阻燃硬质聚氨酯泡沫塑料垂直火蔓延特性研究

通过一步合成法制备了阻燃硬质聚氨酯泡沫，自主搭建保温材料火蔓延实验台，采用中小尺寸实验对比研究了阻燃及非阻燃硬质聚氨酯的垂直火蔓延特性，分析了火焰结构特性、火蔓延速度、火焰温度、质量损失速率等参数的变化规律。结果表明，火蔓延过程中，材料表面均出现了炭化现象，垂直双面燃烧过程中聚氨酯纯样RPUF燃烧最剧烈，阻燃剂膨胀石墨(EG)、次磷酸铝(AHP)和二乙基次膦酸铝(ADP)的加入，抑制了材料的燃烧和蔓延，使材料燃烧的火蔓延速度、质量损失速率及温度等参数都相应降低。RPUF/AHP5垂直双面火蔓延过程中，火焰稳定性差，在20 s后出现熄灭现象，原因是阻燃剂次磷酸铝(RPUF/AHP5)受热挥发出难燃气体。AHP降解后形成的含磷化合物可促进聚氨酯分子链成炭，导致产生熄灭现象。而RPUF/ADP5火蔓延过程中，同样出现了熄灭现象，其熄灭的程度低于阻燃剂次磷酸铝(RPUF/AHP5)试样。RPUF/EG5火蔓延过程中试样表面温度存在两个峰值，由于RPUF/EG5燃烧生成的炭层不稳定所致。当温度高于400℃时炭层被迅速氧化，热量穿透炭层使内部未燃样品热解，生成温度的第二个峰值。     

不同宽度及密度的保温材料EPS的火焰蔓延及燃烧特性

对密度为18和25 kg/m3的保温材料模塑聚苯乙烯(EPS),在不同宽度下进行小尺寸燃烧特性实验,考察了池火区长度、火焰高度及火蔓延速度等. 结果表明,EPS火焰蔓延过程中,火焰形态包括典型形态、逆向形态及重合形态;宽度为8 cm的试样火焰蔓延稳定性较差,逆向形态及重合形态更多. 不同宽度、密度18 kg/m3的EPS的平均池火长度均大于密度25 kg/m3的EPS,主要是由于EPS密度越小其火蔓延速度越大. 密度18 kg/m3的EPS由于孔隙中空气的助燃作用,火蔓延速度约为密度25 kg/m3的EPS的2倍. EPS材料表面火焰区平均火焰高度主要受宽度影响,而池火区平均火焰高度主要受池火区长宽比影响.     

可膨胀石墨和碳纳米管对PMMA火蔓延特性的影响

通过熔融共混法制备了9种PMMA复合阻燃材料,对其进行小尺寸的水平火蔓延实验研究,对比分析了可膨胀石墨(EG)和碳纳米管(Carbon Nanotube, CNTs)阻燃剂的加入对材料燃烧特性的影响,主要研究了火蔓延速度、火焰形态、固相温度、质量损失速率等火蔓延特性参数变化规律。结果表明,EG能产生阻燃效应,随EG含量增加,复合材料的火蔓延速度、质量损失速率、表面热流密度均有所减小;CNTs表现出拮抗和协同阻燃的复合效应。EG含量较低时,添加1% CNTs反而会使火蔓延速率加快;随着EG含量增加,拮抗作用逐渐消失,最后表现为协同阻燃,原因是CNTs的高热导率、“灯芯效应”促进表面燃烧作用和EG/CNTs体系阻燃性之间存在竞争关系;添加EG和CNTs前后,火蔓延过程中表现出明显不同的燃烧行为,未添加阻燃剂前PMMA会产生熔融滴落物积聚成池火,表现为明显的热塑性材料燃烧特征;加入EG和CNTs后则会形成碳层,表现为明显的可碳化材料燃烧特征。     

倾斜角对液体燃料润湿条件下砂床表面火蔓延的影响

利用纹影系统、CCD相机以及K型热电偶对正丁醇润湿条件下不同角度的砂床表面火蔓延特性进行了研究,分析了不同砂床表面倾角对火蔓延的影响机理。研究结果表明:正丁醇润湿条件下变角度砂床表面火焰是稳定匀速蔓延的,向上蔓延时,火焰的高度、黄色发光区以及蔓延速度随着倾角的增加而增大;向下蔓延时,火焰的高度、黄色发光区以及蔓延速度随着倾角的增加而减小;蔓延火焰前方存在预热区,且预热区随表面倾角的增大而增大:砂层内部存在热边界层,且砂床热边界层厚度随表面倾角的增加而减小。得到的火蔓延特性及燃烧机理为此类液体燃料的储存、使用以及环境保护提供了一定的科学依据。     

