乙烯/空气扩散火焰截面烟黑体积分数和温度分布的反投影重建

给出了基于图像双通道辐射能反投影值的火焰截面内烟黑体积分数和温度分布的重建模型,通过试验分析了乙烯/空气扩散火焰不同高度断面内温度和体积分数的分布特性.从数据结果可以看出,与温度相比,同一截面内烟黑体积分数的最大值更靠近火焰边缘,同时受温度和氧浓度影响,火焰中心乙烯气体在离开喷嘴后并没有立即参与燃烧反应,其完全着火燃烧点在火焰中部以上,而烟黑温度和体积分数截面平均的最大值也出现在这一位置.     

反应速率对层流扩散火焰特性的影响

为探究燃烧过程中火焰结构和烟黑特性的变化规律,对层流乙烯/空气扩散火焰进行了数值模拟,分析了不同成核过程和表面生长过程中,反应速率常数的指前因子及活化能对层流乙烯/空气扩散火焰温度和烟黑体积分数的影响。结果表明：成核反应速率常数中,指前因子增大,火焰温度降低,烟黑体积分数增大,当指前因子提高50%时,在轴向高度3 cm位置对应的火焰温度峰值减小0.70%,烟黑体积分数的峰值增大37.98%;活化能增加,火焰温度增大,烟黑体积分数减小,当活化能提高50%时,在轴向高度3 cm位置对应的火焰温度峰值增大3.41%,烟黑体积分数的峰值减小78.92%;表面生长反应速率常数中,指前因子增大,火焰温度逐渐减小,烟黑体积分数逐渐增大,当指前因子提高50%时,在轴向高度3 cm位置对应的火焰温度峰值减小2.03%,烟黑体积分数的峰值增大1.65倍;活化能增加,使火焰温度升高,烟黑体积分数减小,当活化能提高50%,在轴向高度3 cm位置对应的火焰温度峰值增大9.61%,当活化能提高12.5%,烟黑体积分数的峰值减小46.68%。     

微重力蜡烛火焰特征数值模拟

建立了微重力蜡烛火焰的数学模型。计算与分析表明，火焰的形状由空气动力学特征决定，火焰的温度取决于化学反应动力学特征和火焰的热损失。在静止微重力环境中，自然对流的消失使火焰为半球形。辐射热损失对蜡烛火焰温度（颜色）特征的形成有重要贡献，在静止微重力环境下，化学反应放热速率受氧气扩散速率控制，辐射热损失的冷却使火焰温度低于正常重力温度值。但当环境气体的流动速度加大时，辐射热损失的影响逐渐减小，蜡烛火焰的温度逐渐接近正常重力蜡烛火焰的温度。当氧浓度较小时，火焰峰值温度小于烟黑形成的阈值温度（1300k）；当氧浓度较大时，火焰温度大于黑烟形成的阈值温度。     

火焰参数对辐射图像法不同测温模型的影响

对火焰温度分布的实时测量能够了解燃烧过程、验证燃烧机理、预防工业事故、优化燃烧设备。图像法测温在工业现场的火焰三维温度测量上有明显的优势,但通常均考虑火焰为均匀折射率介质,给测温结果带来了不可避免的误差。本文建立了梯度折射率介质下火焰的辐射成像模型和图像法测温模型,验证了方法的正确性,分析了火焰尺寸对成像的影响及炭黑颗粒浓度对温度场重建的影响。得出随着火焰尺寸的增大,图像强度随火焰尺寸出现先增大后减小的趋势,梯度介质模型与均匀介质模型的差异逐渐增大,随着炭黑颗粒浓度的增加,两种模型的重建精度逐渐下降。     

采用发射光谱法检测煤粉锅炉火焰的技术研究

利用以CCD阵列作为光电接收元件的微型光纤光谱仪,在燃煤锅炉现场测量火焰从533nm至1050nm波段的发射光谱。通过对不同工况的在大量实测数据曲线进行分析处理,得到了视场中火焰平均温度和黑度。并发现：（1）煤粉火焰辐射基本上可以作为灰体辐射处理;（2）煤粉燃烧器负荷增大时,火焰黑度相应增大,火焰温度波动减小;（3）炉膛内背景火焰燃烧稳定,黑度远大于燃烧器出口火焰黑度,火焰温度波动明显降低;（4）未着火煤粉的温度较低,波动很小,黑度也很小。火焰发射光谱的这些特征为进行火焰监测和诊断提供了可靠的判据。图6表1参9     

