Scale effect of cup burner on flame-extinguishing concentrations

In an attempt to reduce the amount of chemical used in fire suppression testing of halon alternative agents, smaller cup burner systems than that of ISO were constructed, and the flame-extinguishing concentrations of Halon 1301 for three liquid fuels were measured. Reducing the cup diameter or the chimney diameter of the cup burner changed significantly not only the flame-extinguishing concentrations but also the flame behavior near extinction. Nevertheless, the reduced size cup burners with which the flame-extinguishing concentration was equal to that of the ISO cup burner were found. One cup burner can reduce the amount of extinguishing agent used in testing by 90%.     

Flame-extinguishing concentrations and peak concentrations of N2, Ar,CO2 and their mixtures for hydrocarbon fuels

Fire-extinguishing efficiency of inert gas mixtures was investigated by measuring flame-extinguishing concentrations and peak concentrations for hydrocarbon fuels, because new fire-extinguishing agents composed of inert gas mixtures have been developed as halon alternatives. The flame-extinguishing concentrations of nitrogen, argon, carbon dioxide and their mixtures for n-heptane were measured with the FRI glass cup burner. The peak concentrations of the agents for methane-air and propane-air mixtures were also measured with the tubular flame burner. Chemical equilibrium calculations showed that the adiabatic flame temperatures of the cup burner flames at the extinction condition were almost constant for all the agents. The adiabatic flame temperatures at the flammability limit of the tubular flame for each fuel were also independent of the inert gas agent if the mixtures had the same equivalence ratio. The flame-extinguishing concentrations of the inert gas mixtures were predicted by a simple equation averaging over the flame-extinguishing concentrations of all component gases weighted by mole fraction. The equation has the same form as Le Chatelier's law. For the flammability limits of the hydrocarbon-air mixtures, the same relation was also recognized in the effect of the mixed agents. The facts show clearly that this simple equation for the flame extinction concentrations is useful to estimate the fire suppression efficiency of any mixed agents of the inert gases. At the same time, it appears that the flame-extinguishing concentrations and the flammability limits reported in the paper are consistent.     

灭火剂有效性的燃烧器实验评价方法

对杯式燃烧器、管状火焰燃烧器、Fuss管式燃烧器等几种典型燃烧器的特点进行比较,对各自实验的结果进行对比分析,发展了一种新型的研究细水雾惰化与抑制甲烷/空气预混火焰的管式燃烧器实验方法.     

Experimental study of thermal breakdown products from halogenated extinguishing agents

Thermal breakdown products from four different fire extinguishing agents have been analysed. The agents studied were: bromotrifluoromethane (Halon 1301), pentafluoroethane (HFC 125), heptafluoropropane (HFC 227ea) and dodecafluoro-2-methyl-pentane-3-one (C₆F-ketone). In the tests, the studied agent was introduced into a propane flame in a diffusion flame burner. The combustion products were analysed using both conventional IR-techniques and FTIR. It could be concluded that for all four extinguishing agents that the extinguishing agent takes part in the combustion process resulting in production of CO and CO₂, which was also confirmed by the increase in smoke production with increasing amounts of agent introduced into the flame. Production of HF and COF₂ was found in experiments with all four extinguishing agents. In experiments with Halon 1301, the production of HBr was also determined. It was found that the main fraction of fluorine ends up as HF for HFC 227ea and HFC 125 at lower relative application rates. When approaching extinguishing concentrations, the fraction recovered as COF₂ increases, but the total recovery of fluorine, including HF and the remaining part of the fluorine, is found in various organic breakdown products. The recovery of fluorine as HF and COF₂ for the C₆F-ketone is lower compared to HFC 227ea and HFC 125. There is a clear difference in the recovery of fluorine for Halon 1301 where an almost quantitative recovery as HF or COF₂ is found. Halon 1301 additionally contains bromine, which, to a large extent, is recovered as HBr.     

六氟丙烯的灭火性能研究

六氟丙烯(HFP)因双键的存在满足哈龙替代灭火剂在环保性方面的要求,但目前对其灭火性能研究较少,其与火焰作用的效果尚不清楚.利用杯式燃烧器研究HFP对甲烷和丙烷火焰的灭火性能,并与结构相似的饱和含氟烷烃六氟丙烷(HFC-236fa)和七氟丙烷(HFC-227ea)进行对比.结果表明,HFP比HFC-236fa和HFC-...     

