共查询到20条相似文献,搜索用时 147 毫秒
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碳烟主要是烃类燃料不完全燃烧生成的产物,其对人类健康、空气质量以及燃烧装置的使用寿命都会产生有害影响。碳烟生成是一个复杂的物理化学过程,控制碳烟排放,需要克服碳烟生成和燃烧过程中物理和化学演化的巨大差异,这些差异表现为对碳烟纳观结构和表面官能团随碳烟氧化活性反应变化的深入探索研究。近些年,研究人员对碳烟的生成机理开展了系列研究,对碳烟生成各个物理化学反应阶段有了一定认识。结合光谱诊断技术可深入了解燃烧系统碳烟形成过程,确定碳烟颗粒分子组成、精细结构、浓度分布等特征,也可从碳烟结构变化、黑体辐射强度等方面详细了解碳烟形成过程。该文旨在阐述光谱诊断技术对烃类火焰碳烟表征的研究进展和发展趋势,探讨LIBS, LII和LIF等作为诊断工具在包含背景辐射的火焰中检测碳烟生成过程产生辐射强度准确性等问题。主要介绍了烃类火焰碳烟的形成机理(从前驱体产生、生长到颗粒生成、凝聚,最后进行颗粒氧化)。总结了探测碳烟性质光谱诊断方法的应用以及光谱诊断技术对燃烧过程中碳烟表征的研究现状,包括对碳烟体积分数、温度和基于图像处理的碳烟结构表征,反应碳烟前驱体(多环芳烃)、反应气氛、温度等对碳烟颗粒物生成的影响。最... 相似文献
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煤粉燃烧火焰区域是燃烧过程中温度最高的区域,同时也是温度梯度、组分浓度梯度最高的地方,以及还原和氧化气氛交错存在等复杂环境,这种环境对亚微米颗粒初始形成阶段有着重要的影响,对该区域形成的PM1进行研究有助于深入理解PM1的形成机理.本文基于25 kW一维下行炉内对自维持燃烧的煤粉火焰区域,通过两级稀释水冷等速取样系统和ELPI(荷电低压撞击分离器)系统对颗粒物进行分级收集,以及电镜分析技术,获得PM1的质量和数浓度粒径分布,以及各粒径主要成分分布,并进行单颗粒分析.结果表明火焰区域中形成的亚微米颗粒以含碳物质为主,碳烟、碱金属和硫对超细颗粒有富集的趋势.该区域的亚微米颗粒同时存在多种复杂的形成机理. 相似文献
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采用不同的航空煤油化学反应机理和碳烟成核模型对气态航空煤油扩散火焰中碳烟颗粒的质量浓度和数量浓度进行预测.分别采用航空煤油详细化学反应机理和简化化学反应机理,结合非预混稳态扩散火焰面模型模拟燃烧反应.分别采用C2H2成核模型(基于乙炔浓度)和PAH成核模型(基于多环芳香烃浓度)预测碳烟颗粒浓度分布.研究结果表明,采用详细化学反应机理和PAH成核模型对碳烟体积分数的预测值与试验值吻合很好.相比于C2H2成核模型,采用PAH成核模型对碳烟体积分数的预测精度显著提升. 相似文献
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燃煤锅炉生成的碳烟不仅会增强火焰辐射、影响燃烧外,还排放到大气环境中带来严重危害。为了进一步了解其生成机理从而更好地对其生成量及特性进行控制,对煤粉燃烧过程中颗粒周围碳烟的分布规律进行定量的研究十分必要。本文自行设计了注射式微量给粉装置,成功实现了0.1 g/h量级给粉率下的连续给粉,并通过改进多元扩散燃烧器和以及结合激光诱导白炽光(Laser Induced Incandescence)技术,首次实现了对单颗粒煤粉燃烧过程中碳烟分布的定量测量,发现对于70μm左右的煤粉颗粒,碳烟分布直径约为1 mm。此外还通过控制气氛,研究了含氧量对碳烟生成的影响,发现随着氧含量的上升,碳烟总浓度下降并且峰值出现更早的规律。 相似文献
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空气电晕放电离子风激励器无需旋转部件, 仅通过消耗电能就能直接产生驱动力, 它是一种新型的动力技术, 备受国内外航空航天界的广泛关注. 目前对空气电晕放电离子风激励器的推力产生机理虽有各种解释, 但是现有理论均不能统一各种条件下的实验结果, 仍需要开展进一步的分析与研究. 本文以线-铝箔电极电晕放电激励器为研究对象, 通过实验研究发现作用在线电极与铝箔电极上的静电力不对称, 而且改变铝箔电极纵向高度和气压均能影响激励器的推力大小; 通过理论分析, 考虑电晕层与空间电荷的影响, 建立了线-铝箔电极电晕放电激励器的推力计算模型, 其计算值与实测值比较一致. 基于上述实验现象与理论建模分析, 本文认为线-铝箔电极电晕放电激励器的推力主要来源于线电极电晕产生的空间电荷对电极系统产生了不对称静电力作用, 使激励器出现净静电力作用. 相似文献
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A study on single fuel droplets combustion in vertical direct current electric fields 总被引:1,自引:0,他引:1
Osamu Imamura Yasuyuki Kubo Jun Osaka Junichi Sato Mitsuhiro Tsue Michikata Kono 《Proceedings of the Combustion Institute》2005,30(2):1949-1956
Both the electric force working on flames and the natural buoyancy are body forces, so there is a possibility to control the natural buoyancy by applying than electric field. It is important to discuss the body force in the flame because it induces the convective flow around flames. In this circumstance, combustion behavior of single droplets in vertical direct current electric fields was investigated. Ethanol, n-octane, and toluene were used as fuels, and the flame shape and the burning rate constants were measured. The distance between electrodes is 50 mm, and the applied voltage ranged between −4 and 6 kV as the bottom electrode is ground. When the direction of the electric field is opposite to the natural buoyancy direction, the applied voltage exists that make the flame symmetrical in the vertical direction, and the burning rate constants have local minima for ethanol and n-octane at the voltage. However, the minimum burning rate constants are larger than those under microgravity. This means that the electric force roughly balances with natural buoyancy, but it does not completely balance with the same. When the direction of the electric field is in the same direction as the natural buoyancy, there exist some experimental results, which cannot be explained by the assumption that electric field induces the body force only through the positive ions. This suggests that the additional body force is induced by the negative ions. The effects of negative charged soot particles on the combustion behavior are also discussed for the sooty flame of toluene. 相似文献
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Yilong Zhang Dongchan Kim Lingzhe Rao Sanghoon Kook Kenneth S. Kim Chol-Bum Kweon 《Proceedings of the Combustion Institute》2019,37(4):4847-4855
