基于CONE数据的材料热释放速率随辐射通量变化的研究

采用锥形量热仪测得几种材料在不同辐射通量下的燃烧性能数据，研究了不同的热辐射通量对热释放速率峰值、热释放速率平均值以及材料的点燃时间、到达峰值的时间、熄灭时间的影响。结果表明：同种材料在不同辐射通量下的热释放速率曲线形状是相似的，并且热释放总量是一个定值；平均热释放速率和热释放速率峰值是辐射通量的线性函数关系；点燃时间随着辐射通量的增加而呈指数衰减趋势；到达热释放速率峰值与火焰熄灭的时间基本上随着热辐射通量的增加线性递减。     

热辐射通量对PMMA燃烧特性影响的实验研究

采用锥形量热仪研究了15~65kW/m2范围内不同的热辐射通量对PMMA燃烧特性的影响。结果表明,PMMA的平均热释放速率、质量损失速率和CO2产率与热辐射通量成线性递增关系;计算得到PMMA的气化热为2.35kJ/g;点燃时间和到达峰值时间随着辐射通量的增加而呈指数衰减趋势;CO产率与比消光面积随着热辐射通量的增加而增大;热辐射通量对有效燃烧热和总释放热的影响较小。并将实验得到的PMMA的燃烧特性参数与文献报道的值进行了对比,可以作为PMMA的燃烧性能测试及火灾危险性评价的参考。     

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。     

聚甲基丙烯酸甲酯板材燃烧性能分析研究

应用锥形量热仪测试分析在5种不同的辐射热通量下聚甲基丙烯酸甲酯板材点燃时间、热释放速率、热释放速率峰值与其质量损失速率间的关系。样品长100 mm,宽100 mm,厚2、4、6 mm。辐射热通量为:15、25、35、45、55 kW/m~2,对应的材料表面温度为:387、490、572、645、685℃。研究发现聚甲基丙烯酸甲酯板材的点燃时间与其厚度、辐射热通量呈负相关关系。在低热辐射通量下,浇注型聚甲基丙烯酸甲酯板材点燃时间要大于挤压型板材的点燃时间。引燃后,聚甲基丙烯酸甲酯板材热释放速率峰值随辐射热通量的增加而增加,浇注型板材热释放速率的增速高于同等厚度下挤压型板材的增速。在不同的热辐射强度下,不同工艺下的聚甲基丙烯酸甲酯板材的质量损失速率差距较小。     

碳纤维/环氧层压板的燃烧特性

利用锥形量热仪,热辐射强度选取为15～80 kW/m2,采用电火花引燃和无电火花引燃的自燃两种着火方式研究碳纤维/环氧层压板在不同火灾环境下的燃烧特性,对比分析点燃时间、临界热辐射强度、质量损失速率及热释放速率的变化规律。结果表明:随热辐射强度的增大,两种着火方式下碳纤维/环氧层压板的点燃时间缩短,质量损失速率峰值增大,热释放速率峰值增大且达到峰值时间提前;相同辐射强度下,相比于自燃,强制点燃的点燃时间提前、临界热辐射强度降低,热释放速率峰值升高及达到峰值时间提前;随着热辐射强度的增加,着火方式对点燃时间和热释放速率影响逐渐减小。建立了碳纤维/环氧层压板的点燃时间及质量损失速率的数学模型,得到理论临界热辐射强度和气化热。     

铺地材料临界辐射通量计算与试验验证

介绍临界辐射通量的测量方法及原理。利用锥形量热仪测得试样的点燃时间和所受初始热辐射强度,拟合出两者存在的一次函数关系。对铺地材料临界辐射通量进行近似计算,利用锥形量热仪进行试验验证,给出误差分析。     

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℃。     

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。     

典型汽车内饰材料的燃烧特性研究

采用锥形量热仪实验对涤纶面料丙纶玻璃纤维板、涤纶面料丙纶麻纤维板和 PVC 革丙纶麻纤维板 3 种典型汽车内饰材料在 25、35、50 kW/m2 热辐射强度下的点燃时间、质量损失率、热释放速率等燃烧特性参数进行研究,并选取点燃预测模型计算材料的临界热辐射强度,使用轰燃倾向指数和热释放总量评价其潜在火灾危险性。结果表明,在实验热辐射强度下,涤纶面料丙纶麻纤维板质量损失百分率最大,结构完整性最差;涤纶面料丙纶玻璃纤维板平均点燃时间最短,临界热辐射强度最小,最容易被引燃;PVC 革丙纶麻纤维板热释放速率峰值最大,火灾性能指数最小,发生轰燃的可能性最大。     

聚氯乙烯热解及火灾行为

用热失重法研究了聚氯乙烯在空气中的热分解特性,并建立了聚氯乙烯热解动力学模型。用锥形量热仪对聚氯乙烯在不同热辐射通量强度下的燃烧进行了分析,通过试验数据推导了聚氯乙烯的点燃温度、临界热辐射通量及维持燃烧所需的最小热辐射强度。利用大尺寸墙角火试验对聚氯乙烯材料的真实火灾行为进行了研究。PVC空气中的热解包括脱氯反应过程,环化、芳化和降解过程,碳的氧化反应过程。减小PVC的火灾危害应重点研究如何减少PVC的发烟。     

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.     