对称与非对称碳氢火焰温度场重建实验研究

为了测量碳氢火焰的截面温度场分布,根据火焰烟黑辐射传递特性,提出了基于火焰发射辐射能图像的温度场重建模型,使用最小二乘QR矩阵分解法（LSQR法）求解该模型。数值模拟重建了轴对称和非对称分布的两类温度场,重建结果精度较高。进而对实验室的甲烷扩散火焰截面二维温度场进行了重建,结果与已有文献相比符合较好,特别是对非对称火焰,能准确还原其温度场分布特征,实验得到了较好的结果。     

用光导纤维多色法对柴油机燃烧室内火焰温度与碳粒生成的研究

本文介绍了作者研制的分叉光导纤维４色法测量装置和采用它对直喷式４１３５型柴油机燃烧室内火焰温度和碳烟浓度测量的结果。以双色法为基础的４色法，通过数学方法可优化试验结果，减小测量误差。测量结果表明：在燃烧过程中，碳粒生成时间落后于温度上升时间，持续高温产生碳粒高浓度，后燃烧使碳粒浓度增加。随着负荷的增加，燃烧火焰温度及碳粒浓度增加，它们持续的时间也延长。燃烧终了破粒浓度和排气烟度增大。在喷注区会产生很高的碳粒质量浓度值，稀混合气区火焰温度上升较早。过后燃烧或供油提前角减小，使燃烧终了碳粒浓度增大。     

基于吸收光谱方法的平面非预混Hencken火焰多参数测量

Hencken炉可以产生均匀稳定的平面火焰，常被用作各种激光诊断技术的标定．本研究设计制造了一种适用于吸收光谱测量的Hencken平面炉，利用CO₂在4.2mm带头位置吸收峰的高温敏感性，采用可调谐半导体激光吸收光谱(TDLAS)技术研究了Hencken炉所产生平面火焰的燃烧特性．本研究采用DME作为燃料，同时测量了Hencken炉火焰温度及CO₂体积分数的二维分布．当空气/燃料流速与层流火焰传播速度相当时，DME平面Hencken火焰轴向存在温度、产物浓度稳定区．当火焰燃烧稳定时，在此区域内火焰温度、产物浓度保持不变并接近绝热火焰工况．     

同轴离心式喷注器火焰特性实验研究

为了研究高压补燃循环液氧,煤油发动机燃烧室同轴离心式喷注器的火焰特性,分别用富氧空气和煤油蒸气以及空气和甲烷在大气环境下进行了喷注器的燃烧实验,前者采用红外热像仪测量了火焰温度场,后者采用激光诱导荧光技术测量了火焰中CO2和OH的分子浓度分布.结果表明,该型喷注器的火焰形状和燃烧产物组分随氧化剂和燃料的混合比而变化;火焰稳定在喷注器出口处,剧烈的燃烧发生在火焰中心;平面激光诱导荧光技术用于燃烧过程研究,可以提供燃烧场组分分子浓度的信息.     

基于辐射强度多波长分析的燃烧火焰温度测量方法的实验研究

在研究中,多波长分析用于丁烷－空气混合气体燃烧火焰的温度测量,在测量系统中采用光纤光谱仪对处于可见光波段（５００￣１４００ｎｍ）中的燃烧火焰辐射进行测量,并胜仗火焰温度。测量结果表明,由于采用光谱分析的方法,波开的选择对测量结果的影响明显减小,因而测量结果的稳定性大大提高。其次,采用这种分析方法,还能够找到火焰单色辐射黑度的变化规律。最后,在多波长分析的具体实现步骤中省略了双色法所必需的火焰绝对辐     

A Comparative Exploration of Enhancing Thermal Characteristics of Natural Gas Flame by Synchronous Combustion Technique

This article is a comparative study of how the injection of micro kerosene droplets and pulverized anthracite coal particles affects soot particle nucleation inside natural gas flame and, subsequently, radiation. To this end, the yellow chemiluminescence of soot particles and IR photography were used to locate radiative soot particles and discover their qualitative distribution. The IR filter was tested with a Thermo Nicolet Avatar 370 FTIR Spectrometer for its spectral transmittance to be specified. Also, the spectral absorbance of soot particles, which are formed in flame, was measured by BOMEM FTIR. Furthermore, the variations of flame temperature, transient heat transfer, and thermal efficiency were investigated. The results indicate that, for equal heating values, kerosene droplets are more effective than coal particles in improving the radiation and thermal characteristics of natural gas flame. Also, kerosene droplets cause a higher rise in the temperature in flame downstream and make the axial flame temperature more uniform than coal particles do. In quantitative terms, when kerosene droplets were injected, the radiative heat transfer and thermal efficiency of flame were 93% and 35% higher than the corresponding values for the coal particles injection mode.     

