Blow-Out Stability of Gaseous Jet Diffusion Flames. Part I In Still Air——kalghatgi吹熄
四角切圆燃烧锅炉贴壁还原性气氛现场试验研究
发赵沒禺POWER EQUIPMENT第！4卷第4期2020年7月Vol. 34, No. 4Jul. 2020［运行与改造!性V «««««««« « *•**四角切圆燃烧锅炉贴壁还原性气氛现场试验研究姜 宇，李德波，周杰联，陈 拓，冯永新，钟 俊，苏湛清(广东电科院能源技术有限责任公司，广州510080)摘 要：针对某320 MW 四角切圆燃烧锅炉燃燃烧器，分别在锅炉60%和100%额定负荷下，测试主燃 烧器区域贴壁气氛中H 2S 、CO 、NO 、O 2的体积分数，并通过调整工况获得了贴壁气氛随运行工况变化的规律&结果表明：不同负荷、不同配风方式下，在炉膛水冷壁区域均检测出高体积分数CO,说明炉膛水冷壁区域均存在不同程度的强烈还原性气氛，这是水冷壁产生高温腐蚀的重要原因&建议在运行过程中增加运行氧量，同时控制入炉煤含硫量，加强配煤掺烧，避免水冷壁长期处于还原性气氛下运行而造成高温腐蚀&关键词：锅炉；四角切圆燃烧；贴壁还原性气氛；高温腐蚀；燃烧调整中图分类号：TK223文献标志码：A 文章编号：1671-086X(2020)04-0268-06DOI ：10.19806/ki. fdsb. 2020.04.010Field Test Research on the Near-wall Reduction Atmosphere in a Tangentially Fired BoilerJiang Yu, Li Debo, Zhou Jielian, Chen Tuo, Feng Yongxin, Zhong Jun, Su Zhanqing(Electric Power Research Institute of Guangdong Power Grid Corporation, Guangzhou 510080, China)Abstract : The near-wall volume fractions of H 2S , CO , NO and O 2 in the main burner area of a 320MW tangentially fired boiler were measured at 60% and 100% boiler load , while the variation law of the near-wall reduction atmosphere was analyzed by adjusting the working conditions. Results show that highvoumefractionofCOisdetectednearwaterwa 7inthefurnaceatdifferentboier oadsandindifferentair distribution modes , indicating that strong reduction atmosphere exists in that area , whichisthemaincauseof high-temperature corrosion. In the process of operation, it is suggested increasing the boiler operationoxygen , contro l ngthesulfurcontent,nthecoalbyproperlyblendng wthotherkndsoffuel , soasto preventthe water wa l from hgh-temperature corroson resulted from beng exposed ,n reducton atmospheresforalongtme.Keywords : boiler ； tangential firing ； near-wall reduction atmosphere ； high-temperature corrosion ；combustionadjustment大型燃煤电厂锅炉进行低氮技术改造后，炉膛主燃烧器区域处于还原性气氛，导致水冷壁高 温腐蚀，严重影响锅炉安全稳定运行，因此需要开展主燃烧器区域贴壁气氛测量，准确评估锅炉 水冷壁运行安全&国内一些研究者在防止锅炉高温腐蚀方面开展了理论研究、数值模拟和现场 试验等工作&肖琨等*1+进行了 600 MW 四角切圆燃烧锅炉防高温腐蚀方案研究&贺桂林等*〕进行了 600MW 锅炉低氮燃烧器改造炉膛高温腐蚀分析研究&李德波等旧开展了对冲旋流燃烧煤粉锅炉 高温腐蚀现场试验与改造的数值模拟研究&国内其他研究者开展了现场燃烧优化调整试验研 究，并取得了一些成果*11+。
掺混空气对旋转爆震主燃烧室起爆性能对比试验
收稿日期：2023-02-05基金项目：全国重点实验室项目(61422021190105)资助作者简介：谭峻然（1998），男，在读硕士研究生。
引用格式：谭峻然，宫继双，郑少泉，等.掺混空气对旋转爆震主燃烧室起爆性能对比试验[J].航空发动机，2023，49（2）：19-27.TAN Junran ，GONG Jishuang ，ZHENG Shaoquan ，et parative experiments of air mixing on the detonation performance of the rotating detonation main combustion cham⁃ber[J].Aeroengine ，2023，49（2）：19-27.掺混空气对旋转爆震主燃烧室起爆性能对比试验谭峻然，宫继双，郑少泉，道尔别克·塔布斯（中山大学航空航天学院，广东深圳518000）摘要：为以工程化应用为基础研究旋转爆震燃烧室在涡轮发动机条件下旋转爆震波的传播特性，模拟某离心式涡喷发动机的工况，以常温煤油和496K 高温空气作为燃料和氧化剂，对基于外径为220mm 、环形宽度为40mm 的环形燃烧室和相同大小的含掺混结构的环形燃烧室开展对比试验。
结果表明：在不同当量比工况下，观察到非稳定爆震模态、稳定双波旋转爆震模态和稳定3波旋转爆震模态。
在封闭燃烧室中，当量比较低（低于0.8）或较高（高于1.1）时无法维持爆震波的稳定传播，呈现非稳定爆震模态；在当量比接近1时，呈现稳定双波旋转爆震模态。
随着掺混结构的引入，燃烧室的工作范围得到拓宽（当量比为0.8～1.2），当当量比达到1.1时呈现稳定3波旋转爆震模态。
在对应的工况范围内，掺混空气能显著提高旋转爆震波的传播稳定性。
关键词：涡轮；旋转爆震；燃烧室；爆震模态；掺混空气中图分类号：V218文献标识码：Adoi ：10.13477/ki.aeroengine.2023.02.003Comparative Experiments of Air Mixing on the Detonation Performance of the Rotating Detonation MainCombustion ChamberTAN Jun-ran ，GONG Ji-shuang ，ZHENG Shao-quan ，Daoerbieke Tabusi（School of Aeronautics and Astronautics ，Sun yat-sen University ，Shenzhen Guangdong 518000，China ）Abstract ：In order to study the propagation characteristics of the detonation wave in the rotary detonation combustor under the condi⁃tion of turbine engines based on engineering applications ，under simulated working conditions of a centrifugal turbojet engine by using nor⁃mal temperature kerosene and 496K high-temperature air as fuel and oxidant ，comparative experiments were conducted on a 220mm out⁃er diameter annular combustor with a 40mm flame tube height ，and an annular combustor of the same size with mixing structure.The re⁃sults show that unstable detonation mode ，stable two-wave rotating detonation mode ，and stable three-wave rotating detonation mode are observed under different equivalent ratio conditions.For the closed combustion chamber ，if the equivalence ratio is relatively low （below 0.8）or high （above 1.1），the detonation wave cannot be maintained ，and unstable detonation mode occurs.If the equivalence ratio is close to 1，it exhibits a stable two-wave rotating detonation mode.With the introduction of the mixing structure ，the working range of the combustion chamber is broadened （the equivalent ratio range is 0.8-1.2），and the stable three-wave rotating detonation mode appears at a higher equivalent ratio.In the range of working conditions corresponding to this study ，mixing air can significantly improve the stable prop⁃agation of rotating detonation waves.Key words ：turbine ；rotating detonation ；combustion chamber ；detonation mode ；mixed air第49卷第2期2023年4月Vol.49No.2Apr.2023航空发动机Aeroengine0引言旋转爆震发动机因其具有单次点火便可实现持续爆震燃烧[1-2]和其自增压特性[3]近年来在众多新型推进方式上脱颖而出。
多孔介质微燃烧器的稳燃范围的数值研究
燃烧科学与技术Journal of Combustion Science and Technology 2017，23(3)：231-235DOI 10.11715/rskxjs.R201605033收稿日期：2016-05-20．基金项目：国家自然科学基金资助项目(51306129).作者简介：陈金星（1991— ），男，硕士，chenjinxing@.通讯作者：李 君，男，博士，副教授，lijun79@.多孔介质微燃烧器的稳燃范围的数值研究陈金星，李 君，李擎擎(天津大学机械工程学院，天津 300350)摘 要：应用计算流体力学软件Fluent ，对氢气/空气预混气在部分填充多孔介质的微平板燃烧器中的实验现象进行了模拟，研究了多孔介质热导率、壁面热导率、多孔介质孔隙率对稳燃范围的影响．模拟结果表明：稳燃范围的大小与多孔介质热导率呈正相关趋势，较高的多孔介质热导率将会拓宽稳燃范围；随着壁面热导率的增加，稳燃范围与壁面热导率呈V 型比例；多孔介质孔隙率也是影响稳燃范围的一个重要因素，在0.5～0.9的区间内，随着孔隙率的增大，稳燃范围也随之增大．关键词：微平板燃烧器；多孔介质；稳燃范围；数值模拟中图分类号：TK16 文献标志码：A 文章编号：1006-8740(2017)03-0231-05Numerical Study on Stability Limits of Combustionin Micro -Combustors with Porous MediumChen Jinxing ，Li Jun ，Li Qingqing(School of Mechanical Engineering ，Tianjin University ，Tianjin 300072，China )Abstract ：Based on the experimental phenomena of premixed hydrogen/air combustion in planar micro-combustors partially filled with porous medium ，numerical study was carried out to examine the influence of po-rous medium thermal conductivity ，wall thermal conductivity ，and porosity on stability limits ，using computa-tional fluid dynamics software Fluent ．The results show that stability limits have a positive correlation with porous medium thermal conductivity ，and higher porous medium thermal conductivity will broaden stability limits ．With the increase of wall thermal conductivity ，stability limits will exhibit a V-shaped pattern against it ．Porosity is also an important factor influencing stability limits ．