自由堆积多孔介质内预混燃烧火焰传播

为了解多孔介质内预混燃烧火焰前沿的传播特性,对不同化学当量比（=0.7～1.0）的甲烷/空气预混气体在不同孔隙率（ε为0.37和0.42）的多孔介质内的火焰前沿传播特性进行了研究,多孔介质采用3 mm和6 mm直径的Al₂O₃小球在陶瓷管中堆积而成。结果表明,预混气体在多孔介质中能够形成低速燃烧的稳定燃烧波;其火焰传播速度随化学当量比增大而加快,最大的火焰传播速度为3.52×10^-3 cm·s^-1;多孔介质的结构对火焰前沿传播速度影响很大,即使在孔隙率差别不大的情况下,大球堆积而成的多孔介质比小球具有更高的火焰前沿传播速度。     

爆轰火焰在管道阻火器内的传播与淬熄特性

在水平封闭的直管中,采用自主研制的阻爆实验系统(包括传感器系统、配气系统、数据采集系统、点火系统等)对不同活性预混气体爆轰火焰在波纹管道阻火器内的传播与淬熄过程进行了实验研究。结果显示当可燃气体接近当量浓度时(丙烷4.2%、乙烯6.6%、氢气28.5%,均为体积分数),预混气体从点燃到火焰淬熄过程历时非常短,总体可分为4个阶段,缓慢燃烧阶段、快速燃烧阶段、加速燃烧阶段和超压振荡阶段。丙烷-空气、乙烯-空气预混气体在D=80 mm的管道阻火器中,爆炸压力峰值较高。当管道直径增加至400 mm时,爆炸压力峰值逐渐降低,其中乙烯-空气预混气体的爆炸压力峰值仅为3 MPa左右;氢气-空气预混气体的爆炸压力峰值随管径的增加呈递增趋势。对爆轰速度的研究结果表明,丙烷-空气、乙烯-空气预混气体爆轰速度数值相差不大,丙烷-空气预混气体甚至稍高些;而氢气-空气的爆轰速度数值较高。而且随着管径的增加,管壁热损失增大及其阻力因素等原因影响使预混气体爆轰速度趋向平稳。最后,从经典传热学理论出发,推导出了阻火单元厚度与爆轰火焰速度之间的关系。并结合实验数据,提出了爆轰安全阻火速度的计算方法,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。     

爆轰火焰在管道阻火器内的传播与淬熄特性

在水平封闭的直管中,采用自主研制的阻爆实验系统(包括传感器系统、配气系统、数据采集系统、点火系统等)对不同活性预混气体爆轰火焰在波纹管道阻火器内的传播与淬熄过程进行了实验研究。结果显示当可燃气体接近当量浓度时(丙烷4.2%、乙烯6.6%、氢气28.5%,均为体积分数),预混气体从点燃到火焰淬熄过程历时非常短,总体可分为4个阶段,缓慢燃烧阶段、快速燃烧阶段、加速燃烧阶段和超压振荡阶段。丙烷-空气、乙烯-空气预混气体在D=80 mm的管道阻火器中,爆炸压力峰值较高。当管道直径增加至400 mm时,爆炸压力峰值逐渐降低,其中乙烯-空气预混气体的爆炸压力峰值仅为3 MPa左右;氢气-空气预混气体的爆炸压力峰值随管径的增加呈递增趋势。对爆轰速度的研究结果表明,丙烷-空气、乙烯-空气预混气体爆轰速度数值相差不大,丙烷-空气预混气体甚至稍高些;而氢气-空气的爆轰速度数值较高。而且随着管径的增加,管壁热损失增大及其阻力因素等原因影响使预混气体爆轰速度趋向平稳。最后,从经典传热学理论出发,推导出了阻火单元厚度与爆轰火焰速度之间的关系。并结合实验数据,提出了爆轰安全阻火速度的计算方法,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。     

