少量聚氨酯泡沫样品从阴燃到有焰燃烧的变化研究

试验主要观察处于阴燃状态的少量聚氨酯泡沫样品的流速、氧气浓度和辐射热通量对气／固界面的影响。因为此试验研究对象是少量聚氨酯汽沫，所以阴燃蔓延以厦转化到有焰燃烧时必须借助于降低热损失并同时增加其氧气浓度。试验中，我们把呈平行六面体的样品竖向放置在风道中。样品的其中三个侧边处在高温状态，第四边暴露在上升气流和辐射中。结果发现，随着气流流速的降低以度氧气浓度的增加，或者增加辐射通量，都会加快其变成有焰燃烧的过程，减少这种变化的延误时间。试验结果表明，炭化部位内部的有焰变化因阴燃作用而出现滞后，这已经通过超声波穿透样品内部得到了证实。笔者这里给出了简化了的分析，证明这种变化可以作为一个气相燃烧程序进行处理。     

Radiant smoldering ignition of plywood

This paper investigates the role of self-heating in the smoldering ignition of 18 mm (three-quarter inch) thick maple plywood exposed to radiant heat fluxes between 6 and 15 kW/m² in the cone calorimeter for up to 8 h. The minimum heat flux for smoldering ignition was experimentally determined to be 7.5 kW/m². This compares favorably to predictions made using classical self-heating theory. The role of self-heating was explored via temperature measurements distributed within the specimens. Elevated subsurface temperature profiles indicated self-heating was an important ignition factor resulting in ignition at depth with smolder propagation to the surface and into the material. The ignition depth was shown to be a function of the heat flux with the depth moving towards the surface as the heat flux increased.     

聚氨酯软泡热解动力学与阴燃点燃特性研究

利用热重-红外联用技术研究了无阻燃聚氨酯软泡在空气气氛下的热解行为,采用遗传算法计算得到"4组分4阶段反应"全局表观动力学模型。在自制小尺寸火灾可燃物阴燃试验台上对无阻燃聚氨酯软泡进行点燃实验研究,分析加热至不同温度下可燃物表面温度变化。结果表明,点燃过程可燃物反应机理与表观热解动力学模型趋于一致,点燃过程分为自加热酝酿期(TC1>200℃)、热解吸热期(200℃265℃),聚氨酯软泡的临界阴燃点燃温度为328℃。     

Critical mass flux for flaming ignition of wet wood

Wood is a common building material and can constitute the bulk of the fuel load in structures. Cellulosic, woody material is also the fuel in a wildland fire. Wood and forest fuels are porous and hygroscopic so their moisture content varies with the ambient temperature and relative humidity. A complete understanding of both structural and wildland fire thus involves understanding the effect of moisture content on ignition. The ignition criterion considered in this work is critical mass flux – that a sufficient amount of pyrolysis gases must be generated for a diffusion flame to establish above the surface. An apparatus was built to measure the critical mass flux for sustained flaming ignition of woody materials for varying environmental conditions (incident heat flux and airflow (oxidizer) velocity). This paper reports the variation of measured critical mass fluxes for poplar with externally applied incident radiant heat flux, airflow velocity, and moisture content. The critical mass flux is seen to increase with increasing levels of moisture content, incident heat flux, and airflow velocity. Future work will focus on modeling these experiments and exploring the changes in critical mass flux with species, thickness, and live fuels.     

Ignition of wood under time-varying radiant exposures

Many studies have utilized a small-scale experimental apparatus such as the cone calorimeter to investigate the piloted ignition of wood exposed to constant levels of incident heat flux; however, there is a deficiency of similar studies related to the non-piloted ignition of wood exposed to time-varying heat fluxes which might represent more realistic fire exposures. In this study, a method was established for producing well-controlled, time-varying exposures using the conical radiant heater of a cone calorimeter. Experiments were conducted in which the incident flux, time to non-piloted ignition, and back-surface temperature of spruce wood were measured. Measured data were used in combination with a numerical heat transfer model to compute the time-dependent temperature distribution through each specimen, and thereby deduce the surface temperature at ignition. From the 30 specimens tested, the average surface temperature for non-piloted ignition of wood was determined to be 521±10 °C. From this surface temperature range, the heat transfer model was used to predict the range of time over which non-piloted ignition was likely to occur for a given time-varying exposure. This procedure was found to produce excellent predictions of ignition time for the time-varying exposures considered in this study. In addition, several existing ignition models were considered, and their suitability for predicting the non-piloted ignition of wood was assessed.     

