Measurement of laminar burning velocities and analysis of flame stabilities for hydrogen-air-diluent premixed mixtures

The laminar burning velocities and Markstein lengths of the hydrogen-air-diluent mixtures were meas-ured at different equivalence ratios (0.4―1.5), different diluents (N2, CO2 and 15%CO2+85%N2) and di-lution ratios (0, 0.05, 0.10 and 0.15) by using the outwardly expanding flame. The influences of flame stretch rate on the flame propagation characteristics were analyzed. The results show that both the laminar burning velocities and the Markstein lengths of the hydrogen-air-diluent mixtures decrease with the ...     

火焰拉伸率对层流燃烧速度的影响

将层流火焰消耗速度的概念与反应进程变量(progress variable)的定义相结合,给出了积分层流燃烧速度的广义定义.在准一维稳态系统中,分析了积分层流燃烧速度与未燃气体位移速度和已燃气体位移速度之间的关系.对甲烷空气和丙烷空气拉伸层流预混火焰在常温常压下进行了数值计算,研究不同当量比时,火焰拉伸率对层流燃烧速度的影响.通过火焰前锋放热率的积分层流燃烧速度和燃料消耗率的积分层流燃烧速度进行比较,结果表明,低拉伸火焰的马克斯坦数(Markstein number)与渐进分析一致,也与球形火焰获得的实验数据吻合.     

Flame instability analysis of diethyl ether-air premixed mixtures at elevated pressures

Combustion characteristics of premixed diethyl ether-air mixtures were studied at different equivalence ratios and elevated initial pressures using schlieren photography and spherically propagating flame. Laminar burning velocities, Markstein number and critical radii at onset of cellular structure were obtained. The results show that an increase in initial pressure leads to a decrease in the unstretched laminar burning velocities. Laminar burning velocities give their peak values at the equivalence ratio o...     

碳酸二甲酯层流火焰特性的实验和数值研究

在定容燃烧弹上,利用高速纹影摄像系统对碳酸二甲酯(DMC)的预混层流燃烧特性进行了研究,获得了不同温度、压力和当量比下的层流燃烧速度、马克斯坦长度和胞状结构的临界半径,同时对火焰不稳定性进行了理论分析。研究表明:层流燃烧速度随当量比的增加先提高后下降,在当量比为1.1时达到峰值;层流燃烧速度随初始温度的升高而提高,随初始压力的增加而降低;马克斯坦长度、临界火焰半径随当量比和压力的增加而减小,表明火焰不稳定性随初始压力和当量比的增加而增强;临界贝克来数Pe随当量比的增加而减小。利用Chemkin软件对预混层流燃烧速度进行了数值模拟,结果显示,Glaude机理对DMC层流燃烧速度的模拟值与实验测量值有较大偏差,表明该机理不能很好地预测DMC的层流燃烧速度。     

稀释气体对甲烷层流预混火焰燃烧速度的影响

基于GRI-Mech 3.0详细化学反应机理,利用预混燃烧模型(PREMIX Code)研究了甲烷-空气-稀释气层流预混火焰燃烧特性及火焰结构.重点探讨了不同化学当量比(0.5～1.5)、初始压力(0.05～0.40 MPa)、稀释气体种类(N2,CO2及H2O)和稀释摩尔比(0～0.35)对甲烷-空气-稀释气混合气层...     

基于OH-PLIF技术的合成气燃烧速度

为了解合成气燃烧特性,采用高精度光学测量技术PLIF,研究了不同生物质气化合成气在不同当量比下的燃烧火焰结构、OH基浓度以及火焰传播速度。采用CHEMKIN软件模拟计算了相同工况下合成气火焰传播速度,对引起温度变化和OH基浓度变化的原因进行了化学动力学分析。研究结果表明,合成气中CO含量的增加会使火焰整体结构变小,但对内焰影响程度不大,而H2含量的增加会增大火焰的传播速度。合成气燃烧过程中主要影响OH基生成的是R36:CO+OH=CO_2+H、R43:H+O2+M=HO_2+M和R45:H+HO_2=2OH这3个基元反应。     

甲烷/空气预混气的火焰传播过程

为研究爆炸罐内甲烷/空气预混气中火焰的传播过程,利用高速摄像仪对火焰的传播过程进行了拍摄,用压力测试系统测量了爆炸罐中压力的成长过程,分析了火焰传播特性,计算了层流燃烧速度和不同位置的爆炸特性值.研究结果表明:根据高速摄像仪得到的图片将预混火焰分为火焰稳定成长及剧烈燃烧阶段,用两种方法测得预混气的层流燃烧速度分别为0.344和0.391m/s.爆炸特性值的最大值出现在离点火位置0.75m处,壁面的爆炸特性值偏小.     