Within the range of 0.5 to 0.9，stability limits will expand gradually with the increase of porosity.Keywords ：planar micro-combustor ；porous medium ；stability limits ；numerical simulation随着微小型科技装备的不断涌现，基于燃烧的微小型动力系统相较于化学电池而言，有着能量密度高、效率高、体积小等优点，日益成为便携式能源的潜在选择．相较于传统燃烧，微燃烧器同时也存在着散热损失大、易于壁面淬熄等不足．因此，实现微尺度下稳定、高效的燃烧，成为现阶段微燃烧研究的重点[1]．目前所知，在燃烧器内填充多孔介质是一种有效的稳燃手段，国内外诸多学者针对填充多孔介质的微燃烧做了广泛研究．Norton 等[2-3]分别研究了甲烷/空气、丙烷/空气预混气在微燃烧器中的燃烧特性与火焰稳定性，数值结果表明，壁面热导率是影响火焰稳燃烧科学与技术 第23卷 第3期— 232 —定性的重要因素．Liu 等[4]对Y 型微燃烧器做了数值研究，结果表明，微燃烧器中填充多孔介质相较于不填充多孔介质可以极大地提升燃烧的混合程度，从而有利于火焰的稳定．Zhao 等[5]的数值结果表明，相较于自由火焰燃烧器，填充多孔介质的微燃烧器具有更广阔的可燃下限、更高的火焰传播速度以及更好的火焰稳定性．Zhong 等[6]实验研究了微型瑞士卷燃烧器中的过焓燃烧，发现瑞士卷型设计可以极大地提升燃烧稳定性，同时拓展了预混气的熄火极限．Pan 等[7]研究发现，微多孔介质燃烧器具有较高的外壁面平均温度，与自由火焰燃烧器相比温度梯度更低．本课题组前期工作中，针对填充多孔介质的微平板燃烧器分别进行了实验研究和数值模拟[8-11]．模拟主要应用Fluent 软件研究了全填充多孔介质微平板燃烧器的火焰位置、火焰速度等燃烧特性．实验过程中，研究对象主要为部分填充多孔介质的微平板燃烧器，探索了燃烧器尺寸、多孔介质填充方式、预混气流速等对回火、吹熄等临界状态的影响，并确定了微燃烧器的稳燃范围．微平板燃烧器主要研究用来作为MTPV 的热源，因此，确定燃烧器的稳燃范围，使得高温区域可以集中在平板壁面而非入口或者出口处，对于MPTV 的研究工作具有指导意义．数值研究相对于实验研究而言，可以在更广泛的范围内针对稳燃范围以及其相应的临界条件做探究．本文应用计算流体力学软件Fluent ，对部分填充多孔介质的微平板燃烧器进行数值模拟，分别考察了多孔介质热导率、壁面热导率、多孔介质孔隙率等物性对微燃烧器的稳燃范围以及临界条件的影响．1 实验平台以及数值模型图1为实验系统装置示意．氢气和空气分别经过质量流量计后进入混气罐，混合后经均流器进入微燃烧器，采用红外测温仪读取外壁面温度．平板型微燃烧器的尺寸为10mm ×1mm ×20mm (不计法兰底座高度)，燃烧器材料选用不锈钢316L ，壁厚为0.5mm ．图2(a )展示了多孔介质在微燃烧器中的填充方式．采用不锈钢316L 丝网作为多孔介质材料，放置于微燃烧器内，多孔介质一端距出口7mm ，一端距入口8mm ．数值计算过程中，采用层流预混燃烧模型，多孔介质热导率为20W /(m ·K )，孔隙率0.87，微燃烧器壁面材料热导率为20W /(m ·K )，发射率0.9．如图2(b )所示，微燃烧器的入口取为速度入口，来流为氢气和空气预混气，未燃预混气温度300K .外界环境温度300K ，微燃烧器与外界之间的对流换热系数为20W /(m 2·K )．法兰底座与燃烧器出口处壁面设为绝热壁面，其余设为非绝热壁面，非绝热壁面的热损失包括与外界环境的对流换热损失和热辐射损失两部分．微燃烧器的出口设为压力出口，出口压力为0.1MPa ．氢气和空气的反应机理由9个组分和19个基元反应组成[12]．图1 实验系统示意微燃烧器的截面长宽比为10∶1，燃烧器内的流动可以近似认为二维流动．考虑到物理模型的对称性，计算中简化为二维对称面．（a ）多孔介质在微燃烧器中的填充方式（b ）微燃烧器数值模型的边界条件(非比例图)图2 数值模型示意(单位：mm )因为不锈钢铁丝网在微燃烧器中的填充方式为陈金星等：多孔介质微燃烧器的稳燃范围的数值研究 燃烧科学与技术— 233 —部分填充，故在铁丝网填充区域采用描述多孔介质的控制方程，其他区域仍为自由空间中的流动和燃烧问题．为简化计算，文中做了如下假设：①稳态燃烧；②惰性多孔介质；③多孔介质各向同性；④忽略多孔介质以及气体的辐射；⑤气体与多孔介质之间存在热 平衡[13-15]．本文应用Fluent 软件进行计算，为了保证计算准确性的同时兼顾计算时间效率，进行了网格独立性验证．分别选用5298节点、14688节点、20198节点3种网格，统一初始流速为2m /s ，当量比0.5，对比不同网格数下计算结果的外壁面温度分布曲线．如图3所示，经过网格独立性验证，14688节点的网格可以较好地满足计算需求．图3 网格独立性验证2 模型验证为了验证模型的准确性，针对部分填充多孔介质的微平板燃烧器进行了如下实验．实验过程中，分别采用u ＝1m /s 、u ＝2,m /s 、u ＝3,m /s 3个入口流速．固定预混气入口流速，调节预混气当量比Φ，依次以0.025的间隔从0.25调整到1.0．每调节一次当量比，待燃烧稳定后，读取微燃烧器的外壁面温度，从而获得壁温峰值在壁面上的位置．然后，仿照实验过程，在Fluent 中进行计算，便可得到模拟条件下的壁温峰值位置分布．图4即为3种入口流速下实验与模拟所得壁温峰值位置分布的对比．可以看出，虽然在某些工况下模拟结果与实验结果存在偏差，但是在壁温峰值点位置分布的变化趋势上，二者具有较明显的一致性，因此认为文中采用的数值模型是可行的．由图4可以看出，固定入口流速后，随着当量比的调节，壁温峰值位置在某两个当量比下分别存在着巨大的突变．依据这两种突变定义以下两种临界条件，分别是脱离多孔介质(Φ1)和吹出多孔介质(Φ2).前者为在固定流速下，当量比高于临界值时，壁温峰值的位置将脱离多孔介质，向法兰处移动并最终稳定于法兰附近；后者为在固定流速下，当量比低于某一临界值时，壁温峰值的位置将脱离多孔介质并向出口处移动．由Φ1与Φ2确定的一段当量比范围定义为稳燃范围，壁温峰值以及壁面高温区域稳定在多孔介质填充区域.（a ）u ＝1,m/s（b ）u ＝2,m/s（c ）u ＝3,m/s图4 壁温峰值点的模拟与实验对比3 结果与讨论本文中微平板燃烧器被设计为MTPV 的热源，当入口流速u ＝1,m /s 时，微燃烧器外壁面温度较低，不利于MTPV 的研究利用．因此，文中只针对u ＝2m /s 、u ＝3m /s 进行了参数化研究． 3.1 多孔介质热导率对稳燃范围的影响对于微平板燃烧器而言，壁面高温区域集中在入口或者出口处，都不利于MTPV 的有效利用．在微燃烧器的中间位置填充多孔介质，可以将火焰稳定在多孔介质区域，多孔介质具有良好的储热功能，从而将燃烧科学与技术第23卷 第3期— 234 —壁面高温区域集中于平板表面，有效扩大微燃烧器的高温表面面积，从而实现提升MTPV 效率的目的．因此，多孔介质热导率(k s )是影响微燃烧器稳燃范围的一个重要因素．从图5可以看到，k s 对Φ1、Φ2的影响不尽相同．一方面，随着k s 增大，Φ1经历短暂的下降后趋于平稳，另一方面，Φ2与k s 呈反比关系，即k s 愈大，壁面高温区域愈容易在低当量比下稳定于多孔介质填充区域．这是因为多孔介质在微燃烧器中主要起储热稳燃作用，随着k s 增大，储热效果也更明显，低当量比的未燃预混气更易于在多孔介质区域燃烧并稳定．整体而言，稳燃范围随着ks 增大而增大．（a ）u ＝2m/s （b ）u ＝3m/s图5 多孔介质热导率对稳燃范围的影响同样，由图5可以看出，u ＝3m /s ，k s ＝2W /(m ·K )时，Φ1、Φ2不存在．计算过程中，在该入口流速与多孔介质热导率设置下，预混气无法在微燃烧器腔内稳定燃烧．可以推测，当入口流速较高时，较低热导率的多孔介质并不能起到稳燃作用，燃烧无法在燃烧器腔内稳定存在． 3.2 壁面热导率对稳燃范围的影响微燃烧器壁面对于燃烧特性主要有两方面影响：一方面高温壁面向上游冷壁面导热，可以有效预热未燃预混气，另一方面壁面与外界环境间存在对流换热损失，热损过大有可能导致熄火．因此，壁面热导率(k w )是影响微燃烧器稳燃范围的另一个重要因素．固定入口流速，微燃烧器的稳燃范围随k w 的变化如图6所示．可以看出，当k w 取值逐渐增大时，临界条件Φ1、Φ2相应地产生V 型变化趋势．当k w 取值范围较小时，如2W /(m ·K )、20W/(m ·K )，高温壁面对上游未燃预混气的预热作用较为明显，Φ1、Φ2随着k w 的增加而降低．当k w 继续增大，如50W /(m ·K )，壁面与外界的对流换热损失逐渐占据主导地位，Φ1、Φ2大幅增加．随着k w 增大，如100W /(m ·K )、200W /(m ·K )，可以看到Φ1、Φ2相继消失，稳燃区间也不存在，即k w 过高时，预混火焰将被吹出微燃烧器，甚至熄火．同时，对比不同流速工况下的结果，可以推测在较高流速下，稳燃范围的临界点Φ1、Φ2更容易消失．（a ）u ＝2m/s （b ）u ＝3,m/s图6 壁面热导率对稳燃范围的影响3.3 多孔介质孔隙率对稳燃范围的影响当入口流速固定时，改变微燃烧器内填充多孔介质的孔隙率ε，多孔介质内的实际流速也会发生相应改变，从而对燃烧器的稳燃范围产生一定影响．图7分别展示了微燃烧器的稳燃范围随ε改变而产生的变化趋势．u ＝2m /s 时，随着ε逐渐增大，多孔介质内的实际流速相应地减小，所以预混气可以在更低的当量比下在多孔介质中稳燃，即Φ2与ε呈反比关系．而Φ1则不同，当ε增至某一数值时，Φ1会保持平稳．u ＝3m /s 时，Φ1、Φ2在ε小于0.7的范围里，有着与u ＝2m /s 时相似的变化趋势．当ε趋近0.8并逐渐升高时，Φ1、Φ2的变化趋势会分别出现转折并逐渐增大．当ε处于0.8～0.9的区间时，微燃烧器具有较为宽广的稳燃范围．（a ）u ＝2m/s （b ）u ＝3m/s图7 多孔介质孔隙率对稳燃范围的影响4 结 论本文对氢气/空气预混气在部分填充多孔介质的微平板燃烧器的稳燃范围进行了数值模拟，分别研究了多孔介质热导率、壁面热导率以及多孔介质孔隙率的影响．(1) 随着多孔介质热导率的增加，Φ1基本没有明显的改变，Φ2与多孔介质热导率呈反比关系，稳燃范围也逐步扩大．(2) 壁面热导率与临界条件Φ1、Φ2呈V 型趋势，随着壁面热导率的增加，Φ1、Φ2会经历一个先减陈金星等：多孔介质微燃烧器的稳燃范围的数值研究 燃烧科学与技术— 235 —小后增大的过程．当壁面热导率过高时，Φ1、Φ2会逐渐消失，稳燃范围也不再存在．(3) 多孔介质孔隙率是影响燃烧器稳燃范围的重要因素，在0.5～0.9的区间内，随着孔隙率的增大，稳燃范围也随之增大． 参考文献：［1］ 范爱武，姚 洪，刘 伟. 微小尺度燃烧[M ]. 北京：科学出版社，2012.Fan Aiwu ，Yao Hong ，Liu Wei. 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基于adams的小车式起落架着陆及全机滑跑动态仿真
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基于 ADAMS 的小车式起落架着陆及全机滑跑动态仿真
图清单
图 2.1 多体系统动力学建模与求解一般过程 .....................................................8 图 2.2 ADAMS 软件求解方法及过程....................................................................... 11 图 2.3 飞机数字功能样机组成 ...........................................................................14 图 3.1 小车式起落架的结构 ...............................................................................16 图 3.2 小车式起落架结构模型 ...........................................................................18 图 3.3 外筒受力图 ...............................................................................................18 图 3.4 内筒受力图 ...............................................................................................19 图 3.5 车架受力图 ...............................................................................................20 图 3.6 后轮受力图 ...............................................................................................20 图 3.7 前轮受力模型 ...........................................................................................21 图 3.8 缓冲器结构模型 .......................................................................................22 图 3.9 缓冲器受力图 ...........................................................................................24 图 3.10 圆角方形截面结构 .................................................................................25 图 4.1 起落架 CATIA 三维建模..........................................................................29 图 4.2 设计过程 Step 函数结果曲线 ..................................................................31 图 4.3 IMPACT 函数示意图.................................................................................32 