During air transport, lithium-ion batteries are often stored together with combustibles such as cardboard packaging and liquid fuels. The combustion of these materials may trigger thermal failure in lithium-ion batteries, and the underlying mechanism may differ markedly from that under conventional thermal abuse conditions. However, studies on the thermal failure behavior of the lithium-ion batteries under different combustible environments in aircraft cargo compartments, as well as the evolution of the associated thermal and gas hazards, remain limited. To address this gap, this study established two representative external fire scenarios, namely cardboard fires and oil pool fires, and conducted thermal failure induction experiments on 18650 type lithium-ion batteries. The results showed that the cardboard fire environment more readily caused sustained heat accumulation. It also strengthened the coupling effect of surrounding combustibles on the battery overheating process. Both an increase in the number of cardboard boxes and a higher battery state of charge further aggravate the thermal and gas hazards. By contrast, the oil pool fire environment is more sensitive to the relative position of the battery, and both heat release and gas generation differ markedly with height. As the distance between the battery and the oil surface increases, the total heat release gradually decreases, while the H2/CO-based lower-bound %LEL becomes more pronounced under far-field conditions. This study provides experimental support for controlling combustibles surrounding lithium-ion batteries in air transport scenarios.

Due to the increased risk of phosphate depletion, there is an increasing demand for low-phosphorus or bio-based phosphorus flame inhibitors. Therefore, two novel composites with biologically-based phosphorus sources that chelate transition metal ions were synthesized via assembly method, i.e., Mn-PMC and Ni-PMC, the structure and binding states of the composites were examined by SEM, TEM, FTIR, XRD, XPS, BET and TGA. The results indicated that Mn-PMC and Ni-PMC (i) are nanoscale materials with well dispersed, (ii) have an amorphous structure and have sites that bind to other substances, (iii) contain no halogen elements. Then the combustion inhibition experiments of downward flame spread and TG-IR-MS analysis revealed (i) that the inhibition efficiency of the two prepared inhibitors was higher than that of commercial phosphate-containing inhibitor ADP. Among them, Ni-PMC had the best suppression effect, and the flame of cellulose sample containing it would automatically extinguish after igniting with a smallest dosage, (ii) two inhibitors reduced the laminar flame velocity and flame temperature. (iii) their flame suppression mechanism was indicated as that the pyrolysis releases inert gas to dilute the free radical concentration. This work is helpful for the development of efficient transition metal fire extinguishing agents to replace traditional phosphorus resources.

As industrialization continues to deepen, polymers have become ubiquitous in daily life. However, their flammable characteristics pose significant safety risks. Therefore, supporting the global goal of sustainable development necessitates the development of high-performance, environmentally friendly flame retardants. Biomass phytic acid (PA) has emerged as a promising option because of its high phosphorus content and excellent biocompatibility. However, its combustion behaviors and chemical kinetic mechanisms remain unclear. In this study, quantum chemical calculation methods were used to construct a detailed PA chemical reaction kinetic model. A series of experiments were conducted to validate the model and evaluate PA's flame suppression effect. Utilizing a counterflow flame burner and particle image velocimetry (PIV), the inhibitory effect of various PA concentrations was examined based on the laminar flame speed of CH4/PA/Air mixture. The results revealed that a merely 0.2 % addition of PA could reduce the laminar flame speed by 38.9 %, demonstrating its significant flame suppression effect. Building on the foundational GRI-Mech 3.0 and integrating PA's pyrolysis and reaction mechanism, this study developed for the first time a detailed chemical model of CH4/PA/Air combustion. This model integrated PA's thermal decomposition module and thermodynamic data via ab-initio quantum chemical calculations, thereby accurately predicting global kinetic indicators such as laminar flame speed. Results suggested that the key reactions, such as PO2+H + M-*HOPO + M, HOPO2+H-*PO2+H2O, and HOPO + OH-*PO2+H2O primarily influenced the laminar flame speed. Moreover, the CFD simulation elucidated the complex interaction between PA and flame structures. A detailed analysis of the spatial distribution of key parameters such as temperature, combustion radicals, and effective inhibition radicals unveiled the PA's flame suppression mechanism in support of the practical application of this eco-friendly flame retardant.

