点火条件对密闭管道内预混氢气/空气燃爆特性的影响

基于流体动力学软件Fluent,开展数值模拟,研究点火位置（距管左端壁面100、200和500 mm）、点火温度（1 000、1 500和2 000 K）和点火面积（管左端壁面处半径为50、35和20 mm的点火域）等点火条件对1 000 mm密闭管道中预混氢气/空气（H₂/air）燃爆特性的影响。研究表明:点火位置距管左端壁面越远,中间节点处温度越高,温升越快;不同点火温度下管内最高温升速率基本同步,且提高点火温度,使得燃烧反应更剧烈,能提高管内气体温升速率,但却降低管内的压力峰值;点火面积越小,预混H₂/air燃烧前期温升越快。当采用半径为35 mm的点火域和点火位置距管左端壁面100 mm的点火方式时,预混H₂/air燃爆的各项参数相对较高。不同点火条件对密闭管内气体的动能和内能的影响规律类似于其对管内气体的流速和温度的影响规律,而对涡量的影响不明显。     

点火位置对泄爆空间甲烷-空气爆炸荷载的影响

在12 m3密闭空间内开展了甲烷-空气预混气体（甲烷体积分数为9.5%）的爆炸试验研究,改变点火位置,分析有泄爆口时点火位置对甲烷-空气爆炸超压和火焰形态的影响。结果表明:点火位置对Δp₁的升压速度基本没有影响,Δp₂的峰值随着点火位置远离泄爆口而增大,Δp₄的峰值与点火位置的关系为:中心点火最大,尾部点火次之,前端点火最小。在所有位置,Δp₁随着泄爆阈值的增大而增大,且增量相同;Δp₂在前端点火和中心点火时随泄爆阈值的增加而消失,仅在尾部点火时出现;Δp₄只有在中心点火时随泄爆阈值的增加而增加。外部火焰发展过程可以分为火球阶段和火焰喷射阶段,尾部点火和中心点火的火球大小及火焰喷射长度远大于前端点火。     

高压氢气泄漏自燃形成喷射火的实验研究

为了探究高压氢气泄漏发生自燃时所需的临界初始释放压力随管道长度的变化规律，了解管内自燃火焰向管外喷射火焰转变的发展过程，本文利用压力、光电以及高速摄像等测试系统展开实验研究。实验结果表明:当管道长度相同，初始释放压力较低时，氢气泄漏不容易发生自燃；随着管道长度的增加，氢气发生自燃时的临界初始释放压力先缓慢减小后迅速增大；当管道长度一定时，初始释放压力越大，激波传播速度越快，氢气管内自燃的位置距离爆破片越近；气流通过激波马赫盘后，火焰燃烧加剧；随着时间的增加，火焰长度呈现先增大后逐渐减小的变化趋势，喷射火焰尖端的平均传播速度逐渐减小；火焰宽度呈现先增大后迅速减小至稳定值的变化规律。     

非金属粉末对方管内瓦斯预混火焰传播的影响

为研究非金属粉末对管内瓦斯预混火焰传播的影响,选用煤粉和石粉2类煤矿井下常见粉末,采用微细热电偶、火焰传感器测试得出内铺2种粉末管内瓦斯火焰传播的瞬态温度、火焰阵面位置及火焰传播速度等参数,初步分析2种粉末影响瓦斯火焰传播机制的不同。实验表明:(1)煤粉能够加速管内瓦斯火焰的传播,而石粉则抑制管内瓦斯火焰的传播,但两者影响机制有本质不同;(2)内铺煤粉时,火焰温度瞬时值曲线呈现出明显的双峰结构,反应区宽度增加,表明活性煤粉与瓦斯形成了瓦斯 煤粉复合火焰;(3)内铺石粉时,火焰温度值整体下降,温度半峰宽度变窄,说明撒布岩粉法能有效抑制瓦斯煤尘爆炸发生。     

