焦炉气同轴射流自由扩散火焰的特性

以焦炉气为燃料,纯氧气为氧化剂,采用双通道烧嘴在不同的射流速度下于敞开空间中进行垂直自由扩散燃烧,考察了Fr数、Re数对火焰长度的影响,以及焦炉气射流速度与火焰脱火高度的关系.实验表明,火焰由浮力控制区向动量控制区转变时的Fr数约为197,由层流区向湍流区转变时的Re数约为16000;火焰发生脱火的临界速度约为20 m/s.     

同轴自由射流火焰的实验研究

利用同轴双通道烧嘴,研究敞开环境下氧气-酒精垂直自由射流扩散火焰的特征.计算同轴射流双通道烧嘴的当量直径、Froude数等影响湍流扩散火焰长度的参数,拟合湍流扩散火焰长度的公式.拍摄了曝光时间为1/1000 s的火焰图像,测量液体燃料在不同操作条件下的破裂长度.实验结果表明,湍流火焰的长度在富氧条件下随着酒精流量的增加而增长,当达到完全燃烧条件时火焰长度达到最大值;湍流扩散火焰的液体破裂长度几乎不随操作条件发生变化.     

辐射对CO／H2／N2燃料反向对撞扩散火焰结构的作用

考虑和不考虑辐射作用,在宽广的拉伸率条件下,计算研究了组分CO、H2和N2摩尔分数分别为40%、30%和30%的燃料与空气(79%N2和21%O2)的详细层流对撞火焰结构.使用固有流形分析技术,考虑Leeds氮化学等,对Liu和Rogg发展的38步机理进行了修改.为研究辐射自吸收的作用,采用光细辐射模型(OTM)和窄带辐射模型(NBM),模型计算结果与Drake等的测量结果吻合良好.     

不同扩散效应下一维湍流模拟氢气-空气射流的扩散火焰

应用一维湍流模型（ODT）来研究湍流射流氢气．空气扩散火焰,研究过程中采用详细化学反应机理和多分量输运属性．对于火焰长度、主要燃烧产物及温度的预测较好地符合了实验结果．ODT模拟结果产生了较高的近场扰动．提出了一种旨在通过修改涡事件选择过程从而提高ODT模型精度的新观点．在模拟中检验了微分扩散效应,结果显示当前火焰中存在着显著不同的扩散效应．     

微尺度甲烷扩散火焰特性的数值解析

以均匀空气流中圆管形成的甲烷扩散火焰为对象，用数值解析的方法研究了微尺度扩散火焰的火焰结构和燃烧特性．燃烧反应采用甲烷／空气一步总括反应，喷管壁面绝热．在Re一定的情况下，改变喷口尺寸和喷口流速，考察了微扩散火焰的结构和火焰熄灭的尺度效应．计算结果表明，Re=12条件下，喷口直径为0．07mm时达到熄灭极限；稳定燃烧区的最小总放热率约为0．5W；微尺度条件下，Da对火焰结构和火焰熄灭有显著影响，熄火附近的Da的数量级在0．01．     

甲烷/空气湍流射流扩散火焰的化学动力学模拟

利用几率密度函数方法求解标量场及用统计矩方法求解流场相结合的手段，对甲烷／空气湍流射流扩散火焰结构进行了计算模拟，其中，考虑了从简化到详细的三种不同规模的甲烷氧化反应动力学机理．计算结果与已有的实验结果进行了比较和分析，表明该模型可以很好地预测流场变化．在预测主要组分和温度时，三种机理具有相同的效果，在预测小浓度组分时，详细机理具有更好的效果．此外，简化机理能够极大地缩短计算时间，因而在工程应用中有着巨大的潜力．     

湍流扩散火焰细微结构特性分析

利用光学显微技术和计算机图象处理技术 ,在实验基础上 ,对湍流扩散火焰的细微结构进行分析和研究 ,从经典几何和分形几何两个不同角度对湍流扩散火焰细微结构曲线的特性进行定性描述 ,分析火焰细微结构曲线的两个特性参数——曲线度和分形维数与火焰热辐射强度的关系。     

圆周运动下移动火源扩散火焰的图像特性分析

为了预测和控制移动火源扩散火焰的燃烧,对火焰图像特性的影响因素和规律进行研究.通过高速摄像仪,实时记录移动火源扩散火焰在圆周运动下的形态特征,利用力场分析和MATLAB工具,得到火焰面积随火焰线速度的变化规律以及火焰倾角随火焰线速度的变化.研究发现,燃烧产生热量和气流散热两者综合地导致火焰面积随着线速度的递增而先增大后减小;随着火焰线速度的增大,刚开始火焰倾角升幅较快,后趋于平缓;火焰内外温差会影响浮升力的大小,进而影响燃烧的稳定性.     

