Ghosting flame mechanism under different extinctions modes in ceiling vent cabin

In this paper, large eddy simulation coupled with a low Mach number compressible thermal-drive flow model had been utilized to investigate the development of large-scale engine room fire, and the characteristics of engine room fire were analyzed through based upon the distinctive fire extinction behavior. Results indicated that extinction modes of engine room fire could be divided into oxygen control type and fuel control type. And the flame morphology could be divided into four stages: conical flame, pulsating flame, column flame, and ghosting flame. The appearance of the ghosting flame was affected by the extinction mode, but there were obvious differences in the causes of ghosting flame between the two modes. The cause of ghosting flame was related to the distribution of temperature field under the fuel control type, while the occurrence of ghosting flame in oxygen control type was mainly affected by oxygen concentration. Deflagration should be avoided when extinguishing fire by sealing the cabin.     

二甲醚球形扩散火焰的振荡熄火动力学机理研究

采用详细的化学反应机理和组分输运模型，对二甲醚(DME)微重力球形扩散火焰在热焰与冷焰条件下的振荡熄火机理开展数值研究。结果表明，在微重力条件下可以建立稳定自持的冷焰，而且冷焰反应可以显著拓展熄火的可燃极限。在热焰与冷焰的稳态熄火点之前均观察到了振荡熄火过程。DME热焰的振荡熄火受单个振荡模式所控制，且振荡频率(约1 Hz)与环境氧含量无关。而冷焰的振荡熄灭受两个具有不同频率的双振荡模式所控制，在靠近熄火极限时高频振荡模式的振荡周期急剧增加。此外，高频与低频振荡模式之间存在着强烈耦合作用，导致冷焰的振荡熄火过程更加复杂。基于敏感性分析的结果表明，热焰的振荡熄火受小分子所参与的高温吸热/放热以及链分支/断裂反应之间的竞争关系所控制，而冷焰的振荡熄火受负温度系数机制下低温链分支与断裂反应之间的竞争关系所控制。     

全氟三乙胺和全氟己酮混合气体的灭火效果研究

全氟己酮是一种新型的哈龙替代灭火介质，但是研究人员发现全氟己酮在低浓度时具有助燃效果，未通过美国联邦航空局气溶胶爆炸实验(FAA-ACT)。为抑制全氟己酮的助燃效果，采用混合气体的方法，引入全氟三乙胺作为全氟己酮的协同灭火介质。首先利用杯式燃烧器研究不同浓度全氟己酮作用下的火焰高度、火焰宽度，并获取其临界灭火浓度；以火焰高度和火焰宽度作为助燃现象的判据，实验结果表明全氟己酮浓度为3.00%（占氧化剂体积分数，下同）左右时助燃现象最为显著，临界灭火浓度为5.80%。为研究全氟三乙胺抑制全氟己酮助燃现象的效果，在保持全氟己酮浓度3.00%不变的条件下，逐渐增加全氟三乙胺的浓度，获取火焰高度、火焰脉动频率和混合气体的临界灭火浓度变化趋势；结果表明全氟三乙胺对全氟己酮的助燃现象有抑制作用，且预测全氟三乙胺单独作用下的临界灭火浓度约为4.86%。全氟己酮和全氟三乙胺的混合灭火气体中，全氟三乙胺占灭火剂体积分数超过10.00%后，全氟己酮和全氟三乙胺具有较好的协同灭火效果。     

Unsteady extinction mechanism of nonpremixed flame interacting with a vortex

The extinction mechanism of a CH₄/N₂-air counterflow nonpremixed flame interacting with a single vortex was numerically studied. An augmented reduced mechanism was used to treat the CH₄ oxidation reactions. The contribution of each term in the energy and the OH species equations were evaluated to investigate the unsteady extinction mechanism of nonpremixed flame. The flame temperature began to decrease due to the convection heat loss when the flame interacted with a vortex. The investigation of the radical behavior during the flame-vortex interaction process also provided useful information on the unsteady extinction mechanism. The OH radical concentration could be used as a good tracer of the state of the unsteady extinction of nonpremixed flame. The reduction mechanism of OH concentration was confirmed by analyzing the contribution of each term in the OH species equation. At initial stage of flame-vortex interaction, the OH production and consumption rates increased gradually, while the OH concentration was kept nearly constant. Near the extinction limit, the OH production rate decreased rapidly due to the low flame temperature, and the balance between the OH production and OH consumption by diffusion could not be maintained. The unsteady nonpremixed flame interacting with a vortex under the conditions of regime (V) shown in the spectral combustion diagram [Thévenin, D., Renard, P.H., Fiechtner, G.J., Gord, J.R., Rolon, J.C., 2000. Regimes of non-premixed flame-vortex interactions. Proceedings of the Combustion Institute 28, 2101-2108.] was finally extinguished due to low reactivity, which was induced by the low flame temperature.     