Understanding the atmosphere-fire interaction is of vital importance for the fire management and fire-induced synoptic flow prediction. This work aims to reveal the mechanism of fire dynamics and its interaction with atmospheric boundary layer by considering the complex dual-fires condition that is rarely studied. Thus, the numerical simulations were performed with a detailed analysis of flame geometry, fingering structure, turbulence spectrum, Richardson (Ri) number. The results show that the flame morphological parameters changed significantly as increasing Nc number with the flame drag length reduced from 6.2 to 2.5 m and the flame inclination angle increased from 13.9° to 36.6°, especially an opposite trend of change was observed at buoyancy-driven regime when the dual-fire was considered. A lognormal distribution was indicated for fingering structure spacing, where the average spacing is between 1.4–0.9 m, which was apparently affected by dual-fires when Nc number is high. The profile of Ri also demonstrated the enhanced natural convection and the resulting forces imposed on the upstream flame for dual-fire cases, for which different fire-wind interaction mechanisms can be drawn at different magnitudes. The proper orthogonal decomposition analysis was developed to further reveal that the coherent structures in dual-fires condition were a strong perturbation of the downstream fire induced by the fire-fire interaction.

Tetrahydrofuran (THF) is a biofuel that can be added to improve the solubility of ethanol in diesel. To explore the effect of surfactants, the puffing and micro-explosion characteristics of ethanol diesel/THF (DTE) blend droplets are investigated experimentally in comparison to a counterpart blend of ethanol diesel/biodiesel (DBE). Results show that with a rise in temperature, the puffing delay time decreases rapidly opposite to the fluctuation ratio; however, the puffing delay time rises with the ethanol content, whereas the fluctuation ratio remains about constant. Moreover, the tetrahydrofuran mainly participates in the early evaporation stage resulting in more prone to the edge mode for DTE droplets, which is in contrast to the DBE droplets, which prefer the inner mode. The micro-explosion strength of DTE droplets is lower than that of DBE due to the more likely occurrence of the edge mode, but the corresponding growth rate of DTE (15.2%, 25.4%, and 56.8%) with temperatures of 573 K, 623 K, and 723 K is higher than that of DBE droplets (8.8%, 20.4%, and 48.7%). A numerical model is also established for the present blend droplets, and the simulations reveal that the THF may additionally influence the heat absorption by the liquid and hence the superheat point of ethanol, which is responsible for the bubble formation and the micro-explosion.

The influence of turbulent fluctuation on combustion inhibition by trimethyl phosphate (TMP) is investigated in turbulent premixed methane/air flames. The instantaneous flame structures are detected by OH Planar Laser-Induced Fluorescence (OH-PLIF) system, and some statistical parameters, including the global consumption speed, mean fuel consumption rate and mean heat release rate, are attempted to quantify the inhibition effectiveness of TMP in the turbulent premixed flames. Results show that the turbulent combustion regime of the methane/air flame may be changed from the thin reaction zone (TRZ) to the distributed reaction zone (DRZ) regime, due to the high loading of inhibitor. The addition of agent can obviously decrease the turbulent consumption speed. Meanwhile, the relative inhibition efficiency of TMP in the turbulent flame is much lower than that in the laminar configuration. From the point view of reaction, one possible reason is that the difference of the turbulent transportation between the active radicals (H and OH) and the phosphorus-containing species (PO2, HOPO, HOPO2, etc.) may lead to decreasing the capacity of radical scavenging. By increasing the jet velocity, the mean fuel consumption rate and mean heat release rate decrease for the neat flames, but increase for the inhibited ones. The main reason is that the velocity increment is smaller than the increment of flame volume for the neat cases, but is larger than that for the doped configurations. Because of no consistent tendency, these two statistic variables may not the preferred parameters for the evaluation of turbulent flame inhibition.

The laminar burning velocities (LBVs) and cellular instability of 2-methyltetrahydrofuran (2-MTHF) were investigated at the unburned temperature of 423 K and pressures from 1 to 10 atm in a cylindrical constant-volume vessel. The LBVs of 2-MTHF/air flame exhibit a notably dropping with increasing pressure. The cellular instability analysis indicates that the critical flame radius of 2-MTHF/air mixture monotonically increases with increasing pressure and the flame surface suffers more badly cellularity under higher pressures. The critical flame radius exhibits non-monotonic variation versus phi and the most unstable flames appear at phi approximate to 1.3. It is observed that the measured Markstein length of 2-MTHF/air mixture decreases with increasing phi and P-u, leading to an earlier formation of wrinkling and cracks with respect to preferential-diffusional instability. Further investigation found that by using a mixture of 14.2% oxygen with 85.8% helium in place of air as bath gas at 10 atm can effectively suppress the cellular instability. Two recently developed models were used to simulate the experimental results and explore the chemical kinetic effects on LBV. Reaction path analysis reveals that the most consumption of 2-MTHF/air at stoichiometric conditions is through the abstraction of H-atom to form radical C5H9O-5. While the competitiveness of decomposition by C-C scission yielding CH3 and tetrahydrofuran radical is relatively weak. Sensitivity analysis illustrates that smallspecies reactions show a controlling effect on LBV. The increasing pressure leads to an evident increase in the sensitivity coefficient of the recombination reaction H+O-2 (+M) = HO2 (+M). The reduction of H atom concentration will cause competition to the initiation reaction H + O-2 = O + OH. This could lower the overall oxidation rate and reduce the burning velocity. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