This study shows how the structure of soot particles within the flame changes due to the relative direction of the swirl flow in a small-bore diesel engine in which significant flame–wall interactions cause about half of the flame travelling against the swirl flow while the other half penetrating in the same direction. The thermophoresis-based particle sampling method was used to collect soot from three different in-flame locations including the flame–wall impingement point near the jet axis and the two 60° off-axis locations on the up-swirl and down-swirl side of the wall-interacting jet. The sampled soot particle images were obtained using transmission electron microscopes and the image post-processing was conducted for statistical analysis of size distribution of soot primary particles and aggregates, fractal dimension, and sub-nanoscale parameters such as the carbon layer fringe length, tortuosity, and spacing. The results show that the jet-wall impingement region is dominated by many small immature particles with amorphous internal structure, which is very different to large, fractal-like soot aggregates sampled from 60° downstream location on the down-swirl side. This structure variation suggests that the small immature particles underwent surface growth, coagulation and aggregation as they travelled along the piston-bowl wall. During this soot growth, the particle internal structure exhibits the transformation from amorphous carbon segments to a typical core–shell structure. Compared to those on the down-swirl side, the soot particles sampled on the up-swirl side show much lower number counts and more compact aggregates composed of highly concentrated primary particles. This soot aggregate structure, together with much narrower carbon layer gap, indicates higher level of soot oxidation on the up-swirl side of the jet. 相似文献
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Particle size distribution functions of nascent soot formed in four burner-stabilized, premixed ethylene-oxygen-argon flames were studied in a spatially resolved manner by online sampling/scanning mobility particle sizer. Particle morphology was analyzed by atomic force microscopy (AFM) of substrate-deposited samples. Two of the four flames were doped with benzene. An aerosol electrometer is introduced to extend the lower detection limit to around 1.5 nm in diameter. The results show that the bimodal behavior of particle size is applicable to all premixed ethylene flames studied. The variation of the size distribution from flame to flame is conclusively attributed to flame temperature variation. Under the condition of an equal carbon concentration, benzene doping leads to negligible changes in the characteristics of the size distribution. For all flames studied, AFM observations show that nascent soot is liquid-like and spreads extensively upon impact on a substrate surface. 相似文献
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《Journal of Quantitative Spectroscopy & Radiative Transfer》2007,104(2):266-276
An inversion scheme based on tomographic reconstruction of flame emission spectra has been developed for nonintrusive characterization of soot temperature and volume fraction fields within an optically thin axisymmetric flame by extracting characteristic information on soot refractive index from spectral gradients of emission spectra. Its performance is assessed by providing input data obtained from intensities simulated by a direct code based on experimental data for a flame available in the literature. Proposed method was found to be especially powerful in the near-infrared range for accurate prediction of flame properties where spectral variation of optical constants is significant. 相似文献
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以甲烷、乙烯、氢气混合扩散火焰碳烟为研究对象,采用激光共聚焦拉曼光谱(Raman)和傅里叶红外光谱(FTIR)研究了不同掺甲烷比例下乙烯、氢气混合火焰碳烟有序度及官能团的分布特性,分析了碳烟石墨化和官能团分布,揭示了掺甲烷对乙烯/氢气(氢气比例30%)层流扩散火焰的碳烟生成影响规律。Raman研究表明在甲烷掺混比为3%和7%时,在火焰高度低于4cm位置生成的碳烟有序程度显著降低,表明在此区域存在明显的碳烟生成协同效应;甲烷掺混比增大超过10%时,协同效应基本消失,碳烟有序度上升。FTIR研究表明掺混甲烷对碳烟官能团组成影响明显。掺混甲烷后脂肪族官能团相对含量整体提高。随着甲烷掺杂比的增大,CH2相对含量增大到一峰值后减小。碳烟中芳香族官能团含量随着火焰高度的上升含量下降明显。掺混3%和7%甲烷,芳香族官能团在2和3 cm火焰高度时,芳香族官能团的含量明显上升。掺混甲烷比高于10%时,芳香族官能团的含量则有所降低。表明少量甲烷掺混使得CH3和C3H3生成有了新的途径,CH3和C3H3增加,而C2H4和C2H2减少不明显,从而促进了多环芳香烃(PAHs)的生成。继续增加甲烷因为稀释作用会抑制C2H2生成从而减少PAHs的生成,芳香族相对含量降低,因而降低了碳烟的生成。研究揭示了甲烷对乙烯/氢气层流扩散火焰中碳烟形成的相互作用:在低甲烷掺混比时存在协同效应促进碳烟生成,而在高甲烷掺混比时协同效应消失。 相似文献
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Hyun I. Joo 《Proceedings of the Combustion Institute》2009,32(1):769-775