点火准则和稀释气体对乙烯点火延时的影响

利用矩形截面激波管研究点火准则和稀释气体对乙烯点火延时的影响。采用压电传感器记录测点压力时间历程，采用光谱仪和光电倍增管记录自发光强时间历程，以压力、总自发光强与·OH和·CH自由基特定能级发射光强等信号判定是否发生自点火，给出自点火过程的时间起始点和终止点，得到了不同点火准则和稀释气体对应的乙烯/氧气/氮气和乙烯/氧气/氩气点火延时。结果表明:相同工况的乙烯点火延时测量数据相对误差约为15%，数据验证了本文实验和测量方法可靠性。针对当量比为1.0、压力为0.2 MPa，得到了温度范围为905～1 489 K，稀释气体的摩尔分数为75%氮气和75%氩气时的乙烯点火延时，给出点火延时和温度拟合的Arrhenius型表达式。不同点火准则会影响所测点火延时数据，但多次测量结果确定的点火延时和温度变化规律近似相同。不同稀释气体对激波管自点火流场的影响表现为和流场均匀性以及混合物比热相关。相同工况的乙烯/氧气/氮气点火延时大于乙烯/氧气/氩气点火延时。高温区和低温区的乙烯/氧气/氩气点火延时与温度的拟合关系不同，转折温度约为1 121 K。     

可燃气体中激波聚焦的点火特性

数值模拟了二维平面激波从抛物面上反射在可燃气体中聚焦的过程，研究了形 成爆轰波的点火特性. 对理想化学当量比氢气/空气混合气体，在初始压强20kPa的条件下， 马赫数2.6-2.8的激波聚焦能产生两个点火区：第1个点火区是反射激波会聚引起的，第 2个点火区是由入射激波在抛物面上发生马赫反射引起的. 这种条件下流场中会出现爆燃转 爆轰，起爆点分别分布在管道壁面、抛物反射面和第2点火区附近. 起爆机理分别为激波管 道壁面反射、点火诱导激波的抛物面反射和点火诱导的激波与第2点火区产生的爆燃波的相 互作用. 不同的点火和起爆过程导致了不同的流场波系结构，同时影响了爆轰波传播的波动 力学过程.     

湍流的诱导及其对瓦斯爆炸过程中火焰和爆炸波的作用

在实验的基础上,研究了管内瓦斯爆炸过程中湍流的诱导及其对瓦斯爆炸过程中火焰和爆炸波的影响作用.研究结果表明,管道面积突变对瓦斯爆炸过程中湍流的产生具有重要影响.管道面积突变(变大、变小)时,产生附加湍流,并使下游火焰气流的湍流度增加,瓦斯爆炸过程中火焰的传播速度迅速提高,并可诱导激波的产生.在80×80mm等截面直管中(瓦斯浓度为理论上最猛烈的爆炸浓度9.5%),瓦斯爆炸最大火焰传播速度为40.8m/s,管内各点均为压力波信号,当管道加装一Φ300mm圆管形成面积突扩11倍和突缩11倍两断面后,面积突扩处(L/D=22)火焰速度增大5.05倍,达到64.4m/s,面积突缩处(L/D=28)火焰速度为156.0m/s, 增大4.55倍,并在L/D=48倍处形成激波(超压1.6976atm、波速416.7m/s),在L/D=98倍处,激波强度最大.在面积突变管内加装加速环可使瓦斯爆炸过程中湍流度加剧,火焰的传播速度更高,激波生成的位置(L/D=28)、最强点位置(L/D=70)均前移,激波强度增大.研究结果对指导现场如何防治瓦斯爆炸,减轻瓦斯爆炸的威力具有一定的指导意义.     