A Tunable Diode Laser Absorption Diagnostic for Studying the Fire Suppression Mechanism of Aqueous High Expansion Foams

Using direct-tunable diode laser absorption spectroscopy, we obtained simultaneous oxygen, water vapor, and temperature measurements in situ during aqueous high expansion foam-suppressed fires in a foam-adapted cup burner apparatus. Foams with expansion ratios ranging from 55:1 to 129:1 were delivered at various rates; measurements were obtained 5.5 cm above and 1.5 cm outside the cup burner exit. By monitoring water vapor as foam advances through the cup burner chimney with and without the flame present, we are able to quantify evaporation due to the presence of the thermal and radiating field. We are also able to measure the impact on the oxygen concentration resulting from flame consumption of oxygen versus release of oxygen from evaporating foam bubbles. By analyzing video captured during each foam injection event, foam velocities during fire suppression and in the absence of the flame were measured.     

Guidance for Advanced Fire Suppression in Aircraft

The U.S. Department of Defense (DoD) Next Generation Fire Suppression Program (NGP) was born of necessity. Atmospheric science had made it clear that fully halogenated compounds containing chlorine or bromine posed a threat to the earth’s ozone layer. An extensive, multi-year search by the DoD found that the best commercially available alternative to halon 1301, CF₃Br, for fire suppression in aircraft carried significant weight and storage volume penalties. In 1997, the NGP began, with an objective that evolved to “develop and demonstrate technology for economically feasible, environmentally acceptable and user-safe processes, techniques, and fluids that meet the operational requirements currently satisfied by halon 1301 systems in aircraft.” Ten years later, the NGP has revitalized the science of fire suppression. There have been advances in delivery of a flame extinguishing chemical to a fire, knowledge of chemical interactions with flames (and limitations to the effectiveness of such chemicals), screening of a large number of chemicals as potential fire suppressants, identification of the properties of fluids that make for effective and safe fire suppression, identification of effective fire suppressant chemicals, engineering of non-fluid suppression systems for improved effectiveness and efficiency, and evaluation of the true cost of a new fire suppression system. The final report of the NGP will be available in book form and on CD this autumn. See the NGP web site () for ordering information.     

A New Total Flooding Test Procedure for Evaluating Fire-Suppressant Agents

A simple laboratory apparatus is described for observing the performance of fire extinguishing agents in total flooding applications. Known compositions of agents mixed with dry air are prepared in a 2 L glass combustion flask, and a flame fed by propane, butane, or other gaseous fuel from a pressure cylinder is inserted into the flask through a standard taper joint. Burning times to extinguishment are measured, both in the absence and presence of added physical or chemical agents. From the known rate of propane burning and initial compositions, the percentages of gas volume in the combustion flask at extinguishment are calculated for each burning time. Agents that are not sufficiently volatile to be investigated with the ordinary cup burner method are readily studied with the new technique.An adiabatic flame temperature model previously used to correlate cup burner test results has been applied to obtain limiting agent percentages required for total flooding extinguishment and to accurately predict the effect on burning time of different concentrations of physical and chemical agents and other gases in the flask.     

Interaction of a water mist with a buoyant methane diffusion flame

This work describes observations and measurements from the interaction of a fine water spray from a hollow cone nozzle, with purely buoyant diffusion flames from a natural gas ceramic-plate burner located directly underneath the nozzle. The burner plate was instrumented with thermocouples cemented on its upper and lower surfaces to assess the influence of the spray on the burner temperature. A set of thermocouples was also used to measure plume centerline temperatures above the burner plate. An imaging system was used to record the presence of droplets near the burner surface, and a narrow angle total radiation detector was used to measure changes in local flame radiation. A limited number of measurements of the steady state O₂ and CO concentrations along the plume centerline were also carried out.

