Flame Propagation Characteristics of Propane-Air Mixture in Ducts with Obstacles

An experimental study on acceleration mechanism of flame propagation of propane-air mixture in ducts with obstacles was conducted. The acceleration mechanism of flame propagation is mainly due to the positive feedback of the turbulence region induced by obstacles for combustion process. It can be seen from the experimental results that the maximum explosion pressure can increase by 20%, the maximum rate of pressure rise can increase by 10 times and the flame propagation velocity can increase by 20 times when obstacles are present.

Prediction of Excess Air Factor in Automatic Feed Coal Burners by Processing of Flame Images

In this study, the relationship between the visual information gathered from the flame images and the excess air factor 2 in coal burners is investigated. In conventional coal burners the excess air factor 2. can be obtained using very expensive air measurement instruments. The proposed method to predict ） for a specific time in the coal burners consists of three distinct and consecutive stages; a） online flame images acquisition using a CCD camera, b） extrac- tion meaningful information （flame intensity and bright- ness）from flame images, and c） learning these information （image features） with ANNs and estimate 2. Six different feature extraction methods have been used： CDF of Blue Channel, Co-Occurrence Matrix, L-Frobenius Norms, Radiant Energy Signal （RES）, PCA and Wavelet. When compared prediction results, it has seen that the use of co- occurrence matrix with ANNs has the best performance （RMSE = 0.07） in terms of accuracy. The results show that the proposed predicting system using flame images can be preferred instead of using expensive devices to measure excess air factor in during combustion.

Numerical Simulation of High Temperature Air Combustion Flames Properties

High temperature air combustion (HTAC) is an attractive technology of saving energy and controlling environment. The mathematical models of turbulent jet flame under the highly preheated air combustion condition are conducted in the paper. The mixture fraction/probability density function model is employed. The results show that the maximum flame temperature is decreased, the temperature in the HTAC furnace is more uniform than that in the conventional furnace, and the NO x emission is low. The numerical results are partially validated by some experimental measurements.

Experimental investigation on microstructure behavior of premixed methane-air flame-flow interaction in a semi-vented chamber

To explore the premixed methane-air flame microstructure behavior and the flame-flow interaction, the premixed methane/air flame was studied in a semi-vented chamber. A high speed camera and schlieren images methods were used to record the processes of interaction between rare- faction wave and flame. Meanwhile, a pressure sensor was utilized to catch the pressure variation in the process of flame propagation. The experiment results showed that the interference of rarefaction wave on flame caused the flame front structure change, which led to the flame transition from lami- nar to turbulent quickly. The rarefaction wave intervened in the flame by turning the flame front sur- face into dentiform structure. The violent turbulent combustion began to appear in part of the flame front and spreaded to the whole flame front surface. The rarefaction also decreased the flame propa- gation speed.

细水雾粒径对CH_4/AIR扩散火焰影响数值研究

参考WolfHard-Parker燃烧器构建二维模型,选择有限速率燃烧模型,定量分析水雾直径对抑制熄灭CH_4/AIR扩散火焰的影响。无水雾条件下数值结果与实验结果的对比表明,数值结果与试验结果较为吻合。研究表明,54μm水雾颗粒粒径最能够有效抑制燃烧,对应的火焰峰值温度最低;CO体积分数随雾滴直径变化趋势与温度相反;OH和O体积分数变化规律与温度相似,在高度小于5 mm时,水雾对其影响很小。

RANS Simulation of Methane Diffusion Flame： Comparison of Two Chemical Kinetics Mechanisms

Turbulent non-premixed combustion of gaseous fuels is of importance for many technical applications, especially for the steel and refractory industry. Accurate turbulent flow and temperature fields are of major importance in order to predict details on the concentration fields. The performances of the GRI-Mech 3.0 and the Jones and Lindstedt mechanisms are compared. Detailed chemistry is included with the GRI-Mech 3.0 and J-L kinetic mechanisms in combination with the laminar flamelet combustion model. The combustion system selected for this comparison is a confined non-premixed methane flame surrounded by co-flowing air The simulation results are compared with experimental data of Lewis and Smoot （2001）.

