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湍流预混对冲火焰结构及熄火特性试验研究 总被引:1,自引:1,他引:1
利用激光层析技术和数字图像处理技术对对冲方式下湍流预混火焰的结构及熄火特性进行了试验研究。采用PIV方法测量了冷态对冲面附近的速度场,获得了速度作为衡量流场对锋面燃烧影响的参数。在不同射流工况配置下(Reynolds数,全局应变率,燃料的化学混合当量,不对称动量),观察到随着湍流对冲强度的提高,在高度皱褶的火焰锋面上存在非连续突触和空洞,这是局部熄火的表现,这些局部熄火点影响的扩展会导致火焰的整体熄火。此观点通过局部火焰锋面曲率的概率统计分析得到支持。另外,获得的在火焰熄火的极限条件下,对实际燃烧器的设计有指导意义。 相似文献
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介绍一种特殊的煤气专用燃烧器--大功率双旋流燃烧半预混式燃烧器的设计,该燃烧器具有功率大、混合好、火焰短、燃烧稳定及不回火的特点. 相似文献
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预混稀燃是最具有前景代替传统扩散燃烧的清洁燃烧方式之一.然而,高速流动的预混稀燃中常出现低当量比下火焰吹熄的情况.吹熄给燃烧过程带来了极大的不稳定性.旋流和钝体是实际燃烧中常用的稳焰方式.吹熄的机理研究大多基于钝体或旋流火焰进行,但同时加入两者稳焰时的吹熄研究尚且不足.本研究基于OH-PLIF技术,在旋流加钝体稳焰下,针对CH_4/空气预混稀燃临熄火条件下的火焰面结构进行了测量和表征.研究表明,临熄火过程中火焰根部抬升逐渐增加,火焰面密度减小,火焰趋向于向回流区聚集.结果表明,火焰根部局部熄火对吹熄过程可能有重要影响,同时验证了未燃气回流促进吹熄的结论. 相似文献
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利用自行设计的火焰传播实验系统研究了甲烷火焰穿越水雾区的传播现象;运用数字摄像、光电测速和温度测量等技术研究了不同水雾条件下的甲烷火焰传播速度、火焰阵面轨迹及火焰结构特性。结果发现:水雾与甲烷火焰作用后,火焰颜色明显变红。水雾量较小时,甲烷火焰会被加速;水雾量增大到一定值后,甲烷火焰会在水雾区某一位置滞留一段时间,随后火焰再加速传播或熄灭(对应更高的水雾量)。分析认为这种现象的出现与水雾在甲烷火焰区的吸热、蒸发膨胀和化学阻化等物理化学综合效应有关。 相似文献
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Makoto Asahara Tei Saburi Toshiki Ando Yoshiaki Takahashi Takeshi Miyasaka Shiro Kubota 《International Journal of Hydrogen Energy》2021,46(24):13484-13500
Accelerated adoption of hydrogen gas for energy storage requires improved safety for hydrogen storage. In particular, control of self-ignition of hydrogen vented through tubes by pressure relief devices (overpressure protection devices), such as rupture disks, is needed. We clarify the process of self-ignition in tubes of various lengths during venting of high-pressure hydrogen and observe flame behavior at the tube exit. The importance of distance from the rupture disk for flame front evolution is revealed. Specifically, in a tube longer than a critical value, the self-ignited flame undergoes a quenching process, possibly due to steam formation, before it exits the tube. A tube that is too short does not give the gas sufficient time for hydrogen and air mixing to initiate self-ignition. Finally, at slightly longer tube lengths, the hydrogen ignites, but the flame does not fully develop before it exits, and the vortex formed by expanding gas extinguishes it. 相似文献
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The interacting partially premixed methane and hydrogen flames established in a one-dimensional counterflow field were investigated numerically with the OPPDIF code and GRI-v3.0 was used to consider both fuels. The flame structure and response of the maximum flame temperature, heat-release rate, and flame speed to the equivalence ratios (Φ) and global strain rate (ag) were investigated. The maximum temperature decreased with increasing ag. The maximum temperature for cases with a stoichiometric hydrogen-side flame was higher than for other cases with the same ag.The hydrogen-side flame played a key role in determining the maximum temperature. The maximum heat-release rates (MHRRs) for all cases show different trends. The MHRR of the methane-side flame was affected considerably by the interacting flame structure and hydrogen-side flame condition. However, the MHRRs of the hydrogen were independent of methane-side flame condition. For the cases where Φ of the methane-side flame was varied while the hydrogen-side flame was kept stoichiometric (Var-S), the MHRR and flame speed of the hydrogen-side flame were independent of the methane-side flame conditions. However, the methane-side flames had a negative flame speed except near-stoichiometric conditions. On the other hand, in the cases where Φ of the hydrogen-side flame was varied while the methane-side flame was kept stoichiometric (S-Var), the hydrogen-side flames had the MHRR and flame speed similar to those of an unstretched partially premixed hydrogen flame. 相似文献
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AySu Ying-ChiehLiu 《热科学学报(英文版)》2001,10(3):281-284
1niwtonInveshgations to enhance combushon efficiencyhave been irnportan in the past decad. Most of theimProvementS were coneennd on bog thendulent fluctUations and flow intensihes. The jettodetboinging setup is widely used in rocke engines withseif ignition proPellantS. The pUrPOse of thes reseaxC istO examine the imPinging effeCt on the jet-imPingementdiffesion flame.Two asPeCs of the twinging flame, jetboingeInen heating and combushon enhaneement havebeen inveshgatal. Milson and Chig… 相似文献