将支持向量机(SVM)模型运用于事故前苯储罐泄漏事故风险预测,为使模型性能最优,采用粒子群算法PSO优化SVM模型参数,建立了 PSO-SVM风险预测模型.为验证模型风险预测性能,分别采用遗传算法(GA)和网格搜索法(GS)优化SVM参数,并比较测试集与PSO-SVM、GA-SVM、GS-SVM三种模型预测结果的均方误差及相关系数.然后进一步探讨模型中权重调整方式、种群规模对PSO-SVM模型预测性能的影响.研究发现,权重线性递减所建PSO-SVM预测值与测试集相关系数更高、均方误差更小、预测效果更好,种群规模没有影响PSO-SVM模型预测值但会影响计算时间,这为危化品泄漏事故的风险预测提供了一种新的方法.

This paper reported the preparation, fire suppression efficiency, and suppression mechanism of a new suppression powder. In present work, the new suppressant was designed for combining the ability of terminating the chain reactions into the powder extinguishing agent. The trifluoroacetyl group (COCF3) was grafted onto the silicon dioxide (SiO2), and called the compound SiO2–F. Several tests for characterizing the structure and morphology of the compound powder were done. The results indicated that the powder was prepared successfully. Then, the burning velocity of methane-air flame with powder addition and minimum extinguishing concentration were measured to evaluate the fire suppression efficiency. In comparison with NaHCO3 and SiO2 powders, the SiO2–F powder had more pronounced fire suppression efficiency. Furthermore, the fire suppression mechanism of the powder was systematically studied. The physical and chemical suppression mechanisms worked together to suppress the flame. The physical suppression mainly stemmed from the heat absorption of solid substances, and occupied 23.1% of the total suppression effect. The chemical suppression was mainly due to the termination of chain reactions by the fluorinated species which were released when the powder was exposed to high temperature.

Thermal structure inside flame front during downward flame spread was experimentally measured for XPS foam with thicknesses of 1.6, 2.4, 3.4, and 4.4 cm. The temperature distribution and temperature gradient in the condensed phase, as well as the shape of the molten liquid, were obtained by 2-D heat transfer equations and experimental measurement. The results show that both the temperature and its temperature gradient decrease from the sample surface to the inside of the condensed phase, which results in the inclination of the melting interface. The molten layer is the thinnest near the sample surface and thicker inside the condensed phase. The adhering of the molten liquid to the wall greatly increases the thickness of the molten layer near the back wall, and the higher the thickness, the more molten material adheres to the wall. Finally, there is a relatively flat solid liquid interface near the sample surface and a large inclined solid-liquid interface near the back of the sample, especially for the thicker samples of 3.4cm and 4.4cm. It is indicated that the distribution of the molten layer in the direction perpendicular to the plane of the XPS sheet is a significant factor for dripping and collapsing.

In this study, the influence of fire suppression powder NaHCO3 on premixed flames was investigated experimentally and numerically. To better understand the suppression mechanism of the powder, the physical heat sink and chemical reaction contributions of the addition of the powder on the laminar burning velocity of methane-air flames were analyzed. An improved model was developed to predict the influence of the physical heat sink effect on burning velocity, and the model aligned well with the experiment. The results demonstrated that the physical effect had a non-negligible impact on flame suppression. Thereafter, the chemical reaction effect of NaHCO3 powder was investigated, and the results showed that the chemical effect suppressed flames by scavenging free radicals. When a large quantity of agent was added, the equivalence levels of the free radical concentration resulted in the saturation of the chemical effect. The influence of the initial temperature and pressure on the chemical effect was also studied. Finally, the exact contributions of the two effects were compared under different sizes of the powder particles. The results indicated that the suppression mechanism was under the thermodynamic control when the particle size was large, as that the physical heat sink effect played a more important role than the chemical effect. Conversely, the suppression mechanism was under the kinetic control when the particle size was small, as the chemical reaction effect occupied the dominant position.

