Numerical model of upward flame spread on practical wall materials

The focus of this paper is the development of a thermal, finite difference numerical model to describe one-dimensional upward flame spread on practical wall materials. Practical materials include composite materials and those that char, in addition to clean burning, homogeneous materials. A set of equations used in the model is developed and the methods for obtaining necessary “fire properties” are discussed. Some of the particular features of the model include the use of a correlation for flame heat feedback and the use of an experimentally measured mass loss rate to incorporate the burning characteristics of practical materials. A comparison of the numerical predictions with the experimental results for flame heights and temperatures are shown for Douglas fir particle board. The model correctly predicts trends but underpredicts the flame heights and pyrolysis height in the cases tested. Two additional cases are shown for materials for which experimentally measured heat release rate data are used in place of the mass loss rate data. The flame and pyrolysis height predictions are in much better agreement for these cases. Further efforts to obtain material property data that is appropriate for flame spread modeling is indicated by this work.     

CFD and experimental studies of room fire growth on wall lining materials

CFD simulation and experimental tests have been carried out to study the room corner fire growth on combustible wall-lining materials. In the CFD simulation, the turbulent mass and heat transfer, and combustion were considered. The discrete transfer (DT) method was employed to calculate the radiation with an absorptivity and emissivity model employed to predict the radiation property of combustion products including soot, CO₂ and H₂O, which are usually the primary radiating species in the combustion of hydrocarbon fuels. The temperature of the solid boundary was determined by numerical solution of the heat conduction equation. A simple and practical pyrolysis model was developed to describe the response of the solid fuel. This pyrolysis model was first tested against the Cone Calorimeter data for both charring and non-charring materials under different irradiance levels and then coupled to CFD calculations. Both full and one-third scale room corner fire growths on particle board were modelled with CFD. The calculation was tested with various numbers of rays and grid sizes, showing that the present choice gives practically grid- and ray number-independent predictions. The heat release rate, wall surface temperature, char depth, gas temperature and radiation flux are compared with experimental measurements. The results are reasonable and the comparison between prediction and experiment is fairly good and promising.     

Numerical studies on heat release rate in a room fire burning wood and liquid fuel

Heat release rates of burning gasoline and wood fires in a room were studied by computational fluid dynamics (CFD). Version 5.5.3 of the software Fire Dynamics Simulator (FDS), which is the latest one available, was selected as the CFD simulation tool. Predicted results were compared with two sets of reported data from full-scale burning tests. In the two sets of experiments, the scenarios were set at gasoline pool fire and wood chipboard fire with gasoline respectively. The input heating rate of gasoline pool fire based on experimental measurements was used in the first set of experiments. Three scenarios G1, G2 and G3 with different grid systems were simulated by CFD. The grid system of scenario G2 gave more accurate prediction, which was then used to study the second set of experiments on wood chipboard with gasoline. The combustion model in FDS was used in wood chipboard fire induced by gasoline pool. The wood chipboard was allowed to burn by itself using the pyrolysis model in FDS. The effects of the boundary conditions on free openings for the same set of experiments were studied by three scenarios SOB1, SOB2 and SOB3. Boundary condition SOB2 gave more reliable prediction among the three boundary conditions. Two other scenarios on the effect of moisture content of wood were also studied. The predicted HRR curve was found to agree better with experiment in using SOB2.     

An approach to modeling wall fire spread in a room

An attempt is made to develop a framework for modeling wall fire spread in a room. The zone methodology for treating developing room fires is used, and its characteristic layer equations are discussed. A review is made of studies on the rate of burning and spread on vertical surfaces. Both of these phenomena are shown to depend on the incident radiative heat flux and the local oxygen concentration. Functional expressions are suggested, and a strategy is presented for incorporating these component analyses into a wall flame spread model. The goal of this model would be to assess the risk of rapid fire growth (flashover) relative to wall property data found through fundamental principles and through emperical fire test methods.     

Estimation of chemical heat release rate in rack storage fires based on flame volume

Quantification of heat release rate is crucial to many fire research works. Under certain conditions, such as very large fires and fire tests with sprinklers, measurements of fire heat release rate can be a challenging problem. This study attempted to develop a methodology of estimating chemical heat release rate using flame volume. This method is based on the theory that heat release rate per unit flame volume is relatively invariant, as long as the combustion is controlled by diffusion in buoyant fires under well-ventilated conditions. Test data were examined from a variety of fire experimental conditions to evaluate the proposed method. The results demonstrate that the flame-volume based method can provide reasonable estimation of heat release rate compared to oxygen-consumption based method.     

