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.     

凹型结构下保温材料EPS典型垂直火蔓延特性对比研究

本工作通过自主搭建小尺寸火蔓延的实验平台,研究了凹型结构中保温材料EPS垂直向上和向下火蔓延特性。对比分析了火焰结构特性、火蔓延速度、质量损失速率、火焰温度等参数的变化规律。结果表明,在垂直向上蔓延过程中,EPS出现短暂的停滞现象。一方面由于烟囱效应易形成一个大的浮力压力差,导致火焰不稳定性;另一方面由于凹型结构易于烟气的聚集,导致燃烧不充分。而在垂直向下蔓延过程中,由于逆向烟囱效应的影响,火蔓延速度明显加速。火蔓延过程中质量损失速率,很大程度上受其火焰高度的影响,呈现上下振荡的特性。未燃区域部分,火焰温度经历两个温度峰值,向上蔓延过程中第一个温度峰值大于第二个;而向下蔓延过程中第一个温度峰值小于第二个。这主要是由于火焰结构形态及烟囱效应的方向特点,导致产生两个不同大小的峰值。本研究结果可为实际凹型结构下火蔓延特性研究提供前期理论和参考价值。     

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。     

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。     

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.     

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。     

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。     

气固射流扩散火焰形态研究

利用文丘里效应,自行设计气固射流扩散火焰（气固喷射火）实验装置,分别采用147 μm和178 μm两种粒径均匀的白色石英砂以近似恒定速率卷吸入火焰中,来研究固体颗粒对火焰形态的影响,特别地,通过关闭侧面进砂口所形成的气态射流扩散火焰（气态喷射火）与之相比较。理论分析和实验结果表明,砂子进入火焰中会降低火焰温度,并且粒径为147 μm的砂子进入火焰的质量大于178 μm砂子,导致小粒径气固喷射火具有更低的火焰温度,从而具有更低的层流燃烧速度和更大的火焰Froude数,最终使其具有更高的推举高度和火焰高度。对比分析气固喷射火和气态喷射火实验结果,也表明固体颗粒对火焰温度的冷却作用导致气固喷射火更容易产生推举现象并具有更高的火焰高度。     

两池火耦合作用下柴油拱顶罐热响应的数值模拟

化工园区多池火事故是典型的高后果低概率事件。鉴于目前两池火辐射模型存在一定局限性,本文采用数值模拟方法,以3个直线排布的5000m³柴油拱顶罐为研究场景,从热释放速率、火焰形态、热辐射强度三方面分析两池火燃烧特性,并与单池火场景对比,考虑储罐间距这一影响因素,进一步研究目标储罐热响应。结果表明：采用GB 50160—2008（2018年版）规定的防火间距,两燃烧罐产生的池火会发生耦合作用,并得出目标储罐受到的热辐射强度分布,最高热辐射达17.04kW/m²;两池火作用下目标储罐的温度、Mises应力与失效时间分别为644℃、356MPa、936s,单池火为488℃、280MPa、2880s,目标储罐在两池火作用下的变形也比单池火更为严重;随着储罐间距增加,目标储罐的温度与Mises应力逐渐减小,失效时间逐渐增加,当储罐间距为标准防火间距的2.5倍（20m）时,失效时间为2800s,与单池火作用产生的失效时间2880s较为接近。本研究可为优化储罐防火间距及区域韧性提升提供理论指导。     

The effects of transient heat release rate and crosswind on flame length and tilt angle of flames at different positions in the spread of fire over a diesel pool

The spread of fire over liquid fuel is a common phenomenon, and it has been demonstrated experimentally that the flame length and tilt angle change with the transient heat release rate and different positions of the flame. The coupling relationship between these factors is studied in this paper. The experiments are composed of a rectangular pool with dimensions of 80 cm × 6 cm × 5 cm and crosswind with speeds of 0.8 to 2.4 m/s. Diesel is used as the fuel, and a new method is applied to ensure that the initial temperature of the diesel is constant during ignition. The results show that the traditional method of luminous flame intermittency may not be suitable for studying the geometric characteristics of the spread of fire over a pool, and a new method is proposed. In addition, the transient variation of flame length in different positions of the pool is shown to fluctuate around a mean flame length. The evolution of flame tilt angle along the longitudinal direction of the pool exhibits a U‐shaped curve. Moreover, the multivariate nonlinear relationships of mean flame length and tilt angle among the heat release rate, fire position, and wind speed are established, and relevant coefficients are determined.     

Experimental studies on characteristics of fire whirl in a vertical shaft

An internal fire whirl can be generated readily in a tall shaft model with appropriate gap width at one corner. Experimental study was carried out to investigate the relationship between the characteristics of an IFW and the corner gap width in a 9‐m‐tall vertical shaft model. The vertical shaft had a 2.1 m by 2.1 m square section with gasoline pool fire of different diameters burning inside. The gap width was varied to investigate its impact on fire whirl characteristics, such as flame development, swirling intensity, flame height, flame temperature, and heat release rate of the gasoline pool fire. Vigorous flame swirling motions were generated when the ratio of the gap width to the shaft section perimeter was within the range 0.16 to 0.21. From the flame streamline angle, it was observed that the swirling component was much stronger than buoyancy component near the bottom of burning region. The swirling component decreased and became roughly the same as buoyancy near the middle. Finally, it diminished to being much weaker than buoyancy near the top of the fire. These observations suggest that the Froude number Fr decreased from a large number to 1, and then continued to decrease to 0.     