层流预混火焰传播特性概述

理论研究层流预混火焰的传播可以更好地理解燃烧过程 ,为实际应用时有效地控制燃烧过程提供理论依据。本文对层流预混火焰特性及层流火焰传播速度进行归纳 ,对有化学反应和可压缩的层流边界层进行简单的理论分析 ,介绍了层流火焰传播的火焰焰锋结构及与层流火焰传播速度有关的预混气体物理化学参数的关系。     

含颗粒甲烷/空气预混燃烧的51步简化机理

基于含颗粒甲烷燃烧详细化学动力学机理Gri-Mech3.0,采用层流预混火焰模型计算含颗粒甲烷/空气预混燃烧过程。通过对详细机理的计算结果进行敏感性分析以及产物速度分析提取骨干机理,再根据准稳态假设进一步简化,最终得到一套包含27种组分和51个基元反应的简化机理。将该51步简化机理与详细机理进行对比,结果表明:该简化机理在预测燃烧速度方面具有较高精度,能够在较大热力学参数变化范围内较好地预测含颗粒和不含颗粒2种情况的甲烷/空气预混燃烧现象。     

狭长密闭空间内油气爆炸火焰特性大涡模拟

基于WALE模型和Zimont预混火焰模型对横截面尺寸0.187 m×0.187 m,长2 m的狭长密闭空间内汽油-空气混合物爆炸火焰特性进行了大涡模拟。将大涡模拟与RNG k-e湍流模型计算结果及实验结果进行对比,验证了大涡模拟对于狭长密闭空间中汽油-空气混合物预混爆炸计算的适用性。结果表明：（1）大涡模拟准确再现了火焰传播过程中的形态变化;（2）火焰锋面后已燃区壁面两侧和中轴线两侧涡旋结构分别对Tulip形火焰的形成和消散有显著影响,且形成及消散前的两种涡旋结构方向相反;（3）当量比浓度下汽油-空气混合物爆炸未燃区气体流动始终保持正向传播,且爆炸超压、火焰传播速度和火焰传播形态三者间存在显著的耦合性。     

气固射流扩散火焰形态研究

利用文丘里效应,自行设计气固射流扩散火焰（气固喷射火）实验装置,分别采用147 μm和178 μm两种粒径均匀的白色石英砂以近似恒定速率卷吸入火焰中,来研究固体颗粒对火焰形态的影响,特别地,通过关闭侧面进砂口所形成的气态射流扩散火焰（气态喷射火）与之相比较。理论分析和实验结果表明,砂子进入火焰中会降低火焰温度,并且粒径为147 μm的砂子进入火焰的质量大于178 μm砂子,导致小粒径气固喷射火具有更低的火焰温度,从而具有更低的层流燃烧速度和更大的火焰Froude数,最终使其具有更高的推举高度和火焰高度。对比分析气固喷射火和气态喷射火实验结果,也表明固体颗粒对火焰温度的冷却作用导致气固喷射火更容易产生推举现象并具有更高的火焰高度。     

微型定容燃烧腔内C2~C4烷烃/空气火焰传播

在直径35 mm、高度2 mm光学可视的定容燃烧腔内,实验研究了常温常压静止乙烷/空气、丙烷/空气和正丁烷/空气预混气在燃烧腔中心由电火花点燃后向外传播的火焰传播特性。结果表明：3种燃料空气混合气可形成火焰传播的当量比范围不同,范围由大到小排序为乙烷>丙烷>正丁烷;3种燃料均存在由光滑火焰面向褶皱火焰面转变的传播形态;在微型定容燃烧腔内,3种燃料的火焰传播速度均低于常规尺度下定容燃烧弹内火焰传播速度,且火焰传播速度随半径增加而减小;随着当量比增加,火焰锋面容易出现褶皱和断裂现象,在高当量比情况下,火焰传播会出现短暂停滞。     