棉被阴燃火灾实验研究

针对烟头引燃棉被的火灾案例,实验测量烟头的表面温度及热辐射强度,得到烟头表面最高温度可达289 ℃,很容易引燃棉被等可燃物.通过无被套棉被的阴燃实验和有被套棉被的阴燃转明火实验发现,在没有被套的情况下,棉絮间空隙较大,无法积聚热量,只能阴燃而无明火;有被套情况下,产生的热量大部分被阻隔在棉被内部,散热速度较慢,提供了棉被阴燃转明火所需的热量.     

Applied Heat Flux Distribution and Time Response Effects on Cone Calorimeter Characterization of a Commercial Flexible Polyurethane Foam

The burning behavior of a commercial flexible polyurethane foam has been studied in a cone calorimeter using standard ASTM procedures. It is shown that burning takes place in two distinct stages, with the first primarily due to the release of species derived from the isocyanate used in the manufacture of the foam and the second due to species derived from the polyether component. Experiments showed that approximately 40% of the original foam mass is lost during the first burning stage. Due to the low density and high flammability of the foam, burning takes place at a high rate, and experimental times are relatively short. As a result, the heat release rates measured by the cone calorimeter are distorted by the non-uniform heat flux distribution of the cone heater over the sample volume and the instrument’s finite time response. Two heat release models were developed and applied to approximately correct for the effects of finite time response and non-uniform heat flux distribution. Values reported include mass loss rate, heat release rate, heat of combustion, and heat of gasification for each of the burning stages. The measurement results are compared with earlier published findings for similar foams. The results are found to fall into two distinct classes with different heat release rate behaviors. Possible reasons for the differences are discussed.     

Coupled analytical approach to predict piloted flaming ignition of non-charring polymers

Classical thermal theory of piloted ignition is extended by coupling the heat balance at the exposed sample surface and the finite-rate pyrolysis in the material volume. Approximate analytical solutions for the sample temperature are obtained for an arbitrary sample thickness, with the external radiative heating, surface re-radiation, heat of gasification, and the convective heat flux corrected for blowing taken into account. The volatile mass flux is evaluated by integrating the pyrolysis rate throughout the layer, with the assumption of high activation energy limit. Critical mass flux of combustible volatiles is used as the ignition criterion. This enables the ignition temperature to be evaluated instead of being pre-assumed as is done in the classical thermal theory. Coupled analytical approach proposed in this work is verified by comparisons to the numerical solution obtained by the Pyropolis model for the same problem setup. This approach has also been validated by comparisons to published experimental data (ignition temperatures and times to ignition) for three non-charring thermoplastics: polymethylmethacrylate, polyethylene and polypropylene.     

Characterization of the California technical bulletin 133 ignition source and a comparable gas burner

The California Bulletin (CB) 133 upholstery ignition source is based on the use of crumpled newsprint. The present work examined the reproducibility of several aspects of this source when placed on an inert chair mock-up. The tendency of this source to heat the side arms of a chair, the area of the seat back subjected to high heat fluxes, the peak flux there and the flux duration all showed substantial variability. For inherently lesser variability a gas burner is preferred. A gas burner, derived from that developed at the British Fire Research Station, was shaped so as to deposit a similar pattern of heat to that of the CB 133 source. The two sources were tested for comparability both on chair mock-ups and on full-scale chairs made from a wide variety of materials. The results indicate that the gas burner, as used here, is a somewhat less severe ignition source than is the CB 133 igniter.     

Material fire properties and predictions for thermoplastics

Ignition and burning rate data are developed for nylon 6/6, polyethylene, polypropylene and black polycast PMMA in a cone calorimeter heating assembly. The objective is to examine a testing protocol that leads to the prediction of ignition and burning rate for thermoplastics from cone calorimeter data. The procedure consists of determining material properties, i.e. thermal inertia, specific heat, thermal conductivity, ignition temperature, heat of gasification and flame heat flux from cone data, and utilizing these properties in a model to predict the time to ignition and transient burning rate. The procedure is based on the incident flame heat flux being constant in the cone calorimeter which occurs for flames above the top of the cone heater. A constant net flame heat flux of approximately 20 kW/m² for nylon 6/6, 19 kW/m² for polyethylene, 11 kW/mP² for polypropylene and 28 kW/m² for black PMMA is obtained for irradiation levels ranging from 0 to 90 kW/m². The burning rate model is shown to yield good accuracy in comparison to measured transient burning in the cone assembly.     

