氨气/甲烷贫预混旋转湍流火焰稳定性及NO生成

为了研究氨气/甲烷掺混燃气在贫预混旋转湍流状态下的火焰稳定性及NO的排放特性,设计建造了一个可视化的旋转湍流燃烧装置,开展了一系列的实验测量研究。研究表明：随着当量比增大,氨气火焰稳定燃烧的范围有所扩大,但当氨气掺混比大于0.60时火焰出现上下振荡现象,继续增加将导致火焰吹熄;NO的排放水平随当量比增加而提高;但在相同的当量比下,NO的排放随氨气掺混比的增加先升高再下降。此外,分别采用化学反应器网络（CRN）方法和一维层流预混火焰计算方法,对相应的火焰状态进行了数值计算分析,虽然计算结果与实验结果误差较大,但其预测的NO排放特性随氨气掺混比、当量比的变化趋势是一致的,对三者之间误差的来源进行了分析。     

含氨燃料预混火焰的层流火焰速度及NO排放特性

将甲烷或氢气与氨气共燃可以克服NH₃火焰的点火能量高、燃烧速度慢的缺点。为了解NH₃作为燃料的燃烧特性,对含NH₃燃料进行一维层流预混火焰数值模拟,研究其层流火焰速度及NO排放特性。采用文献中5个简化反应机理进行数值计算,发现Okafor机理模拟NH₃/CH₄/air火焰精度更高;Xiao机理模拟NH₃/H₂/air、NH₃/air精度适中,计算时间较短。此外,开展了当量比、燃料混合物组分比例、压力等参数对含NH₃燃料燃烧时烟气中NO浓度影响的研究。研究发现：含NH₃燃料燃烧时NO主要通过OH、H、O自由基和O₂分子的消耗而生成,主要通过与NH_i（i=0, 1, 2）自由基反应消耗;含NH₃燃料在富燃状态下燃烧可有效减少NO排放,但富燃燃烧效率低,可采用富燃-贫燃分级燃烧技术来提高燃烧效率,同时保持NO的低排放;掺有较多NH₃的含NH₃燃料在中高压下燃烧时可有效减少NO排放。     

甲烷/乙烷/空气预混火焰层流燃烧速度与火焰稳定性的数值研究(英文)

A numerical study on premixed methane/ethylene/air flames with various ethylene fractions and equivalence ratios was conducted at room temperature and atmospheric pressure. The effects of ethylene addition on laminar burning velocity, flame structure and flame stability under the condition of lean burning were investigated. The results show that the laminar burning velocity increases with ethylene fraction, especially at a large equivalence ratio. More ethylene addition gives rise to higher concentrations of H, O and OH radicals in the flame, which significantly promotes chemical reactions, and a linear correlation exists between the laminar burning velocity and the maximum H + OH concentration in the reaction zone. With the increase of ethylene fraction, the adiabatic flame temperature is raised, while the inner layer temperature becomes lower, contributing to the enhancement of combustion. Markstein length and Markstein number, representative of the flame stability, increase as more ethylene is added, indicating the tendency of flame stability to improve with ethylene addition.     

湍流氢氧预混燃烧流场的二维数值模拟

基于Cantera化学动力反应模型库,采用工程计算开源软件OpenFOAM建立应用半隐式压力校正方程SIMPLE算法求解定常可压缩湍流燃烧流动问题的数值模拟方法,设计出适合于稳态求解的可压缩燃烧反应的求解程序,并对燃烧室内的氢氧燃烧过程进行二维数值模拟。通过计算结果与试验数据的直观对比分析表明:所建立的数值计算方法对定常可压缩燃烧流动问题有很好的计算仿真效果,体现了其可行性与正确性,同时对解决其他燃烧流动问题也具有较高的参考价值。     