工业燃烧室天然气湍流扩散火焰长度影响因素分析

通过1.3MW级工业燃烧器实验验证商用CFD软件计算天然气湍流扩散火焰长度的有效性。以天然气（含有95%CH4和5%N2）为燃料，以直径为300mm、长度为1200mm的圆筒形燃烧室中、燃气孔径基本尺寸2mm的同轴射流扩散火焰为研究对象。采用数值计算的方法研究了燃气流量、喷孔孔径、助燃风特性等多种因素对火焰长度的影响规律。研究结果表明：在天然气湍流扩散火焰中，当孔径不变燃气流量增加一倍，火焰长度由652mm增加到782mm，增长19.9%。当燃气流量不变孔径增加一倍，652mm增加到1012mm，增长55.2%。改变燃气孔径是控制湍流扩散火焰长度的有效手段；在一定氧含量范围内，与助燃风氧含量相比，湍流火焰长度对助燃风速度的变化更加敏感。该研究对评估天然气燃烧装备性能和优化燃烧室设计具有重要的应用价值。     

燃烧器不同因素对燃料转化率影响的数值计算

随着天然气、煤层气的不断开采和广泛应用,对甲烷-空气非预混燃烧特性的研究显得尤为重要.基于涡耗散理论,采用有限容积法建立组分燃烧与输运控制方程,针对长2 m,直径为0.9 m的圆筒形燃烧器内甲烷-空气非预混燃烧过程进行数值计算.分析了组分不同入口流速、温度对燃烧过程燃料转化率的影响.结果表明:随着空气入口流速的不断增加...     

Nitrogen dilution effect on flame stability in a lifted non-premixed turbulent hydrogen jet with coaxial air

The nitrogen dilution effect on flame stability was experimentally investigated in a lifted non-premixed turbulent hydrogen jet with coaxial air. Hydrogen gas was used as the fuel and coaxial air was injected to initiate flame liftoff. Hydrogen was injected into an axisymmetric inner nozzle (d_F = 3.65 mm) and coaxial air jetted from an axisymmetric outer nozzle (d_A = 14.1 mm). The fuel jet and coaxial air velocities were fixed at u_F = 200 m/s and u_A = 16 m/s, while the mole fraction of the nitrogen diluent gas varied from 0.0 to 0.2 with a 0.1 step. For the analysis of the flame structure and the flame stabilization mechanism, the simultaneous measurement of PIV/OH PLIF was performed. The stabilization point was in the region of the flame base with the most upstream region and was defined as the point where the turbulent flame propagation velocity was found to be balanced with the axial component of the local flow velocity. The turbulent flame propagation velocity increased as the nitrogen mixture fraction decreased. The nitrogen dilution makes the flame structure more premixed. That is, the stabilization mechanism shifts from edge flame propagation based mechanism toward premixed flame propagation based mechanism. We concluded that the turbulent flame propagation velocity was expressed as a function of the turbulent intensity and the axial strain rate, even though the mole fraction of the nitrogen diluent varied.     

Effects of initial temperature on the structure of laminar CH4-air premixed flames

The growing popularity of natural gas as a eco-friendly fuel, is of paramount motivation of present investigation. In the present paper, the effect of initial temperature on the flame structure have been investigated in which laminar one-dimensional planar propagating flames of CH₄/air mixtures is simulated numerically using detailed chemical kinetic scheme and realistic transport models. The burning velocities are fundamentally important in developing models to predict progress of combustion. Hence, the burning velocities as a function of initial temperature of unburnt gas have been computed for stoichiometric mixture. The present predictions of burning velocities are compared with reported experimental data of Stone et al. [Combust. Flame. 114 (1998) 546], Hill and Huang [Combust. Sci. Technol. 60 (1980) 7] and Rallis and Garforth [Combust. Flame 31 (1978) 53]. The present prediction lies within the scatter of experimental data. A correlation in the form of S_u/S_u,0=(T_u/T_u,0)^1.575 has been developed to describe the dependence of initial temperature on the burning velocity for stoichiometric mixture. The structures of flame are investigated in details for initial temperature of 300 and 600 K which clearly indicate that detailed chemical kinetics are essential for prediction of the effects of initial temperature on the burning velocities. The present study will help in designing and developing the regenerative combustion systems.     

