丙烷-空气爆燃火焰通过平行板狭缝时的淬熄研究

对丙烷－空气预混气的爆燃火焰在平行板狭缝中传播时的淬熄现象进行了实验和理论研究，给出了火焰传播速度与淬熄直径、淬熄长度的关系，对爆燃火焰在狭缝中淬熄机理作了探讨，并得到了有实用价值的结论。     

丙烷-空气爆燃火焰通过平行板狭缝时的淬熄研究

对丙烷－空气预混气的爆燃火焰在平行板狭缝中传播时的淬熄现象进行了实验和理论研究，给出了火焰传播速度与淬熄直径、淬熄长度的关系，对爆燃火焰在狭缝中淬熄机理作了探讨，并得到了有实用价值的结论。     

无约束条件下甲烷/空气预混气体燃爆特性研究

为研究无约束条件下甲烷(CH₄)/空气(air)预混气体的燃爆特性,以乳胶气球为反应容器开展了甲烷爆炸实验,结合Chemkin模拟和改进的比色测温技术,研究了不同当量比下甲烷/空气预混气体的火焰传播速度、爆炸超压及温度场分布等特征以及静置时间对预混气体燃爆特性的影响。实验结果表明：甲烷/空气预混气体的爆炸火焰传播速度呈振荡分布,当量比为0.83、1.06、1.30和1.55时的平均火焰传播速度分别为1.554m·s^-1、2.122m·s^-1、1.892m·s^-1和1.428m·s^-1;峰值超压随当量比的增加呈先增大后减小的趋势,当量比为1.06时基元反应CH₃·+O₂?O·+CH₃O·的敏感性系数最大,从而加速了生成二氧化碳(CO₂)的链反应,使得燃烧化学反应最彻底,峰值超压值最大;静置时间对火焰传播速度和爆炸峰值压力影响显著,最佳静置时间为6min;随着当量比的增大,爆炸火焰的平均温度呈现...     

汽油蒸气/空气预混火焰的无拉伸层流燃烧速率

为了研究汽油蒸气/空气的爆炸特性,介绍了汽油蒸气/空气预混火焰的无拉伸层流燃烧速率。通过实验研究了无拉伸层流燃烧速率,与汽油的主要组分异辛烷和正庚烷与空气的预混火焰层流燃烧速率做了对比,发现汽油蒸气/空气的无拉伸层流燃烧速率小于异辛烷和正庚烷与空气的预混火焰无拉伸层流燃烧速率,但无拉伸层流燃烧速率随当量比的变化规律相同,随着当量比增大,无拉伸层流燃烧速率呈先增大、再减小的变化趋势,最大值在当量比为1处取得。     

甲烷/空气预混气体火焰的传播特征

利用高速纹影摄像等技术探讨了密闭管道内不同当量比的甲烷/空气预混气体火焰的传播特征。结果表明,当甲烷含量接近当量值时,预混气体火焰传播中会发生火焰阵面由向未燃区弯曲到向已燃区弯曲的转折过程,逐渐由层流燃烧转变成湍流燃烧,并形成Tulip火焰结构;当甲烷含量偏离当量值一定程度时,预混火焰呈现出典型的层流燃烧特征,不会发生火焰阵面由向未燃区弯曲到向已燃区弯曲的转折过程。Tulip火焰结构形成于火焰传播速度迅速降低的区间里,且只有当减速阶段的最大加速度的绝对值大于某一数值时才能形成;Tulip火焰结构是预混火焰由层流燃烧向湍流燃烧转变的一个中间过程。     

耦合火焰自加速传播的氢气云爆炸超压预测

通过揭示当量比对氢气云爆炸火焰形态、火焰半径和爆炸超压峰值的影响规律,本文拟建立耦合火焰自加速传播的氢气云爆炸超压预测模型。结果表明:氢气云爆炸火焰传播速度由大至小对应的当量比依次是Φ=2.0、Φ=1.0和Φ=0.8。Le＜1.0和Le＞1.0的氢气云爆炸火焰表面均出现胞格结构,胞格结构的出现必然会增加火焰燃烧表面积,进而出现“火焰自加速”现象。对于特定的当量比,随着压力监测点和点火位置间距的增加,爆炸超压峰值的正值和负值绝对值均单调减小;对于特定的压力监测点,爆炸超压峰值的正值和负值绝对值随当量比的关系存在些许差异;不同当量比和监测点位置的爆炸超压峰值的负值绝对值大都高于正值。耦合火焰自加速传播的氢气云爆炸超压预测模型可成功预测不同压力监测点薄膜破裂前氢气云爆炸超压的发展过程。     

