催化肋片对微燃烧室内燃烧特性的影响

针对带有催化肋片的微燃烧室内部的氢氧预混合燃烧过程,利用CFD计算软件建立数值模型,在实验验证的基础上进行了模拟计算。结果表明:不同流速下,燃烧室内布置催化肋片能提高燃烧室外壁面平均温度以及燃烧效率。在低流速时催化肋片布置越靠近入口,表面催化反应对气相反应的抑制程度越大;肋片位置越靠近出口,燃烧室外壁面平均温度越高。在高流速下,催化肋片位置越靠近出口,表面催化反应对气相反应的促进作用越明显,使得燃烧室外壁面温度分布越均匀、燃烧室出口截面温度越高。     

氢气预混合微尺度催化燃烧的数值模拟

通过耦合计算流体力学软件FLUENT和化学反应动力学软件CHEMKIN并采用空间气相和表面催化详细化学反应机理,对氢气和空气的预混合气体在微型管道内的催化燃烧过程进行了数值模拟,讨论了不同反应模型的燃烧特性以及预混合气体入口速度、当量比Φ和管径对催化燃烧反应的影响。计算结果表明：表面催化反应对空间气相反应有抑制作用;随着入口速度的增大,燃烧过程同时存在着表面催化反应和空间气相反应两种控制因素;当量比Φ和管径对氢气的催化燃烧过程有重要的影响。     

烷烃催化燃烧的数值模拟

对甲烷、乙烷在表面涂有催化剂的微元管内的催化燃烧进行了模拟．讨论了微元管入口速度、直径、入口温度以及混合气中甲烷与氧气的摩尔比对甲烷催化燃烧特性的影响;分析了单体式蜂窝块中甲烷的着火温度及单个微元管中气体温度、主要气相组分与表面组分的质量分数的变化趋势．分析了不同混合气及不同混合气摩尔比下乙烷的催化燃烧特性,数值模拟结果与实验结果基本一致;提出了碳原子数为3或大于3的烷烃催化反应简化机理的建立方法．为在内燃机中实现催化燃烧以降低氮氧化合物、未燃碳氢化合物及一氧化碳的排放,及扩展燃烧极限提供了理论依据．     

Numerical simulation of model scramjet combustor flowfield

A new concept has been raised and adopted in this paper to enlarge the scope of the two‐dimensional model particularly for the purpose of dealing with three‐dimensional normal injection cases. Meanwhile, the method has a very good performance for its short cyclic period. The new idea was realized through special resolution with continuity equations; i.e., mass flow was directly added in the source term of the continuity equation. To prove the robustness of this illuminating method, comparisons using calculations were carried out, and the results are satisfactory. A model scramjet combustor tested on the free‐jet scramjet test facility was illustrated and underwent numerical calculations with the two‐dimensional program, adopting the above simplified injecting method. To simulate the chemical reaction process in the scramjet tunnel, a five‐species, single‐step reaction model was introduced in the calculation process. This research presents the major aerodynamic parameters and components of mass fraction distribution within the model combustor channel, which made it easy to observe and analyze the flowfield. Finally, wall pressure comparisons between the numerical and experimental results were carried out to verify the accuracy of the calculation model. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(5): 295– 302, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20159     

Numerical study of rich catalytic combustion of syngas

The rich catalytic combustion of syngas/air mixtures over platinum has been investigated numerically in a two-dimensional circular channel using steady simulations and detailed hetero-homogeneous chemistry. The channel dimensions are representative of a catalytic monolith. Simulations have been conducted in the pressure range of 1–10 bar and Φ = 3–5 with varying inlet velocities, residence time, H₂/CO ratio and CH₄ percentage. Detailed kinetic studies including the reaction path diagram (RPD) in a plug flow reactor have also been conducted to understand the kinetic interactions between H₂, CO, and CH₄. It has been observed that the homogeneous reaction rates are significant at higher pressures and cannot be neglected, although they were highly localized. The channel temperature significantly affected the relative conversion of H₂ and CO. The kinetic coupling between H₂ and CO oxidation was studied and the reason for the differential consumption of O₂ by the reactants was addressed by analyzing the reaction pathways. The residence time in the channel affected the species oxidation and four operation regimes were identified. Both the water-gas shift reaction and the reverse water-gas shift reaction were observed under varying conditions of pressure and equivalence ratio. The effect of H₂/CO ratio has also been investigated. The present study shows that rich catalytic combustion of syngas is fundamentally different from lean combustion.     