A Kinetic Model of Chromium in a Flame

Chromium has been identified as a carcinogenic metal. Incineration is the useful method for disposal of toxic chromium hazard waste and a chromium kinetic model in a flame is very important to study chromium oxidation. Chromium chemical kinetics over a range of temperatures of a hydrogen/air flame is proposed. Nine chromium compounds and fifty eight reversible chemical reactions were considered The forward reaction rates are calculated based on the molecular collision approach for unknown ones and Arrhenius’s Law for known ones. The backward reaction rates were calculated according to forward reaction rates, the equilibrium constants and chemical thermodynamics. It is verified by several equilibrium cases and is tested by a hydrogen/air diffusion flame. The results show that the kinetic model could be used in cases in which the chromium kinetics play an important role in a

障碍物阻塞率对氢-空气爆燃的影响

为深入了解氢气在不同阻塞率条件下的爆燃特性,以提升氢能使用的安全性,并为氢能在船舶和生活领域安全应用以及抗爆减灾设计提供科学依据。研究利用Open FOAM软件结合大涡模拟(LES)模型,对半开敞管道内氢气在不同阻塞率条件下的爆燃火焰动力学特性进行了深入分析。研究发现障碍物的阻塞率显著影响氢气爆燃的火焰传播速度和爆燃压力;火焰结构的演化过程可划分为球形、指形、射流和漩涡4个阶段;在面积阻塞率为0.7时,火焰传播速度达到极大值177.5 m/s,相较于阻塞率为0.5和0.3时分别快1.31倍和1.82倍;相同阻塞率下,不同厚度的障碍物对火焰速度的影响不大;爆燃压力在阻塞率为0.7时达到峰值74.7 kPa,较阻塞率为0.5和0.3时分别高出1.32倍和1.7倍,同时火焰结构和行为受到未燃气体流场的显著影响,为氢能设备的安全设计和布置提供重要的理论基础,并对氢气爆炸的抗爆减灾设计具有重要的理论支撑作用。通过这项研究,可更有效地预防和减轻氢气爆燃带来的风险,确保氢能在船舶和生活领域的安全应用。

麻地梁煤矿首采综放面收作期间防灭火技术研究

麻地梁煤矿507首采面是采用放顶方法开采埋藏浅特厚的长焰煤,漏风严重,丢煤多,尤其在工作面收作期间未进行放顶,采空区遗煤量更大。另外,工作面未采阶段推进速度慢,遗煤氧化时间长,极易引起采空区煤自然发火。针对以上情况,采取注氮降氧、高位钻孔注浆和注高固水材料覆盖隔氧、堵漏控风等的综合防灭火措施,保证了该工作面支架的安全撤出,为类似回采条件的工作面收作期间的防灭火提供参考。

坡度条件下不同长宽比矩形火源燃烧火焰贴地长度实验研究

利用可变角度实验台,改变斜坡角度(10°~50°)、热释放速率(12.3~24.6 kW)以及燃烧器长宽比(1~6),开展了一系列燃烧实验,研究了火焰贴地长度随这3个因素的演变规律.结果表明,随着斜坡角度、火源热释放速率及燃烧器长宽比的增加,火焰贴地长度增加.对于相同的坡度和火源热释放速率,随长宽比增大,贴地长度增幅范围在65%~105%之间.基于斜坡诱导压差与火羽流浮力共同作用的物理机制分析,并考虑到燃烧器长宽比对火焰卷吸行为的影响,提出了无量纲火焰贴地长度预测模型.

二次风倾斜角度对高温预热燃料贫氧燃烧火焰特性影响试验

预热燃烧是气化飞灰资源化处置的有效途径,通常搭配主燃室空气分级以协同实现高效清洁燃烧,因此,研究高温预热燃料的贫氧燃烧火焰特性非常有必要。搭建了250 kW高温预热燃料火焰特性试验平台,通过高温火焰可视化监测及其图像编程处理,研究了主燃室二次风倾斜角度对气化飞灰预热燃烧的贫氧火焰特性的影响规律。试验表明,随着二次风倾斜角度从30°增大到60°,贫氧燃烧火焰逐渐远离热烧嘴出口,脱火距离无量纲值从1.04增大到3.73,火焰宽度无量纲值则从4.09逐渐减小至3.47。当主燃室二次风倾斜角度为30°和45°时,燃烧系统的碳转化率分别为71.6%和70.3%。综合考虑二次风倾斜角度对热烧嘴运行稳定和气化飞灰燃尽的影响,主燃室二次风倾斜角度的优选值为45°。