Study of low-pressure premixed laminar n-heptane+ propane/oxygen/nitrogen flames

Low-pressure premixed laminar n-heptane+propane/oxygen/nitrogen flames were investigated with tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam sampling mass spectrometry. Three flames with different mass percentage of propane in the fuel blends of 0%, 10%, and 20% were studied. The combustion intermediates were identified by comparing the measured IEs with those values in literatures. Mole fraction profiles of the main species were compared among the three flames. The experime...     

部分预混层流火焰结构的数值研究

针对部分预混层流火焰,在分析了常见火焰面方程不足的基础上,使用了一套详细考虑了组分不同输运系数的火焰面方程对其进行数值模拟.模拟结果与物理空间求解结果间的比较表明,此套方程能够在保证相容性的同时获得相当好的模拟精确度.此外,在火焰面方程中采用不同的标量耗散率模型对部分预混火焰进行了数值计算,结果显示标量耗散率模型的精确程度对于模拟结果有着重要影响.进一步利用火焰面方程数值研究了部分预混层流火焰结构对于标量耗散率变化的响应,捕捉到其在低标量耗散率下区别于非预混火焰的双火焰结构的存在,并讨论了此现象产生的原因.     

直流电场对预混CH4/O2/N2火焰传播特性影响的试验研究

为研究直流电场及其极性对火焰传播行为的影响,利用高速摄像法和球形扩展火焰理论在定容燃烧弹上展开了正负直流电场作用下预混CH4/O2/N2火焰传播规律的试验研究.试验结果表明:对于化学计量空燃比混合气,施加电场后球形火焰面在水平方向上被拉伸,拉伸火焰传播速率、无拉伸层流燃烧速率以及马克斯坦长度均随着输入电压幅值的增大而增大,且负电场比正电场的作用更加显著.当输入电压为-5 kV与5 kV时,火焰传播速率相对于未加电场时分别增加了10.85％和5.66％,而层流燃烧速率则分别增加了13.13％和6.98％.因此,电场能有效促进火焰传播,改善燃烧以及提高燃烧稳定性.     

水流层流失稳的一般规律

以力学系统的相对性原理和流场的局部稳定性理论为基础,对水流层流运动进行了理论上的分析,认为层流的不稳定性是由变形引起的,并对变形作进一步的演化,给出了层流运动稳定性的最大剪切失稳原则。     

边界条件对SK型静态混合器层流流场的影响

以SK型静态混合器为研究对象,针对入口流速按平均速度均匀分布和按实际速度抛物线分布两种边界条件,运用流体力学计算软件对层流状态下管内速度分布进行对比研究。计算结果表明,两种不同边界条件对混合器入口半个混合元件内的流体速度分布有较大影响,最大相对偏差可达67.7%,而对半个混合元件以后的流体速度分布影响不大,最大相对偏差仅为7.37%,对径向速度影响要大于轴向速度和切向速度。     

Experimental study on interference effect of rarefaction wave on laminar propagating flame

In order to study the interference effect of rarefaction wave on the laminar flame propagating structure and pressure characteristics of methane-air mixture, a small scale combustion chamber has been built. The techniques of high speed Schlieren photograph, pressure measurement and so on, are used to study the influence of rarefaction wave on the laminar flame propagating through methane-air mixture. The results show that, after the rarefaction wave acts on the propagation laminar flame, the laminar combustion is fully transformed into turbulent combustion just during several milliseconds, which leads to a sharp increase in the burning surface area and the pressure rise rate.     