Flame penetration and burn testing of fire blanket materials

Materials were evaluated in laboratory tests for a fire blocking blanket to protect stores of U.S. Army munitions from burning material and hot fragments. The objective of testing was to evaluate and rank materials' ability to resist the penetration of flame and heat and to limit flame spread. Materials in all tests were subjected to an oxyacetylene torch with temperatures in excess of 3000°C. Inorganic fiber‐based fabric, insulation and blankets evaluated in flame penetration tests were rated by their time to limit backside temperature rise to 100°C above ambient and 500°C for a given material areal mass. Carbon fiber fabric performed the best of the fabrics tested. Silica aerogel insulation was the top performing insulation material group. The blanket with carbon fiber sandwiching silica aerogel insulation performed best. Horizontal and vertical flame burn tests were conducted on several candidate blanket cover materials. Fabrics coated with polyvinyl chloride, polytetrafluoroethylene and silicone rubber coatings were all found to be immediately self‐extinguishing when the flame was removed. Burn damage was confined locally to the heated zone beneath and around the lit torch tip's flame. All flames were immediately self‐extinguishing beyond those regions, with zero flame‐out times recorded. Published in 2008 by John Wiley & Sons, Ltd.     

哈龙替代型含氟灭火剂灭火过程中HF生成及灭火机理研究进展

三氟甲烷(CHF3)、五氟乙烷(C2HF5)、六氟丙烷(C3H2F6)和七氟丙烷(C3HF7)四种典型的氢氟烃(HFCs)是目前常用的哈龙替代型灭火剂,具有灭火高效、性能可靠且无残留的特性. 4种典型含氟灭火剂在灭火过程中会产生有毒气体HF,热分解过程中产生的含氟自由基与火焰中的O, H, OH等燃烧自由基反应,导致燃烧过程中化学链式反应中断.缩短达到灭火浓度所用时间、减少灭火剂与火焰作用时间和加入抑制剂或添加剂可降低有毒气体HF生成量. 未来应进一步借助全尺度实验和理论计算,深入研究HFCs类灭火剂在不同使用条件下的灭火机理,获取HFCs灭火剂灭火浓度、灭火毒性、腐蚀性及相容性等实际数据,为提高其灭火性能、降低灭火过程中有毒气体的生成、拓宽使用领域和开发性能更优异的HFCs类灭火剂奠定一定的理论和应用基础.     

Testing ogranophosphorus, organofluorine, and metal-containing compounds and solid-propellant gas-generating compositions doped with phosphorus-containing additives as effective fire suppressants

The development and investigation of new effective and environmentally clean flame suppressants is a promising direction in fire extinguishing. Organophosphorus and metal-containing compounds are the most promising candidates for the replacement of CF₃Br. However, for many of these compounds, data on their minimum extinguishing concentration are not available. In the present work, the minimum extinguishing concentrations for a number of new phosphorus-and metal-containing compounds and some of their mixtures, solid-propellant gas-generating compositions containing phosphorus additives were determined using the cup-burner technique and a setup with a turbulent flame source and transient application of flame suppressants. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 6, pp. 64–73, November–December, 2006.     

Studies of fundamental physical–chemical mechanisms and processes of flame extinguishing by powder aerosols

Theoretical and experimental studies on mechanisms of interaction of the fire‐extinguishing aerosol with flame are carried out. The factors of heterogeneous inhibition of flame free radicals (O, OH, H, CH_x) on a crystal surface of inorganic salts being the basic components of fire‐extinguishing powders and aerosols are measured using laboratory equipment. The semi‐empirical calculations by methods of quantum chemistry for heterogeneous and homogeneous inhibition reactions of burning are executed. The thermal mechanism for fire extinguishing is evaluated. The universal mechanism of influence on flame of a crystal surface of a fire‐extinguishing powder particle is offered. Copyright © 2007 John Wiley & Sons, Ltd.     

Performance evaluation of bromofluoropropene in extinguishing liquid fuel spray fires

Liquid fuel spray fires emit high radiation heat fluxes, posing great threat to humans. The study of suitable agents and techniques for extinguishing this particular type of fire is of great importance. In this study, degradable 2‐bromo‐3,3,3‐trifluoropropene (BTP), a new clean fire extinguishing agent, was tested for its effectiveness in extinguishing three types of liquid fuel spray fires, namely diesel, gasoline, and ethanol. Bench‐scale experiments were conducted in a 6 × 5 × 3 m compartment with natural ventilation. The liquid fuels sprayed at varying pressures were ignited by a small open flame and then extinguished by a portable BTP extinguisher. Results showed that BTP of less than 60.0 g could extinguish all liquid fuel spray fires of 0.20 to 1.0 MPa in less than 2.0 s. The results also showed that when compared with fire sparked by gasoline and diesel, it is significantly easier to put out ethanol spray fires because of its high flame temperature and low flame power. Based on well‐established fire suppression theories and experimental results, the detailed mechanism of how BTP functions as an extinguishing agent in the suppression of liquid fuel spray fires will be discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