The effects of pressure on soot formation and the structure of the temperature field were studied in co-flow methane-air laminar diffusion flames over a wide pressure range, from 10 to 60 atm in a high-pressure combustion chamber. The selected fuel mass flow rate provided diffusion flames in which the soot was completely oxidized within the visible flame envelope and the flame was stable at all pressures considered. The spatially resolved soot volume fraction and soot temperature were measured by spectral soot emission as a function of pressure. The visible (luminous) flame height remained almost unchanged from 10 to 100 atm. Peak soot concentrations showed a strong dependence on pressure at relatively lower pressures; but this dependence got weaker as the pressure is increased. The maximum conversion of the fuel’s carbon to soot, 12.6%, was observed at 60 atm at approximately the mid-height of the flame. Radial temperature gradients within the flame increased with pressure and decreased with flame height above the burner rim. Higher radial temperature gradients near the burner exit at higher pressures mean that the thermal diffusion from the hot regions of the flame towards the flame centerline is enhanced. This leads to higher fuel pyrolysis rates causing accelerated soot nucleation and growth as the pressure increases. 相似文献
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It is increasingly recognized that soot particles play an important role in the radiative heat transfer from flames and smoke. After their formation, these minute particles usually conglomerate into different forms, with the limiting shapes being the spheres and long chains which can be modeled as infinite cylinders. The present work analyzes the effect of soot shape on soot radiation. The spectral extinction coefficient of spheres, being lower than that of the cylindrical particles, falls off rapidly in the near i.r. The shape effect on soot radiation is found to be more pronounced at low temperatures than at high temperatures. In flame radiation calculations the radiative contribution of the various conglomerated soot shapes can be properly accounted for by assuming spherical and polydisperse soot particles. Based on the extinction characteristics of the particles, an experimental method for determining the amount of spherical and cylindrical particles in a soot cloud is suggested. 相似文献
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Numerical simulations of laminar coflow methane/air diffusion flames at atmospheric pressure and different gravity levels were conducted to gain a better understanding of the effects of gravity on soot formation by using relatively detailed gas-phase chemistry and complex thermal and transport properties coupled with a semi-empirical two-equation soot model. Thermal radiation was calculated using the discrete-ordinates method coupled with a non-grey model for the radiative properties of CO, CO2, H2O, and soot. Calculations were conducted for three coflow air velocities of 77.6, 30, and 5 cm/s to investigate how the coflowing air velocity affects the flame structure and soot formation at different levels of gravity. The coflow air velocity has a rather significant effect on the streamwise velocity and the fluid parcel residence time, especially at reduced gravity levels. The flame height and the visible flame height in general increase with decreasing the gravity level. The peak flame temperature decreases with decreasing either the coflow air stream velocity or the gravity level. The peak soot volume fraction of the flame at microgravity can either be greater or less than that of its normal gravity counterpart, depending on the coflow air velocity. At sufficiently high coflow air velocity, the peak soot volume fraction increases with decreasing the gravity level. When the coflow air velocity is low enough, soot formation is greatly suppressed at microgravity and extinguishment occurs in the upper portion of the flame with soot emission from the tip of the flame owing to incomplete oxidation. The numerical results provide further insights into the intimate coupling between flame size, residence time, thermal radiation, and soot formation at reduced gravity level. The importance of thermal radiation heat transfer and coflow air velocity to the flame structure and soot formation at microgravity is demonstrated for the first time. 相似文献