高浓度丙酮VOCs高温预热近极限贫燃预混火焰特性的数值分析

为进一步对一种丙酮挥发性有机化合物（VOCs）焚烧炉进行设计优化和运行参数调节,本文对其在不同的燃料当量比、预热温度下的火焰特性进行了数值模拟,分析了其绝热火焰温度、着火延迟时间、火焰传播速度和一维火焰产物分布特性。研究结果表明：典型当量比（约0.113）下的绝热火焰温度为850~900℃,属于中低温燃烧,绝热火焰温度随预热温度和当量比（0.06~0.4）的升高均线性升高。预热温度和化学当量比对着火延迟时间的影响十分敏感。在其典型贫燃条件下,层流火焰传播速度随预热温度升高呈指数函数关系增大,随化学当量比增大而缓慢升高,且其层流火焰传播速度不超过150cm/s。反应过程首先发生丙酮的分解和部分氧化,并持续时间较长,仅当混合物的温度升高一定程度后才发生较剧烈的CO氧化。     

湍流非预混燃烧数值模拟的代数二阶矩模型

湍流燃烧数值模拟是研究燃烧的一种重要手段,采用的湍流燃烧模型是否恰当直接影响最终结果的准确性。在湍流燃烧中,化学反应速率不仅取决于当地的组分浓度和温度,而且与组分的湍流脉动也有密切关系。通过对湍流燃烧模型进行探讨,发现代数二阶矩模型（ASOM）能综合考虑湍流和反应动力学因素的影响,而且比其他复杂的模型简单。研究将组分混合速率对化学反应速率的影响在一个修正的代数二阶矩模型（RASOM）中进行考虑,更准确地计算出化学反应速率。为了验证模型的准确性,RASOM模型被应用到Sandia实验室测量的甲烷-空气非预混燃烧（Flame-D）的数值模拟中。模拟得到的结果与实验结果以及修正的涡破碎模型（EBU-A）和原ASOM模型的结果进行了对比,发现RASOM模型的效果较好。     

位移钝体稳燃的旋流预混燃烧污染物生成特性

石化炉、加热炉等设备中燃烧过程的污染物控制具有重要意义。旋流预混燃烧过程具有低NO _x 排放的潜力,引发了学术界和工业界的广泛关注。结合钝体燃烧和旋流燃烧各自的优势,本文设计了带有位移钝体的旋流预混燃烧器。首先研究了不同钝体结构下的污染物的生成情况,确定了最优的钝体结构,在此基础上进一步研究了在不同旋流数下污染物生成、火焰形态和温度场分布情况。研究发现,钝体角度为30°、体积较小的倒锥形钝体具有较低的NO _x 和CO生成量。NO _x 生成量随着旋流数从0增加到0.83呈先减小后增加的趋势,并且当旋流数为0.25时,NO _x 生成量最低。在同一热功率下,火焰高度随着旋流数的增加而减小。在同一旋流数下,火焰宽度随热功率增大呈增大趋势。NO _x 生成量变化规律与其火焰温度分布规律一致,即NO _x 生成量最低的工况下火焰温度也比较低。由此推测旋流引发的温度变化是NO _x 生成量变化的主要影响因素之一。本文的研究结论对旋流预混燃烧器的设计提供了理论基础。     

甲烷-空气预混燃烧数值模拟仿真实验设计及教学应用

燃烧学是安全工程专业的一门理论性强、难度大的专业基础课程,其中可燃气体燃烧及火焰传播相关知识点的教学存在理论抽象、不够直观等问题。作者将理论学习、实验研究、数值模拟有机结合,基于CFD方法设计了数值模拟仿真实验系统,并以球形容器内甲烷-空气预混燃烧为例,介绍了该系统在燃烧学课程教学中的应用。实践表明,虚拟仿真实验教学能够有效增强学生对相关理论知识的理解,充分调动学生的学习积极性,提升课程的高阶性、创新性和挑战度。     

含颗粒甲烷/空气预混燃烧的51步简化机理

基于含颗粒甲烷燃烧详细化学动力学机理Gri-Mech3.0,采用层流预混火焰模型计算含颗粒甲烷/空气预混燃烧过程。通过对详细机理的计算结果进行敏感性分析以及产物速度分析提取骨干机理,再根据准稳态假设进一步简化,最终得到一套包含27种组分和51个基元反应的简化机理。将该51步简化机理与详细机理进行对比,结果表明:该简化机理在预测燃烧速度方面具有较高精度,能够在较大热力学参数变化范围内较好地预测含颗粒和不含颗粒2种情况的甲烷/空气预混燃烧现象。     