Burning rate and flame heat flux for PMMA in a cone calorimeter

Ignition and burning rate data are developed for thick (25 mm) black Polycast PMMA in a cone calorimeter heating assembly. The objective is to establish a testing protocol that will lead to the prediction of ignition and burning rate from cone data. This is done for a thermoplastic like PMMA. The incident flame heat flux, for irradiation levels of 0–75 kW/m², is found to be approximately 37 kW/m² for black PMMA. Its constancy is shown due to the geometry of the cone flame. Also, this flame is shown to be nearly transparent for cone irradiance (>90%). The heat of gasification of the black PMMA used is found to be approximately 2.8 kJ/g; higher than values reported for other PMMA samples. This is believed to be due to differences in molecular structure or pigmentation of the PMMA tested. A burning rate model is demonstrated to yield good accuracy in comparison to measured transient values. An exact solution is found for constant heat flux conditions.     

Experimental measurements of upward flame spread on a vertical wall with external radiation

The overall objective of the project is to gain an understanding of the flame spread phenomenon under simulated surrounding fire conditions. In this phase of the project, emphasis is placed on obtaining experimental data for upward flame spread with applied external radiation on practical wall materials. A second phase (not yet reported) is the development of a numerical flame spread model and the experimental results presented here will be used for comparison with model predictions. Flame height, and in some cases pyrolysis height, were recorded as functions of time for 120 cm×30 cm samples; and these data were used to quantitatively investigate the effect of external radiation on several materials. Infrared heating panels were used to supply radiant fluxes of up to 15 kW/m² to the sample. Many wood-based materials do not exhibit flame spread to the top of the sample when ignited without applied external flux. With moderate levels of external radiation (5–10 kW/m²), many of these materials sustained flame spread to the top of the sample. With increasing external radiation levels, flame spread was also more rapid. A comprehensive series of tests was run on particle board to investigate the effect of igniter strength, preheat of the sample, and sample thickness. Igniter strength was not a significant factor and did not cause the flame spread to be sustained; the effect of preheat, even at moderate levels of radiant flux, was important; and sample thickness had a slight effect, with thicker samples burning slower. Total heat feedback to the sample was measured and the maximum values for various samples are reported. Experimental data obtained in this project will be used to aid in the development and validation of a numerical flame spread model.     

加大加快新型墙材推广应用步伐

经过１２年的努力 ,我国新型墙材比例已由当年的４．３２ %提高到２０００年的２８ % ;自１９９１年～１９９９年累计节约生产能耗４７６１．３５万ｔ标煤 ,推广新型墙材建筑４．３６亿ｍ２,推广节能建筑９４２１．５４万ｍ２,节约采暖能耗８１１１．１７万ｔ标煤 ,节约土地４３．４万亩（１亩＝６６７ｍ２） ,利用废渣２．３亿ｔ,获得了显著的社会效益和经济效益。然而墙改工作任重而道远 ,目前还存在不少困难和问题。当前最突出的问题是新型墙材产品在建筑上推广应用难的局面没有根本改变 ,尤其是在大规模住宅建筑中推广应用的步伐还不快…     

Computer program for calculating the daylight level in a room

A computer program has been developed that calculates the total quantity of daylight provided to an arbitrary place in a room by direct incident daylight, by reflected daylight from opposite buildings and ground, and by interreflected daylight from walls, ceilings and floors. Input data include the geometry of the room, the reflection coefficients of walls, ceiling, and floor, and the dimensions of the building itself and surrounding buildings.The program calculates daylight levels at all relevant places in the room. The calculation of reflected light is based on view factors and total exchange factors between rectangular surfaces, and we assume that all light is reflected diffusely from all surfaces. Using this approach we can compute the influence of reflectances from surfaces whose colors differ from that of the wall (such as doors).The program contains the formulae describing the distribution of sky luminance for CIE Standard Overcast Sky [1] and CIE Standard Cloudless Sky [2]. For a cloudless sky, the program computes the shadow patterns of the surrounding buildings. It is also possible to calculate the illuminance provided by artificial lighting.     

挤塑聚苯乙烯泡沫塑料热释放速率试验研究

通过对挤塑聚苯乙烯泡沫塑料(XPS)进行热释放速率的试验,对其燃烧性能进行了研究.在此基础上,与现行常用的燃烧性能试验方法对于热塑型泡沫塑料燃烧性能的合理性进行对比分析.通过分析比较,客观评价热释放速率试验方法的可行性,为制定建筑材料燃烧性能分级的相关标准提供参考.     

受限空间木垛火的热释放速率分析与研究

通过理论分析、试验研究以及拟合分析相结合的手段研究了木垛火在受限空间内的燃烧特性,着重总结了受限空间木垛火在不同阶段的燃烧特性及热释放速率的增长规律,并且讨论了热释放速率曲线的叠加问题,给出了热释放速率以一阶指数增长的数学关系,以及t2增长的火灾增长系数.     