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Ethanol is a renewable alternative fuel in many application areas. The external electric field is applied to assist the small ethanol diffusion flame in this study. The electrical response of flame under the uniform electric field is discussed. A reduced chemical mechanism of ethanol is used to establish a numerical model corresponding to the experimental system. The characteristics of current-electric field strength, equivalent resistance, distribution of charged species, velocity field, and reaction rate are studied. The results show that the electric field brings significant effects on the combustion and electrical characteristics of flame. As the electric field strength increases, the current through the circuit and the equivalent resistance of the flame show a three-stage variation. The current increases first (0-40 kV/m), then stabilizes (40-70 kV/m) and then continues to increase (70-100 kV/m) with the increase of the electric field strength. It shows that the flame has certain electric resistance characteristic. The number density of charged species in the flame increases, and the distributions of charged species tend to move upstream by the effect of electric field. When the electric field strength is high as 100 kV/m, the charged species density increases by 10%. Meantime, the gas velocity near the flame front is accelerated and the chemical reaction rate also increases by the effect of electric field. When the electric field strength reaches 100 kV/m, the corresponding reaction rate and the corresponding flow velocity are increased by about 40% and 20%, respectively, compared with those without electric field. The calculated ionic wind velocity increases greatly with the electric field strength and shows a nearly linear increasing trend. The combined effects of the enhanced ionic wind effect, the intensified chemi-ionization process, and the increase of the concentration of charged species are considered as the main reason for the effect of electric field. 相似文献
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Experimental investigations on impinging diffusion flames mixing with inert gas were conducted. The combustion results and temperature measurements show that the non-reactive gas might dilute the local fuel concentration in the diffusion process. The shape of the column flame was symmetrical due to the flame stretch force. The results showed that a conical flame was changed by the addition of inert gas to the pure methane fuel. The weakening of the stretch boundary enhanced the mixing rate between the fuel and oxidizer, which would improve the fluctuation phenomenon. The impinging flame became shorter and bluer so the combustor size can be reduced. Nitrogen gas has the advantage that we can visualize the impinging mechanism with different gases in the impinging flame. The color in the mixing plane becomes blue and transparent. The penetration length is about 8 mm near the impinging point for Re=145. 相似文献
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William F. Carnell Jr. 《Combustion and Flame》2005,141(4):350-359
In nonpremixed combustion, edge flames can form as a region of flame propagation or flame recession. Forwardly propagating edge flames, as occur in lifted flames, have a local gas velocity at the flame edge that is from unburned partially premixed fuel and air into the flame. These flames represent an ignition process, and permit the flame itself to either stabilize against an incoming gas stream or propagate into unburned fuel and air. Negative edge flames represent the opposite case of a local gas velocity from burned products through the flame edge. The negative edge flame represents a local extinction process, and occurs, for example, during vortex-induced extinction of a nonpremixed flame sheet. A technique for generating steady negative edge flames in a standard counterflow burner is presented, which permits detailed examination of their properties. A coannular counterflow burner is used to create a strain gradient that quenches a central diffusion flame. Unlike previous research on strain-induced flame edges, the axisymmetric flow field ensures gas flow from products through the edge. Measurements of the edge flame's sensitivity to global strain rates and fuel mixtures are presented, along with measurements of the edge flame structure using OH fluorescence and CH emission imaging. 相似文献
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《International Journal of Hydrogen Energy》2014,39(36):21335-21342
Laminar hydrogen flame propagation in a channel with a perforated plate is investigated using 2D reactive Navies-Stokes simulations. The effect of the perforated plate on flame propagation is treated with a porous media model. A one step chemistry model is used for the combustion of the stoichiometric H2–air mixture. Numerical simulations show that the perforated plate has considerable effect on the flame propagation in the region downstream from the perforated plate and marginal effect on the upstream region. It is found to squeeze the flame front and result in a ring of unburned gas pocket around the flame neck. The resulting abrupt change in flow directions leads to the formation of some vortices. Downstream of the perforated plate, a wrinkled “M”-shape flame is observed with “W” shape flame speed evolution, which lastly turns back to a convex curved flame front. Parametric studies have also been carried out on the inertial resistance factor, porosity, perforated plate length and its location to investigate their effects on flame evolution. Overall, for parameter range studied, the perforated plate has an effect of reducing the flame speed downstream of it. 相似文献