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。     

增强型喷射器对爆轰波DDT过程的影响

在激波、火焰及射流同时存在的流场中，组织燃烧转爆轰过程是脉冲爆震发动机实现点火、起爆的关键问题。设计一类喷射器，采用C₂H₂/O₂/Ar反应，数值验证了该喷射器能增强爆震室燃料燃烧转爆轰的可行性，并讨论了流场中热点的点火机制。结果显示:该装置在流场中可激发不稳定性，产生漩涡，加速能量、质量的交换。流场产生热点，促进火焰速度加快，追赶前导激波。喷射器位置影响前导激波的运动速度。在一定范围内，前导激波速度越大，碰撞产生的热点越容易激发燃烧转爆轰过程。     

点火能对丙烷-空气预混气体爆炸过程及管壁动态响应的影响

在长12 m的无缝不锈钢直管中,通过改变初始点火能量,探究了点火能对封闭管道内丙烷-空气混合气体爆炸传播特性和激波对管壁动态加载的影响。结果表明,初始点火能对预混气体爆炸火焰传播规律以及管壁的动态响应有显著影响:点火能越大,爆炸越剧烈,爆炸压力峰值压力和管壁最大应变就越大,且压力波和管壁应变的发展一致。火焰在传播过程中受到管道末端反射波的作用会发生短暂熄灭和复燃;管壁承受冲击波加载,应变信号主要分布在0~781.25 Hz,管壁最大应变率大于10-3 s-1,实验工况下管壁应变属动态响应。     

Investigation of high-speed combustible gas ignited by a hot gas jetproduced in the shock tube

The high-speed combustible gas ignited by a hot gas jet, which is induced by shock focusing, was experimentally investigated. By use of the separation mode of shock tube, the test section of a single shock tube is split into two parts, which provide the high-speed flow of combustible gas and pilot flame of hot gas jet, respectively. In the interface of two parts of test sections the flame of jet was formed and spread to the high-speed combustible gas. Two kinds of the ignitions, 3-D “line-flame ignition” and 2-D “plane-flame ignition”, were investigated. In the condition of 3-D “line-flame ignition” of combustion, thicker hot gas jet than pure air jet, was observed in schlieren photos. In the condition of 2-D “plane-flame ignition” of combustion, the delay time of ignition and the angle of flame front in schlieren photos were measured, from which the velocity of flame propagation in the high-speed combustible gas is estimated in the range of 30–90m/s and the delay time of ignition is estimated in the range of 0.12–0.29ms. PACS 47.40.Nm; 82.40.FpPart of this paper was presented at the 5th International Workshop on Shock/Vortex Interaction, Kaohsiung, October 27–31, 2003.     

大尺度开敞空间油料蒸气云爆炸超压与火焰传播机制研究

为探究大尺度开敞空间油气爆燃动态发展过程,利用自行设计并搭建的大尺度开敞空间油气爆燃模拟实验条件测试系统,通过可视化监测手段及对压力与火焰信号的采集获得了油气爆燃过程中关键参数的变化规律。结果表明:在不同的初始油气浓度下引燃预混油气混合物将形成三类主要的燃烧模式;油气浓度接近爆炸极限范围内时火焰主要分布于台架的内场、点火面后方及正上方,根据动态超压时序发展曲线可将爆燃过程划分为3个子阶段;爆燃火焰传播速度呈波动性下降趋势,并可与超压发展阶段相互耦合;随着初始油气浓度的增加,超压峰值呈现出先减后增的趋势,形成峰值耗时则呈现相反规律;爆燃火焰的温度梯度与火焰行进方向相关,火焰峰面温度梯度通常小于尾端火焰;爆燃辐射峰值形成时间与火焰强度相比具有一定的延时性,爆燃传播末期更易于形成高强度辐射。     

Shock tube studies of thermal radiation of diesel-spray combustion under a range of spray conditions