薄型材料竖向贴壁火蔓延的试验研究

薄型材料竖向贴壁火蔓延试验研究，主要是对常见材料的贴壁火蔓延形态、火蔓延速度、温度分布进行测试，并对预热段和热解段进行了探讨。     

Effect of fuel soaked time and fuel ratio on the flame spread rate over a porous bed wetted with liquid fuel

An experimental investigation was conducted to explore the rate of flame spread over an unconsolidated porous bed of sand wetted with 2-propanol under a range of operating conditions. Video cinematography was employed to determine the rate of flame spread and characterise the combustion behaviour of the system. The rate of flame spread strongly correlated with: (i) the ratio of fuel volume to the weight of the sand bed, referred to as FR, and (ii) the flame initiation delay, referred to as FID. The rates of flame spread associated with no initiation delay cases were found to rise with increasing FR while for cases associated with any given flame initiation delay the rate of flame spread was found to decrease with increasing FR. In addition, the rate of change in flame spread was observed to be different for beds containing finer particles in comparison to those containing coarser ones.     

通风对受限空间燃油热释放率的影响

在全尺寸热释放率实验台的基础上,搭建了不同通风形式下的油池火燃烧实验台,研究了在受限空间中风速、油盘面积、风口与油盘距离、风口朝向角度及风口直径等对乙醇燃烧过程中热释放率的影响。结果显示:在第1、第2阶段中,热释放率随风速的增大而增大,随风口朝向角度与45°的差值逐渐增大而减小,随风口直径增大而减小;热释放率峰值随油盘面积的增大而增大,随风口与油盘距离的增大而减小。     

On the significance of transient heat release rate excursions above a set limit

When a heat release rate limit for a consumer product is set by a regulatory agency, it is of interest to know whether small excursions above that limit, such as may occur due to production line variability, represent a disproportionate increase in fire hazard. This paper presents a methodology to examine this issue. The heat release rate curve of the object is described by a Gaussian time variation; a perturbation peak, also Gaussian, is added to this main peak. The impacts of the perturbation peak on the build up of hazardous conditions in a room fire (where the object is the only item burning) and on the threat of ignition of secondary items are examined. For the peak heat release rate domain studied here, only the ignition threat is significantly affected by the perturbation peak. The results quantify the trade-off between the height of the perturbation peak and its duration for a fixed percentage of increase in the room area threatened by secondary object ignition. The results show that the increased threat is of the same order as the relative perturbation in heat release rate.     

单个小汽车火灾热释放速率影响因素分析

系统调研国内外单个小汽车全尺寸火灾试验结果,对点火时间、持续燃烧时间、火灾发展到HRR峰值所用时间和火灾HRR峰值进行统计分析,重点分析热释放速率的影响因素。结果表明,影响小汽车火灾试验结果的因素主要有:小汽车本身的燃烧性能、点火部位和点火方式、试验空间的围合状态以及油箱材质和油料数量等。     

集热墙式附加阳光间的冬季对流供热特性研究

将被动式太阳能建筑中的普通特朗伯集热墙系统的空气间层深度增大,形成附加阳光间。本文利用Design Builder软件的CFD模块对比分析了大空腔附加阳光间和小空腔空气间层的对流特性,并据此计算分析其冬季利用太阳能采暖供热量。结果表明:(1)附加阳光间的进深达到1.2 m可使出风口速度相对于空气间层0.1 m的集热墙提高12%,室内空间中心点温度提高约1.0℃,对流供热量提高30%以上;(2) 1.2 m进深附加阳光间情况下,集热墙大风口组合相比小风口组合对出风口速度和对流供热量影响不大,但室内空间中心点温度略有降低。     

一种新型防火衬纸防火性能的研究

采用锥形量热仪对一种新研制的防火衬纸的防火隔热性能进行了比较全面的研究 ,研究结果表明 ,该防火衬纸具有较好的防火性能 ,具有实用价值     

Flame size, heat release, and smoke points in materials flammability

The concept of using the flame size as a surrogate for heat release rate (HRR) has been explored. A technique for simultaneously obtaining the HRR, flame size (height and area), and the smoke point of the flame solely from visual images has been developed. The technique has been demonstrated on gaseous flames (methane, propane, ethylene, and propylene) and explored for five burning solid polymers. Estimations of the flame area from images of the stoichiometric contour based on the CH chemiluminescent region of the flames yielded a good linear correlation with measured HRR, valid for all of the gaseous and solid compounds tested, for burning rates above or below the smoke point. In contrast, flame heights and luminous images (i.e., from soot emission) were confounded by differing behavior above and below the smoke point.