有障碍物半开口管道内氢气燃烧数值模拟研究

基于有障碍物氢气燃烧实验装置进行数值模拟研究,采用Fluent软件分析了半开口管道内障碍物对氢气/空气燃烧特性的影响。结果表明:障碍物会促进实验管段内氢气火焰加速,随着障碍物阻塞率和数量的增加,火焰加速更快且燃烧压力峰值更大;在相同阻塞率下,障碍物形状对氢气火焰速度和燃烧压力峰值的影响很小;燃烧压力随障碍物间距的增大先增大后减小,障碍物间距为3倍管道内径时产生的燃烧压力峰值最大。     

立体结构障碍物对甲烷预混火焰传播影响的研究

使用自行设计的火焰加速试验系统,研究了3种立体结构障碍物对管道内预混火焰传播速度和超压的影响。选用长方体、正四棱柱和圆柱,其阻塞比均为40%。结果表明,管道内障碍物对火焰传播的初始阶段起阻碍作用,当火焰越过障碍物后,障碍物加速火焰传播过程。有障碍物时管道内最大火焰传播速度和峰值超压比无障碍物时要大。随着点火距离的增大,管道中最大火焰传播速度和超压先变大后减小。当障碍物位于约6倍管径处时,对管道中火焰传播速度和超压影响最大。点火距离的改变对火焰传播速度的影响大于对管道内超压的影响。     

5种结构障碍物对火焰传播影响的试验研究

为了研究障碍物结构对预混甲烷管道内火焰传播速度和峰值超压的影响,自行设计一套火焰加速系统。在火焰加速管道上安装光电传感器和压力传感器分别测定火焰传播速度和超压,试验中选取5种结构障碍物,即平板、长方体、三棱柱、四棱柱和圆柱,其阻塞比分别为20%,40%和60%3种。研究结果表明:初始阶段障碍物阻碍火焰传播,当火焰越过障碍物后,障碍物能显著加速火焰传播。随着阻塞比增加,相同结构障碍物的火焰传播速度总体上不断增加,而峰值超压先变大后减小。相同阻塞比下,平板、三棱柱对火焰传播速度和超压影响相对较大;长方体居中;圆柱、四棱柱对增加火焰传播速度和超压作用相对较小。较小阻塞比障碍物管道内超压与无障碍物管道中的超压相比显著增加,但此后,管道中超压随阻塞比变化不明显。     

障碍物对油气-空气混合气体泄压爆炸火焰传播特性影响

为了研究障碍物对油气泄压爆炸火焰传播特性的影响规律,进行了不同数量障碍物工况下的对比实验,并利用纹影仪和高速摄影仪记录了火焰传播过程,针对障碍物对火焰形态、火焰锋面位置及火焰传播速度的影响规律进行了研究,结果表明:圆柱体障碍物会导致油气泄压爆炸火焰形态产生褶皱和弯曲变形,诱导层流火焰向湍流火焰转变,加速火焰的传播,对油气泄压爆炸火焰的初始传播形态有显著影响;随着障碍物数量的增多,火焰锋面传播距离点火端的最大距离增大,但到达最远距离的时间减少;障碍物能够增强火焰的传播速度,尤其对障碍物下游火焰影响最为显著,随着障碍物数量的增多,火焰传播的最大速度也随之增大,但达到最大火焰传播速度的时间却随之减少;障碍物的存在增大了油气泄压爆炸过程外部爆炸压力,并且随着障碍物数量的增多,外部爆炸压力峰值增长幅度增大。     

障碍物管道中预混火焰传播物理机理的试验研究

研究氢气/空气预混火焰加速过程的物理机理对氢气爆炸灾害预防和控制有重要意义。采用压力-时间记录法和纹影法两种测试方法,开展了常温常压下二元燃料氢气/丙烷和空气混合气体在带有阻塞比为0.5的孔板形障碍物、40 mm×40 mm×3 000 mm的方管中预混火焰传播物理机理的试验研究。结果表明,由压力传感器所测的火焰传播速度沿管道轴线方向先增加后逐渐减小。通过纹影法所测的火焰传播速度在可视化范围内逐渐增加。火焰加速初始阶段的主要物理机理是火焰表面积增加、燃烧产物膨胀和障碍物间的延迟燃烧等。     