Numerical computation of a circulating fluidized bed combustor

A mathematical model to describe a circulating fluidized-bed combustor is presented. A modified two-phase model which was used in the bubbling fluidized-bed combustor is considered to simulate the dense zone of the bottom section. For the upper section of the bed the momentum and energy-balance equation are used to predict the temperature and velocity profiles for the gas and the particles. The model performs mass balances for the chemical gas species (O₂, H₂O, CO, CO₂ and SO₂) with consideration being given to the last for retention by limestone particles. The model is applied to typical conditions of a circulating atmospheric fluidized-bed boiler and the simulation results show the expected trends. © 1998 John Wiley & Sons, Ltd.     

微燃烧器内甲烷催化燃烧的数值模拟

联合使用CFD软件、FLUENT和化学反应动力学软件DETCHEM对甲烷—空气混合物在有逆流换热的微燃烧器内的催化燃烧进行了数值模拟。计算中只考虑了甲烷在催化表面上的反应。燃料一空气混合物的当量比为0．4,燃烧器外壁面分剐采用等温边界条件和与环境的对流换热边界条件,并比较了这两种边界条件对可燃混合气燃烧的影响。计算结果表明,催化燃烧可以实现常规方法无法实现的甲烷低温、高效转变。     

Bifurcation behaviors of catalytic combustion in a micro-channel

Bifurcation analysis of ignition and extinction of catalytic combustion in a short micro-channel is carded out with the laminar flow model incorporated as the flow model. The square of transverse Thiele modulus and the residence time are used as bifurcation parameters. The influences of different parameters on ignition and extinction behavior are investigated. It is shown that all these parameters have great effects on the bifurcation behaviors of ignition and extinction in the short micro-channel. The effects of flow models on bifurcation behaviors of combustion are also analyzed. The results show that in comparison with the flat velocity profile model, for the case of the laminar flow model, the temperatures of ignition and extinction of combustion are higher and the unsteady multiple solution region is larger.     

燃气轮机燃油燃烧室改用双燃料流场数值分析

针对燃气轮机燃油燃烧室改成双燃料燃烧室对燃料喷嘴进行一体化概念设计,并采用CFD技术对其双燃料燃烧流场进行数值模拟。针对燃烧室燃用C7H16和裂解气燃料的不同情况,采用标准κ-ε湍流模型、化学平衡条件下的快速化学反应系统和简单概率密度函数（PDF）燃烧模型、液体燃料的喷雾模型以及SIMPLE算法。模拟并对比分析了两种燃料燃烧时的燃烧效率、出口温度均匀性、壁面最高温度以及速度分布等参数随工况变化的趋势,并得出结论：1）不同燃料燃烧时的流场特征基本保持一致;2）裂解气燃料燃烧时,其燃烧效率较高,但出口温度均匀性较差;3）在加入相同焓值的燃料进入燃烧室时,裂解气燃料燃烧得到的出口温度低于燃油的燃烧状态。     

甲烷/空气预混气体在微通道中催化转化的数值模拟

用详细化学反应机理研究了微型直通道中甲烷／空气预混气体在镀Pt热壁上的催化燃烧问题．联合使用计算流体力学软件FLUENT和可以计算表面催化反应的化学反应动力学软件DETCHEM,对微型直通道中当量比在0．01～10．0范围之间的甲烷/空气预混气体的催化燃烧进行了数值模拟．计算结果表明,在微尺度催化燃烧中当量比和温度对甲烷催化转化率、转化速度有重要的影响．     

