions which lead to instability and sudden fire spread. It uses as a starting point one of the non-linear models for major fire spread which have been developed by the author over many years and assumes that a water mist system operates.The case considered assumes the existence of a longitudinal forced ventilation and predicts the critical heat release rate needed for a fire to spread from an initial fire to an item with a given assumed shape; in the presence of water mist. There is assumed to be no flame impingement on the target object. The target object may be taken to approximate a vehicle. The illustrative case approximating fire spread from an initial fire to a heavy goods vehicle (HGV) is presented; it is not restricted to this case, however. The model is being identified with the name FIRE-SPRINT C1, which is an acronym of Fire Spread in Tunnels, Model C, Version 1. It has been developed from an earlier model, FIRE-SPRINT A3 and considers a case where, in the absence of a fire fighting system, there is the potential for a major fire.     

高压细水喷雾的灭火机理

火灾是燃料和空气中的氧气发生化学反应的过程。维持燃烧的前提条件是：燃料（可以是固态、液态或是气态的）；氧气；火源；和不间断的链式反应同时存在。     

细水雾技术的更新

一般灭火目的的细水雾技术的更新、日益增加的专门针对海上及陆上的各种广泛应用,以及细水雾系统相对于传统灭火剂的特殊优势在过去的二十多年里已经在许多文章中讨论过。     

细水雾与固体木垛火相互作用的实验研究

为了更好地研究细水雾熄灭固体火焰的机理及其有效性 ,建立了单流低压细水雾灭火模拟实验平台 ,在 3m× 3m× 3m的受限空间中开展了一系列的灭火实验。实验过程中采用了两种不同功率的木垛火源 ,利用热电偶和红外热像仪对细水雾施加前后的火焰的温度场进行了实时观察研究 ,结果表明当细水雾的压力低于 0 .2 MPa时 ,细水雾不能有效地扑灭木垛火 ,当细水雾的压力较低时 ,喷嘴距火焰表面的距离和细水雾施加的流量是影响细水雾灭火有效性的关键因素 ;同时 ,功率越大的木垛火 ,越易被细水雾扑灭。