不同点火位置时乳胶泡沫火蔓延特性

在边缘点火和中间点火条件下对多孔乳胶泡沫进行小尺寸燃烧,研究了不同点火位置时火焰的蔓延过程和规律,考察了材料表面温度分布、火蔓延速率和火焰高度随时间的变化.结果表明,边缘和中间点火时,平均火蔓延速率分别为0.42和0.24cm/s,蔓延至整个材料表面的时间分别为84和74s,最大火焰高度分别为68.6和82.7cm.随火焰区不断增大,火焰温度不断升高,传递给未燃区的热量增多,加速了材料热解,火蔓延速率增大.     

点火位置对乳胶泡沫水平火蔓延规律的影响

为研究点火位置对乳胶泡沫材料水平方向火蔓延规律的影响。搭建小尺寸实验平台,在距离材料中心点0（x1）、3.54 cm（x2）、7.08 cm（x3）、10.62 cm（x4）、14.16 cm（x5）、17.70 cm（x6）位置处点火,研究了试样表面温度、质量损失、火焰高度、火蔓延速度等特性参数的变化规律。结果表明,随着点火位置由材料中心点向边缘点移动,平均火蔓延速度分别为0.24、0.23、0.19、0.31、0.42、0.51 cm·s^-1,呈现先减小后增大的规律;x3点火位置时的平均火焰高度较低,燃烧时间较长,平均质量损失速率较低,主要与火蔓延过程中的热量传递方式有关。研究结果显示了乳胶泡沫的火蔓延过程,得到了点火位置对火蔓延的影响规律。     

点火位置对乳胶泡沫水平火蔓延规律的影响

为研究点火位置对乳胶泡沫材料水平方向火蔓延规律的影响。搭建小尺寸实验平台,在距离材料中心点0(x1)、3.54 cm(x2)、7.08 cm(x3)、10.62 cm(x4)、14.16 cm(x5)、17.70 cm(x6)位置处点火,研究了试样表面温度、质量损失、火焰高度、火蔓延速度等特性参数的变化规律。结果表明,随着点火位置由材料中心点向边缘点移动,平均火蔓延速度分别为0.24、0.23、0.19、0.31、0.42、0.51 cm·s~(-1),呈现先减小后增大的规律;x3点火位置时的平均火焰高度较低,燃烧时间较长,平均质量损失速率较低,主要与火蔓延过程中的热量传递方式有关。研究结果显示了乳胶泡沫的火蔓延过程,得到了点火位置对火蔓延的影响规律。     

乳胶泡沫引火位置对火蔓延特性的影响

利用自行搭建的小尺寸实验平台,开展了对不同点火位置的乳胶泡沫材料燃烧过程的对比实验,通过对火蔓延过程中的部分重要参数（如最大火焰高度、火蔓延速度和蔓延过程中样品表面温度变化等）的测定,分析了点火位置不同时,乳胶泡沫材料的火蔓延特性。结果表明：边缘点火和中间点火条件下,最大火焰高度分别为397和491 mm,火蔓延速度分别为1.8和0.97 mm·s^-1;边缘点火时的乳胶泡沫材料表面火蔓延过程中的温度低于中间点火情况下。     

乳胶泡沫引火位置对火蔓延特性的影响

利用自行搭建的小尺寸实验平台,开展了对不同点火位置的乳胶泡沫材料燃烧过程的对比实验,通过对火蔓延过程中的部分重要参数(如最大火焰高度、火蔓延速度和蔓延过程中样品表面温度变化等)的测定,分析了点火位置不同时,乳胶泡沫材料的火蔓延特性。结果表明:边缘点火和中间点火条件下,最大火焰高度分别为397和491 mm,火蔓延速度分别为1.8和0.97 mm·s~(-1);边缘点火时的乳胶泡沫材料表面火蔓延过程中的温度低于中间点火情况下。     