A tailored interface shock tube and an over-tailored interface shock tube were used to measure the thermal energy radiated during diesel-spray combustion of light oil, α-methylnaphthalene and cetane by changing the injection pressure. The ignition delay of methanol and the thermal radiation were also measured. Experiments were performed in a steel shock tube with a 7 m low-pressure section filled with air and a 6 m high-pressure section. Pre-compressed fuel was injected through a throttle nozzle into air behind a reflected shock wave. Monochromatic emissive power and the power emitted across all infrared wavelengths were measured with IR-detectors set along the central axis of the tube. Time-dependent radii where soot particles radiated were also determined, and the results were as follows. For diesel spray combustion with high injection pressures (from 10 to 80 MPa), the thermal radiation energy of light oil per injection increased with injection pressure from 10 to 30 MPa. The energy was about 2% of the heat of combustion of light oil at P _inj = about 30 MPa. At injection pressure above 30 MPa the thermal radiation decreased with increasing injection pressure. This profile agreed well with the combustion duration, the flame length, the maximum amount of soot in the flame, the time-integrated soot volume and the time-integrated flame volume. The ignition delay of light oil was observed to decrease monotonically with increasing fuel injection pressure. For diesel spray combustion of methanol, the thermal radiation including that due to the gas phase was 1% of the combustion heat at maximum, and usually lower than 1%. The thermal radiation due to soot was lower than 0.05% of the combustion heat. The ignition delays were larger (about 50%) than those of light oil. However, these differences were within experimental error.

---

An abridged version of this paper was presented at the 18th Int. Symposium on Shock Waves at Sendai, Japan during July 21 to 26, 1991 and at the 19th Int. Symposium on Shock Waves at Marseille, France during July 26 to 30, 1993.     

爆燃波在含内构件管道中传播现象的实验研究

为了评估高温气冷核反应堆热交换器H2泄漏、爆炸的安全性,研究含内构件管道的H2/空气爆燃传播现象,建造了几何相似、尺寸相同的实验管道（真空筒）。分别充入不同初压和当量比H2/空气混合物,在真空筒顶部点火并引发爆燃,利用多通道瞬态压力测量和数据采集系统,记录各测点压力时间曲线。结果表明:对化学计量比H2/空气混合物,在慢化剂室和真空筒顶部空间产生爆燃,邻近测点的压力时间曲线显示了冲击波特征。该冲击波通过慢化剂室和真空筒侧壁的狭缝（2.5 mm）,进入含内构件的扩张管道并形成爆燃。冲击波在真空筒端部反射、向后传播并与火焰相互作用,爆炸流场波系复杂。对富油和低初压化学计量比混合物,在慢化剂室和真空筒顶部空间产生燃烧,高温富油燃气的压力上升速率较慢。当燃气通过上述狭缝时,在真空筒突扩空间内再次点火并形成较强爆燃,压力时间曲线显示了冲击波特征及其在端面的反射。     

Coupling Relation Between Air Shockwave and High-Temperature Flow from Explosion of Methane in Air

After a methane-in-air explosion in a coal mine tunnel, a secondary explosion of coal dust is prone to happen. The shockwave in the gas explosion produces a coal dust suspension, and the peak temperature band may detonate that suspension. This secondary detonation depends on the space-time relation between the shockwave and the peak temperature band. This paper presents a methodology to estimate the coupling relation between the air shockwave and high-temperature flow from the explosion of methane in air. The commercial software package AutoReaGas was used to carry out the numerical simulation for the explosion processes of methane in air in the tunnel. Based on the numerical simulation and its analysis, the coupling relation between the leading shock wave and high-temperature flow was demonstrated for a methane-in-air explosion in a tunnel. In the near field of the ignition point, the deflagration wave transmits energy by heat, and the temperature load is in the front of the pressure wave. With development of deflagration and deflagration-to-detonation transition, the corresponding mechanism of energy transmission is changed from heat conduction to shock compression, and a precursor pressure wave is formed gradually. The time interval between the precursor pressure wave and high-temperature flow behind the wave increases with distance. Attenuation of the precursor shock wave and high-temperature flow depends on the length of the methane-in-air space in a tunnel. Beyond the methane-in-air space, the quantitative relation of the time interval between the precursor shock wave and high-temperature flow with axial distance from ignition and the length of methane-in-air space was proposed.     