图 4.4 ADAMS 仿真模型 .....................................................................................32 图 4.5 缓冲器随行程变化曲线 ...........................................................................35 图 4.6 空气弹簧力随行程变化曲线 ...................................................................35 图 4.7 油液阻尼力随行程变化曲线 ...................................................................35 图 4.8 缓冲器的功量图 .......................................................................................36 图 4.9 轮胎作用力 ...............................................................................................36 图 4.10 后轮冲击载荷 .........................................................................................37 图 4.11 前轮冲击载荷..........................................................................................37 图 4.12 缓冲器行程变化曲线 .............................................................................38 图 4.13 不同重量下的缓冲器行程 .....................................................................39 图 4.14 不同重量下起落架对机身的冲击载荷 .................................................39 图 4.15 空气弹簧力随行程变化的比较曲线 .....................................................40 图 4.16 缓冲器的功量图 .....................................................................................41 图 5.1 理想的变油孔面积曲线形式 ...................................................................46
多孔介质燃烧_换热器内燃烧和传热的数值模拟
第 25卷第 6期 2010年 11月热能动力工程J OURNAL OF ENG I N EER ING FOR THERMA L ENERGY AND POW ER Vo. l 25, No . 6N ov . , 2010收稿日期 :2009-09-23; 修订日期 :2010-02-25基金项目 :辽宁省教育厅科学研究计划基金资助项目 (2008491; 辽宁省博士启动基金资助项目 (20081073; 国家自然科学基金资助项目(50476073(, , .文章编号 :1001-2060(2010 06-0648-05多孔介质燃烧 -换热器内燃烧和传热的数值模拟徐有宁 1, 史俊瑞 1, 解茂昭 2, 薛治家1(1. 沈阳工程学院沈阳市循环流化床燃烧技术重点试验室 , 辽宁沈阳 110136;2. 大连理工大学能源与动力学院 , 辽宁大连 116024摘要 :通过建立二维数值模型研究了多孔介质燃烧 -换热器内的燃烧和传热。
研究系统配置对燃烧 -换热器热效率和压力降的影响。
结果表明 , 换热管的纵向距离对燃烧器内温度分布、传热速率和压力损失有显著的影响。
减小换热管纵向距离 , 热效率和压力损失增大 , 而换热管的水平距离对热效率和压力损失的影响很小。
另外 , 增大小球直径导致热效率增大和压力损失的急剧减小。
数值模型的有效性通过实验进行验证。
关键词 :多孔介质 ; 燃烧换热器 ; 二维单温模型 ; 传热 ;压力损失 ; 温度中图分类号 :TK411. 1 文献标识码 :A引言将多孔介质燃烧器和换热器集成于一体的多孔介质燃烧 -换热器 , 具有功率调节范围大、结构紧凑、热效率高和污染物排放低等优点[1~3]。
Tri m i s和 Durst 设计的多孔介质燃烧 -换热器 [1], 比同功率常规换热器体积缩小了 20倍 , 负荷调节为 1 20, 在过量空气系数为 1. 1~1. 8时 , 烟气排放中 CO 体积分数小于 10-5, NO x 体积分数为 (2~20 10-6。
钝体阶梯扩管型微燃烧器内氢气-空气燃烧特性及协同性分析
钝体阶梯扩管型微燃烧器内氢气-空气燃烧特性及协同性分析左青松;朱鑫宁;张建平;王志奇;张彬【摘要】In order to improve combustion stability and combustion efficiency, micro-combustor mathematical simulation was studied based on bluff body and backward-facing step combuster. The results show that the backward-facing step in combustion chamber can increase the flame propagation speed and expand the blow-off limits of flame, and both increases with the increase of the equivalence ratio (that is, the ratio of the theoretical air mass of complete combustion to the actually air mass). Furthermore, the combustion efficiency of combustors increases firstly and then decreases with the continual increase of inlet velocity or equivalence ratio, and combustion efficiency of combustor with backward-facing step is higher than that of without step under the same conditions. While the heat dissipation ratio of the two types of micro combustors increases with the decrease of inlet velocity, and it increases firstly and then decreases with the increase of equivalence ratio. With the increase of inlet mixed gas velocity, field synergy numbers of the micro combustor with and without the backward-facing step increase firstly and then decrease, but increase again.%为提高微燃烧器燃烧稳定性和燃烧效率,基于钝体直管和钝体阶梯扩管燃烧器进行微尺度燃烧数值模拟分析研究.研究结果表明:在钝体微燃烧器中加入阶梯扩管结构有助于促进火焰传播和扩大火焰稳定燃烧极限,而且两者的吹熄极限均随当量比(即完全燃烧所需的理论空气质量与实际供给的空气质量之比)的增大而增大;燃烧器的燃烧效率均随当量比和入口混合气速度的增大而降低,而且钝体直管型燃烧器的燃烧效率要比扩管型燃烧器低;散热损失比均随当量比增大呈先增大后降低,随入口速度增大而降低;钝体直管燃烧器协同数高于钝体阶梯扩管,两者的协同数都随入口的混合气速度增大先增大后降低再增大.【期刊名称】《中南大学学报（自然科学版）》【年(卷),期】2017(048)011【总页数】9页(P2926-2934)【关键词】微燃烧器;钝体;阶梯扩管;吹熄极限;热扩散率;协同数【作者】左青松;朱鑫宁;张建平;王志奇;张彬【作者单位】湘潭大学机械工程学院,湖南湘潭,411105;湘潭大学机械工程学院,湖南湘潭,411105;湘潭大学机械工程学院,湖南湘潭,411105;湘潭大学机械工程学院,湖南湘潭,411105;湖南大学机械与运载工程学院,湖南长沙,410082【正文语种】中文【中图分类】TK421随着微机电系统(micro electro mechanical systems，MEMS)技术的迅速发展，人们对微型动力系统性能提出了更高的要求。
安全阀样本--HTO-HTB-HTOA-HTBA样本
4
目 录 Contents
简
介
性 能、特 点
型号编制
结
构
材
料
Fluent_Combustion_14.5_L02_Finite_Rate
• Detailed chemistry
• Laminar stiff chemistry solver • Eddy Dissipation Concept • PDF transport
• Surface chemistry
Mixture Fraction Model (Non-Premixed model) • Equilibrium
• Equilibrium chemistry PDF model • Laminar flamelet model
• Model detailed chemistry (stiff chemistry)
– Progress variable (premixed model) – Mixture fraction and progress variable (partially premixed model)
– CPU intensive – Typically requires use of very small time steps to achieve numerical stability and convergence
• Can be impractical
– Use of the stiff chemistry solver will allow larger time steps to be used
Time required for convection and diffusion is much larger that for chemical reactions • Problem can be simplified since it eliminates parameters
associated with chemical kinetics
某重型燃气轮机的燃烧特性分析
３ ．中航 工业 沈 阳黎 明航 空发 动机 （ 集 团） 有 限责任公 司 ， 沈 阳 １ １ ０ ０ ４ ３ ）
摘 要： 为 了深入研究 某重型燃气轮机燃烧 室的燃烧性能 ， 在燃烧性能试验基础上 ， 本文建立 了包括 扩压 器 、
旋流器 、 火焰筒等部件在 内的环管燃烧室全尺寸 Ｕ Ｇ模型和数学模型 。用 Ｒ ｅ ａ ｌ ｉ ｚ ａ ｂ ｌ ｅ ｋ一￡湍流模 型模 拟气相
烧 室 的流体 模 型进行 了合 理 的简化 ， 气 膜孑 Ｌ 采 用 了
为 了深 入分 析某 重 型燃 气 轮机 内复杂 的燃 烧化 学反 应 问的相 互作 用 ， 探 索 重 型燃 气 轮 机 的设 计 和
收 稿 日期 ： ２ ０ １ ３— ０ ７— ２ ５ 改 稿 日期 ： ２ ０ １ ３— ０ ９—１ １
湍流流动 ， 离散项 （ Ｄ Ｐ Ｍ） 模 型用 以模 拟柴 油雾 化颗粒 的随机运动 ， 燃烧化学反应与湍流间的耦 合采 用 Ｅ Ｄ Ｃ多 步反应模型预测 ， 压力与速度耦合计算采用 Ｓ Ｉ ＭＰ Ｌ Ｅ算法 。在与试验 相 同的操 作条件 下 ， 对 环管燃烧 室 的两 相流流动 、 燃烧 、 传热过程以及燃烧 性能进 行 了 ３种 负荷状态 下 的 Ｃ Ｆ Ｄ数值模 拟。计算 结果 与试验值 相符
第 １ 期
某重型燃气轮机 的燃烧特性 分析
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合 。对 比分 析 所 得 结 论 为 改 进 燃 烧 室 设 计 和 燃 烧 室 性 能 改 善 提 供 了 依 据 。
关
键
词： 重 型燃气轮机 ； 燃烧室 ； 数值模拟 ； 燃 烧特性 ； 燃烧性能
谱分析和结构信息：烟灰和相关含碳材料的显微拉曼散射光谱