泄爆夹层内障碍物对泄爆效果影响的数值模拟研究*

为研究泄爆夹层内障碍物位置对燃气泄爆效果的影响,以某大型商业综合体暗厨房为研究对象,考虑泄爆夹层中结构梁不同位置的泄爆效果,对暗厨房燃气爆炸的泄爆过程开展数值模拟研究。研究结果表明:在火焰没有到达泄爆窗前的爆炸初始阶段,障碍物对火焰结构和传播速度基本没有影响,当火焰进入泄爆夹层后,障碍物的存在可引发火焰加速现象;当障碍物距离泄爆窗1.7 m时,火焰加速现象较为明显,火焰最大传播速度可达591.5 m/s,此时厨房内压力峰值约2.9 MPa,约为没有结构梁情况下1.42倍;障碍物距离泄爆窗较近时,二者将协同影响火焰传播;厨房内压力峰值随着障碍物与泄爆窗距离的增大遵循增大-突降-增大的规律。研究结果可为商业综合体暗厨房泄爆设计提供一定理论依据。     

障碍物对瓦斯煤尘爆炸火焰传播规律的影响

为了进一步探究瓦斯煤尘耦合爆炸火焰的传播规律,用自行搭建的半封闭垂直管道爆炸试验系统,研究障碍物对瓦斯煤尘耦合爆炸火焰传播规律的影响。研究结果表明:障碍物能显著提高瓦斯煤尘爆炸火焰的传播速度,其加速机理主要是障碍物诱导的湍流区会促进火焰的传播;火焰在传播过程中的加速度不是一直增加,随着火焰速度的增加会出现上下波动;煤尘的加入会使瓦斯爆炸产生的火焰传播速度显著增大及速度的最大值距离点火端较远;通过障碍物时爆炸产生的火焰形状发生较大的改变,出现拉伸和褶皱现象。     

置障空间可燃气体火焰传播特性数值模拟研究

为揭示置障管道内丙烷浓度对火焰传播特性影响,借助ANSYS Fluent软件,利用Zimont燃烧模型开展了置障管道内不同丙烷浓度预混气体燃爆规律的大涡模拟研究。结果表明:在阻塞率为0,0.5,0.7,0.9障碍物管道中火焰锋面速度峰值均随给定初始浓度的增加呈现先增大后减小的趋势,且峰值速度随阻塞率的增大而增大,丙烷体积分数为4.5%、阻塞率为0.9时,火焰传播峰值速度可达178.93 m/s;阻塞率越大,涡团规模越大,导致流场紊乱程度增大,湍流脉动增强,火焰面与流场相互作用,促使火焰面褶皱破碎,加速了已燃气体与未燃气体分子间的无规则运动,对燃烧反应起到激励作用;数值模拟结果直观展示了火焰传播进程及火焰结构的发展细节。     

初始温度和初始压力对气体爆轰参数影响的研究

利用已有的气体爆炸模型和包含初始压力、初始温度的气体爆轰参数的计算公式,从理论上研究初始压力和初始温度对气体爆轰参数的影响情况。使用VisualBasic语言编写计算程序,将计算值与文献值进行对比,具有较好的一致性。以甲烷-空气混合物为例,计算在98000Pa,280～400K及298K,0.1～0.5MPa的气体爆轰参数。计算结果表明,初始压力一定,混合物的爆轰压随初始温度的升高而减小,爆轰波速增大;初始温度一定,混合物的爆轰压随初始压力的增大而增大,爆轰波速基本不变;在初始温度和初始压力两个影响因素中,初始压力对混合物爆轰参数的影响明显大于初始温度。     

障碍物对开敞空间贫燃天然气爆炸特性的影响研究

为揭示贫燃条件下障碍物对开敞空间天然气爆炸特性的影响,试验记录了火焰传播形态和爆炸压力,并对火焰结构和压力空间分布进行了数值分析.结果表明:在无障碍物工况下,火焰近似以球形向外膨胀传播,火焰表面较为连续,火焰传播速度较慢,爆炸压力较低;而在障碍物的湍流扰动下,火焰表面出现较大的"褶皱"结构,火焰燃烧表面积显著增大,火焰传播速度升高,爆炸压力也相应增大.相比于由障碍物引起的火焰加速作用,因流体动力学不稳定性产生的失稳效应可忽略不计.由温度分布可清晰观察火焰表面"褶皱"结构的形成过程,计算所得的爆炸压力达到峰值时间较早,且超压峰值相比试验值较低.     

Experimental study on DDT for hydrogen–methane–air mixtures in tube with obstacles

An experimental study of flame propagation, acceleration and transition to detonation in stoichiometric hydrogen–methane–air mixtures in 6 m long tube filled with obstacles located at different configurations was performed. The initial conditions of the hydrogen–methane–air mixtures were 1 atm and 293 K. Four different cases of obstacle blockage ratio (BR) 0.7, 0.6, 0.5 and 0.4 and three cases of obstacle spacing were used. The wave propagation was monitored by piezoelectric pressure transducers PCB. Pressure transducers were located at different positions along the channel to collect data concerning DDT and detonation development. Tested mixtures were ignited by a weak electric spark at one end of the tube. Detonation cell sizes were measured using smoked foil technique and analyzed with Matlab image processing toolbox. As a result of the experiments the deflagration and detonation regimes and velocities of flame propagation in the obstructed tube were determined.     