Three-Dimensional Simulation of Turbulent Hot-Jet Ignition for Air-CH<Subscript>4</Subscript>-H<Subscript>2</Subscript> Deflagration in a Confined Volume

This work describes essential aspects of the ignition and deflagration process initiated by the injection of a hot transient gas jet into a narrowly confined volume containing air-CH₄-H₂ mixture. Driven by the pressure difference between a prechamber and a long narrow constant-volume-combustion (CVC) chamber, the developing jet or puff involves complex processes of turbulent jet penetration and evolution of multi-scale vortices in the shear layer, jet tip, and adjacent confined spaces. The CVC chamber contains stoichiometric mixtures of air with gaseous fuel initially at atmospheric conditions. Fuel reactivity is varied using two different CH₄/H₂ blends. Jet momentum is varied using different pre-chamber pressures at jet initiation. The jet initiation and the subsequent ignition events generate pressure waves that interact with the mixing region and the propagating flame, depositing baroclinic vorticity. Transient three-dimensional flow simulations with detailed chemical kinetics are used to model CVC mixture ignition. Pre-ignition gas properties are then examined to develop and verify criteria to predict ignition delay time using lower-cost non-reacting flow simulations for this particular case of study.     

Experimental study of gas deflagration temperature distribution and its measurement

Explosion temperature is one of the main factors in combustible gas explosion accidents. Despite all this, this problem has not yet received considerable attention, especially few fundamental data related to the temperature distribution of gas explosions in closed vessels in literatures. According to characteristics of gas deflagrations, this work developed a gas explosion temperature measurement system whose response time to temperature is approximate 10 μs. By using this system, an experimental study was carried out which is concerned with the deflagration temperature distribution of premixed methane-air mixtures in the 20 L spherical vessel with a diameter of 168 mm. Experimental results show that temperatures on or near the wall are obviously lower than those in the center part of the vessel and there is a conspicuous gradient from the wall to the center part of the vessel. In the inside of the vessel, the deflagration temperature of premixed methane-air mixtures near the ignition spot at the center of the vessel can approximately reach 1200 °C, while near the wall, only 300 °C. This result throws a light on the specific regularity of gas temperature distribution near the boundary. It is possible to provide an important basis for understanding the general characteristics of gas deflagrations in closed vessels as well as choosing good measurement designs. Otherwise, if the ignition is located in the geometrical center of the spherical vessel, velocity of the flame increases with the distance away from the center inside the vessel, and when the flame arrives at the inner wall, this velocity descend sharply.     

Behavior of detonation waves at low pressures

With respect to stability of gaseous detonations, unsteady behavior of galloping detonations and re-initiation process of hydrogen-oxygen mixtures are studied using a detonation tube of 14 m in length and 45 mm i.d. The arrival of the shock wave and the reaction front is detected individually by a double probe combining of a pressure and an ion probe. The experimental results show that there are two different types of the re-initiation mechanism. One is essentially the same as that of deflagration to detonation transition in the sense that a shock wave generated by flame acceleration causes a local explosion. From calculated values of ignition delay behind the shock wave decoupled from the reaction front, the other is found to be closely related with spontaneous ignition. In this case, the fundamental propagation mode shows a spinning detonation. Received 10 March 1997 / Accepted 8 June 1997     

Determination of ignition delay times of different hydrocarbons in a new high pressure shock tube

The impending scarcity of fossil fuel in the future requires continued development in hydrocarbon combustion research. Biofuels offer a promising alternative to traditional fossil fuel-based combustion. To optimize engine design for biofuels, adequate combustion characteristics for new fuels have to be known. In this study, a new high pressure stainless steel shock tube for measuring ignition delay times is presented. When compared with other shock tubes for investigating ignition delays, the new tube provides superior maximum working pressures and geometric properties. Shock tube performance is determined by reference experiments with air as driven gas. These experiments allow to determine the available test time and the influence of shock attenuation. Owing to the large inner diameter of the shock tube, shock attenuation is <1% as it is typical for low pressure shock tubes. However, contrast to typical low pressure shock tubes, non-diluted fuel–air mixtures at high pressures can be investigated in the new shock tube due to the high allowable working pressure. First experiments concerning the ignition delay time have been performed with methane and n-heptane. The results of these experiments show a good agreement to literature data. As a first biofuel ethanol has been investigated at elevated pressures up to 40 bar.