Raman microspectroscopy of soot and relatedcarbonaceous materials:Spectral analysis and structural informationA.Sadezkya,1,H.Muckenhuber b ,H.Grothe b ,R.Niessner a ,U.Po ¨schla,*a Institute of Hydrochemistry,Technical University of Munich,Marchioninistr.17,D-81377Munich,GermanybInstitute of Materials Chemistry,Vienna University of Technology,Veterinaerplatz 1/GA,A-1210Vienna,AustriaReceived 6September 2004;accepted 10February 2005Available online 23March 2005AbstractExperimental conditions and mathematical fitting procedures for the collection and analysis of Raman spectra of soot and related carbonaceous materials have been investigated and optimised with a Raman microscope system operated at three different laser excitation wavelengths (514,633,and 780nm).Several band combinations for spectral analysis have been tested,and a com-bination of four Lorentzian-shaped bands (G,D1,D2,D4)at about 1580,1350,1620,and 1200cm À1,respectively,with a Gaussian-shaped band (D3)at $1500cm À1was best suited for the first-order spectra.The second-order spectra were best fitted with Lorentz-ian-shaped bands at about 2450,2700,2900,and 3100cm À1.Spectral parameters (band positions,full widths at half maximum,and intensity ratios)are reported for several types of industrial carbon black (Degussa Printex,Cabot Monarch),diesel soot (particulate matter from modern heavy duty vehicle and passenger car engine exhaust,NIST SRM1650),spark-discharge soot (Palas GfG100),and graphite.Several parameters,in particular the width of the D1band at $1350cm À1,provide structural information and allow to discriminate the sample materials,but the characterisation and distinction of different types of soot is limited by the experimental reproducibility of the spectra and the statistical uncertainties of curve fitting.The results are discussed and compared with X-ray diffraction measurements and earlier Raman spectroscopic studies of comparable materials,where different measurement and fitting procedures had been applied.Ó2005Elsevier Ltd.All rights reserved.Keywords:Soot,Graphitic carbon;Raman spectroscopy;Microstructure1.IntroductionSoot is technically defined as the black solid product of incomplete combustion or pyrolysis of fossil fuels and other organic materials.It plays important roles as an industrial filler and pigment on the one hand (carbon black),and as a traffic-related air pollutant on the other hand (diesel soot).Soot is primarily composed of carbon (>80%)and consists of agglomerated primary particleswith diameters on the order of 10–30nm comprising crystalline and amorphous domains.The graphite-like crystalline domains typically consist of 3–4turbostrati-cally stacked graphene layers,with average lateral exten-sions (L a )of up to $3nm and interlayer distances ofabout 3.5A˚,and can be regarded as highly disordered graphitic lattices [1,2].In an ideal graphitic lattice the distance between parallel graphene layers (planar hexag-onal structures of sp 2-hybridized carbon atoms withcovalent bond lengths of 1.42A˚)is 3.35A ˚,and the lay-ers are arranged in an alternating sequence ABAB.This corresponds to a hexagonal closest crystal structure with unit cells of four C atoms at two types of lattice sites with different coordination (two or no neighbouring C atoms on a perpendicular axis through the adjacent0008-6223/$-see front matter Ó2005Elsevier Ltd.All rights reserved.doi:10.1016/j.carbon.2005.02.018*Corresponding author.Tel.:+49218078238;fax:+4989218078255.E-mail address:ulrich.poeschl@ch.tum.de (U.Po ¨schl).1Now at Laboratoire de Combustion et de Systemes Reactifs,CNRS,F-45071Orleans,France.Carbon 43(2005)1731–1742/locate/carbonparallel layers).The amorphous(i.e.non-graphite-like) domains are composed of polycyclic aromatic com-pounds,which can be regarded as graphene layer pre-cursors in irregular or onion-like arrangements (fullerenoid structures),and other organic and inorganic components(aliphatics,sulfate,metal oxides,etc.).The actual physical and chemical structure of soot,its ele-mental composition(carbon,hydrogen,oxygen,etc.), and the ratio of crystalline graphite-like to amorphous organic carbon depend on the starting materials and conditions of the combustion or pyrolysis process(fuel type,fuel/oxygen ratio,flame temperature,residence time,etc.[2,3])The graphitic carbon fraction of soot can be increased by annealing procedures at high tem-peratures[2–5].For the structural characterisation of highly ordered solid materials(crystalline long-range order)diffraction techniques are usually the methods of choice.For highly disordered materials such as soot,however,Raman spectroscopy is more promising,because it is sensitive not only to crystal structures but also to molecular structures(short-range order).The Raman signals of graphite crystals result from lattice vibrations and are very sensitive to the degree of structural disorder.The spectrum of near-ideal graphite,which is observed for large single graphitic crystals and highly oriented poly-crystalline graphite(HOPG),significantly differs from the Raman spectra of disturbed graphitic lattices,such as regular polycrystalline graphite or boron-doted HOPG[6–17](Table1).Among the substances investi-gated in earlier studies are different types of graphite [6,12,13,17–19],diamondfilms[15,20],glassy carbon [18,19,21],amorphous and graphitic carbonfilms [4,22],coal,pitch and coalfibres[18],activated carbon [18,19],and fullerenes[23].Rosen and Novakov [24,25]havefirst used Raman spectroscopy to prove the presence of graphite-like carbon in diesel engine soot,and their investigations have been followed up in several other studies[3,5,13,22,26,27].Some of these studies found that different types of soot could be distin-guished according to their degree of graphitisation [3,5,13,18,19,26].In the acquisition,analysis,and inter-pretation of the broad and overlapping Raman bands of soot,however,a wide range of different approaches has been followed.The spectral parameters correlated to the degree of graphitisation have been determined in different ways,which makes the results hard to com-pare and limits their conclusiveness.Thus we have set out to investigate the applicability of Raman micro-spectroscopy for the structural characterisation of soot by systematic experiments and spectral analyses.Raman spectra have been recorded for a wide variety of soot and related materials(diesel soot,spark discharge soot, industrial carbon black,graphite,polycyclic aromatic hydrocarbons)under varying measurement conditions using a Raman microscope system with three different excitation wavelengths(k0).The Raman spectra have been analysed by curvefitting with different band com-binations,and the obtained spectral parameters and their structural information are discussed in view of the results of earlier studies.2.Experimental2.1.SamplesEight different types of industrial soot(carbon black) were available as powder samples(Degussa:S160,Prin-tex140U,Printex25,Printex60,Printex75,Printex90, and Printex XE2;Cabot:Monarch77,Monarch120). Spark