共查询到19条相似文献,搜索用时 140 毫秒
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CO气相反应对碳颗粒燃烧的影响——连续膜理论的一种简化模拟方法 总被引:7,自引:1,他引:6
本文提出了一种新的考虑了颗粒边界层内CO气相反应效应的碳颗粒燃烧简化模型——移动火焰锋面(MFF)模型。该模型成功地实现了在“碳颗粒着火时表面等效生成物为CO_2”与“扩散扩制时全部成为CO”这两个极限之间的各种中间燃烧工况的连续转变,并很好地预报了Young等人测量得到的褐煤碳颗粒表面温度超过现有单膜模型理论极限值的实验结果。 相似文献
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本文用自行研制的具有快速加热、快速分析功能的加压燃烧炉,进行了永安无烟煤和高纯石墨在不同空气压力下的燃烧试验,测定了试样重量和温度变化的连续曲线,得到了空气压力对碳燃烧速率的影响规律。在应用单反应扩散燃烧模型修正碳粒表面氧气分压力的条件下,由实验结果计算得到永安无烟煤和高纯石墨与氧反应时的反应级数。 相似文献
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炭/碳粒燃烧速率的通用计算方法 总被引:2,自引:1,他引:1
本文介绍了计算炭/碳粒燃烧速率的通用方法。提出了一个新的无因次准则——燃烧速率控制准则(称F_b准则),它可定量地确定炭/碳粒处于动力、扩散还是动力-扩散控制;并得到了一种供工程计算用的计算炭/碳粒在空气中燃烧时的燃烧速率的通用曲线法。 相似文献
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关于碳/炭粒表面氧化反应生成物CO/CO_2比值的研究 总被引:1,自引:0,他引:1
本文通过严格的求解一组包括空间反应在内的微分方程,并辅以准确的碳粒燃烧速率及其温度的实验测定,得到了计算碳/炭粒表面氧化反应生成物C0/CO_2比值的通用表达式,它较之前人的经验公式更准确、通用。从而为碳/炭粒的温升历程及其着火温度的预报提供了可靠的理论基础。 相似文献
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采用亚网格动能(k方程)应力模型、二阶矩(SOM)燃烧模型和欧拉拉氏两相流模型,对乙醇-空气液雾燃烧进行了大涡模拟(LES)。瞬态结果显示:在火焰的高温区域,旋涡强度较大;在高温区边缘附近存在的拟序结构有脱落的趋势。在燃烧装置的燃料进口附近,近喷嘴中心区域,大量液滴聚集在条状湍流拟序结构的周围。LES模拟的统计结果给出的温度分布与实验结果吻合较好。说明SOM燃烧模型适用于液雾两相湍流燃烧研究,计算结果经过和实验数据对比发现,LES-SOM燃烧模型优于RANS-PDF及LES-FA计算结果。数值计算结果与实验结果的误差主要是由于采用统观一步反应机理引起的,表明燃烧模型还有待进一步改进。 相似文献
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《Combustion Theory and Modelling》2013,17(2):417-433
This study used a numerical model to investigate the combustion process in a premixed iso-octane homogeneous charge compression ignition (HCCI) engine. The engine was a supercharged Cummins C engine operated under HCCI conditions. The CHEMKIN code was implemented into an updated KIVA-3V code so that the combustion could be modelled using detailed chemistry in the context of engine CFD simulations. The model was able to accurately simulate the ignition timing and combustion phasing for various engine conditions. The unburned hydrocarbon emissions were also well predicted while the carbon monoxide emissions were under predicted. Model results showed that the majority of unburned hydrocarbon is located in the piston-ring crevice region and the carbon monoxide resides in the vicinity of the cylinder walls. A sensitivity study of the computational grid resolution indicated that the combustion predictions were relatively insensitive to the grid density. However, the piston-ring crevice region needed to be simulated with high resolution to obtain accurate emissions predictions. The model results also indicated that HCCI combustion and emissions are very sensitive to the initial mixture temperature. The computations also show that the carbon monoxide emissions prediction can be significantly improved by modifying a key oxidation reaction rate constant. 相似文献
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In order to examine extinction of carbon particle in the course of combustion, an attempt has been made to obtain its critical condition. Main concern has been put on the particle extinction in the lower limit that can occur at the end of the particle combustion although not only the lower limit but also the upper limit of the critical conditions has been obtained. By conducting asymptotics, with focusing on the temporal variation of the particle temperature, an analytical expression has been obtained for the limit of the particle diameter, as functions of the pressure ratio, oxygen mass-fraction, ambient temperature, and/or radiative heat flux. An approximate expression is also obtained from the analytical solution. It is found that the approximate expression can fairly represent the limits. In addition, use has been made of the Arrhenius plot of a comprehensive parameter, consisting of the particle diameter and pressure ratio, in order to identify regions for the particle combustion sustained, which are next to those for the particle extinction. Comparisons have also been conducted by use of experimental data in the literature, with presenting a fair degree of agreement, as far as the trend and approximate magnitude are concerned. It has been confirmed that the formulation has captured the essential feature, that the reduction in particle size does not necessarily favor the particle combustion, and that the particle extinction can occur when the particle diameter is reduced to the critical value. 相似文献
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《Proceedings of the Combustion Institute》2023,39(3):3539-3549
An improved model of fine particulate matter formation coupling the mechanism of mineral coalescence and char fragmentation under different pulverized coal combustion environments has been constructed. Firstly, based on the theoretical model of char fragmentation and percolation, the included minerals with different types and particle sizes are constructed in the model, and a three-dimensional char particle sub-model is established. And the type, content and particle size distribution of included minerals are introduced as input parameters by using computer controlled scanning electron microscopy (CCSEM) technology. All of the above makes it more in line with the actual distribution of the included minerals. Then a sub-model of char fragmentation is built based on the sub-model of the char particle. And considering the influence of char combustion reaction on the particle formation process and melting characteristics of included minerals, a sub-model of mineral melting coalescence under different combustion environments is established. Finally, based on this improved model, we compared the calculation results with the experimental data and the calculation results of the traditional model. Fully considering the process of mineral coalescence and char fragmentation, which contains the characteristics of different included minerals, the results show that the newly established model has a good fitting effect for the experiment and is closer to the actual process of char particle combustion to generate particles. By the new model, the influence of the factors (mineral content, particle size distribution and porosity) on the formation of particulate matter is preliminarily analyzed. 相似文献