热扩散不稳定和流体动力学不稳定对氢气/空气爆炸胞状火焰的影响

为揭示氢气/空气爆炸球形胞状火焰的传播特性,运用高速摄影技术实验研究了热扩散不稳定和流体动力学不稳定对胞状火焰结构、临界火焰半径、临界Peclet数和火焰燃烧速度的影响。结果表明:随着流体动力学不稳定的凸显,Lewis数大于1的火焰胞格尺度远大于Lewis数小于1的胞格尺度;同一初始压力下,火焰厚度随着当量比的增大呈先减小、后增大的趋势,临界火焰半径会随着当量比的增大而增大;同一当量比下,火焰厚度和临界火焰半径都会随着初始压力的升高而减小;当量比低于2.0时,不同初始压力下的临界Peclet数会随当量比的增大而线性增大;当量比为0.6,初始压力为0.05 MPa时的火焰燃烧速度最大。     

甲烷/煤尘复合爆炸火焰的传播特性

为揭示甲烷/煤尘复合爆炸火焰的传播机理,利用气粉两相混合爆炸实验系统,在低于甲烷爆炸下限条件下,采用高速摄影机记录火焰传播图像,通过热电偶采集火焰温度,研究了煤尘种类以及甲烷体积分数对甲烷/煤尘复合火焰传播特性的影响。结果表明:挥发分是衡量煤尘燃烧特性的主导因素;随着煤尘挥发分的升高,燃烧反应增强,火焰传播速度升高,火焰温度升高;挥发分含量差异较小时,水分含量越低,燃烧反应越剧烈;在相同条件下,焦煤的燃烧反应强度最高,其次为长焰煤,最后为褐煤;随着甲烷体积分数的增加,煤尘颗粒的燃烧可由释放挥发分的扩散燃烧转变为气相预混燃烧,燃烧反应增强,火焰传播速度和火焰温度显著升高;热辐射和热对流作用促进煤尘颗粒热解,释放挥发分进行燃烧反应,维持复合火焰的持续传播;随着混合体系中甲烷体积分数的增加,混合爆炸机制由粉尘驱动型爆炸转为气体驱动型爆炸,燃烧反应增强;甲烷/煤尘复合爆炸火焰可由未燃区、预热区、气相燃烧区、多相燃烧区和焦炭燃烧区5部分组成,湍流扰动导致燃烧介质空间分布存在差异,使得燃烧区无规则交错分布。     

波纹管道阻火器内火焰传播的实验与数值模拟研究

对乙烯-空气预混火焰在波纹管道阻火器中的传播与淬熄过程进行了实验和数值模拟研究,实验结果显示:当乙烯接近当量浓度时,预混气体爆炸压力变化过程可分为4个阶段,等压燃烧阶段、缓慢上升阶段、快速上升阶段和压力振荡阶段;在爆炸过程中,由于反射压力波和火焰相互作用的影响,超压值出现多次振荡,压力振荡阶段一般可以持续数十毫秒;乙烯-空气火焰传播速度随管径增加、阻火单元波纹高度减小呈递增趋势,而且随着阻火单元厚度的增加,阻火器的阻火能力明显提高,可以更有效地使火焰淬熄。数值模拟结果显示:在管道封闭端点火后,火焰面呈半球形并以层流扩散的方式向四周传播;当火焰传播到管道壁面时,在管道壁面的约束作用下,火焰面发生变形,壁面附近的火焰逐渐超过了管道轴线附近的火焰,最后形成了“郁金香”状的火焰结构;当爆燃火焰经过阻火单元时,高温已燃气体被其吸收大量热量,同时在反应区产生的稀疏波作用下,气体温度逐渐降低、化学反应速率迅速减小,最终导致火焰被熄灭。通过模拟计算结果可以看出,在整个爆炸过程中,火焰传播速度与爆炸压力波动均较为明显。并提出了孔隙率和阻火单元厚度对火焰传播的影响机制。基于传热学理论模型,并结合实验数据,得出了爆燃火焰速度与爆炸压力之间的关系,为工业装置阻火器的设计和选型提供更为准确的参考依据。     

富氢燃料气射流预混火焰回火特性的研究进展

燃气轮机是一种重要的动力设备,是碳中和的重要环节,燃用富氢燃料气是降低其碳排放的有效途径.由于氢气的化学反应活性高、燃烧速率快,使得燃烧室内预混射流火焰发生回火的风险大大增加,即火焰有可能从燃烧室向上游预混气管道传播.文章综述了近20年来富氢燃料气射流火焰回火的代表性实验及数值模拟的研究进展,介绍了包含燃料氢含量、来流温度及工作压力等参数、喷嘴结构与尺寸、热声振荡和微混燃烧器等对回火特性影响的研究成果,现有研究表明,边界层内火焰传播速度超过来流速度是造成回火的主要因素,控制来流速度、来流温度、改变局部燃料浓度可以克服或者减缓回火.根据目前的研究现状和发展动态,对未来的研究方向进行了展望.     