discharge soot was taken from a glassflask at the outlet of a Palas GfG1000aerosol generator(pow-der sample).Diesel soot was available as a standard reference material(SRM1650,NIST;powder sample)and in the form of polycarbonate and glassfibrefilter samples collected from the exhaust of modern diesel engines(ATable1First-order Raman bands and vibration modes reported for soot and graphite(vs=very strong,s=strong,m=medium,w=weak)Band a Raman shift(cmÀ1)Vibration mode bSoot Disordered graphite c Highly ordered graphite dG$1580cmÀ1,s$1580cmÀ1,s$1580cmÀ1,s Ideal graphitic lattice(E2g-symmetry)[6,17]D1(D)$1350cmÀ1,vs$1350cmÀ1,m–Disordered graphitic lattice(graphene layer edges,A1g symmetry)[6,17]D2(D0)$1620cmÀ1,s$1620cmÀ1,w–Disordered graphitic lattice(surface graphene layers,E2g-symmetry)[17]D3(D00,A)$1500cmÀ1,m––Amorphous carbon(Gaussian[26]or Lorentzian[3,18,27]line shape)D4(I)$1200cmÀ1,w––Disordered graphitic lattice(A1g symmetry)[10],polyenes[3,27],ionic impurities[18]a Alternative band designations of earlier studies are given in brackets.b Lorentzian line shape unless mentioned otherwise.c Polycrystalline graphite(<100nm)and boron-doted HOPG[17].d Single graphitic crystals(>100nm)and HOPG[17].1732 A.Sadezky et al./Carbon43(2005)1731–1742and B:heavy-duty vehicles;C and D:passenger cars). Graphite was investigated in the form of a solid elec-trode bar as used in the spark discharge generator (99.9995%,Johnston-Matthey)and in the form of pow-der samples(SHER graphite,<100l m,Heraeus;syn-thetic graphite,1–2l m,Aldrich).The polycyclic aromatic hydrocarbon hexa-benzo-coronene(HBC) was synthesized and supplied by the research group of K.Mu¨llen(Max Planck Institute for Polymer Research, Mainz,Germany).2.2.X-ray diffractionThe investigated soot and graphite powder samples were placed on the sample support(silicon)of the X-ray diffractometer(Philips XÕpert PW3050/60)and illu-minated with Ni-filtered copper radiation(Cu K a1: k1=1.54051A˚;K a2:k2=1.54433A˚).The diffraction pattern was recorded at room temperature in the2H range from10to60°(resolution0.02°,counting time 5s per interval).2.3.Raman measurement and spectral analysisThe applied Raman microscope systems(Renishaw, System2000;Yobin Yvon,LabRAM HR)consisted of a light microscope(Leica DL-LM;Olympus BX)cou-pled to a Raman spectrometer with three different exci-tation lasers.The microscope was equipped with four objectives with5·,20·,50·,and100·magnification, respectively,and with an eyepiece with10·magnifica-tion.The microscope optics were used to focus the excitation laser beam onto the sample and to collect the backscattered light(180°).The Rayleigh scattering component was removed by a Notchfilter,and the Raman-scattered light was dispersed by an optical grid and detected by a CCD camera(maximum sensitivity at500–850nm wavelength).The excitation lasers were an Ar ion laser(k0=514nm,source power17mW),a He–Ne laser(k0=632.8nm,source power25mW), and a NIR diode laser(k0=780nm,source power 26mW).The laser beam power was adjustable from 1%to100%of the source power.The diameter of the laser spot on the sample surface was1l m for the fully focused laser beam,and40l m for the fully defocused laser beam at50·objective magnification.The spectral resolution was about6cmÀ1at514nm,4cmÀ1at633 nm,and2cmÀ1at780nm.The instrument was cali-brated against the Stokes Raman signal of pure Si at 520cmÀ1using a silicon wafer((111)crystal plane sur-face).Instrument control and spectral analysis were per-formed with the software packages Renishaw WiRE (Renishaw)and GRAMS/32(Galactic).For the powder samples,a dense layer of about one millimeter thickness was pressed with a steel spatula onto a silicon wafer (macroscopically smooth surface)and placed on the microscope sample holder;filter samples and the graph-ite bar were placed directly on the sample holder.The microscope was focused onto the sample surface using the white light source and the objective with50·magni-fication.Then the white light was replaced by the laser beam and Raman spectra were recorded(Stokes Raman shift500–4000cmÀ1).The Raman spectrometer was generally operated in the continuous scanning mode. The power of the excitation laser beam(1–100%relative intensity),spot diameter(0–100%defocusing),and exposure time have been varied tofind optimum mea-surement conditions.For soot samples spectra of high-est quality and reproducibility were generally obtained with fully defocused laser beam,laser beam powers of 10%(514nm)to100%(780nm),and exposure times of at least120s.For graphite samples,on the other hand,best results were generally obtained with100% of the laser source power and fully focused laser beam, and exposure times of at least10s.Depending on the sample type and excitation wavelength,modified mea-surement conditions also yielded high quality spectra (e.g.100%laser power and25%defocusing for soot with k0=633nm).Curvefitting for the determination of spectral para-meters was performed with the software program GRAMS/32(Galactic,Levenberg–Marquardt algo-rithm).The goodness-of-fit was indicated by the reduced v2value,which would be unity for perfect agreement be-tween the calculatedfit curve and the observed spectrum. Values between1and3imply that the curvefit converges towards the observed spectrum;values larger than3indi-cate that the iteration has reached a minimum,but does not converge[28].First-and second-order spectra were fitted separately withoutfixing or limiting the range of any spectral parameter in the iteration procedure.Dif-ferent combinations offirst-order Raman bands andTable2Band combinations tested for curvefitting offirst-order Raman spectra of soot in this work and in earlier studies(initial band positions;line shapes: L=Lorentzian,G=Gaussian)Band Initial position(cmÀ1)(I)[18](II)[26](III)(IV)[19](V)[3,27](VI)(VII)(VIII)(IX)G1580L L L L L L L L LD11360L L L L L L L L LD21620–––L––L L LD31500L G––L G–L GD41180––L–L L L L LA.Sadezky et al./Carbon43(2005)1731–17421733their initial positions tested in this study are listed in Table2.3.Results and discussion3.1.X-ray diffractogramsThe diffraction pattern of the synthetic graphite sam-ple exhibits four distinctive narrow reflections in the2H range10–60°,which can be indicated as follows:26.8°(002layer),42.3°(100),44.5°(101)and54.9°(102). In contrast,the investigated soot samples show only two broad reflections with