开放/封闭空气层下水分对阻燃织物热防护性能的影响

为了研究不同种类空气层下水分对消防服用织物热防护性能的影响,基于TPP值测试装置,构建了开放和封闭式空气层,分别从内和从外润湿织物,在不同种类空气层下测试含水织物的TPP值。结果表明:当外层润湿时,开放和封闭空气层促进了水分对热防护性能的积极影响;当内层润湿时,封闭空气层下织物的TPP值先减少后增加,在润湿水平为15%时达到最小值,而开放空气层下,织物TPP值则随润湿水平的增加而增加;外层润湿时防水透气层能有效阻挡水蒸气到达传感器,对热防护性发挥重要作用,而内层润湿时防水透气层则不利于水蒸气向外层转移,对热防护性有消极影响,但开放空气层下此消极影响不明显,TPP值有大幅度增加。

点火位置对甲烷/空气预混爆炸特性影响的数值模拟研究

密闭容器内预混气体爆炸非常复杂,为研究点火位置对甲烷/空气预混气体爆炸特性的影响,在初始压力为101 kPa和初始温度为300 K的环境下,开展1 m^(3)密闭球形爆炸容器中10 vol%甲烷浓度的中心点火爆炸实验,并使用Fluent数值模拟软件,采用LES湍流模型和Zimont燃烧模型,研究不同点火位置(中心点火、0.5R点火、R点火)对容器内甲烷/空气预混气体爆炸特性的影响,包括火焰结构演化、爆炸温度、爆炸压力、爆炸压力上升速率。结果表明:(1)在中心、0.5R和R处点火时,火焰分别向四周膨胀直至容器壁面、轮廓由最初的“左薄右厚”逐渐转变为“左侧凸起的尖角”和在壁面处从“圆弧形”逐渐拉伸转变成“尖形”向左侧发展;(2)不同点火位置下温度场存在温度梯度,升温规律均由点火中心能量持续向外释放,温度不断积聚升高;(3)不同点火位置下爆炸压力变化趋势基本一致,由于壁面绝热,最终最大爆炸压力均稳定在766 kPa左右;(4)中心点火时最大爆炸压力上升速率最大,较0.5R点火和R处点火分别增大了94.5%和141.8%。

密闭管道内非连续分布甲烷/空气爆炸特性

在长度900 mm、截面为100 mm×100 mm的矩形密闭管道内开展预混气体非连续分布对甲烷/空气爆炸影响的试验研究。通过分段通入甲烷体积分数为9.5%的预混气体,形成甲烷/空气-空气和甲烷/空气-空气-甲烷/空气两种非连续分布模式。研究发现,随着空气区域缩短,火焰传播距离、火焰尖端速度和爆炸超压均增大。特别是在甲烷/空气-空气-甲烷/空气分布中,当中间空气区域小于500 mm时,火焰会穿越并引发二次爆炸,且其超压随空气区域减小而增加。研究结果可为天然气爆炸事故防控提供理论支持。

气流输运工况玉米淀粉爆炸火焰传播与压力特性实验研究

利用自主搭建的2 m长气流输运管道实验装置开展了不同气流速度下玉米淀粉爆炸实验,通过高速摄影和压力传感器获得火焰信息和压力参数。基于实验结果分析了气流输运工况气流速度对玉米淀粉爆炸火焰传播行为和爆炸特性的影响规律。结果表明:随着气流速度的增加,粉尘爆炸火焰亮度、火焰传播速度及最大爆炸压力呈先增大后减小的趋势,存在火焰呈螺旋状向管道末端传播的现象。气流速度从5 m/s升至10 m/s,火焰最大传播速度从74.07 m/s增加到89.51 m/s,最大爆炸压力由17.08 kPa增至23.42 kPa。气流速度提高到15 m/s时,火焰最大传播速度和爆炸压力均有所下降,质量浓度为300 g/m3时受影响最大,爆炸压力降低41%,500 g/m3时受影响最小,爆炸压力下降7.4%。