等离子发生器燃烧过程的数值研究

用湍流扩散燃烧的简单概率密度函数模型对等离子发生器燃烧流场进行了数值模拟。其中概率密度分布采用函数,使用RNG湍流模型得到了流场各参数同平均混合分数,混合分数脉动均方值的关系图及等离子发生器内部温度、压力、速度、密度、湍动能及各种燃烧产物等一系列湍流燃烧流场的特性参数分布,为研究燃烧室等离子强化燃烧机理奠定了基础。     

乙醇微型燃烧室燃烧特性的数值模拟研究

为了解决化石燃料储备不足与环境污染问题,生物质燃料作为石油替代能源得到大力提倡,如何合理地将化石燃料替换为生物质燃料且维持设备正常运行成为工程上亟待解决的问题。本文采用CFD软件研究了车载5 kW生物乙醇微型燃烧室的燃烧特性,对比分析了不同功率（0.5~5 kW）和出口温度（840~960 K）时的回流区长度与宽度、回流量、出口温度分布系数（OTDF）、出口NO体积分数等特征参数。结果表明：随着出口温度升高,回流区长度逐渐缩短,回流量减少,出口温度均匀性逐渐变差,出口NO体积分数明显增加;随着燃烧室功率增大,回流区长度变长,回流量增加,OTDF先增大后减小,NO体积分数随着功率的降低而显著升高,最大值出现在1 kW时,达到满负荷时的7倍。因此,为了实现稳定燃烧和减少污染物排放,该乙醇微型燃烧室应在较高的空燃比（即较低的出口温度）和功率下运行。     

Effect of inserted baffles on hydrogen heterogeneous reaction in planar catalytic micro combustor

Heterogeneous reaction characteristics of premixed H₂/Air mixture are numerically investigated in micro combustor with coating platinum (Pt) catalyst on the inner wall. The well-designed combustor with the inserted baffle is committed to improving the transport of bulk species on the catalytic surface, therefore enhancing the fuel conversion ratio. A two-dimensional numerical model with detailed heterogeneous reaction mechanism is developed and verified. In this work, the numerical results reveal that the heterogeneous reaction rate and fuel conversion ratio are significantly improved in the combustor with inserted baffle. The velocity of gaseous mixture swiftly increases between the baffle and catalytic surface, resulting in the increasing adsorption-desorption of bulk species on the catalytic surface. The main influencing factors of inserted baffle body comprise of slit width between two ribs in the same row (W), rib length (L), distance between adjacent baffles row (D), number of baffle row (n) which are studied to obtain a set of optimized parameters of baffle in the well-designed combustor. The optimized parameters of the baffle are W = 0 mm, L = 0.4 mm, D = 4 mm and n = 4, which are employed in the combustor to obtain a high hydrogen conversion ratio. Moreover, the effect of different inlet velocities and equivalent ratios of the mixture on the heterogeneous reaction characteristics are carried out in the designed combustor. As the designed combustor performs well, and the improvement effect of the optimized baffle gradually increases together with the inlet velocity, particularly for high inlet velocity (7 m/s). The promotion effects of baffle in the designed combustor are presented when the rich and lean fuel are adopted at inlet velocity of 7 m/s. Finally, the relative parameters of this work can serve as a reference and guidance for the design of micro scale combustor.     

负荷变化对900 MW超临界锅炉炉内燃烧影响的数值模拟

利用Fluent软件对1台900 MW四角切圆燃烧锅炉在不同负荷下炉内燃烧过程进行了数值模拟,分析了负荷变化对炉内流动和传热的影响规律.结果表明:在高负荷工况下运行时,炉内燃烧充分且稳定,但是炉内火焰更容易冲刷水冷壁,可能发生局部结渣现象;在低负荷工况下运行时,炉内火焰充满度较差,切圆燃烧的稳定性显著下降,炉膛水冷壁灰污表面温度也相应降低,水冷壁表面结渣的倾向弱化,沿高度方向水冷壁吸热不均匀性增大.由于该锅炉的低NOx燃烧器采用了分离燃尽风,使得高温区扩展,火焰中心高度比采用有关标准推荐的方法计算所得结果高4~5 m.     