高原与平原环境下PS板宽度及放置角度对其燃烧火焰结构和火蔓延特性的影响

在高原环境(低压低氧)的拉萨和平原环境(常压常氧)的合肥,研究了不同宽度(W=4, 8, 12, 16 cm)的保温材料在不同放置角度(0o, 15o, 30o, 90o)下的火焰结构及火蔓延特征. 结果表明,外界环境对火焰角度、池火长度、火蔓延速度(vf)均有影响,相同放置角度下相同宽度的模塑聚苯乙烯泡沫板(EPS)和挤塑聚苯乙烯泡沫板(XPS)试样在拉萨的火焰角度均大于合肥;燃烧剧烈的XPS对火焰角度的影响明显高于EPS,池火长度随材料宽度及放置角度不同呈现分段递增、逐渐增长、流淌滴落等特点;在拉萨试样更易出现二次点燃现象;无论在拉萨还是合肥,90o放置角度下,EPS和XPS试样vf均随材料宽度增加呈先增加后减小的特点,火蔓延过程中火焰辐射热通量受宽度影响,宽度较小时vf遵循vfμ1-e-kW,宽度较大时遵循vfμTh4.     

不同放置角度的建筑装饰材料PMMA的火焰蔓延特性

为揭示建筑装饰材料聚甲基丙烯酸甲酯(有机玻璃,PMMA)在不同放置角度下的火焰蔓延特性,通过自主搭建的小尺寸火焰蔓延实验平台,研究了宽3 cm、厚2 mm的PMMA试样在不同放置角度下的火焰蔓延特性. 结果表明,放置角度对PMMA火焰蔓延过程中热解区域及预热区长度影响很大,由15°到30°及由?60°到?75°时(顺流火焰蔓延时放置角度为正,逆流火焰蔓延时放置角度为负),平均火焰倾角增加幅度最大. 顺流火焰蔓延的火焰长度随放置角度增加先略减小后逐渐增加,逆流火焰蔓延的火焰长度随放置角度的绝对值增加而略减小. 放置角度由0°到15°时,顺流火焰蔓延的平均速度呈跃变增长,逆流火焰蔓延的平均速度随放置角度绝对值增加而略降低.     

The effects of angular orientation and ultraviolet aging on ETFE wire flame spread

This paper considers the solid phase heat conduction along with the effect of ultraviolet (UV) aging on the flame spread and separately discussed the upward and downward flame spread. The 0.15‐mm‐thick ethylene‐tetrafluoro‐ethylene (ETFE) insulated with a 0.5‐mm‐diameter copper core used in the paper. The flame spread was measured at various inclined angles (vertical ± 90^○, to horizontal 0^○) in the directions of gravity assistance (up) and gravity opposition (down). The ETFE was categorized into two groups: the unaged ETFE (ETFE‐U) and the UV aged ETFE (ETFE‐A). The kinetic parameters of samples were obtained from thermogravimetric analysis (TGA) test. The flame spread experimental results showed that the bigger the absolute inclined angle, the higher the flame spread rate. Besides, the effect of UV aging on the upward spread is greater than that of the downward spread. A theoretical system was established through the flame spread experiments and TGA test. The heat flux and the flame spread rate of upward and downward equations were presented to reveal the effects of solid conduction, orientation, inclination, and UV aging on wire flame spread.     

Image analysis of flame behavior for polyolefins and polystyrene in vertical flame test

Although the UL-94 vertical flame test is often used to evaluate the flammability of polymers based on ignition time and combustion duration parameters, a significant amount of information regarding the time course of combustion is difficult to analyze in detail. Herein, image analysis of the time course of the upper and lower end heights, total area, and color division of flame was performed for polyolefins and polystyrene with different molecular weights in the vertical flame test. The combustion process was classified into two stages: before and after the first drip. In the first stage, the upward spread velocity, oscillation, and color of flame were analyzed. It was assumed that the difference in the fuel production rates or thermal decomposition products depends on the molecular structure. In the second stage, the melt flowability, flame position, and combustion continuity differed vastly depending on the molecular structure or molecular weight.     

Natural Buoyant Turbulent Diffusion Flame near a Vertical Surface

The structure and dynamics of a natural buoyant turbulent diffusion flame near a vertical surface with combustible gas exhaustion are numerically studied by using the FDS model and computer code. The flame is considered near the surface through which gaseous propylene is injected with a prescribed flow rate. Requirements are determined for the grid cell size in the near-wall region, which ensure sufficient spatial resolution of the boundary layer structure. It is shown that the predicted value of the total heat flux at the surface agrees with the measured results. Investigations of ignition and combustion of a vertical plate of non-charring thermoplastic (polymethylmetacrylate) with allowance for the material pyrolysis reaction show that the ignitor parameters determine the duration of the transient period, but weakly affect the growth of the heat release rate and the height of the pyrolysis region at the stage of developed burning. Significant effects of the ignitor shape, size, and temperature, as well as lateral entrainment of air on the velocity of the upward flame spread rate over the plate surface and on the shape of the pyrolysis front are revealed. The existence of critical parameters of the ignitor separating flame decay from developed burning is demonstrated. Three flame spread regimes with different pyrolysis front shapes are identified.     