W型火焰锅炉炉内气流组织优化及模拟研究

利用计算流体力学(CFD)软件,建立W型火焰锅炉数值模型,研究冷态试验前后,炉内气流组织变化以及飞灰冲蚀和炉膛壁面磨损情况。研究结果表明:经冷态试验优化气流组织,可以得到良好的W形态;调平后炉膛内部流场优化,炉膛内部整体磨损情况改善,磨损速率由调平前的4×10^(-6)kg/(m^(2)·s)降低到1.5×10^(-6)kg/(m^(2)·s);合理的气流组织对炉膛壁面的磨损影响较大,调平前波动幅度最大达到25×10^(-7)kg/(m^(2)·s),调平后波动幅度则在5×10^(-7)kg/(m^(2)·s),合理配风是保证炉膛壁面磨损减弱的重要因素。

高辐射热下高性能纤维阻燃织物的热防护性能研究

针对阻燃织物在高辐射热量暴露下热防护性能和力学性能均受到不同程度损失的问题,研究芳纶1313、芳纶1414、聚酰亚胺、聚对苯撑苯并二噁唑纤维单层及芳纶1313、芳纶1414、聚酰亚胺混配织造的双层织物的阻燃性能、热稳定性能、40 kW/m^(2)辐射热通量下的热防护性能及20 kW/m^(2)热通量作用后的断裂强力变化。结果表明,不同材料的单、双层织物均有较好的阻燃性能;芳纶1313织物在260℃下尺寸变化率5%左右,其他织物的尺寸变化率均在1.5%以内;在辐射热40 kW/m^(2)的热通量下,织物的辐射热防护性能与材料的耐温和织物结构有较大的关系,热分解温度较高的芳纶1414、PBO、聚酰亚胺材料经辐射热作用后的断裂强力损失率小于10%;当芳纶1313/聚酰亚胺/芳纶1414(20/30/50)双层织物接结纱间隔为1.2 cm×1.2 cm,且表里层密度配比达到1.6∶1时,具有较好的辐射热防护值。

阻燃桔红333 dtex/288 f涤纶DATY生产工艺探讨

文章介绍了在TMT高速纺设备上生产磷系阻燃桔红128 dtex/72 f涤纶POY、在宏源HY 1000V加弹机上生产阻燃桔红167 dtex/144 f微网DTY的工艺技术,并对牵伸比、T_(1)张力、T_(2)张力、第一热箱温度和D/Y比等参数对试验样品物性指标的影响进行了分析。之后,在Barmag FK6T-80空气变形丝机上对阻燃167 dtex/144 f微网DTY和256 dtex/144 f POY进行变形加工,探讨了拉伸倍数、温度等对变形丝物理性能的影响。

汽车座椅用织物的复合工艺及其性能

为降低汽车座椅用织物的制备成本,表层织物利用双层小提花组织设计,采用一定比例的阻燃涤纶与普通涤纶进行交织,兼顾装饰、阻燃、耐磨等性能;中间层使用不同结构的经编间隔织物(WKSF)替代海绵,提高透气性、环保性及缓压性能;里层织物采用涤纶针织物。采用热塑性聚氨酯(TPU)热熔胶网膜黏合剂将3层织物复合层压,研究复合工艺中温度、时间、施胶量等参数对复合材料性能的影响。结果表明:优化复合工艺的温度为120℃、时间为100 s、施胶量为50 g/m^(2);当间隔织物网眼数为45个/(25 cm^(2)),厚度为7.12 mm,间隔丝密度为39.71根/cm^(2)时,中间层织物对复合材料的剥离强力、透气性等性能最佳。通过该复合工艺设计的汽车座椅面料可将阻燃、透气、装饰、绿色环保等功能集于一体,从而适应高档汽车座椅用纺织品的需要。

微焰燃烧技术在小体积燃气热水器上的研究与应用

本文主要针对燃气热水器中现有燃烧器火焰高度高、燃烧系统体积大等问题进行了测试分析,并采用数值分析与实验验证相结合的手段,提出了相应的优化方案。通过对燃烧器引射段、头部、火口形状的重新设计,提出了微焰燃烧技术,并实现了火焰高度降低25 %以上。并通过设计无盘管风冷降温燃烧系统,以及对燃烧系统的一、二次空气系数、火焰均匀性等进行了优化,实现了燃烧系统体积缩小,使微焰燃烧技术应用在小体积燃气热水器上。