基于CONE的超高温耐火电缆火灾危险性分析

利用锥形量热仪对超高温耐火电缆在不同辐射功率下的点燃时间（TTI）、热释放速率（HRR）、质量损失速率（MLR）和燃烧残余物进行了研究。研究表明,随着辐射功率增加,耐火电缆的TTI逐渐缩短,HRR和MLR逐渐增大,火灾危险性逐渐增加。超高温耐火电缆在35 kW/m2和50 kW/m2辐射功率下火灾性能指数相比于25 kW/m2分别增加了44.4%和176.5%,火灾增长指数分别增加了30.4%和83.0%。结合理论分析可以得出,耐火电缆的临界辐射功率为3.61 kW/m2、零辐射平均热释放速率为36.5 kW/m2,表现出较低的火灾危险性。     

XPS挤塑板燃烧特性实验研究

进行XPS挤塑板燃点温度测定和辐射引燃实验。研究表明:XPS挤塑板点燃温度约为355℃;0.019 4kW/(m2.s)的辐射热流增量不足以引燃挤塑板试样,当辐射热流大于0.060 4kW/(m2.s)时挤塑板试样能够被引燃,引燃温度分别为362、385℃。辐射引燃实验过程中挤塑板表面温度最大值分别为975、996℃。辐射引燃过程中XPS保温板质量损失速率呈现三个阶段:平缓减少阶段、急剧骤减阶段和相对稳定阶段。质量骤减阶段保温板质量呈明显的线性变化。     

辐射热流下有限厚度PMMA着火特性研究

探究透明PMMA（聚甲基丙烯酸甲酯）厚度和4种不同恒定热流对材料表面温度、质量损失率、着火时间及着火温度的影响。利用反演模型并结合部分实验数据得到PMMA的热物性参数,将其他工况模拟结果与实验测量值及理论分析值相互对比,验证了数值模型和理论分析的准确性和可靠性。结果表明,PMMA着火时间的下降趋势随热流的增大而逐渐变缓。PMMA厚度小于3 mm时,表面温度和质量损失率随厚度增大而减小。PMMA厚度大于3 mm时,着火温度的平均值为（628±20） K,其着火特性几乎不随厚度的变化而变化,故着火温度可作为PMMA着火判据。     

锥形量热计研究木材临界辐射能流和点燃温度

锥形量热计不但可以直接测量出材料的某些燃烧特性数据（如热释放速率、质量损失率、点燃时间等），而且可以根据所测得的数据间接得出材料的其它燃烧特性数据。笔者介绍了一种从锥形量热计测得的数据推导临界辐射能流和点燃温度的方法。     

热塑性高分子材料强制点燃过程模拟与分析

采用锥形量热仪对典型热塑性高分子材料——聚甲基丙烯酸甲酯(PMMA)在不同外部入射热通量下进行了强制点燃的实验研究。在气相反应和固相反应动力学及传递过程分析的基础上，建立了热塑性高分子材料强制点燃过程的数学模型，通过数值分析的方法将点燃数据相关联，得到PMMA强制点燃的点燃时间与临界表面温度的表达式，并计算了PMMA不同外部入射热通量下强制点燃时间及点燃的临界表面温度。模拟计算结果与实验结果的比较表明，二者基本吻合。采用所得到的数据关联式对强制点燃过程的影响因素进行了定量分析。     

Foams and gels as fire protection agents

Fire protection foams and gels are used as temporary barriers to protect samples from incident thermal radiation thus delaying their ignition. Comparative measurements of the thermal behavior of these agents are made using a radiant heat exposure. The results of this comparison clearly show that thermal protection is obtained by two different mechanisms. The conduction-dominated gel operates at near saturation conditions (100°C). The radiation-dominated foam provides complete protection at ambient conditions (20–30°C) for about half the transient duration. Thereafter, the residual foam layer cannot prevent a rapid heat-up of the sample. Tests are performed applying the agents to a flat sample that is then positioned vertically and exposed to radiant heat. The lateral ignition and flame spread test (LIFT) apparatus is used to determine the ignition delay time for the gel. Due to the sample size restrictions associated with the LIFT apparatus, data collection for foams is not possible. Therefore, measurements are conducted in a Radiant Exposure Apparatus (REA) which allows for larger samples subjected to uniform heat fluxes up to 18 kW/m². The data gathered from the LIFT and REA are compared to establish the consistency between the two measurement sets.     

An experimental evaluation of critical surface temperature as a criterion for piloted ignition of solid fuels

With a view to developing a simple engineering method for the prediction of piloted ignition, the validity of the critical surface temperature criterion for piloted ignition is examined experimentally for seven thermoplastic materials. The results indicate that the surface temperature at piloted ignition for each material studied varies by ±15 K or less. As such, the surface temperature criterion appears to be suitable for engineering calculations.

Analysis of time-surface temperature histories shows that the radiant heat source temperature has a significant effect on the material heating over the range of source temperatures utilized (700–1050 K). The variations in material heating are of sufficient magnitude to cause changes in ignition times by a factor of two or more for different heat sources present in typical fire scenarios.