Experimental study of lean flammability limits of methane/hydrogen/air mixtures in tubes of different diameters

Lean limit flames in methane/hydrogen/air mixtures propagating in tubes of internal diameters (ID) of 6.0, 8.9, 12.3, 18.4, 25.2, 35.0, and 50.2 mm have been experimentally studied. The flames propagated upward from the open bottom end of the tube to the closed upper end. The content of hydrogen in the fuel gas has been varied in the range 0–40 mol%. Lean flammability limits have been determined; flame shapes recorded and the visible speed of flame propagation measured. Most of the observed limit flames in tubes with diameters in the range of 8.9–18.4 mm had enclosed shape, and could be characterized as distorted or spherical flame balls. The tendency was observed for mixtures with higher hydrogen content to form smaller size, more uniform flame balls in a wider range of tube diameters. At hydrogen content of 20% or more in the fuel gas, limit flames in largest diameters (35.0 mm and 50.2 mm ID) tubes had small, compared to the tube diameter, size and were “lens”-shaped. “Regular” open-front lean limit flames were observed only for the smallest diameters (6.0 mm and 8.9 mm) and largest diameters (35.0 and 50.2 mm ID), and only for methane/air and (90% CH₄ + 10% H₂)/air mixtures, except for 6 mm ID tube in which all limit flames had open front. In all experiments, except for the lean limit flames in methane/air and (90% CH₄ + 10% H₂)/air mixtures in the 8.9 mm ID tube, and all limit flames in 6.0 mm ID tube, visible flame speeds very weakly depended on the hydrogen content in the fuel gas and were close to- or below the theoretical estimate of the speed of a rising hot bubble. This observation suggests that the buoyancy is the major factor which determines the visible flame speed for studied limit flames, except that last mentioned. A decrease of the lean flammability limit value with decreasing the tube diameter was observed for methane/air and (90% CH₄ + 10% H₂)/air mixtures for tubes having internal diameters in the range of 18.4–50.2 mm. This effect has been attributed to the stronger combined effect of the preferential diffusion and flame stretch in narrower tubes for flames which resemble rising bubble.     

半封闭空间明火引燃油气特性实验

为研究明火引燃油气着火爆炸特性,建立了半封闭着火爆炸实验平台。通过高速摄影仪拍摄的火焰图像,研究不同油气体积分数下的火焰传播特性。根据高频压力传感器采集的容器内压力变化情况,分析不同油气体积分数下的压力发展特性。结果表明,油气体积分数对火焰组分、火焰传播速度、压力和压力变化速率有显著影响;火焰具有明显的分区现象,可分为燃烧核和火焰阵面,并且纵向火焰阵面速度大于横向火焰阵面速度;容器内压力发展历程可分为4个阶段,而且会形成压力双峰现象;油气爆炸过程中,火焰结构与压力波形成了强烈的耦合作用。     