A numerical model for flame spread along combustible flat solid with charring material with experimental validation of ceiling flame spread and upward flame spread

This paper gives a numerical model for flame spread along combustible flat solid with charring materials. The presented model consists of a one‐dimensional flame spread model coupled with a one‐dimensional pyrolysis model. The existing experimental data (the ceiling flame spread beneath medium density fibreboard) are used for comparison to validate the model. In addition, the model can also be used to predict upward flame spread; only some expressions are changed. A comparison with full‐scale experimental data on the upward flame spread over plywoods from the literature is performed. The results obtained from numerical simulations using the model are consistent with these two kinds of experimental tests. Thus, the presented model is appropriate for modelling not only the ceiling flame spread, but also the upward flame spread. Copyright © 2007 John Wiley & Sons, Ltd.     

Comparison of flame propagation properties of petroleum coke and coals of different rank

Ignition and flame propagation characteristics of 18 kinds of coal and a petroleum coke were investigated through a laser ignition experiment. Flame stability was strongly influenced by amount of volatile matter and pyrolysis rate. Lean limit of flame propagation was strongly influenced by amount of volatile matter. Flame propagation was observed when pyrolized volatile matter was mixed with surrounding air or oxygen, until the concentration of pyrolized volatile matter reached a constant value. Flame propagation velocity was strongly influenced by pyrolysis rate. As the pyrolysis rate increased, the flame propagation velocity increased. The flame propagation velocity of petroleum coke was higher than that of coal with the same volatile content. The flame propagation of petroleum coke was superior to what was expected based on the volatile content, primarily because the high pyrolysis rate caused a shorter ignition delay than what would be expected given the volatile content. A database for the lean limit of flame propagation was used to develop a flame stability model to estimate lean flammability of a large-scale burner. The model could predict the effect of the coal rank, the particle diameter distribution for lean flammability limit. The estimated lean flammability limit of petroleum coke (volatile content 11.5%) was equal to that of lv bituminous coal with volatile content of about 15%.     

Study of pyrolysis and upward flame spread on charring materials—Part I: Experimental study

In this paper, we describe the results from an experimental campaign, focused on vertical upward flame spread over a charring material. First, for validation purposes of simulation tools, we report on cone calorimeter results for square (9.8cm×9.8cm), 1.65 cm thick, medium density fibre samples, mounted horizontally. Temperature is shown at the surface and at different depths. The mass of the sample is continuously measured. From the raw data, we derive the temporal evolution of the mass loss rate due to pyrolysis. Different externally imposed heat fluxes are investigated (20, 30 and 50kW/m²), onto dry and wet material. Afterwards, for the configuration of two particle board plates (0.025 m thick, 0.4 m wide and 2.5 m high), vertically mounted face to face is considered. Two different horizontal spacing distances between the two plates are studied (30.5 and 10.5 cm). The purpose of this set‐up is to investigate the vertical upward flame spread with strong radiative heat feedback. To that purpose, the temporal evolution of surface temperature is measured over the height of the plates. The measurement data are used to test a pyrolysis model in numerical simulations. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of shielding rates on upward flame spread over extruded polystyrene foam in vertical channel and heat transfer mechanism

Fire hazard of extruded polystyrene (XPS) thermal insulation materials has aroused public concern. In order to develop flame spread theory and the guideline for fire risk assessment of XPS, an experimental study on upward flame spread behavior and heat transfer mechanism of XPS in a vertical channel with different frontal shielding rates was conducted. Maximum temperature at the place 2 cm from XPS surface and at the center of channel first increase and then decrease as the shielding rate rises. The former is higher than the latter. Experimental value of average flame height rises as the shielding rate increases. A model for predicting the flame height is built, and the predicted results are consistent with the experimental results. Moreover, the relation between flame height and pyrolysis height under different shielding rates is obtained. The flame spread rate rises as the shielding rate increases. A prediction model of flame spread rate is established, and its prediction results are more accurate compared with those from previous models. The model also predicts that radiative heat transfer is the dominant heat transfer mode, accounting for 93% of the total heat transfer. This work is beneficial for fire risk assessment and fire safety design of building façade.