Our current level of understanding of piloted ignition is shown to be insufficient to support extrapolation procedures to determine the minimum incident radiant flux required for piloted ignition. An experimental approach to determination of the minimum radiant flux required for piloted ignition is demonstrated to be feasible.     

EcoSmart Fire as Structure Ignition Model in Wildland Urban Interface: Predictions and Validations

EcoSmartFire is a Windows program that models heat damage and piloted ignition of structures from radiant exposure to discrete landscaped tree fires. It calculates the radiant heat transfer from cylindrical shaped fires to the walls and roof of the structure while accounting for radiation shadowing, attenuation, and ground reflections. Tests of litter burn, a 0.6 m diameter fire up to 250 kW heat release under a Heat Release Rate (HRR) hood, with Schmidt-Boelter heat flux sensors in the mockup wall receiving up to 5 kW/m² radiant flux, in conjunction with Fire Dynamic Simulator (FDS) modeling verified a 30% radiant fraction, but indicated the need for a new empirical model of flame extinction coefficient and radiation temperature as function of fire diameter and heat release rate for use in ecoSmartFire. The radiant fluxes predicted with both ecoSmartFire and FDS agreed with SB heat flux sensors to within a few percent errors during litter fire growth. Further experimental work done with propane flame heating (also with 30% radiant fraction) on vertical redwood boards instrumented with embedded thermocouples validated the predicted temperature response to within 20% error for both models. The final empirical correlation for flame extinction coefficient and temperature is valid for fire diameters between 0.2 and 7.9 m, with heat release rates up to 1000 kW. From the corrected radiant flux the program calculates surface temperatures for a given burn time (typically 30 s) and weather conditions (typically dry, windy, and warm for website application) for field applications of many trees and many structural surfaces. An example was provided for a simple house exposed to 4 burning trees selected on a Google enhanced mapping that showed ignition of a building redwood siding. These temperatures were compared to damage or ignition temperatures with output of the percentage of each cladding surface that is damaged or ignited, which a homeowner or a landscaper can use to optimize vegetation landscaping in conjunction with house exterior cladding selections. The need for such physics-based fire modeling of tree spacing was indicated in NFPA 1144 for home ignitability in wildland urban interface, whereas no other model is known to provide such capability.     

Heat feedback to the fuel surface of a pool fire in an enclosure

As a part of an effort to determine the energy balance at the pool fire surface in compartments, a series of fire experiments were conducted to study heat flux of the flame in a vitiated environment formed with air and combustion products gases. This paper presents experimental results of the burning behaviour of a heptane pool fire in a reduced scale compartment equipped with a mechanical ventilation network. Measurements of heat fluxes, fuel mass loss rate, oxygen concentration and temperature are performed for heptane fires of 0.26 and 0.3 m diameter pans at different ventilation flow rates. An original method to separate effects of the radiant heat flux of the flame and of the external heat feedback to the fuel surface is developed. This was achieved by using an additional heat flux measurement located under the pool fire. A correlation was also developed to determine the temperature rise on the plume centerline in the compartment as a function of the heat release rate. The results indicate a decrease in the fuel mass loss rate, flame temperature and heat fluxes to the fuel surface as the oxygen concentration measured near the fuel decreases by varying the air refresh rate of the compartment. The flame radiation fraction shows a similar behaviour, whereas the convective fraction of the flame heat flux increases when oxygen concentration decreases. Based on these experimental findings, it was discussed that any classification of the burning regime of a pool fire should consider both the effects of pan diameter and the burning response to vitiated air.     

海洋环境对软质聚氨酯泡沫材料燃烧特性影响的实验研究

对常见软垫家具填充物软质聚氨酯泡沫（FPUF）的燃烧特性及其燃烧烟气中窒息性气体组分生成量的变化特性展开实验研究,并采用有效剂量分数FED 模型对烟气毒性进行评价。结果表明：无论是在强制点火模式抑或是非强制点火模式中,不同盐湿度雾滴沉降作用下FPUF 热释放速率（HRR）曲线的发展规律基本相似。FPUF 的着火时间在无强制点火模式中随着空气中雾滴盐度的增加而延长,而在强制点火模式中则基本相近;不同盐湿度空气中FPUF 燃烧生成的各烟气组分生成量的变化规律具有相似性,当量比Φ 值在0.9~1.6 时,高盐湿度空气对各烟气组分生成量影响较大。并且高盐湿度空气中NaCl 的存在将促进窒息性气体组分的生成;高盐湿度空气中盐度的增加对于FPUF 燃烧产生的烟气毒性具有一定的增强作用。