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.     

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.     

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.     

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。     

Contribution to flashover modelling: Development of a validated numerical model for ignition of non-contiguous wood samples

A computational model of flashover is presented that closely follows the experimental setup at CNRS-ENSMA-Poitiers. A propane burner with thermal power of 55 kW is used as a primary source of fire and square beech wood samples (30 mm×30 mm×5 mm) as fire spread targets. The computational model describes the wood pyrolysis with a progress variable. Using the conservation of heat fluxes at the solid–gas interface, the thermal diffusion in the wood samples is coupled with the convective and the radiative heat transfer in the ambient gas phase. The incoming heat flux at the upper surface of the wood samples reaches values between 20 and 30 kW/m². With the ignition and subsequent combustion of the pyrolysis volatiles, the heat flux increases by approx. 12 kW/m². The results show that the ignition of the wood samples is triggered at an approx. surface temperature of 650 K. Due to large local variations in incident heat flux, significant differences in the ignition times of the wood samples are observed. The comparison of the calculated and the experimentally measured temperature shows a good agreement for the first wood sample and the model predicts the ignition time very well. But for the second and the third wood samples the model overpredicts the temperature, which leads to a premature ignition of these wood samples.     

Fire behaviors of polymers under autoignition conditions in a cone calorimeter

Besides piloted ignition, autoignition is also an important aspect to real fire development as combustible materials may be ignited without independent flame. Fire behaviors of non-charring and charring polymers were then investigated in a cone calorimeter under autoignition conditions. Fire risk of non-charring polymers are higher than those of charring polymers because of high heat release, and the increase of heat release rate is much obvious with a higher heat flux or thickness. Charring polymers seem to have a higher CO yield, while non-charring polymers have a higher CO₂ yield. Ignition methods have influences to combustion efficiency of non-charring polymers as effective heat of combustion under autoignition are observed lower than those reference data under piloted ignition conditions. Its influences to charring polymers are not obvious. Both CO and CO₂ yields under flaming combustion are higher than those under non-flaming combustion, but mass percent of carbon seem to has limited effect. Experimental data in this study can provide a guidance to fire risk evaluation of non-charring and charring polymers.     

Radiative ignition mechanism of solid fuels

Transmittance of external radiation from a CO₂ laser through a boundary layer of decomposition products over a vertical sample surface is measured during the ignition period. The results indicate that there is significant absorption of the external radiation for PMMA, and a lesser but still not negligible amount, for red oak. An increase in gas phase temperature over surface temperature is observed over much of the ignition interval. Using the experimentally measured incident flux at the sample surface, surface temperature history was calculated from a model that included re-radiation and convection losses from the surface, endothermic decomposition and conduction into the material. The results confirm the significant effect of gas phase absorption on surface temperature. Steady-state-derived surface regression rate expression was used for PMMA in this model. The results raise questions about the validity of such data for the dynamic heating conditions during the ignition period. Further studies needed to understand the radiative ignition mechanism are identified.     

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。     

Piloted ignition times,critical heat fluxes and mass loss rates at reduced oxygen atmospheres

Ignition, pyrolysis and burning of materials in reduced oxygen atmospheres occur when recirculating combustion gases are mixed with the air flowing into an enclosure. Still the incoming air can be sufficient for the complete combustion of the pyrolysis gases. Thus, for the prediction of fires in enclosures it is essential to understand the ignition and burning of materials in a reduced oxygen atmosphere even when plenty of oxidizer is available for complete combustion. Previous work employing gaseous fuels has shown that under these conditions, but before extinction, burning of gaseous fuels issuing from a nozzle is complete but radiation from the flames decreases owing to the reduction of their temperature. Complementary to that work, piloted ignition of solids is investigated here at reduced oxygen concentrations by measuring the ignition times and mass loss rates of the solid at ignition.These results were obtained in a cone calorimeter modified to supply air at reduced oxygen concentrations. Two types of plywood, normal and fire retardant 4 mm thick were examined at three imposed heat fluxes 25, 35 and 50 kW/m² and at oxygen concentrations of 21%, 18% and 15% by volume. Because heating at these heat fluxes and material thickness corresponds to intermediate thermal conditions (i.e. neither thin nor thick), novel analytical solutions are developed to analyze the data and extract the thermal and ignition properties of the material. The same novel solutions can be applied to modeling concurrent or countercurrent flame spread. Moreover, a theory for piloted ignition explains why the ignition times and mass pyrolysis rates are weakly dependent on reduced oxygen concentrations.