选用氯化钠为基体制备金属火灾超细干粉灭火剂.应用反溶剂法对其改性,使纳米疏水二氧化硅吸附在氯化钠晶体表面,其中分散剂为PEG-1000.结果表明,纳米疏水二氧化硅的添加有利于细化氯化钠颗粒,但过量的添加会起反作用,最佳用量为3 wt％左右,平均粒径为2.18μm.镁片灭火实验证明超细复合干粉的灭火性能明显好于传统氯化钠灭火剂(商用D类灭火剂),纳米疏水二氧化硅最佳添加量为3 wt％,此时灭火时间仅需传统灭火剂的一半.最后利用FDS5.0模拟干粉颗粒与燃烧火焰作用过程,模拟结果表明干粉覆盖对火焰具有一定的抑制效果,并分析了复合干粉灭火机理.

顶棚下方最高温度是隧道火灾发展蔓延时的重要参数.针对火焰撞击顶棚并受到顶棚侧墙限制的强羽流驱动的顶棚射流,利用FDS模拟了18种缩尺寸隧道火灾工况,研究了顶棚下方最高温度随着火源功率、火源与顶棚距离的变化规律.结果表明:火焰撞击区域附近顶棚下方温度随着火源功率的增大而降低,随火源与顶棚距离的增大而升高;相反,在远离火源区域顶棚下方的温度随火源功率增大而升高,随火源与顶棚距离增大而降低;同时,通过分析隧道中心面上顶棚下方温度分布规律,提出了火焰撞击受限顶棚时顶棚下方最高温升的预测模型,研究结果能为实际的隧道消防提供一些参考.

Dense smoke released during the combustion of polystyrene (PS) potentially limits its applications in some fields. In this study, a Zr-based metal-organic framework (UiO-66) was prepared via the solvothermal method and added to PS to suppress its smoke emission. Well-defined UiO-66 particles showed an excellent dispersion state and good compatibility in the PS matrix. The introduction of UiO-66 improved the flame retardancy and smoke suppression of PS. The peak heat-release rate and total heat release were reduced by 26.8% and 14.7%, respectively, for PS/ UiO-66-5 wt%. Moreover, the smoke emissions of PS composites were evidently suppressed, and more than a 35% reduction in total smoke production was obtained with 5-wt% UiO-66. Through the analysis of the residues and pyrolysis products of PS composites, the mechanisms of enhanced flame retardancy and smoke suppression can being speculated as the promoted char-forming and heat barrier of UiO-66. This work offers a significant reference for the further study of UiO-66 and polymer materials.

The XPS foam is an economical and popular material for building insulation. The fire hazard of the polymer foams is a big threat due to their fast burning with melting, dripping and flowing. The objective of this work is to investigate the complicated downward flame spread characteristics of a wide polymer foam. An image division and calculation method is used to analyze the dynamic downward movement of the irregular flame leading curves based on the experiments. The results show that the lagged sub-flames might suddenly spread downward fast and catch up the neighboring flames. And the increasing of the flame spread velocity and flame height illustrate the acceleration of the downward burning, which is induced by the dripping and accumulating of liquid fuel. Additionally, the local peaks of the flame spread velocity arrive later than the flame height for both overall flame and detailed sub-flames. The flame height increases in the stage of liquid fuel accumulation but decreased in the dripping stage. The dripping of liquid fuel results in the increasing of the flame spread velocity and decreasing of the flame height. The results also show that the relationship between the non-dimensional local peak sub-flame flow velocities and the corresponding non-dimensional peak sub-flame heights can be well described with a power function, which indicates that the introduction of the small sub-flames is effective to model the complicated downward flame spread behaviors of XPS foams with stochastic dripping. Finally, most of the delay times of local peak sub-flame velocities here are in the range of [15 s, 25 s].

以苯储罐为研究对象,利用ALOHA软件模拟了不同大气温度、风速、地面粗糙度、泄漏口直径和测点条件下苯浓度的变化.将ALOHA模拟数据作为训练样本,建立苯泄漏区域浓度的粒子群-支持向量机(PSO-SVM)预测模型.为验证模型预测性能,采用遗传算法支持向量机(GA-SVM)模型和支持向量机(SVM)模型进行预测,并与PSO-SVM模型对比.结果表明,PSO-SVM模型预测效果优于GA-SVM和SVM模型.