Extinction effectiveness of pyrogenic condensed-aerosols extinguishing system

We studied the extinction effectiveness of pyrogenic condensed-aerosols in gaseous fire extinguishing systems through the ISO (International Organization for Standard) 15779. The thermal characteristics of solid aerosols as an extinguishing agents were evaluated by using TG and DTA. The modified closed pressure vessel test (MCPVT) and the conductivity of the solid aerosol extinguishant were also measured to ensure the safety of extinguishant. The TG and DTA result showed that the resin added to the main component of Potassium Nitrate (PN) has the effectiveness to mitigating the exothermic reaction of the pyrogenic condensed-aerosol extinguishant. The results of maximum height test revealed the extinguishing capability of a pyrogenic condensed-aerosol extinguishing agent as a gaseous extinguishing system.     

灭火剂发展现状与未来

合理选择灭火剂是即时有效扑灭燃烧火焰和防火防爆的关键。对常用的物理灭火剂和化学灭火剂的特点、灭火机理和适用范围作了归纳 ,着重介绍了哈龙和哈龙替代品的灭火机理 ,并对物理灭火剂和化学灭火剂之间的协同作用作了重点阐述     

添加剂降低气溶胶发生剂火焰温度的研究

研究了两种添加剂对一种气溶胶发生剂（EBM灭火剂）的火焰温度的影响,发现这两种添加剂具有明显降低气溶胶发生剂燃烧火焰温度的作用,当两种添加剂同时使用时,改性样品具有更加优良的综合性能。     

A theory for flame extinction based on flame temperature

The extinction and suppression of diffusion flames is examined theoretically. The effects of oxygen reduction and external heat flux are examined compared to data in the literature. An application of extinction in compartment fires is also examined. The theory developed is based on a critical flame temperature, and that theory includes transient effects and the addition of water as well. Copyright © 2004 John Wiley & Sons, Ltd.     

Modeling the process of methane-air plume extinguishing by a solid-propellant pulse aerosol generator

Operation of a pulse aerosol system of fire fighting designed for effective extinguishing of fires in gas wells is modeled by an example of quenching a methane-air subsonic plume escaping from a nozzle. The system consists of two separate parts: a charge of a unitary solid propellant (gas generator) and a container with fine-grain powder of a flame retardant. The combustion of the mixture is described by a one-step global reaction; the effect of the concentration of flame-retardant vapors on the combustion process is taken into account through reduction of the pre-exponent in the Arrhenius law and is described by an empirical dependence. A computational experiment shows that the use of the pulse aerosol system of fire fighting ensures effective transport of fine aerosol particles of the flame retardant and its vapors to the combustion zone in amounts sufficient to suppress the ignition spot. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 26–34, May–June, 2009.     

Some basic aspects of flame resistance of polymeric materials

For a better insight into flame resistance and flame extinction it is useful to split the combustion process into its constituent elements. It then appears that the thermal decomposition is the first link in a series of reactions and therefore a better understanding of this decomposition is a prerequisite. Further, it is found that the amount of char and the amount of incombustible gases that may be formed in thermal decomposition are very important quantitative measures of flame resistance. For a large number of model substances the char residue upon pyrolysis has been determined. The residue is found to be very clearly related to the chemical structure of the polymer, so much so that the amount of char can be predicted from the structure. Finally, it has been demonstrated that there is a very significant relation between the pyrolysis residue (%) and the (limiting) oxygen index.     

NaOH和Na2SiO3对纤维板阻燃性能的比较研究

通过对比在纤维板表面涂覆NaOH和Na2SiO3溶液,基于小室燃烧法、垂直燃烧仪和极限氧指数等研究其阻燃性能.结果表明,表面改性纤维板的阻燃性能排序为:涂Na2SiO3纤维板>涂NaOH+Na2SiO3纤维板>涂NaOH纤维板>未处理纤维板>泡水处理纤维板,单面涂覆的阻燃性能优于双面涂覆,极限氧指数可达25.2%.提出了NaOH与Na2SiO3对中密度纤维板的阻燃机理,涂覆NaOH溶液易使纤维板的阻燃物质迁移至表面,掺入的Na2SiO3可在纤维板表面形成含(=)Si-O-Si(=)链的三维网状硅质层,进而提高其阻燃性能.     