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.     

Experimental study of horizontal flame spread over rigid polyurethane foam on a plateau: effects of sample width and ambient pressure

The effects of sample width and ambient pressure on horizontal flame spread over horizontal rigid polyurethane foams are experimentally studied. A series of comparative experiments are conducted at two places with different altitudes in China. The sample surface temperature, spread rate, and height of flame are measured over a range of sample widths from 4 to 16 cm. Experimental results show that the horizontal flame spread rate decreases as the sample width increases in a negative power law at both two altitudes and the flame spread rate in the Hefei plain (at an altitude of 30 m) is larger than that on the Tibetan plateau (at an altitude of 3658 m) of the same width. The horizontal flame spread mechanism on the rigid polyurethane foam is analyzed qualitatively in comparison with the results of the flame spread rate of expanded polystyrene foams. The relationship between the dimensionless flame height (H_f/W) and the sample width (W) is obtained by using Froude number similarity. It is found based on the experimental data under two different ambient pressures that the average value of the exponent of the ambient pressure in the power law for the horizontal flame spread rate is about 1.9, which is in good agreement with the theoretical value 2.0. Copyright © 2014 John Wiley & Sons, Ltd.     

Experimental study of flame spread over PE-insulated single copper core wire under varying pressure and electric current

In this study, the flame spread over a thin wire with overload current (0-16 A) has been experimentally investigated at both normal pressure (Hefei: altitude 50 m, 100 kPa) and reduced pressure (Lijiang: altitude 2400 m, 76 kPa; Lhasa: altitude 3650 m, 64 kPa). Polyethylene-insulated single-core wires, comprising Cu as the inner core of diameter 0.30, 0.50, and 0.80 mm and insulation thickness 0.15 and 0.30 mm, are used as samples. The experimental results clearly indicate that the height of the flame increases with the electric current and ambient pressure, but the flame width changes only slightly. At identical conditions, the finer the wire, the faster the flame spreads. The flame spread rate increases with the electric current and ambient pressure. A simplified thermal balance analysis concerning the load current is developed to calculate the flame spread rate, and the calculated flame spread rates are shown to be fairly consistent with the experimental values at different electric currents for different wires at both ambient pressures. In addition, the coupled effect of electric current and ambient pressure on the flame spread is discussed. These results may be meaningful for promoting the research process of wire fire safety.     

Reconstruction of Grenfell Tower fire. Part 1: Lessons from observations and determination of work hypotheses

The Grenfell Tower fire occurred on 14 June 2017, killing 72 people. The pattern and speed of vertical and horizontal fire spread characterize this catastrophic event. Plentiful video and photographic data of the fire spread available has been carefully verified and concatenated into a database. The verified data have been superimposed on a projection of the Grenfell Tower in order to track the development of the fire. The surface that is unburnt, burning, or extinguished, as well as the presence of internal fire at any given location, is thus recorded for the duration of the fire. An analysis of the results showed that the initial vertical propagation can be divided into three phases. After the façade ignited at the fourth floor, vertical propagation over time is linear, with a vertical fire spread rate of around 3.5 m/min until the fire reached the sixth floor. Then fire propagation decelerated. Finally, fire spread accelerated with a power four dependence. The maximum vertical fire spread rate was around 8 m/min as the fire reached the crown at the top of the building. Horizontal spread proved to be greatest at the level of the crown (0.293 ± 0.005 m/min). There is a linear relationship between speed of horizontal fire spread and height. These correlations and observations yield important conclusions, and eight different hypotheses capable of explaining the global behaviour of the fire are suggested.     

高开启压力条件下粉尘爆炸泄压火焰特性

为得到高开启压力条件下粉尘泄爆过程中火焰传播特性,采用20L球形爆炸装置,在开启压力为(0.78~2.1)×10⁵Pa的条件下对粉尘浓度为400~900g/m³的玉米粉尘开展爆炸泄放试验研究。结果表明：火焰泄放过程分为点火与破膜、欠膨胀射流火焰、湍流射流火焰、湍流燃烧火焰、火焰回燃5个阶段,最大火焰宽度出现在火焰泄放过程的第2阶段,最大火焰长度出现在火焰泄放过程的第3阶段;不同开启压力下,泄爆火焰长度和火焰传播速度随时间先增大后减小;泄放火焰最大宽度变化范围为0.146~0.269m,泄放火焰的最大长度变化范围为0.41~0.666m。通过预测计算得出泄放火焰可能出现的最大范围为S_max1=0.179m²,采用MATLAB软件定量计算求得的泄放火焰可能出现的最大范围的横截面积为S_max2=0.122m²,定量计算得到的S_max2达到预测值S_max1的68%。