Decomposing detonation and deflagration properties of ozone/oxygen mixtures

In this study, the decomposing detonation and deflagration properties of ozone/oxygen mixtures of up to 20 vol.% of ozone in oxygen under high pressure of up to 1.0 MPa in a tube were experimentally investigated. The mixtures were ignited by an electric spark at the end of the tube. Flame propagation properties such as flame velocity and pressure were measured with thermocouples and piezo electric transducers mounted along the tube. Slow and constant flame propagation profiles were obtained. We also investigated the quenching ability of a wire gauze as well as the concentration limit for flame propagation. However, in spite of slow flame propagation velocity and easy flame quenching properties under these experimental conditions, direct initiation of detonation by the driver detonation of the stoichiometric oxy-hydrogen mixture was easily achieved at much lower concentrations than the limit of deflagration. The observed detonation properties, such as wave velocity and pressure, agreed fairly well with C–J calculated values. The detonation velocity (900–1200 m/s) and the pressure ratio to initial pressures (5–9.5) were not affected by the initial pressure of the mixtures. Near the detonation limit, typical spinning detonations with oscillatory pressure waves were observed.     

An experimental study of flame acceleration and deflagration to detonation transition in representative process piping

The paper summarizes the results of experimental tests and accompanying analyses to investigate the factors that govern flame acceleration and potential transition to detonation in a relatively long unobstructed piping system. The overall aim of the work was to obtain sufficient experimental data so as to be able to develop and evaluate methodologies for classifying and predicting potential detonation flame acceleration and deflagration to detonation transition (DDT) hazard in industrial process pipes and mixtures. The present results show that the flame acceleration process in an unobstructed pipe exhibit three distinct phases: an initial establishment phase; a second rapid acceleration phase and a final transition to detonation phase. Test results with ethylene indicate that the acceleration process is not sensitive to initial pressure (all other parameters remaining constant) but can be sensitivity to initial pipe wall temperature or possibly mixture humidity. The presence of bends increases the local rate of turbulent combustion, an effect attributed to the additional turbulence generated downstream of the bend. For straight pipes, detonation was only observed to develop for hydrogen–air and ethylene–air mixtures. Detonation was not observed with methane, propane or acetone as fuel in the present piping apparatus.     

Experimental study of flame acceleration and the deflagration-to-detonation transition under conditions of transverse venting

Results of experiments on critical conditions for flame acceleration and the deflagration-to-detonation transition in tubes with transverse venting are presented. Tests were made with hydrogen mixtures in two tubes (inner diameter of 46 and 92 mm) with obstacles. Ratios of vent area to total tube area were 0.2 and 0.4. Venting was shown to influence flame acceleration significantly. The greater the vent ratio, the more reactive the mixture necessary for development of fast flames. Critical conditions for flame acceleration in tubes with venting, expressed through a critical mixture expansion ratio σ_cr, were found to be σ_cr/σ₀1+2, where σ₀ is the critical value for a closed tube. Critical conditions for detonation onset in a vented tube were found to be very close to those in a closed tube with similar configuration of obstacles.     

Effect of ignition position on the run-up distance to DDT for hydrogen-air explosions

The method described in this paper enabled reliable and accurate positioning of an overdriven detonation by calculation of shock wave velocities (detonation and retonation) for hydrogen explosions in a closed 18 m long horizontal DN150 pipe. This enabled an empirical correlation between the ignition position and the run-up distance to DDT to be determined. It was shown that the initial ability of the flame to expand unobstructed and the piston-like effect of burnt gas expanding against the closed end of the tube contributed to initial flame acceleration and hence were able to affect the run-up distance to overdriven detonation. Flame speeds and rates of initial pressure rise were also used to explain how these two competing effects were able to produce a minimum in the run-up distance to DDT. The shortest run-up distance to DDT, relative to the ignition position, for this pipe and gas configuration was found when the ignition position was placed 5.6 pipe diameters (or 0.9 m) from the closed pipe end. The shortest run-up distance to DDT relative to the end of the pipe was recorded when the ignition source was placed 4.4 pipe diameters or 0.7 m from the pipe end.     