For the conditions tested, the plume-to-spray thrust ratio was large, resulting in negligible direct penetration of the droplets into the fire region. A consequence of the low spray thrust was an almost droplet-free region above the flame. The observed cooling of the ceramic burner when the spray was applied was due to decreased radiant emission from the flame as well as deposition and evaporation of droplets entrained into the plume near the burner. The centerline plume temperatures did not change significantly upon application of the spray, at least within the error limits of thermocouple measurements. However, there was a significant decrease in O₂ and an increase in CO concentrations along the plume centerline upon application of the spray. An energy balance on the ceramic-plate burner, together with the experimental data, yielded estimates of the water deposition rate on the burner surface.     

含NH4Cl添加剂细水雾对油池火灭火效果的研究

受限空间内的火灾是消防救援与火场疏散的难题。细水雾灭火系统能最大限度保护设备,与其他灭火剂相比具有良好的环保性能。为了更好地发挥灭火效果,采用在水中加入添加剂的方式以探究其对灭火的影响,在受限空间内开展含NH₄Cl添加剂的细水雾对雾化效果的影响和灭油池火的实验,研究火焰形状变化、受限空间内温度变化以及添加剂浓度不同时的灭火效果,对受限空间内氧含量的变化进行监测分析。研究表明：在水中加入NH₄Cl添加剂后,改变了喷雾的分布,雾场中心雾滴较密集,且随着NH₄Cl浓度的增加雾滴粒径增大,雾化锥角变小。采用不同浓度的NH₄Cl添加剂细水雾灭火时,受限空间内氧含量及灭火时间呈不同的变化,当添加剂浓度为2%时,物理与化学灭火的耦合机制能更好地发挥,灭火效果最佳。     

Entrainment in fire plumes

A new technique for measurement of mass flow rates in buoyant fire plumes is described. The characteristics of 10–200 kW methane diffusion flames stabilized on porous-bed burners of 0.10–0.50 m dia. are described. A transition in the dependence of flame height on heat input and burner size was observed when the flame height was about four times the burner diameter. The mass flow rates in the buoyant plumes produced by the fires were measured for a range of elevations starting just below the time-averaged top of the flame and extending to six times this flame height. The mass flow rates in this region of the plume were correlated by the use of a simple plume model. Atmospheric and forced disturbances in the air being entrained increased the entrainment rate of the plume.     

侧向喷射条件下细水雾扑灭水平表面流淌火研究

为探讨侧向喷射条件下细水雾扑灭流淌火的技术可行性,针对水平表面流淌火,在考虑火焰辐射、燃料与垫层之间的对流换热基础上,建立细水雾在开敞空间扑灭流淌火理论模型,实验研究细水雾喷头排数、倾斜角度对火焰形状、火焰温度、灭火机理和灭火时间的影响。结果表明：细水雾冲击燃料加快其流淌时可以增强灭火能力;采用单排喷头水平喷射时可有效抑制一侧火焰且对火焰拉伸作用最强;采用双排喷头水平喷射时,可有效抑制两侧火焰且灭火速度最快;当喷头向上倾斜15°时,细水雾冷却燃料能力减弱并使灭火时间变长。     

Development of a Cup Burner Apparatus for Fire Suppression Evaluation of High-Expansion Foams

We developed a bench-scale high-expansion aqueous foam generator and integrated it into a traditional cup burner apparatus. Foam expansion ratios ranging from 50:1 to 590:1 could be achieved using air flow rates from 16 l/min to 38 l/min and liquid foam solution flow rates of 50 ml/min to 140 ml/min. The flow rates, foam expansion ratios, and cup burner flame extinction behavior with nitrogen provide a suitable bench-scale platform for controlled, systematic investigations of foam/flame interactions for a range of foam properties. Foams with an expansion ratio of 200:1 contain 81% water by mass. When evaporated completely, this amount of water should be insufficient to extinguish propane flames in oxidizer streams with 60% oxygen based on extinction of these flames by water mist. However, the 200:1 foam easily extinguishes a propane flame even in 100% oxygen.     

The physical and chemical action of fire suppressants

This work measures the suppression action of inert gas phase agents in extinguishing an air/liquid organic fuel pool fire. It then gives a predictive model for determining the physical contribution involved in non-inert agent fire suppression. Chemical suppression effectiveness can then be calculated. Further, studying the CF₃Y and SF₅Y (Y = F, Cl, Br, I) series allows quantitation of chemical suppression action of the individual radical moieties. CF₃ is shown to be a strong chemical suppressant while SF₅ is a flame promoter. CF₃Br (Halon 1301) suppression action is 20% physical, 25% chemical due to CF₃, and 55% chemical due to Br. Such quantitation provides guidance in selecting alternative fire suppressants to replace ozone layer depleting halons.     