热流量法测量高压CH4/O2/N2/CO2的层流火焰速度

热流量法成功应用在高压(0.5 MPa)下甲烷稀释气的绝热无拉伸层流火焰速度的测量.针对当量比为0.6～1.6、不同含氧量和固定含氧量时不同CO_2稀释度的火焰速度进行了实验和动力学探究.模拟采用GRIMech和HP-Mech两个反应机理,在不同压力下均给出了十分吻合实验值的预测结果.层流火焰速度的相对增量独立于当量比和压力的变化.总反应级数随氧含量提高和CO_2稀释度降低而增大,相同的绝热火焰温度的总反应级数相近.在不同稀释度情况下CO_2对层流火焰速度的热扩散贡献在50%以上,且随着压力提高,热扩散贡献减小而化学反应贡献增加.     

多股射流瓦斯燃烧器湍流扩散火焰尺度的实验研究

用火焰图像分析方法,对一种多股射流燃烧器燃烧富含氢气的瓦斯产生的湍流扩散火焰的尺度进行了实验研究,研究了燃烧器结构参数和操作参数对火焰长度和长宽比等尺度特性的影响规律。结果表明,火焰长度随燃烧器喷孔总面积的增大和燃气流量的增大而增大,随助燃空气过剩系数的增大而减小;火焰长度和长宽比随上层喷孔位置角的增大而减小。同时发现,瓦斯中氢气含量对火焰尺度影响较大,随着氢气含量增大,火焰长度和长宽比都明显减小。     

低温等离子体对甲烷/氧反扩散火焰影响的实验研究

为探究低温等离子体对甲烷/氧反扩散火焰的影响,通过对同轴式喷注器环缝甲烷射流施加介质阻挡放电产生甲烷等离子体,综合采用多种测量手段实验研究了多种工况下该低温等离子体特性及火焰关键参数的变化。结果显示,放电击穿电压随混合比增大而减小,电流脉冲数量和幅值则随混合比增大而先增加后减小;甲烷等离子体呈灰白色,低电压下提高气体流量则放电有所减弱;受等离子体气动效应作用,放电后甲烷射流角有所增大,且电压越高射流角越大,增幅则逐渐减小,过高激励强度下射流发生失稳;等离子体通过改变燃料和氧化剂的掺混而影响甲烷/氧反扩散火焰的形态,使得火焰中心高度总体有所下降,特征长度缩短,释热强度则有所增加,其中小流量、低混合比条件下作用效果更明显;喷注器功率则随混合比上升而先增大后减小。     

Study on stretch extinction limits of CH4/CO2 versus high temperature O2/CO2 counterflow non-premixed flames

Extinction limits of counterflow non-premixed flames with normal and high temperature oxidizers were studied experimentally and numerically for development of new-type oxygen-enriched mild combustion furnace. Extinction stretch rates of CH₄/CO₂ (at 300 K) versus O₂/CO₂ flames at oxygen mole fractions of 0.35 and 0.40 and oxidizer temperatures of 300 K, 500 K, 700 K and 1000 K were obtained. Investigation was also conducted for CH₄/N₂ (at 300 K) versus air (O₂/N₂) flames at the same oxidizer temperatures. An effect of radiative heat loss on stretch extinction limits of oxygen-enriched flames and air flames was investigated by computations with optical thin model (OTM) and adiabatic flame model (ADI). The results show influence of radiative heat loss on stretch extinction limits was not significant in relative high fuel mole fraction regions. The extinction curve of the oxygen-enriched flames with oxygen mole fraction of 0.35 was close to that of the air flames at the oxidizer temperature of 300 K. However, the extinction curve of air flames with high temperature oxidizer was comparable with that of oxygen-enriched flames with oxygen mole fraction of 0.40. Scaling analysis based on asymptotic solution of stretch extinction was applied and it was found that stretch extinction limits can be expressed by two terms. The first term is total enthalpy flux of fuel stream based on thermo-physical parameters. The second term is a kinetic term which reflects an effect of the chemical reaction rate on stretch extinction limits. OH radicals which play important roles in chain propagating and main endothermic reactions were used to represent the kinetic term of both oxygen-enriched and air flames. The global rates of OH formation in these two cases were compared to understand the contribution of kinetic term to stretch extinction limits. Variation of extinction curves of oxygen-enriched flames and air flames was well explained by the present scaling analysis. This offers an effective approach to estimate stretch extinction limits of oxygen-enriched flames based on those of air flames at the same oxidizer temperature.     