intensity maxima at24.9°and43.6°(Printex XE2)and at24.2°and43.4°(Printex 90),respectively(Fig.1).In the diffractogram of Printex90an additional nar-row signal appears at42.9°(marked by*);this is not due to the carbonaceous material but can be attributed to acontamination with tungsten carbide.Curvefitting yields the full width at half maximum(FWHM)of these reflexes,and the Debye-Scherrer formula can be used to estimate the average size of the crystallites or graphite-like crystalline domains contained in the samples[29]. These were250nm for the synthetic graphite,4nm for Printex XE2,and only2nm for Printex90.These values indicate a higher degree of order and graphitisation for Printex XE2compared to Printex90,which is consistent with the Raman spectroscopic results discussed below.3.2.Raman spectra of graphiteThe spectrum of the SHER graphite sample(Fig.2)is characteristic of an undisturbed graphitic lattice and exhibits only onefirst-order band,the G(‘‘Graphite’’) band at around1580cmÀ1corresponding to an ideal graphitic lattice vibration mode with E2g symmetry.Such spectra are generally observed for highly ori-ented polycrystalline graphite(HOPG),and for single graphitic crystals,whose edge length L a parallel to the graphene layers is larger than100nm.The spectrum of the graphite bar,on the other hand,exhibits addi-tionalfirst-order bands(D or‘‘Defect’’bands),which are known to be characteristic for disordered graphite and to grow in intensity relative to the G band with increasing degree of disorder in the graphitic structure. The most intensive of them is the D1band,which appears at$1360cmÀ1and corresponds to a graphitic lattice vibration mode with A1g symmetry.Another first-order band accounting for structural disorder is the D2band at$1620cmÀ1which can be observed as a shoulder on the G band.Like the G band,the D2 band corresponds to a graphitic lattice mode with E2g symmetry[9,10,18].The relative intensities of both the D1and D2bands increased with increasing k0(Fig.3), which can be attributed to resonance effects[30].Spectra similar to that of the graphite bar have been observed for HOPG doted with0.5mol%of boron[17] Fig.1.X-ray diffractograms of graphite,Printex90,and Printex XE2.1734 A.Sadezky et al./Carbon43(2005)1731–1742or polycrystalline graphites with L a smaller than1000A˚[6,8–16,21].Theoretical calculations have shown that each of thefirst-order Raman bands visible in spectra of highly ordered and disordered graphites can be attrib-uted to a vibrational mode of the ideal graphitic lattice [8,10].For an ideal graphitic crystal(space group D46h with unlimited translational symmetry)only a few of these vibrational modes are Raman active.In case of structural disorders,however,some ideally forbidden vibrational modes can become Raman active.The D1 band has been suggested to arise from graphene layer carbon atoms in immediate vicinity of a lattice distur-bance like the edge of a graphene layer[14,17]or a het-eroatom in case of doted graphite[17].Moreover,this band has been observed in Raman spectra taken directly on the edge planes perpendicular to the graphene layers of large graphite single crystals and HOPG[14,17]. Thus,in polycrystalline carbonaceous materials consist-ing of large numbers of small graphitic crystallites car-bon atoms at the edge of graphene layers are considered as the most probable origin of the D band [14,17].The D2band was assigned to a lattice vibration analogous to that of the G band but involving graphene layers at the surface of a graphitic crystal[31],i.e.graph-ene layers which are not directly sandwiched between two other graphene layers.Indeed,the D2band was ob-served to replace the G band in intercalation compounds [9].In polycrystalline graphitic materials it can be re-garded as an indicator for the surface to volume ratio of graphitic crystals[19].For both samples the Raman spectra recorded with k0=514nm exhibited second-order bands at about2450,2720,and3240cmÀ1.The band at2720cmÀ1is the most intensive one and can be attributed to thefirst overtone of the D1band, (2*D1)[17,18].The spectrum of the SHER graphite exhibits a split of the(2*D1)band into a peak at $2720cmÀ1,(2*D1)1,and a pronounced shoulder at $2680cmÀ1,(2*D1)2.This split has been described be-fore as a characteristic feature of undisturbed or highly ordered graphitic lattices[18].The graphite bar exhibits no pronounced split but a relatively broad(2*D1) band.Indeed all recorded second-order graphite spectra were bestfitted with two rather than one Lorentzian-shaped(2*D1)bands.The band at3240cmÀ1can be assigned to thefirst overtone of the D2band,(2*D2) [17].The band at2450cmÀ1can be attributed to the Ra-man-activefirst overtone of a Raman-inactive graphitic lattice vibration mode at$1220cmÀ1[10,17,32].We denominate it(2*D4)in analogy tofirst and second-or-der bands of soot with similar Raman shift.For the graphite bar an additional higher-order band is observed at2950cmÀ1,which has been assigned to a combination of the G and D modes characteristic for disturbed graphitic structures,(G+D)[17,18].All ob-served second-order Raman bands can be attributed to overtones and combinations of known lattice vibration modes.Upon spectral analysis all signals except the very weak(G+D)band could befitted with Lorentzian-shaped bands and v2values below2.3.3.Raman spectra of sootFig.4shows typical Raman spectra observed for dif-ferent types of soot with k0=514nm.Thefirst-order spectra of soot generally exhibit two broad and strongly overlapping peaks with intensity maxima at$1350cmÀ1 and at$1585cmÀ1.As discussed above and summa-rized in Table1,the structure and Raman spectra of soot can be interpreted in terms of highly disordered graphitic structures.Accordingly,earlier studies have described the intensity maxima at$1350cmÀ1andA.Sadezky et al./Carbon43(2005)1731–17421735$1585cmÀ1as D and G bands analogous to those of graphite[3,5,18,26].Cuesta et al.[18],Jawhari et al.[26]and Sze et al.[19]suggested,that the peak at $1585cmÀ1comprises not only the G but also the D2 band known from graphitic lattices,but only Sze et al.[19]included it in spectral analysis by curvefitting. The curvefitting results obtained in the present study and presented below clearly support the inclusion of the D2band.The high signal intensity between the two peak max-ima can be attributed to another band at$1500cmÀ1, which has been designated D3band in a couple of ear-lier studies(Table1).Cuesta et al.