冰盖下层流速度场和温度场的理论探讨

冰盖下水流慢速流动时,大多数属于层流状态,尤其大体积水体流动时(如水库)更是如此。文章对层流条件下冰盖下输水时的N-S方程和能量方程进行了理论上的探讨,分析了冰盖下的水流速度场和温度场,结果表明,在概化的边界条件下,水流速度场是对称的抛物线分布,水流的温度场与水深的4次方成比例。     

小尺度沸溢油池火灾燃烧速率特性试验研究

使用胜利原油对小尺度沸溢火灾燃烧速率特性进行了试验研究。分别记录了直径为0.1、0.15、0.2 m的原油沸溢油池火灾的燃烧过程,测量了燃烧速率和温度随时间的变化。根据燃烧速率和火焰高度变化对沸溢火灾燃烧进行阶段划分。探讨了不同直径及初始油层厚度对沸溢火灾燃烧速率的影响,在燃烧速率基础上建立沸溢强度模型。结果表明:沸溢火灾燃烧可以分为预燃、准稳态燃烧、沸溢燃烧、火焰熄灭4个典型燃烧阶段;沸溢燃烧阶段的燃烧速率和火焰高度显著大于准稳态燃烧阶段;沸溢火灾各阶段燃烧速率均随油池直径的增大而增大,且沸溢燃烧阶段的增幅明显大于准稳态燃烧阶段的增幅;准稳态燃烧阶段的稳定燃烧速率与初始油层厚度无关,随油池直径的增大而增大;沸溢强度随初始油层厚度的增加及油池直径的减小而增大,并与初始油层厚度和油池直径间的比值成正比。     

平板层流边界层近似速度分布计算方法的改进

根据模仿权残法的思想,用积分方程近似求解零攻角平板边界层层流问题。在满足四个基本边界层条件的基础上,推出改进的平板边界层的近似速度分布多项式。其对应的摩擦阻力计算公式与精确解完全相同。同时,该多项式对应的曲线与精确解的速度分布曲线拟合很好。     

层流中粉尘的火焰传播速度

建立了筛落式粉尘火焰试验装置和火焰信的号光电测量系统。提出确定火焰前沿位置的“最大斜率切线法”和判定火焰传播稳定性的“相对入射能量法”。测定了硅钙粉和煤粉的火焰传播速度和火焰厚度。结果表明数据合理,测量装置和方法可用于速度范围很宽的粉尘火焰传播研究,用修正的田中达夫模型计算的硅钙粉层流火焰传播速度与实验值接近。     

An experimental study of premixed laminar methane/oxygen/argon flames doped with hydrogen at low pressure with synchrotron photoionization

Laminar premixed stoichiometric methane/hydrogen/oxygen/argon flames were investigated with tunable synchrotron vacuum ultraviolet （VUV） photoionizaUon and molecular-beam sampling mass spectrometry techniques. The methane/hydrogen fuel blends with hydrogen volumetric fraction of 0, 20%, 40%, 60% and 80% were studied. All observed flame species, including stable intermediates and radicals in the flames, were detected by measuring photoionization mass spectra and photoionization efficiency （PIE） spectra. Mole fraction profiles of major species and intermediates were derived by scanning burner at some selected photon energies near ionization thresholds. The influence of hydrogen addition on mole fraction of major species and intermediates was analyzed. The results show that the major species mole fraction of CO, CO2 and CH4 decreases with the increase of hydrogen fraction. The mole fraction of intermediates measured in this experiment decreases remarkably with the increase of hydrogen fraction. This would be due to the increase of H and OH radicals by hydrogen addition and the high diffusivity and activity of H radical promoting the chemical reaction. In addition, the increase of H/C ratio with the increase of hydrogen fraction also leads to the decrease of the mole fraction of carbon-related intermediates and contributes to the decrease of unburned and incomplete combustion products.     

有机混合液体声速混合定则的研究

根据Jacobson理论及液体声速与分子自由程的关系 ,推导出有机混合液体声速与各组分声速之间满足的混合定则 ,并通过实验进行了验证。结果表明 ,实验测量结果与理论计算结果符合较好 ,最大误差为 3.4 % ,可以用来进行多元体系的声速计算。     

Study of low-pressure premixed laminar n-heptane+propane/oxygen/nitrogen flames

Low-pressure premixed laminar n-heptane+propane/oxygen/nitrogen flames were investigated with tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam sampling mass spectrometry. Three flames with different mass percentage of propane in the fuel blends of 0%, 10%, and 20% were studied. The combustion intermediates were identified by comparing the measured IEs with those values in literatures. Mole fraction profiles of the main species were compared among the three flames. The experimental results provide detailed data in understanding the combustion of n-heptane and n-heptane/propane blends in engine. They are also helpful in establishing and verifying the kinetic models. Supported by the National Natural Science Foundation of China (Grant Nos. 50636040 and 50521604)