CO2稀释对甲烷-高温空气扩散燃烧及NO生成特性影响的化学动力学分析

基于GRI-Mech 3.0详细化学反应机理,利用OPPDIF Code研究了CO2稀释比、预热温度及拉伸率对甲烷-高温空气层流对冲扩散火焰温度、热释放率、组分摩尔分数及NO生成特性的影响.研究结果表明,CO2稀释助燃空气能有效降低火焰中H、O及OH等基团摩尔分数,抑制燃烧过程链传播及链引发反应,从而减缓CH4氧化速率.随着助燃空气中CO2稀释比的增加,火焰最高温度逐渐降低,主氧化区及第二氧化区放热峰值变小,燃烧反应高温区变窄,NO生成指数E显著降低.当稀释比大于20%时,热力型NO随助燃空气温度升高规律并不明显.随着CO2稀释比的增加,快速型NO对NO生成量影响逐渐增强,成为高CO2稀释比下甲烷-高温空气扩散燃烧NO生成的主要路径.     

常温高预混度甲烷火焰燃烧特性研究

使用自行研制的微型天然气燃烧装置,利用FTIR发射透射技术,借助傅立叶变换红外光谱仪在线测量了常温高预混度条件下甲烷火焰的温度和辐射力。通过试验得出了较高预混度条件下常温甲烷火焰的碳黑生成、火焰辐射和火焰温度等方面的燃烧特性。     

Explosion behavior of CH4/O2/N2/CO2 and H2/O2/N2/CO2 mixtures

In this work, the explosion behavior of stoichiometric CH₄/O₂/N₂/CO₂ and H₂/O₂/N₂/CO₂ mixtures has been studied both experimentally and theoretically at different CO₂ contents and oxygen air enrichment factors. Peak pressure, maximum rate of pressure rise and laminar burning velocity were measured from pressure time records of explosions occurring in a closed cylindrical vessel. The laminar burning velocity was also computed through CHEMKIN–PREMIX simulations.     

The effects of composition on burning velocity and nitric oxide formation in laminar premixed flames of CH4 + H2 + O2 + N2

Experimental measurements of adiabatic burning velocity and NO formation in (CH₄ + H₂) + (O₂ + N₂) flames are presented. The hydrogen content in the fuel was varied from 0 to 35% and the oxygen content in the air from 20.9 to 16%. Nonstretched flames were stabilized on a perforated plate burner at 1 atm. The heat flux method was used to determine burning velocities under conditions when the net heat loss of the flame is zero. Adiabatic burning velocities of methane + hydrogen + nitrogen + oxygen mixtures were found in satisfactory agreement with the modeling. The NO concentrations in these flames were measured in the burnt gases at a fixed distance from the burner using probe sampling. In lean flames, enrichment by hydrogen has little effect on [NO], while in rich flames, the concentration of nitric oxide decreases significantly. Dilution by nitrogen decreases [NO] at any equivalence ratio. Numerical predictions and trends were found in good agreement with the experiments. Different responses of stretched and nonstretched flames to enrichment by hydrogen are demonstrated and discussed.     

An experimental and kinetic modeling study of premixed NH3/CH4/O2/Ar flames at low pressure

An experimental and modeling study of 11 premixed NH₃/CH₄/O₂/Ar flames at low pressure (4.0 kPa) with the same equivalence ratio of 1.0 is reported. Combustion intermediates and products are identified using tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry. Mole fraction profiles of the flame species including reactants, intermediates and products are determined by scanning burner position at some selected photon energies near ionization thresholds. Temperature profiles are measured by a Pt/Pt-13%Rh thermocouple. A comprehensive kinetic mechanism has been proposed. On the basis of the new observations, some intermediates are introduced. The flames with different mole ratios (R) of NH₃/CH₄ (R0.0, R0.1, R0.5, R0.9 and R1.0) are modeled using an updated detailed reaction mechanism for oxidation of CH₄/NH₃ mixtures. With R increasing, the reaction zone is widened, and the mole fractions of H₂O, NO and N₂ increase while those of H₂, CO, CO₂ and NO₂ have reverse tendencies. The structural features by the modeling results are in good agreement with experimental measurements. Sensitivity and flow rate analyses have been performed to determine the main reaction pathways of CH₄ and NH₃ oxidation and their mutual interaction.     

有辐射热损射流扩散火焰条件矩模型数值模拟

假设火焰辐射区域为光学薄，将辐射计算的代数模型嵌入到条件矩模型中（CMC（rad）），对甲烷－空气射流扩散值班火焰进行了模拟。并将此模型的模拟结果分别与实验和未考虑辐射热损的条件矩模型（CMC（ad））的结果进行了比较。结果表明采用代数模型计算辐射热损失是合适的，且考虑辐射的条件矩模型对温度场和NO的浓度的模拟结果相比未考虑辐射热损条件矩模型的模拟结果，与实验结果符合得要好。