The propagation mechanism of high speed turbulent deflagrations

The propagation regimes of combustion waves in a 30 cm by 30 cm square cross–sectioned tube with an obstacle array of staggered vertical cylindrical rods (with BR=0.41 and BR=0.19) are investigated. Mixtures of hydrogen, ethylene, propane, and methane with air at ambient conditions over a range of equivalence ratios are used. In contrast to the previous results obtained in circular cross–sectioned tubes, it is found that only the quasi–detonation regime and the slow turbulent deflagration regimes are observed for ethylene–air and for propane–air. The transition from the quasi–detonation regime to the slow turbulent deflagration regime occurs at (where D is the tube “diameter” and is the detonation cell size). When , the quasi–detonation velocities that are observed are similar to those in unobstructed smooth tubes. For hydrogen–air mixtures, it is found that there is a gradual transition from the quasi–detonation regime to the high speed turbulent deflagration regime. The high speed turbulent deflagration regime is also observed for methane–air mixtures near stoichiometric composition. This regime was previously interpreted as the “choking” regime in circular tubes with orifice plate obstacles. Presently, it is proposed that the propagation mechanism of these high speed turbulent deflagrations is similar to that of Chapman–Jouguet detonations and quasi-detonations. As well, it is observed that there exists unstable flame propagation at the lean limit where . The local velocity fluctuates significantly about an averaged velocity for hydrogen–air, ethylene–air, and propane–air mixtures. Unstable flame propagation is also observed for the entire range of high speed turbulent deflagrations in methane–air mixtures. It is proposed that these fluctuations are due to quenching of the combustion front due to turbulent mixing. Quenched pockets of unburned reactants are swept downstream, and the subsequent explosion serves to overdrive the combustion front. The present study indicates that the dependence on the propagation mechanisms on obstacle geometry can be exploited to elucidate the different complex mechanisms of supersonic combustion waves. Received 5 November 2001 / Accepted 12 June 2002 / Published online 4 November 2002 Correspondence to: J. Chao (e-mail: jenny.chao@mail.mcgill.ca) An abridged version of this paper was presented at the 18th Int. Colloquium on the Dynamics of Explosions and Reactive Systems at Seattle, USA, from July 29 to August 3, 2001.     

方孔障碍物对瓦斯火焰传播影响的实验与大涡模拟

为揭示置障管道内甲烷/空气预混火焰传播特性,运用高速摄影技术对甲烷/空气预混火焰的形状变化和火焰前锋的速度特性进行实验,并利用大涡模拟对管道内的流场结构进行数值分析。结果表明:置障管道内依次出现了球形火焰、指尖形火焰及“蘑菇”状火焰,且“蘑菇”状火焰出现之后,火焰开始反向传播;“蘑菇”状火焰是双涡旋结构与火焰前锋面相互作用的结果,而火焰的反向传播是由流场中出现逆流结构引起的;障碍物对火焰前锋有明显的加速作用;大涡模拟成功再现了实验中观察到的火焰形状、火焰前锋速度及流场结构,说明大涡模拟适用于置障管道内预混火焰传播特性的研究。     

Self-Turbulent Flame Speeds

This paper reports an experimental investigation of premixed propane and methane-air flames propagating freely in tubes 1.5?m long and with diameters ranging from 26 to 141?mm. The thermo-acoustic instability was eliminated by means of a novel acoustic absorber placed at the closed end of the tube. We first remark that the flame can adopt different shapes either quasi-axisymmetric and normal to the mean direction of propagation, or inclined with a larger propagation speed because of the increase in flame surface area. The minima of the propagation speeds, corresponding to non-tilted flame propagation, are then analyzed using analytical models for the self-turbulent flame propagation. The concept of a cut-off wavelength appears to be relevant to explain the different behaviors observed on the rich side of methane-air and propane-air flames.     

Experimental investigation of dynamics of premixed acetylene–air flames in a micro-combustor

This paper describes a detailed experimental study performed to investigate the flame propagation behaviour of premixed flames in micro-channels. A novel, modular, stackable micro-combustor was developed for this purpose. For a chosen planar channel geometry, the flow condition and the mixture equivalence ratio of premixed acetylene–air were varied to investigate various modes of operation. Three different modes of operation were observed; they were (i) stable periodic operation – consisting of ignition, flame propagation, flame extinction, and re-ignition, (ii) a-periodic operation, and (iii) anchored flame condition. The present work also aims to provide quantitative information on the dynamics of premixed acetylene–air flames propagating inside micro-channels. A novel measurement approach based on OH^* chemiluminescence measurements employing a single photomultiplier unit was developed for this purpose. The data recorded were post processed using an in-house developed MATLAB code to evaluate the mean flame propagation speed measured between three different spatial locations along the length of the micro-channel. The results from the flame propagation speed measurements performed during ‘periodic’ mode of operation indicated that the flame travelled at higher propagation speed in the mid-length region of the channel compared to that at the initial entry point, suggesting flame acceleration. This flame acceleration could be attributed to a situation where the flame experienced different local equivalence ratio conditions at different upstream locations. The results suggest that after completion of a cycle of operation consisting of ignition, flame propagation and flame extinction, the fresh mixture that filled the channel was diluted with the exhaust gas from the previous cycle. This pocket of diluted mixture convected downstream with time, thus enabling the spatial variation in local equivalence ratio along the micro-channel.     