气体爆轰波在弯曲管道中传播特性的实验研究

对丙烷 -空气爆轰波通过 90°弯管道时的传播特性作了实验研究 ,主要是气体爆轰波通过弯管道前后的火焰速度以及加速情况的研究 ,初步得出 ,爆轰波经过弯管道后单位距离上的火焰速度增量显著增加。这一研究结果证明 ,弯曲管道对于爆燃与爆轰波火焰有明显的加速作用     

Numerical simulation of flame acceleration and deflagration-to-detonation transition of ethylene in channels

Ethylene (C₂H₄) is a hydrocarbon fuel and widely used in chemical industry, however, ethylene is highly flammable and therefore presents a serious fire and explosion hazard. This work is initiated by addressing the hazard assessment of ethylene mixtures in different scale channels (d = 5 mm, 10 mm and 20 mm) from the aspect of flame acceleration (FA) and deflagration-to-detonation transition (DDT) by using large eddy simulation (LES) method coupled with the artificially thickened flame (ATF) approach. The fifth order local characteristics based weighted essentially non-oscillatory (WENO) conservative finite difference scheme is employed to solve the governing equations. The numerical results confirm that flame velocity increase rapidly at the beginning stage in three channels, and the flame acceleration rate is slower in the subsequent stage, afterwards, the flame velocity has an abrupt increase, and the onset of detonation occurs. Due to the fact that wall effect is significant in the narrow channel (e.g.,5 mm), especially in the ignition stage of the flame, flames have different shapes in wider channels (10 mm and 20 mm) and narrow channel (5 mm). Both the pressure and temperature profiles confirm DDT run-up distances are 0.251 m, 0.203 m and 0.161 m in 20 mm, 10 mm and 5 mm channels, respectively, which indicates that a shorter run-up distance is required in narrower channel. The cellular detonation structures for the ethylene-air mixture in different channels indicate that multi-headed detonation structures can be found in 20 mm channel, as the channel width decreases to 10 mm, detonation has a single-headed spinning structure, as the width is further reduced to 5 mm, only large longitudinal oscillation of the pressure can be observed.     

Crimped metal ribbon flame arrestors for the protection of gas measurement systems

This paper summarises the results of extensive research to determine the limit of safety against flame transmission for flame arrestors of relatively small size fitted with arrestor elements made of crimped metal ribbon. Depending on the reactivity of the fuel gas/air mixture and the tube geometry the running up to detonation and hence the stressing of a flame arrestor by a detonation is possible in longer tubes with relatively small diameters. Only with reactive gas phases of explosion group I this stressing case for a flame arrestor can be excluded. With detonative gas phases the stressing of the flame arrestor decisively depends on the place of installation with respect to the point of transition from deflagration to detonation in the system considered. Five different stressing cases with a probably very different limiting pressure of safety against flame transmission must be distinguished. The results of the investigations will help to evaluate the results from testing of flame arrestors carried out according to the requirements in national and international standards or regulations.     

Efficient simulation of flame acceleration and deflagration-to-detonation transition in smooth pipes

Evaluation of accident scenarios including flame acceleration and deflagration-to-detonation transition (DDT) in chemical plant piping systems increases the need for an efficient numerical simulation tool capable of dealing with this phenomenon. In this work, a hybrid pressure-density-based solver including deflagrative flame propagation as well as detonation propagation is presented. The initial incompressible acceleration stage is covered by the pressure-based solver until the flame velocity reaches the fast flame regime and transition to the density-based solver is done. The deflagration source term is formulated in terms of a turbulent flame speed closure model incorporating various physical effects crucial for flame acceleration at low turbulence conditions (Katzy and Sattelmayer, 2018). Modelling of the detonation source term is based on a quadratic heat release function (Hasslberger, 2017). The presented numerical approach is validated in terms of DDT locations and pressure data from Schildberg (2015) as well as recently completed flame tip position measurements. For this purpose, H₂/O₂/N₂ mixtures ranging from 25.6 vol-% H₂ to 29.56 vol-% H₂ in two different pipe geometries are considered. The focus of the current work is on predicting the DDT location correctly and good agreement is observed for the investigated cases.     

管道内瓦斯爆炸传播的试验研究

运用大型试验管道对瓦斯爆炸传播规律进行试验研究,并对瓦斯爆炸压力峰值、火焰速度和呈现时间进行分析,得出:在不出现爆轰的前提下,爆源点附近的压力峰值是全管道的最大值;爆炸压力峰值在沿管道的传播过程中从爆源点附近是先增大后减小,然后再逐渐增大且压力峰值最早呈现在出口附近;火焰传播速度随着传播距离的增大而逐渐增大且在爆炸初期增大速率更快;瓦斯浓度对爆炸压力峰值、火焰传播速度和呈现时间等都有重要影响。