Pyrolysis kinetic modeling of polymers is important for the analyses of their combustibility and flame spread mechanism in fire safety science and engineering. The objective of this work is to improve the reliable kinetic parameter analyses for polymers by introducing a new idea of the linear dependence of kinetic triplets on the heating rates in Thermogravimetric Analysis (TGA) experiments. The virtual kinetic triplets are also introduced for the case with the infinitely slow heating rate. Pyrolysis kinetic analyses are conducted by Genetic Algorithm (GA) optimization for the TGA data based on the single-scan, multi-scan and the new method here with the modified kinetic triplet series. The results show that the fitting errors for the independent case based on the single-scan method can be as small as 0.1–0.5%. But Kinetic Compensation Effects (KCE) problem is its main restriction to hinder the determination of reliable kinetic triplets. The results also show that based on the multi-scan method, the relatively reliable kinetic parameters can be calculated but with large total fitting errors in the range of 4.7–9.8%. Finally, the total fitting error can be minimized to about 0.6–1.7% by the new method here, which illustrates its obvious improvement for the reliable pyrolysis kinetic modeling of fuels. The new method based on the kinetic triplet series here is a modified multi-scan method, in which the traditional multi-scan method is also included as the case with the linear coefficient of zeros.

Nowadays, plant biomaterials have been used in several types of industries for related purposes for example energy and electricity production, as our world is facing energy shortage problems. In this paper, the combustion behavior of a typical plant biomaterial, corn cob, was investigated using TG-DSC technique. Combustion experiments were conducted from room temperature to 900 °C at three heating rates of 10, 20 and 30°C/min in air atmosphere. It is observed that the process can be divided into three stages: dehydration (25°C-150°C), pyrolysis (150°C-380°C) and combustion (above 380°C). Besides, ignition and burnout temperature were investigated based on DSC profiles. Finally, two model-free methods (FWO and KAS) were adopted to perform the kinetic analysis for combustion reaction process. It is found that activation energies values against conversion rate present a rising trend (from about 172.40 KJ/mol to 326.95 KJ/mol) in the pyrolysis stage, while an opposite tendency was observed in the combustion stage (from about 365.55 KJ/mol to 202.86 KJ/mol), indicating that corn cob combustion is a complex process and relatively complex reaction schemes should be adopted to describe its combustion. It is anticipated that our current work could be helpful in providing reference to the design of energy conversion facilitates.

As is well known, building integrated photovoltaic (BIPV) technology is becoming more commonly used in residential and commercial buildings. Fire assessment of photovoltaic (PV) modules as a whole is still insufficient. This work focuses on the thermal properties and combustion behavior of CIGS (copper, indium, gallium and selenium) thin-film modules. Cone calorimeter experiments were conducted at different external heat flux of 25, 30, 35, 40 and 45 kW m−2. Several parameters are discussed, including surface temperature, ignition time, heat release rate (HRR), mass loss rate, carbon monoxide (CO) and carbon dioxide (CO2) concentrations. The results show that CIGS thin-film solar modules are inflammable at intermediate or high flashover risk. A correction calculation for the gas toxicity index has been used to reduce the well-ventilation condition effect. Compared with the uncorrected calculation, peak fractional effective dose (FED) and lethal concentration for 50% of the population (LC50) are almost double. This work will help to determine a more stringent fire safety provision for PV modules.

Phosphorus-containing compounds are the promising halon alternatives for flame inhibitions. However, some literatures suggested that the phosphorus-related inhibitors may behave as the unfavorable ones that will increase the burning velocity under lean-burn conditions, and this indeed posed potential threats to the fire prevention and fighting. To seek deeper insights into the reaction process, a numerical investigation was actualized to study the phosphorus-related effects on methane-air flames. By replacing a phosphorus-related inhibitor with the corresponding decomposed molecules, the detailed promoting and inhibiting effects of combustion were separated from the general chemical effect. A comparative study was carried out to identify the interaction between the two effects under different combustion conditions. It is observed that the promoting effect becomes the dominant factor during the reaction process when the equivalence ratio is smaller than 0.60. In this lean-burn condition, the exothermic reactions were faster than the others within the reaction chains due to the reduction of radical recombination in hydrocarbon oxidation. The results are believed to be useful for the further application and improvement of flame inhibitors.