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.     

七氟丙烷对磷酸铁锂储能电池的灭火效果

以七氟丙烷灭火剂为灭火介质,研究其在不同喷射方式下对磷酸铁锂储能电池火灾的灭火效果。研究发现：不同喷射方式均可在8 s 内扑灭明火,但灭火效果存在一定差异。七氟丙烷垂直喷射时,扑灭明火仅用2 s,且瞬时降温速率最大可达43 ℃/s。抑制复燃时间长,持续升温时间以及持续冒烟时间短。在喷射方式的选择上应尽量保证灭火剂喷口能够覆盖在电池正上方,这样能够最大化发挥七氟丙烷的灭火效果。     

我国氢氟碳化物灭火剂淘汰模式分析

2021年9月,《基加利修正案》（以下简称《修正案》）对我国正式生效,氢氟碳化物的淘汰与管控工作即将开启新的历史篇章。作为哈龙灭火剂的主要替代品,氢氟碳化物灭火剂产品将于2024-2045年接受削减淘汰。本文对《修正案》关于中国淘汰目标以及消防行业氢氟碳化物灭火剂产品生产、消费概况进行了介绍。通过对以往消防行业哈龙整体淘汰模式的梳理与总结,对我国即将开展的消防行业氢氟碳化物整体淘汰模式进行了预估与分析。     

Estimating Thermal Radiation Fields from 3D Flame Reconstruction

The dominant mechanism for the spread of a fire in a building is radiative heat transfer from flames. Therefore, in order to understand how a fire might develop it is necessary to determine the thermal radiation field surrounding a fire. The heat flux at any target location depends upon the flame’s emissive power and the shape factor between the flame’s surface and the target. To determine the shape factor, it is necessary to define the geometry of the flame surface, and develop a method for obtaining the shape factor for that geometry. In this article we describe a method for determining the flame geometry using image-processing techniques. Images of the fire are recorded using two cameras and the flame is reconstructed in three dimensions. Once the surface of the flame has been defined it is possible to calculate the shape factor at a given target. Using the shape factor and an estimate of the emissive power of the flame, the heat flux at the target can be determined. Repeating this process for multiple targets builds a thermal radiation field. Results from applying the method to a controlled flame produced by a diffusion burner show a high correlation between estimated and measured heat flux values.     

Suppression of fuel and air stream diluted methane–air partially premixed flames in normal and microgravity

The effects of fuel and air stream dilution (ASD) with carbon dioxide on the suppression of normal and microgravity laminar methane–air partially premixed coflow jet flames were experimentally and numerically investigated. Experiments were conducted both in our normal-gravity laboratory and at the NASA Glenn Research Center 2.2 s drop tower. Measurements included flame topology and liftoff heights of diluted flames, critical diluent mole fractions for flame blowout, and the radiant heat loss from flames. The flames were also simulated using an axisymmetric unsteady numerical code that utilizes detailed chemistry and transport models. In addition, counterflow flame simulation results were used to examine similitude between the counterflow and coflow flame suppression, and further characterize the effectiveness of fuel stream versus ASD on flame extinction. A smaller relative fuel stream dilution (FSD) extinguishes partially premixed flames (PPFs) with increasing premixing as compared to dilution of the air stream. Conversely, smaller ASD is required to extinguish PPFs as they become less premixed and approach nonpremixed (NP) behavior. Fuel stream diluted PPFs and air stream diluted NP flames extinguish primarily through a reactant dilution effect while fuel stream diluted NP flames and air stream diluted PPF are extinguished primarily by a thermal cooling effect. Normal gravity flames lift off and blow out with a smaller diluent mole fraction than microgravity flames. The difference between the fuel and ASD effectiveness increases as the gravitational acceleration is reduced. Radiation heat losses are observed to increase with increasing diluent mole fraction and decreasing gravity.     

三氟甲烷在灭火系统中的应用

文章介绍了三氟甲烷灭火剂的物理、化学性质，讨论了三氟甲烷灭火系统的结构，工作原理及系统应用中的局限性。