氢气/丙烷/空气预混气体爆轰性能的实验研究

通过采用压力传感器和烟灰板两种测试设备,开展了常温常压下氢气/丙烷和空气混合气体爆轰性能的实验研究。实验过程中观察到自持爆轰波,爆轰速度比值在0.99~1之间,爆轰压力比值在0.8~1.2之间。爆轰胞格尺寸在10~50 mm范围内,建立了爆轰胞格尺寸和化学诱导长度的关系式。随着丙烷不断添加,爆轰速度减小,而爆轰压力和胞格尺寸增加。这种变化趋势起初较快,而后变缓。因为起初氢气摩尔分数较大,混合气体趋向于氢气/空气的爆轰性能;而后因丙烷摩尔质量较大,丙烷逐渐起主要作用,混合气体表现出丙烷/空气的爆轰性能。     

Explosive-driven shock wave and vortex ring interaction with a propane flame

Experiments were performed to analyze the interaction of an explosively driven shock wave and a propane flame. A 30 g explosive charge was detonated at one end of a 3-m-long, 0.6-m-diameter shock tube to produce a shock wave which propagated into the atmosphere. A propane flame source was positioned at various locations outside of the shock tube to investigate the effect of different strength shock waves. High-speed retroreflective shadowgraph imaging visualized the shock wave motion and flame response, while a synchronized color camera imaged the flame directly. The explosively driven shock tube was shown to produce a repeatable shock wave and vortex ring. Digital streak images show the shock wave and vortex ring propagation and expansion. The shadowgrams show that the shock wave extinguishes the propane flame by pushing it off of the fuel source. Even a weak shock wave was found to be capable of extinguishing the flame.     

Synthesis of TiO2 nanoparticles by propane/air turbulent flame CVD process

Synthesis of TiO2 nanoparticles by the oxidation of titanium tetrachloride (TiCl4) in high-strength propane/air turbulent flame is investigated tentatively for mass production ofTiO2 nanoparticles. Effects of reactor heat flux varying from 247 to 627 kJ/m2 s, initial TiO2 number density from 2×1020> to 1 × 1021 m-3, and apparent residence time of TiO2 nanoparticles in reactor from 0.06 to 0.9 s, on particle morphology, phase composition, UV absorption and photoluminescence (PL) spectra are studied. The TiO2 nanoparti-cles synthesized, with mean size of 30-80 nm and rutile mass fraction from 0.155 up to 0.575, exhibited a strong PL signal at the wavelength of 370-450 nm, with a wide peak signal at 400-420 nm, reflecting significant oxygen vacancies on the surface of the TiO2 nanoparticles.     

Microgravity experiments and numerical studies on ethanol/air spray flames

Spray flames are known to exhibit amazing features in comparison with single-phase flames. The weightless situation offers the conditions in which the spray characteristics can be well controlled before and during combustion. The article reports on a joint experimental/numerical work that concerns ethanol/air spray flames observed in a spherical chamber using the condensation technique of expansion cooling (based on the Wilson cloud chamber principle), under microgravity.We describe the experimental set-up and give details on the creation of a homogeneous and nearly monosized aerosol. Different optical diagnostics are employed successfully to measure the relevant parameters of two-phase combustion. A classical shadowgraphy system is used to track the flame speed propagation and allow us to observe the flame front instability. The complete characterization of the aerosol is performed with a laser diffraction particle size analyser by measuring the droplet diameter and the droplet density number, just before ignition. A laser tomography device allows us to measure the temporal evolution of the droplet displacement during flame propagation, as well as to identify the presence of droplets in the burnt gases. The numerical modelling is briefly recalled. In particular, spray-flame propagation is schematized by the combustion spread in a 2-D lattice of fuel droplets surrounded by an initial gaseous mixture of fuel vapour and air.In its spherical expansion, the spray flame presents a corrugated front pattern, while the equivalent single-phase flame does not. From a numerical point of view, the same phenomena of wrinkles are also observed in the simulations. The front pattern pointed out by the numerical approach is identified as of Darrieus–Landau (DL) type. The droplets are found to trigger the instability. Then, we quantitatively compare experimental data with numerical predictions on spray-flame speed. The experimental results show that the spray-flame speed is of the same order of magnitude as that of the single-phase premixed flame. On the other hand, the numerical results exhibit the role played by the droplet radius in spray-flame propagation, and retrieve the experiments only when the droplets are small enough and when the Darrieus–Landau instability is triggered. A final discussion is developed to interpret the various patterns experimentally observed for the spray-flame front.