基于热电偶扫描的炭烟火焰温度场测量

提出了一种热电偶扫描快速测量炭烟火焰温度场的方法,并对McKenna燃烧器形成的乙烯/空气平面炭烟火焰温度场进行测量.结果表明:在1450～1700 K火焰温度时,由炭烟沉积导致热电偶热辐射损失的修正温度偏差为200～240 K,修正后的火焰温度测量值与其他测温方法结果吻合良好,证实了该方法可以快速测量炭烟火焰温度场;...     

Soot formation, spray characteristics, and structure of jet spray flames under high pressure

Coaxial jet spray flames of kerosene and oxygen are experimentally studied over a pressure range of 0.1–1.0 MPa to determine the relationship between flame structure, droplet behavior, and soot formation region, which varies with changes in pressure. The direct images and chemiluminescence spectra show that the spray flames have three regions: the blue flame region, which has a peak of CH* and C₂* radical chemiluminescence, luminous flame region caused by soot emission, and blue emission region caused by CO₂ emission. With increase in ambient pressure, the flame length shortens drastically, the luminous flame region envelopes the blue flame region, and the blue emission becomes more intense. The result of phase-Doppler anemometry shows that a large number of small droplets evaporate and disappear near the burner, and the evaporation of large droplets also occurs rapidly under high pressure. The result of temperature measurements shows that high-temperature regions appear near the burner. The flame temperature drastically decreases along the central axis, and a minimum temperature point appears. This point moves upstream with increase in ambient pressure because evaporation of the droplets occurs further upstream. A laser-induced incandescence measurement shows that the soot volume fraction does not monotonously increase or decrease with increase in ambient pressure. The soot volume fraction at the central axis becomes low upstream and high downstream. As pressure increases, the vertical position at which the peak of soot volume fraction appears at the central axis moves upstream.     

Effects of radiation on spray flame characteristics and soot formation

Two-dimensional numerical simulations are applied to spray flames formed in a laminar counterflow and the effects of radiation on spray flame characteristics and soot formation are studied. N-Decane (C₁₀H₂₂) is used as the liquid fuel, and the droplet motion is calculated by the Lagrangian method. A single-step global reaction is employed for the combustion reaction model. A kinetically based soot model with a flamelet model is used to predict soot formation. Radiation is taken into account using the discrete ordinate method. The results show that radiation strongly affects the spray flame behavior and soot formation. Without the radiation model, flame temperature and soot volume fraction are greatly overestimated. The soot is formed in the diffusion flame regime, and its radiation emission increases with the increase in the equivalence ratio of the droplet fuel. This trend is in good agreement with that of the luminous flame behavior observed in the experiments.     

Measurements of soot production and thermal radiation from confined turbulent jet diffusion flames of methane

Turbulent methane/air jet diffusion flames at atmospheric and elevated pressure have been studied experimentally to provide data for coupled thermal radiation and soot production model development and validation. Although methane is only lightly sooting at atmospheric pressure, at elevated pressure the soot yield increases greatly. This allows the creation of a highly radiating flame, of moderate optical depth, within a laboratory scale rig. Spatially resolved flame properties needed for model validation have been measured at 1 and 3 atm. These measurements include detailed maps of mean mixture fraction, mean temperature, mean soot volume fraction, and mean and instantaneous spectrally resolved, path integrated radiation intensity.     

Flame radiation

Flame radiation is generally recognized as an important factor in fire phenomena and many combustion systems. Accurate prediction of flame radiation requires a good understanding of the radiative transport theory as well as detailed information on the radiative properties of the combustion products which generally consist of a mixture of gases plus soot particles. In this article the physics of gas radiation and its application to non-luminous flame calculations are first introduced. Subsequent formulation of luminous flame radiation incorporates properly the continuous soot emission. Effects of non-homogeneous distributions of temperature and gas partial pressures along the pathlength are discussed for both luminous and non-luminous flames. For engineering applications, useful radiation quantities such as the total emissivity, the mean absorption coefficient, and the radiation conductivity are expressed in simple analytical representations in terms of pertinent flame parameters.     