Large Eddy simulation for lean premixed combustion

In comparison to previous numerical studies interested in the ORACLES benchmark (One Rig for Accurate Comparisons with Large Eddy Simulations), the present study demonstrates the advantages of LES‐WALE model in both inert and reacting flows using the Fluent‐CFD. So, the confirmation is based on the experimental research effort that was involved in the European Union‐funded research program MOLECULES (Modelling of Low Emissions Combustors Using Large Eddy Simulations), for three parameters: longitudinal velocity, longitudinal velocity fluctuation, and length of recirculation zone. In line with what was observed by the experimental reference study, the dynamic model (LES‐WALE) predicts, respectively, as well as the asymmetry and the symmetry, for both inert and reacting flows. In addition, the simulation succeeds to predict the zones of recirculation and shows the differences between the two cases, inert and reacting flows. Moreover, results have been compared with those of the k–ε model performed by Kurenkov and Obserlack [Kurenkov and Obserlack, Flow Turbulence Combustion 74, 387–407 (2005)] study. © 2012 Canadian Society for Chemical Engineering     

Simulation of swirling combustion and NO formation using a USM turbulence-chemistry model

A unified second-order moment (USM) turbulence-chemistry model is used to simulate methane-air swirling combustion and NO formation for different swirl numbers. The simulation results are compared with those using the EBU-Arrhenius (E-A) combustion model, the simplified PDF model of NO formation in turbulent flows and the corresponding experimental results. The comparison indicates that the USM model is obviously better than the E-A model and the simplified PDF model. The E-A model cannot reasonably simulate the finite-rate kinetics, while the simplified PDF model, using a product of two single-variable PDF's instead of a joint PDF, remarkably under-predicts the NO reaction rate. The USM model gives the best agreement with the experimental results. Predictions show that as the swirl number increases the total NO formation at first decreases and then increases, which is in agreement with the experimental results.     

自由堆积多孔介质内预混燃烧火焰传播

为了解多孔介质内预混燃烧火焰前沿的传播特性,对不同化学当量比（=0.7～1.0）的甲烷/空气预混气体在不同孔隙率（ε为0.37和0.42）的多孔介质内的火焰前沿传播特性进行了研究,多孔介质采用3 mm和6 mm直径的Al₂O₃小球在陶瓷管中堆积而成。结果表明,预混气体在多孔介质中能够形成低速燃烧的稳定燃烧波;其火焰传播速度随化学当量比增大而加快,最大的火焰传播速度为3.52×10^-3 cm·s^-1;多孔介质的结构对火焰前沿传播速度影响很大,即使在孔隙率差别不大的情况下,大球堆积而成的多孔介质比小球具有更高的火焰前沿传播速度。     

Numerical investigation of turbulent non-premixed combustion of a wood pyrolysis gas

A fully compressible database of turbulent non-premixed flames of a wood pyrolysis gas is developed by means of direct numerical simulation (DNS). A reduced kinetic mechanism is used to model the combustion of a pyrolysis gas-air mixture. The instantaneous flame surface density evolution equation based on the concept of a displacement speed is examined. The normal component of the displacement speed is nearly constant with respect to curvature, while the curvature-related component tries to restore the flame front to a planar shape. The strain-rate term is mainly a source as the flame is mostly extended. The normal displacement is responsible for both positive and negative contributions to the flame area. The displacement/curvature term is primarily a sink, since it is dominated by its curvature component. Effects of strain and curvature are analyzed by considering their correlations with reaction rates. Reaction rates are enhanced with increased positive strain rates owing to an increase in the flame surface area and to a decrease in curvature. The analyzed results aid in the development of turbulent combustion models. Finally, a new model for a mean variance of the scalar dissipation rate, based on a scale similarity approach, is proposed and examined. A comparison with DNS results shows that the proposed model provides a significant improvement over existing models. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 15–34, May–June, 2007.     