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基于孔隙尺度,结合活性炭与甲醛的真实物性参数,利用格子Boltzmann方法,选取热质耦合的LBGK模型对填充有球形活性炭的方腔内部双扩散混合对流、流固共轭传热及吸附特性进行数值模拟。分别采用二维D2Q9模型描述速度温度场,D2Q5模型描述浓度场,研究活性炭颗粒直径、孔隙率以及颗粒的排列方式对整个动态吸附性能的影响。结果表明:在孔隙率为0.85时,随着颗粒直径的增大,活性炭吸附甲醛的速率减小,达到饱和吸附状态所需的时间增长;当直径为0.43 mm时活性炭的吸附速率最大,达到饱和状态的时间最短;活性炭颗粒的吸附速率与达到吸附饱和所需的时间几乎与孔隙率无关;与活性炭颗粒的错列与顺列排列方式相比,随机且不粘连排列方式的动态吸附性能更好。 相似文献
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Jian-Xin Nie 《中国物理 B》2022,31(4):44703-044703
The combustion mechanism of aluminum particles in a detonation environment characterized by high temperature (in unit 103 K), high pressure (in unit GPa), and high-speed motion (in units km/s) was studied, and a combustion model of the aluminum particles in detonation environment was established. Based on this model, a combustion control equation for aluminum particles in detonation environment was obtained. It can be seen from the control equation that the burning time of aluminum particle is mainly affected by the particle size, system temperature, and diffusion coefficient. The calculation result shows that a higher system temperature, larger diffusion coefficient, and smaller particle size lead to a faster burn rate and shorter burning time for aluminum particles. After considering the particle size distribution characteristics of aluminum powder, the application of the combustion control equation was extended from single aluminum particles to nonuniform aluminum powder, and the calculated time corresponding to the peak burn rate of aluminum powder was in good agreement with the experimental electrical conductivity results. This equation can quantitatively describe the combustion behavior of aluminum powder in different detonation environments and provides technical means for quantitative calculation of the aluminum powder combustion process in detonation environment. 相似文献
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V. M. Gremyachkin E. P. Mazanchenko 《Russian Journal of Physical Chemistry B, Focus on Physics》2010,4(6):963-968
The diffusive-kinetic model of porous carbon particles gasification is developed. The model considers the processes of heat
and mass transfer both inside the porous particle and above it. Analysis of the model shows that heat and mass transfer have
an influence to the gasification process to a marked degree. Gasification of carbon particle by carbon dioxide is impossible
if particle temperature is lower about 850 K because concentration of carbon dioxide at the particle surface becomes lower
than its equilibrium concentration. The rate of the carbon particle gasification is determined as a function of the porous
particle internal surface area for different pressures and furnace temperatures. 相似文献
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Sima Farazi Antonio Attili Seongwon Kang Heinz Pitsch 《Proceedings of the Combustion Institute》2019,37(3):2867-2874
The ignition and combustion of coal particles are investigated numerically under conventional and oxy-fuel atmospheres. Devolatilization is computed using the chemical percolation devolatilization (CPD) model. The CPD model is coupled with a Lagrangian particle tracking method in the framework of a multiphysics, multiscale Navier–Stokes solver. Combustion in the gas phase is described using finite rate chemistry. The numerical results for ignition are compared with available experimental data and a remarkably good agreement is observed. The effect on flame ignition of the different phases characterizing the release of volatile gases is assessed. These different phases manifest themselves in two distinct peaks in the devolatilization rate and it is observed that ignition can occur during the first volatile release or on the onset of the second, depending on the particle size and gas temperature. It is found that an increase of ignition delay time in oxy-atmosphere compared to the air case is related to the depletion of radicals that react with the abundant carbon dioxide of the oxy-atmosphere, while the increased heat capacity of the mixture does not play a role. 相似文献
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V. M. Gremyachkin E. P. Mazanchenko 《Russian Journal of Physical Chemistry B, Focus on Physics》2009,3(4):595-601
Diffusive-kinetic model of porous carbon particle gasification by steam is developed. The model considers the processes of heat and mass transfer both inside the porous particle and above it. Heat losses by radiation to the particle from furnace wall are taken into account. Heterogeneous reactions of carbon with steam and carbon with carbon dioxide and homogeneous reaction of carbon monoxide with steam are considered. Pressure variation caused by gas mass increasing inside the particle is considered too. The analysis of the model inside the porous particle made possible determining the correlation between the reaction rate of carbon with steam and the reaction rate of carbon with carbon dioxide. The homogeneous reaction is supposed to be equilibrium. It is considered that the kinetics of heterogeneous reactions is known, than the equations of the model may be solved; and consequently the dependences of the particle gasification rate and the composition of the gasification products vs. composition, pressure and temperature of ambient gas and the internal surface of the porous particle are determined. 相似文献