Structure of laminar sooting inverse diffusion flames

The flame structure of laminar inverse diffusion flames (IDFs) was studied to gain insight into soot formation and growth in underventilated combustion. Both ethylene-air and methane-air IDFs were examined, fuel flow rates were kept constant for all flames of each fuel type, and airflow rates were varied to observe the effect on flame structure and soot formation. Planar laser-induced fluorescence of hydroxyl radicals (OH PLIF) and polycyclic aromatic hydrocarbons (PAH PLIF), planar laser-induced incandescence of soot (soot PLII), and thermocouple-determined gas temperatures were used to draw conclusions about flame structure and soot formation. Flickering, caused by buoyancy-induced vortices, was evident above and outside the flames. The distances between the OH, PAH, and soot zones were similar in IDFs and normal diffusion flames (NDFs), but the locations of those zones were inverted in IDFs relative to NDFs. Peak OH PLIF coincided with peak temperature and marked the flame front. Soot appeared outside the flame front, corresponding to temperatures around the minimum soot formation temperature of 1300 K. PAHs appeared outside the soot layer, with characteristic temperature depending on the wavelength detection band. PAHs and soot began to appear at a constant axial position for each fuel, independent of the rate of air flow. PAH formation either preceded or coincided with soot formation, indicating that PAHs are important components in soot formation. Soot growth continued for some time downstream of the flame, at temperatures below the inception temperature, probably through reaction with PAHs.     

An experiment on the effect of oxygen content and air velocity on soot formation in acetylene laminar diffusion flame produced in a burner with a parallel annular coaxial oxidizer flow

The effect of oxygen content and of the combustion air velocity on soot formation was studied in acetylene diffusion flames. These flames were produced in a burner with a parallel annular coaxial flow of oxidizer. The effect on the flame axial temperature profile was also evaluated. The soot volume fraction was calculated by the laser light extinction methodology. The oxygen content in the combustion air was smaller than 30%, which does not require significant retrofit of existent equipment when the combustion conditions are varied. The results suggest that the parallel manipulation of the oxygen content and of the oxidizer velocity can provide means for managing soot formation and distribution. The formation of soot in industrial combustion systems is of interest in engineering, because the presence of soot in the flame enhances the heat transfer from the combustion gases by thermal radiation, increases the need for burner maintenance, and constitutes an environmental problem when emitted in the atmosphere.     

Flow-field effects on soot formation in normal and inverse methane–air diffusion flames

We investigate the effects of the flow-field configuration on the sooting characteristics of normal and inverse coflowing diffusion flames. The numerical model solves the time-dependent, compressible, reactive-flow, Navier-Stokes equations, coupled with submodels for soot formation and thermal radiation transfer. A benchmark calculation is conducted and compared with experimental data, and shows that computed peak temperatures and species concentrations differ from the experimental values by less than 10%, while the computed peak soot volume fraction differs from the experimental values by 10–40%, depending on height. Simulations are conducted for three normal diffusion flames in which the fuel/air velocities (cm/s) are 5/10, 10/10, and 10/5, and for an inverse diffusion flame (where the fuel and air ports have been reversed) with a fuel/air velocity of 10/10. The results show significant differences in the sooting characteristics of normal and inverse diffusion flames. This work supports previous conclusions from the experimental work of others. However, in addition, we use the ability of the simulations to numerically track soot parcels along pathlines to further explain the experimentally observed phenomena. In normal diffusion flames, both the peak soot volume fraction and the total mass of soot generated is several orders of magnitude greater than for inverse diffusion flames with the same fuel and air velocities. In normal diffusion flames, soot forms in the annular region on the fuel-rich side of the flame sheet, while in inverse flames, the soot forms in a fuel-rich region on top of the flame sheet. Surface growth is the dominant soot formation mechanism (compared to nucleation) for both types of flames; however, surface growth rates are much faster for normal diffusion flames compared to inverse flames. Soot oxidation rates are also much faster in normal flames, where the dominant soot-oxidizing species is OH, compared to inverse flames, where the dominant soot-oxidizing species is O₂. In the inverse flames, surface growth continues after oxidation has ceased, causing the peak soot volume fraction to be sustained for a long period of time, and causing the emission of soot, even though the quantity of soot is small. Comparison of soot formation among the three normal diffusion flames shows that the peak soot volume fraction and total mass of soot generated increases as the fuel-to-air velocity ratio increases. A larger fuel–air velocity ratio results in a longer residence time from the nucleation to the oxidation stage, allowing for more soot particle growth. When the fuel-to-oxidizer ratio decreases, there is less time for surface growth, and the particles cross the flame sheet (where they are oxidized) earlier, resulting in decreased soot volume fraction.