Heat propagation in thermally conductive polymers of PA6 and hexagonal boron nitride

Thermally conductive polymers offer new possibilities for the heat dissipation in electric and electronic components, for example, by a three‐dimensional shaping of the heat sinks. To face safety regulations, improved fire performance of those components is required. In contrast to unfilled polymers, those materials exhibit an entirely different thermal behavior. To investigate the flammability, a phosphorus flame retardant was incorporated into thermally conductive composites of polyamide 6 and hexagonal boron nitride. The flame retardant decreased the thermal conductivity only slightly. However, the burning behavior changed significantly, due to a different heat propagation, which was investigated using a thermographic camera. An optimum content of hexagonal boron nitride for a sufficient thermal conductivity and fire performance was found between 20 and 30 vol%. The improvement of the fire performance was due to a faster heat release out of the pyrolysis zone and an earlier decomposition of the flame retardant. For higher contents of hexagonal boron nitride, the heat was spread faster within the part, promoting an earlier ignition and increasing the decomposition rate of the flame retardant.     

Evaluation of small scale n-heptane fire extinguishing efficacy by natural antioxidants based pyrotechnic compositions: An experimental study

The conventional pyrotechnic compositions (PCs) for firefighting application mostly consist of potassium nitrate, chlorate or perchlorate as oxidants and organic resin-like phenol-formaldehyde, melamine-formaldehyde, epoxy resin and polyurethanes are used as reducers. Unfortunately, there are also some potential disadvantages to the use of conventional compositions. These are related to high combustion temperature with the generation of heat and flame which may cause secondary fire chances and hazards associated with the use of organic resins. Exposure to phenol, melamine, epoxy resins and polyurethanes are considered as a life-threatening occupational hazard. Under the present study, new pyrotechnic compositions were prepared with the combination of natural antioxidants like ascorbic acid and gallic acid as reductant and mixture of potassium nitrate with potassium chlorate as oxidant. Fire extinguishing efficacies, calorific value, burn rate, the flame temperature of newly developed compositions was evaluated against potassium nitrate and phenol-formaldehyde resin-based conventional composition. Although both the new and conventional composition has shown good fire extinguishing efficacies, extinguishing 4.57 KW of small scale n-heptane pool fire in 3 to 4 seconds, these newly developed compositions showed 67% to 76% reduction in flame temperature. It was also found that these new compositions exhibit a faster burn rate and lower calorific value than the conventional composition. To understand the fire extinguishing mechanism by the discharged aerosol particulate, its physical and chemical characteristics were assessed by a series of techniques viz; HRXRD, SEM, FTIR, EDX.     

油浸变压器水喷雾灭火系统的设计探讨

通过分析室外大型油浸变压器的火灾危险性和相关防火规范的要求,介绍日前常用的保护各类油浸变压器的灭火系统,描述了水喷雾灭火系统的灭火原理及其系统组成,并以某化工项目变电所室外油浸变压器的水喷雾灭火系统设计为例,介绍该系统的设计流程及应注意的问题。     

低碳醇改性无氟泡沫的性能分析与扑灭油池火的实验研究

针对现有氟碳类泡沫灭火剂关键组分PFOS因国际环境公约出于环保和健康而限用,以及现有泡沫灭火剂还存在析液速度快而影响灭火能效等问题,在前人及团队探究无氟泡沫复配方案基础上,基于火灾化学理论与表面活性剂技术,遴选碳氢/有机硅表面活性剂(LS-99/SDS)为基剂,通过引入可改善气泡聚并的低碳醇(乙醇、正丙醇和异丁醇)调控泡沫的发泡倍数和25%析液时间等性能,开展含醇泡沫和无醇泡沫的灭火对比实验,考察低碳醇引入后的泡沫灭火能效。结果表明,引入适量浓度低碳醇可显著影响LS-99/SDS复配体系的发泡倍数和25%析液时间。相比乙醇和正丙醇,当异丁醇质量分数为0.1%时,可有效延缓含醇泡沫的析液进程和降低析液速率。通过灭火过程的火焰温度测定,发现含醇泡沫作用下10 cm和20 cm高度处的火焰最大降温速率为20.1℃·s^-1和11.2℃·s^-1,相较于无醇泡沫体系降温效果显著,降温增幅分别为39.58%和14.29%。含醇泡沫灭火剂相对于无醇泡沫灭火时间缩短了3.6 s,缩短幅度为37.5%。适量浓度的异丁醇引入到无氟泡沫体系中,可有效延缓泡沫析液进程,提高泡沫体系的发泡倍数及稳泡性能,为无氟泡沫的优化设计提供了一条新路径。建立了基于25%析液时间、平均析液速度、最大降温速率和灭火时间等综合指标的灭火效果考察方法,为泡沫灭火效能的实验室评价提供了参考依据。