环形喷嘴预混无焰燃烧的数值模拟(英文)

This paper reports an investigation of Computational Fluid Dynamics (CFD) on the influence of injection momentum rate of premixed air and fuel on the flameless Moderate or Intense Low oxygen Dilution (MILD) combustion in a recuperative furnace. Details of the furnace flow velocity, temperature, O2, CO2 and NOx concentrations are provided. Results obtained suggest that the flue gas recirculation plays a vital role in establishing the premixed MILD combustion. It is also revealed that there is a critical mo-mentum rate of the fuel-air mixture below which MILD combustion does not occur. Moreover, the momentum rate appears to have less significant influence on conventional global combustion than on MILD combustion.     

Effects of hydrogen addition on flame structure and forced flame response to velocity modulation in a turbulent lean premixed combustor

Flame transfer function measurements were performed in a turbulent premixed lean combustor with various blends of hydrogen and natural gas. The fuel mixture was completely premixed with air upstream of a choked inlet to the combustor to avoid equivalence ratio fluctuations. A variable speed siren was used to modulate fluctuations in the inlet velocity, which was measured using a hot wire anemometer as an input parameter of the flame transfer function. Heat release oscillations as an output function were determined using chemiluminescence measurements from whole flames. Stable flame images were captured to understand general flame behavior over a range of operating conditions and fuel blends. Experimental results showed that the stable flames’ COMs (centers of mass) laid along a common path in a 2-D plane for all of the operating conditions and tested fuel compositions at a given injector geometry, and that variations in the stable flame shape could be characterized by the location of the common path of the flame’s COM. It was also shown that changes in the fuels significantly affected the flame shape; as a result, flame dynamics varied with changes in flame geometry. Accordingly, flames that were close together on the characteristic flame COM curve were shown to have similar forced flame responses.     

预混气体爆炸火焰与压力的耦合振荡特性

为研究预混气体爆炸火焰和压力的耦合振荡特性,自行搭建了尺寸为80 mm×80 mm×1000 mm透明有机玻璃爆炸管道实验平台。实验结果表明,在氧气浓度E和泄爆面积比S变化的条件下,会对CH₄/O₂/N₂预混气体爆炸火焰与压力的耦合振荡产生影响。当氧气浓度E从0.21到0.40变化时,火焰传播时间逐渐缩短,火焰结构发生动态演变,火焰后期的振荡现象愈加明显,同时测到的压力曲线在后期也存在振荡增强现象;当泄爆面积比S从0.125到1.000变化时,E=0.21工况下S=0.125和S=0.250两个工况与其他工况的压力曲线有所不同,出现了一个更高的压力峰值,E=0.30工况下S=0.125也出现了新的压力峰值,E=0.30和E=0.40两种工况的压力峰值都逐渐减小,压力后期的振荡幅值与泄爆面积比有关。     

可燃工质氨的燃烧及阻燃机理的研究

当前环境问题日益突出,天然工质氨作为环保性制冷剂再次引起科学界的广泛重视。但NH₃存在可燃可爆性问题,在实际应用中存在着一定的安全隐患。采用量子化学密度泛函理论计算方法,在M06-2X/6-311+G（d,p）的计算水平上,对NH₃的燃烧及阻燃机理开展研究,得到反应过程的微观反应路径。研究表明,NH₃可通过三种方式发生燃烧微观反应,一是发生自身裂解反应,生成H自由基;二是与氧气发生碰撞反应,生成OOH自由基;三是与活性自由基发生碰撞反应,生成新的活性自由基,NH₃可与H、O、OH自由基反应,反应能垒较低。此外,还计算了两种典型的阻燃基团F和CF₃对可燃分子NH₃的微观阻燃路径,验证其阻燃效果。本文从微观分子的角度考察了可燃工质氨的燃烧及阻燃机理,为新一代低温室效应工质的燃烧及阻燃机制提供了参考。