氢氧加湿燃烧的数值模拟

介绍了利用CHEMKIN 4.1软件中封闭的全混同性反应器模型模拟加湿情况下氢氧燃烧的方法,同时基于详细的氢氧燃烧化学反应动力学机理分析了初始反应温度、反应压力及水蒸气添加量等对氢氧燃烧的影响。模拟结果表明,初始反应温度、反应压力及水蒸气添加量等因素均会对氢氧燃烧的点火延迟时间和燃烧最高温度产生一定程度的影响,其中水蒸气添加量的变化对氢氧燃烧的最高温度及火焰传播速度的影响较为显著。这对后续在实验室中进行氢氧加湿燃烧研究可提供有益的指导。     

催化燃烧技术的应用进展

介绍催化燃烧的实质和特点,论述催化燃烧技术在汽车尾气处理、提高锅炉燃煤效率、提高铁矿烧结质量等领域中的应用,以及在炉管烧焦过程中应用的前景。催化燃烧技术有利于资源的合理利用,是环境友好的过程,加快和扩展催化燃烧研究的领域,对生产进步有促进作用。     

Numerical investigation of spray combustion in jet mixing type combustor for low NOx emission

The present paper describes a numerical investigation of spray combustion in a jet mixing type combustor. In this combustor, kerosene spray was injected with a pressure atomizer, and high speed combustion air was introduced towards the spray flow through some inlet air nozzles to improve mixing of the spray and the air. In the numerical simulation, the conservative equations of mass, momentum and energy in the turbulent flow field were solved in conjunction with the k–ε two equation turbulence model. The effects of the diameter and the number of air inlet nozzles on the combustion behavior and NO emission were numerically investigated. When the diameter of the inlet air nozzle decreased from 8 to 4 mm, the calculated NO mole fraction in the exhaust gas was drastically decreased by about 80%. An increase in the inlet velocity resulted in improvement of the mixing of the spray and the air, and hence, the high temperature region where thermal NO was formed became narrow. As a result, the exhaust NO mole fraction decreased. Furthermore, a decrease in exhaust NO mole fraction was explained by a decrease in the residence time in the high temperature region above 1800 K.     

燃气轮机燃料轴向分级燃烧室的数值分析

为改善燃气轮机燃烧室的火焰筒壁温较高以及污染物排放等问题,提出了在火焰筒的壁面增加二次燃料喷口的轴向分级燃烧模式。利用ANSYS CFX软件并根据化学反应机理计算和分析了燃气轮机轴向分级燃烧室的流场和温度场,并与非分级燃烧室的结果进行了比较。结果表明:增大二次燃料比例可以使火焰筒壁面温度降低、出口污染物质量分数及出口不均匀系数减小,但出口平均温度会随之降低,导致做功能力减小。过量空气系数会影响火焰筒壁温、出口平均温度与NO质量分数。合理的二次燃料比例区间取决于多个条件。     

Numerical simulation of the combustion processes in a W‐shaped boiler furnace under different operating conditions

Numerical simulations of gas–solid flows, heat transfer and gas–particle turbulent combustion have been conducted for a three‐dimensional, W‐shaped boiler furnace. The gas–particle flow, distributions of temperature and concentrations of gaseous constituents, distributions of the rates of heat release, burnout rates of coal particles, and formations of volatiles have been predicted. The results indicate that a steady high‐temperature zone is formed under the arch of the W‐shaped flame boiler, this zone would be of benefit to the ignition and carbon burn‐out and suggest that the W‐shaped flame boiler is suitable for burning low‐quality coals and can operate well under different operating conditions for full and partial loads. Copyright © 1999 John Wiley & Sons, Ltd.