[18]and Jawhari et al.[26]suggested that the D3band originates from the amorphous carbon fraction of soot(organic mole-cules,fragments or functional groups).Cuesta et al.[18]and Dippel et al.[3,27]assumed Lorentzian line shape for this band,whereas Jawhari et al.[26]proposed Gaussian line shape due to a statistical distribution of amorphous carbon on interstitial places in the disturbed graphitic lattice of soot.The spectral analyses presented below support the Gaussian line shape.The peak at$1350cmÀ1exhibits a shoulder at $1200cmÀ1,which we denominate as D4(Table1). Dippel et al.[3,27]observed this band at$1190cmÀ1 in Raman spectra offlame soot and tentatively attrib-uted it to sp2-sp3bonds or C–C and C=C stretching vibrations of polyene-like structures.Sze et al.[19]ob-served a similar feature for glassy carbon,but did not in-clude it in the spectral analysis by curvefitting.Thecurvefitting results obtained in the present study and presented below support the inclusion of a D4band with Lorentzian line shape at$1180cmÀ1in the Raman spectra of all investigated types of soot.In some soot spectra very small peaks could be ob-served at$900cmÀ1(Fig.4,GfG1000,Printex90,S 160).Such signals have not yet been reported for soot, but they might correspond to very weak bands reported by Wang et al.[17]for boron-doted HOPG(A1u vibra-tion mode of graphitic lattice).Due to their very low intensity and irregular occurrence,these signals were not taken into account in the spectral analyses presented below.In the Raman spectra recorded with k0=514nm all soot samples exhibited broad signals in the range of about2300cmÀ1to3300cmÀ1(Fig.4).According to Cuesta et al.[18]these can be attributed to second-order bands,i.e.overtones and combinations of graphitic lat-tice vibration modes.The two pronounced peaks at $2700cmÀ1and2900cmÀ1have been assigned to the (2*D)overtone and(G+D)combination,respectively. Additional shoulders at$3100cmÀ1and$2400cmÀ1 can be assigned to the(2*D2)and(2*D4)overtones, respectively.This interpretation is consistent with the re-sults of earlier studies[18]and with the spectral analyses by curvefitting presented below.With k0=633nm the second-order signals were less pronounced,and with k0=780nm they could not be observed at all.Fig.5shows the Raman spectra of Printex XE2soot measured with k0=514,633,and780nm.The change of relative signal intensities with excitation wavelength is consistent with earlier studies,can be attributed to reso-nance effects,and will be discussed below[11,13,17,30].Fig.6shows the Raman spectrum of the poly-cyclic aromatic hydrocarbon(PAH)hexabenzocoroneneFig. 6.Raman spectrum of hexabenzocoronene(HBC)with k0=633nm.1736 A.Sadezky et al./Carbon43(2005)1731–1742(HBC),which can be regarded as a graphene layer sec-tion with lateral extensions of about 1.5nm and thus as a model for the building blocks of small graphitic do-mains in soot.Indeed the main peaks occur at similar positions as in the spectra of soot:G band at $1600cm À1and D band at $1320cm À1.The peak at $1250cm À1,however,is more pronounced than the comparable D4band,whereas HBC exhibits no signifi-cant D3band.The observations are in good agreement with theoretical calculations for the vibration modes of HBC and other PAH [33].3.4.Spectral analysis by curve fittingFor the analysis and determination of spectral parameters by curve fitting nine different combinations of first-order Raman bands have been tested.These band combinations are summarised in Table 2with the applied line shapes (Lorentzian or Gaussian)and initial band positions.Most earlier analyses of soot Raman spectra have considered only three bands:G,D (comprising D1and neighbouring bands),and either D 0(D2)or D 00(D3,Table 1).Here we present the first systematic inter-comparison of these earlier approaches with a new approach including all reported first-order Raman bands of soot (G and D1–D4,Table 1).The goodness-of-fit achieved with the different band combi-nations is indicated by the reduced v 2values summa-rized in Table 3.For all investigated soot samples and excitation wavelengths the best results,i.e.the lowest v 2values were obtained with combination (IX),which includes the Lorentzian-shaped bands G,D1,D2,and D4and the Gaussian-shaped band D3.Exemplary curve fits are illustrated in Fig.7for SRM 1650diesel soot and Printex XE2.In most cases the second-best results were obtained with combination (VIII)consisting of five Lorentzian-shaped bands,while the combinations con-sisting of fewer bands yielded substantially higher v 2val-ues.On the other hand,test calculations including anadditional,hypothetical sixth band did not lead to a sig-nificant reduction of v 2compared to the fitting results obtained with five bands.To corroborate these findings,multiple spectra have been recorded under identical experimental conditionsTable 3Goodness-of–fit for the Raman spectra of exemplary soot samples obtained with different band combinations (Table 2)and indicated by reduced v 2values (v 2=1ideal fit;v 2<3convergence;v 2>3minimum without convergence)Sample k 0(I)(II)(III)(IV)(V)(VI)(VII)(VIII)(IX)SRM 1650514 2.46 2.0211.4912.62 1.77 1.41 2.46 1.25 1.12Printex XE251423.3219.8916.7323.327.22 4.289.68 2.99 1.58Printex XE26339.057.9411.819.05 3.71 2.67 3.71 2.34 1.66Diesel A a 6339.577.2013.7319.651.952.117.211.33 1.24Diesel B a 633 1.77 1.49 1.34 1.28Diesel C a633 1.71 1.90 1.60 1.51Monarch 77b 633 6.70 4.49 6.70 6.70 1.96 3.95 6.26 1.62 1.32Monarch 120a 633 1.58 2.93 1.33 1.18GfG 1000c6336.965.7318.6020.822.682.466.981.931.53a 6spectra.b 12spectra.c11spectra.A.Sadezky et al./Carbon 43(2005)1731–17421737(k0=633nm,100%laser power,25%defocusing)for six different soot samples(Table3,superscripts a–c).Aver-aging over the47spectra yields v2=1.3±0.2for band combination(IX),v2=1.6±0.3for combination(VIII), v2=2.5±0.5for combination(VI),and v2=2.0±0.5 for combination(V)which had been applied by Dippel et al.[3,27].All other combinations,including those ap-plied by Cuesta et al.[18],Jawhari et al.[26],and Sze et al.