Modeling combustion of lycopodium particles by considering the temperature difference between the gas and the particles

The effect of the temperature difference between the gas and the particles on propagation of premixed flames in a combustible mixture containing volatile fuel particles uniformly distributed in an oxidizing gas mixture is analyzed in this paper. It is presumed that the fuel particles vaporize first to yield a gaseous fuel, which is oxidized in the gas phase. The analysis is performed in the asymptotic limit, where the value of the characteristic Zel’dovich number is large, which implies that the reaction term in the preheating zone is negligible. Required relations between the gas and the particles are derived from equations for premixed flames of organic dust. Subsequently, the governing equations are solved by an analytical method. Finally, the variation of the dimensionless temperatures of the gas and the particles, the mass fraction of the particles, the equivalence ratio ϕ _g as a function of ϕ _u , the flame temperature, and the burning velocities of the gas and the particles are obtained. The analysis shows that the calculated value of ϕ _g is smaller than unity for certain cases, even though ϕ _u ⩾1. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 49–57, May–June, 2009.     

Experimental and numerical study of CH4/CH3Cl/O2/N2 premixed flames under oxygen enrichment

A comprehensive experimental and numerical study has been conducted to understand the influence of CH₃Cl addition on CH₄/O₂/N₂ premixed flames under oxygen enrichment. The laminar flame speeds of CH₄/CH₃Cl/O₂/N₂ premixed flames at room temperature and atmospheric pressure are experimentally measured using the Bunsen nozzle flame technique with a variation in the amount of CH₃Cl in the fuel, equivalence ratio of the unburned mixture, and level of oxygen enrichment. The concentrations of major species and NO in the final combustion products are also measured. In order to analyze the flame structure, a detailed chemical kinetic mechanism is employed, the adopted scheme involving 89 gas-phase species and 1017 elementary forward reaction steps. The flame speeds predicted by this mechanism are found to be in good agreement with those deduced from experiments. Chlorine atoms available from methyl chloride inhibit the oxygen-enhanced flames, resulting in lower flame speeds. This effect is more pronounced in rich flames than in lean flames. Although the molar amount of CH₃Cl in the methane flame is increased, the temperature at the post flame is not significantly affected, based on the numerical analysis. However, the measured concentration of NO is reduced by about 35% for the flame burning the same amount of methyl chloride and methane at the oxygen enrichment of 0.3. This effect is due to the reduction of the concentration of free radicals related to NO production within the flame. In the numerical simulation, as CH₃Cl addition is increased, the heat flux is largely decreased for the oxygen-enhanced flame. It appears that the rate of the OH + H₂ → H + H₂O reaction is reduced because of the reduction of OH concentration. However, the function of CH₃Cl as an inhibitor on hydrocarbon flames is weakened as the level of oxygen enrichment is increased from 0.21 to 0.5. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 6, pp. 103–111, November–December, 2006.     

Comparison of the structures of methane-air and propane-air partially premixed flames

A comparison of flame structures between methane-air and propane-air laminar partially premixed flames has been made through the centerline concentration distributions of selected species measured using gas chromatography. The concentrations of fuel, major species like O₂, CO and CO₂ and those of the intermediate hydrocarbons like C₂H₆, C₂H₄, C₂H₂ and CH₄ (for the propane flame only) have been compared. Distinct double flame structures are observed for the experimental conditions under study. With approximately the same equivalence ratio and jet velocity for the primary mixture, the height of the inner flame for propane is less than that of methane. The peak concentration of C₂H₆ in the propane flame is found to be only a little higher than that in the methane flame, while the peak concentrations of C₂H₄ and C₂H₂ are much greater in the propane flame than in the methane flame. In a methane partially premixed flame, the hydrocarbon concentrations drop from their peak values very rapidly at the inner flame tip, but in the propane flames it is more gradual. In a methane partially premixed flame, CO is formed at the inner flame and burns at the outer flame to CO₂. Similar distributions of CO and CO₂ are found in the propane flame also. However, the peak CO concentration in the propane flame is found to be higher than in methane flame. A radial measurement of species distribution for a particular case in the propane partially premixed flame is also done to ascertain the species distributions across the flame.     

Effect of the addition of triphenylphosphine oxide,hexabromocyclododecane, and ethyl bromide on a CH<Subscript>4</Subscript>/O<Subscript>2</Subscript>/N<Subscript>2</Subscript> flame at atmospheric pressure

The chemical and thermal structure of a Mache-Hebra burner stabilized premixed rich CH₄/O₂/N₂ flame with additives of vapors of triphenylphosphine oxide [(C₆H₅)₃PO], hexabromocyclododecane (C₁₂H₁₈Br₆), and ethyl bromide (C₂H₅Br) was studied experimentally using molecular beam mass spectrometry (MBMS) and a microthermocouple method. The concentration profiles of stable and active species, including atoms and free radicals, and flame temperature pro.les were determined at a pressure of 1 atm. A comparison of the experimental and modeling results on the flame structure shows that MBMS is a suitable method for studying the structure of flames stabilized on a Mache-Hebra burner under near-adiabatic conditions. The relative flame inhibition effectiveness of the added compounds is estimated from changes in the peak concentrations of H and OH radicals in the flame and from changes in the flame propagation velocity. The results of the investigation suggest that place of action of the examined flame retardants is the gas phase. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 12–20, September–October, 2007.     

Combustion of residual steel gases: laminar flame analysis and turbulent flamelet modeling

In recovery combustion systems operating in the steel industry, energy is provided by boilers burning residual gases of blast furnace and coke oven. To help understand combustion of this particular type of fuels, a numerical study is conducted where the major chemical properties of steel gas flames are collected. The chemical composition of representative fuel and oxidizer steel gas is varied over a large range in calculations using detailed chemistry and complex transport properties. The chemical equilibrium compositions, premixed flame speeds and diffusion flame extinction strain rates are determined. The advantages and shortcomings of the use of vitiated air emerge, and its introduction into the boiler appears as an interesting alternative to reduce NO_x emission. The detailed information obtained with laminar flame calculations is also introduced in flamelet turbulent combustion modeling. Reynolds Averaged Navier Stokes (RANS) simulations of a test case burner are performed and some comparisons between numerical predictions and experimental results are presented.     

Effect of trimethylphosphate additives on the flammability concentration limits of premixed methane-air mixtures

The effect of small additives of trimethylphosphate (TMP) on the lean and rich flammability concentration limits of CH₄/air gas mixtures were studied using an opposed-flow burner and numerical modeling based on detailed kinetic mechanisms. TMP was found to narrow the flammability concentration limits of premixed CH₄/air mixtures. Modeling using a previously developed model for flame inhibition by phosphorus compounds showed that the model provides a satisfactory fit to experimental results on the effect of TMP additives on the lean concentration limit. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 1, pp. 12–21, January–February, 2008.     

Comparative study of the influence of CO<Subscript>2</Subscript> and H<Subscript>2</Subscript>O on the chemical structure of lean and rich methane-air flames at atmospheric pressure

A comparative study of the influence of CO₂ and H₂O on both lean and rich CH₄-air laminar flames is performed. Six premixed flames are stabilized on a flat flame burner at atmospheric pressure: lean (with the equivalence ratio maintained constant at ? = 0.7) and rich (with the equivalence ratio maintained constant at ? = 1.4) CH₄-air, CH₄-CO₂-air, and CH₄-H₂O-air flames. These flames are studied experimentally and numerically. The [CO₂]/[CH₄] and [H₂O]/[CH₄] ratios are kept equal to 0.4 for both flames series. Species mole fraction profiles are measured by gas chromatography and Fourier transform infrared spectroscopy analyses of gas samples withdrawn along the vertical axis by a quartz microprobe. Flames structures are computed by using the ChemkinII/Premix code. Four detailed combustion mechanisms are used to calculate the laminar flame velocities and species mole fraction profiles: GRI-Mech 3.0, Dagaut, UCSD, and GDFkin®3.0.