[19]yielded average v2values substantially higher than3(minimum but no convergence of Levenberg–Marquardtfit algorithm).The results clearly indicate that allfive bands(G,D1, D2,D3,D4)should be taken into account for a complete analysis and interpretation of soot Raman spectra in the range of1200–1600cmÀ1,and that the shape of the D3 band is indeed Gaussian rather than Lorentzian.The second-order bands of the recorded soot spectra were bestfitted with a combination of four Lorentzian-shaped bands with their initial positions at2450,2700,2900,and 3100cmÀ1,yielding reduced v2values lower than 2. Exemplary curvefits are illustrated in Fig.8for SRM 1650diesel soot and Printex XE2.3.5.Band parametersFor all investigated soot and graphite samples spec-tral parameters have been determined by curvefitting with band combination(IX).The complete data set with mean values and standard deviations offirst-order band positions(Raman shift),full widths at half maximum (FWHM),and intensity(peak area)ratios is given in the electronic supplement(up to12spectra per sample; Tables S1–S3with k0=514,633,and780nm,respec-tively).Characteristic features will be outlined below.The mean values of the G band positions(Stokes Raman shift)observed for different types of soot and graphite ranged from1571cmÀ1to1598cmÀ1with standard deviations(s.d.)up to18cmÀ1,without signifi-cant dependencies on k0or significant differences be-tween soot and graphite.The mean values of the G band FWHM observed for different types of soot ranged from46cmÀ1to101cmÀ1(s.d.630cmÀ1).Significantly lower values were observed for graphite:20–22cmÀ1 (s.d.64cmÀ1)for the graphite bar and15–16cmÀ1 (s.d.63cmÀ1)for the highly-ordered SHER graphite.The D1band position exhibited a pronounced depen-dence on the laser excitation wavelength,with mean val-ues of1301–1317cmÀ1(s.d.62cmÀ1)for k0=780nm, 1323–1339cmÀ1(s.d.68cmÀ1)for k0=633nm,and 1343–1358cmÀ1(s.d.68cmÀ1)for k0=514nm,with-out significant difference between graphite bar and dif-ferent types of soot.The D1band FWHM were significantly lower for the graphite bar(42–49cmÀ1, s.d.67cmÀ1)and for Printex XE2soot(101–116cmÀ1,s.d.65cmÀ1)than for all other investigated types of soot(157–227cmÀ1,s.d.615cmÀ1),as will be discussed below.In contrast to the band position, however,the FWHM exhibited no systematic depen-dence on k0.The D1/G band intensity(peak area)ratios, I D1/I G,generally increased with the excitation wave length.For the graphite bar I D1/I G increased from0.2 (s.d.0.1)at k0=514and0.4(s.d.0.3)at633nm to2.7 (s.d. 1.0)at780nm.For the different types of sootI D1/I G was highly variable and increased from3.0to9.1(s.d.63)at k0=514nm and3.3–10.5(s.d.62.7)at 633nm to9.1–21.7(s.d.61.9)at780nm.The depen-dency of D1band position and intensity on laser excita-tion wavelength is consistent with earlier studies and can be attributed to resonance effects[11,13,17,30].The mean values of the D2band position ranged from 1599cmÀ1to1624cmÀ1(s.d.612cmÀ1).The D2band FWHM were significantly lower for the graphite bar (13–22cmÀ1,s.d.67cmÀ1)than for soot(31–72cmÀ1, s.d.614cmÀ1).For the graphite bar I D2/I G increased from0.02(s.d.0.01)at k0=514and0.07(s.d.0.04)at 633nm to0.2(s.d.0.05)at780nm.For the different types of soot I D2/I G varied in the range of0.3–1.4 (s.d.60.9)and exhibited no systematic increase with k0.The D3and D4bands were observed for soot only.1738 A.Sadezky et al./Carbon43(2005)1731–1742。
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PLEASE SCROLL DOWN FOR ARTICLEThis article was downloaded by: [University of Southern California]On: 9 March 2011Access details: Access Details: [subscription number 911085157]Publisher Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
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Blow-Out Stability of Gaseous Jet Diffusion Flames. Part I: In Still AirGautam T. Kalghatgia
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To cite this Article Kalghatgi, Gautam T.(1981) 'Blow-Out Stability of Gaseous Jet Diffusion Flames. Part I: In Still Air',Combustion Science and Technology, 26: 5, 233 — 239
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Blow-OutStabilityofGaseousJetDiffusionFlames.PartI:InStillAirGAUTAMT.KALGHATGIShellResearchl.td..ThorntonResearchCentre,PO.Box7,ChesterCH73SH(ReceivedApril20./981)Abstract-v-Auniversalnon-dimensionalformulathatdescribestheblow-outstabilitylimitofgaseousjetdiffusionflamesinstillairhasbeenfoundexperimentally.Itsvalidityhasbeenestablishedoverawiderangeofparametersthataffecttheblow-outlimit.Itsextrapolationtocaseswheretheburnerexitflowischokedsuggeststhatforagivengasthereisacriticalburnerdiameterabovewhichastableflamecanexistatanynowrate.
INTRODUCTIONAjetdiffusionflameinstillairwillliftoffthetipoftheburnerandformastableliftedflamewhentheflowratethroughtheburnerisincreasedbeyondalimitingvalueknownasthelift-offstabilitylimit.Iftheflowrateisincreasedfurther,theflameisextinguishedatsomelimitingrateknownastheblow-outstabilitylimit.Thelift-offstabilityandthestructureoftheturbulentlifteddiffusionflameinstillairhavereceivedsomeattentioninthepast(e.g.,Wohletal.,1949;VanquickenborneandVanTiggelen,1966;ScholefieldandGarside,1949).Thestabilityofflamesofco-flowingstreamsofhydrogenandairhasbeenstudiedbyVranosetal,(1968).TakenoandKotani(1975)conductedsimilarexperimentsbutwiththeaimofunder-standingtheeffectofthetemperatureoftheairstreamonthestabilityoftheflame.Morerecently,BaevandYasakov(1976)andAnnushkinandSverdlov(1979)havepublishedpapersthatcon-centrateontheblow-outstabilityofdiffusionflames.Inparticular,AnnushkinandSverdlov(1979)proposeasemi-empiricalformulathatcanbeusedtocalculatetheburnerexitvelocityatblow-outfordifferentburnerdiametersforpropane,methaneandhydrogen.However,theexperimentalverificationprovidedbythemfortheirpredictionsisratherlimited.Moreover,theirformulacannotbeusedtofindtheblow-outlimitsforfuelsotherthanthoseusedbythem.Thispaperdescribestheresultsofasystematicexperimentalstudyoftheblow-outstabilityofjetdiffusionflamesinstillair.Thefuelgasesusedaremethane,propane,ethylene,acetylene,commercial233butanesandhydrogen.Burnerdiametersrangefrom0.2mmto12mm.Fromdimensional
analysis,itispossibletoidentifynon-dimensionalgroupingsofthevariousflowandgasparameters
thataffectblow-out.Anempiricalformulaintermsofthesenon-dimensionalgroupingscanbe
foundtodescribetheblow-outstabilitylimitsof
allthedifferentgasesused.Thevalidityofsucha"universal"formulaisfurtherconfirmedbystudyingtheblow-outofflamesofmixturesofmethane/air,rnethane/Co-,propane/airandpropane/C02,Finally,anattemptismadetoextrapolatetheseresultstocaseswheretheflowattheburnerexitischokedatblow-out,bytaking