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1、燃烧理论,姚 强 李水清 清华大学热能工程系（Department of Thermal Engineering) 热能动力工程与热科学重点实验室(Key laboratory of thermal science and power Engineering) 煤清洁燃烧国家工程研究中心(NERC-CCC),八 层流预混火焰,2020/6/22,3,祝大家青年节快乐！,卷面成绩分布,2020/6/22,4,期中总体成绩分布,2020/6/22,5,第1题,要组成1摩尔的C8H18-空气混合物，当=2/3时，需要多少空气量？如果这一混合物进行燃烧，请给出燃烧后的产物的组成（分别按质量分数和摩尔分
2、数来表示），假设燃烧为完全燃烧。,2020/6/22,6,=2/3时反应方程式为： 即： 所以对1mol的混合物，需要的空气量为： mol,2020/6/22,7,第2题,假设在化学当量比条件下，计算C3H8 和 O2 燃烧的理论燃烧温度，产物有50%的回流，并假设产物分解（H，O，OH,）等可以忽略。即产物仅考虑为水和二氧化碳。（且燃料温度为298K，氧气浓度为398K，回流的烟气的温度为448K，理想气体，压力为1atm）,2020/6/22,8,2020/6/22,9,在化学当量比条件下的反应方程式为：,在有50%的产物回流的时候，最后平衡时的反应方程式为：,定压绝热燃烧，所以反应物和产
3、物的焓应相等，TFuel=298K, TOxygen=398K，Trecirculation=448K，所以，假设理论燃烧温度为3100K，定性温度约为1700K，则有： T=3108K,第3题,2020/6/22,10,假设对化学反应H2O+CO=CO2+H2 ，其在1100K和p=1大气压下的平衡常数K=1，试计算在at p=8 atm , T=1100K下的平衡常数K 答：平衡常数,对于一个反应来说，,是只与温度有关的一个函数，所以从公式可以看出，平衡常数与压力无关，只和温度相关。所以，在p=8 atm , T=1100K下的平衡常数K=1。,第4题,2020/6/22,11,下述反应中
4、哪些是基元反应，哪些不是？哪些又是没有更多的信息是无法确定是否是基元反应？,基元反应： 3，5：只断一个键，生成一个键； 7，只形成一个新键，M传递能量； 9，只断一个键，M传递能量； 非基元反应： 1，断两个键，生成两个键，且对碰撞的方向要求高； 2，断三个键，形成四个键，且对碰撞的方向要求高； 4，断三个键，形成两个键； 6，断两个键，形成两个键，且对碰撞的方向要求高 附加条件： 8，断一个键，形成两个键，在高压高温的情况下可能为基元反应。,第5题,2020/6/22,12,在各种工业品的制造中都需要加入阻燃剂，一般采用卤素类元素作为阻燃剂，试从你学习的化学动力学知识分析其阻燃原理。 答：
5、卤素元素结合自由基形成稳定的化合物，使得自由基的浓度减少，从而减缓反应的进行，达到阻燃的目的。,第6题,2020/6/22,13,2020/6/22,14,2020/6/22,15,内容,概述 物理描述 简化分析 完全分析 影响火焰速度和厚度的因素 不同燃料的火焰速度 熄火，可燃性和点火 火焰稳定性 总结,2020/6/22,16,概述,应用: 对湍流火焰研究的重要性 基本特征 简化分析 完全分析 实验数据 火焰速度；火焰形状；火焰稳定性；吹熄（blow-off; blow-out）；回火 可燃性；点火；熄灭（ extinction）,2020/6/22,17,2020/6/22,18,物理描
6、述,定义 主要参数 典型的实验室火焰,2020/6/22,19,Understanding Flames,Jet Burner: 2000W/cm2 Stoichiometric burn temperature,Premixed Flame: 1000 W/cm2 Stoichiometric burn temperature,Diffuse Flame: 0.1-10 W/cm2 Lower burn temperature; non- stoichiometric,燃料與潔淨燃燒實驗室,2020/6/22,21,Triple-pump CARS measurements performe
7、d in laminar hydrogen/air diffusion flame. Simultaneous acquisition of single-shot H2/N2 and H2/O2 spectra demonstrated.,Triple-Pump CARS Experiments,2020/6/22,22,Premixed,Results from gaseous reactants that are mixed prior to combustion Flame propogates at velocities slightly less than a few m/s Co
8、nsidered constant pressure combustion Reacts quite rapidly,Example: Spark Ignition Engine,2020/6/22,23,Laminar,Premixed Ex. Bunsen Burner Flame moves at fairly low velocity Mechanically create laminar conditions Diffusion Ex. Candle Flame Fuel: Wax, Oxidizer: Air Reaction zone between wax vapors and
9、 air,Principle of Flame Stabilization by Low-swirl,Vane Swirler for Practical LSBs,Angled vanes to induce swirling motion in annulus Center channel allows some premixture to bypass swirl annulus Screen balances pressure drops between swirl and center flows New definition of swirl number, S, for scal
10、ing to different sizes,Ratio of center channel radius to burner radius 0.8 R = Rc/Rb = 0.5 Straight or curved vane with angles 37o a 45o Ratio of mass flow rates through center channel and swirl annulus 0.3 m 0.5,2020/6/22,26,Unique Features of LSB Can Overcome Limitations of Premixed Combustion,Fre
11、ely propagating premixed turbulent flame Unattached and lifted flame Flame stabilization does not rely on flow recirculation Stable under very rich to ultra lean conditions High turn-down exceeding 50:1 Emissions not highly sensitive to degree of mixing Simple design compatible to current hardware F
12、lashback conditions can be predicted No flame oscillations towards lean blow-off,2020/6/22,27,Vane Swirler Scalable to Different Sizes,2.54 cm LSB for water heaters (6 kW to 30 kW),12.7 cm LSB for boilers (150 kW to 3 MW),6.35 cm LSI for gas turbines (7 MW),Applied swirl number criterion 0.4 S 0.55
13、to scale LSB up to 30 cm diameter at 8 MW output,2020/6/22,28,Evaluate 12.7 cm LSB in Commercial Watertube Boiler with External FGR,Use blower and controls for the commercial product Performance targets NOx 0.87, 35% FGR LSB exceeded most targets 9 ppm NOx with 12% FGR at f = 0.87 at 1.2 MW Pressure
14、 slightly higher than conventional burners 2nd prototype can reduce pressure requirement by 40%,2020/6/22,29,5 ppm NOx Concept: LSB + FGR and Partial Reformed Natural Gas,Exploit combustion features of hydrogen-enriched natural gas flames Use LSB to capture these benefits Incorporate a partial refor
15、mer to produce proper H2:CH4 ratio Demonstrated in water heater simulator,Natural Gas,Radiant section,of boiler,Convective section,Stack,Reformer,flue gas,Steam,Air,fan,Flue,gas,A,B,Burner,0.7 f 0.9 0 FGR 0.3 PRNG = 0 and 0.05 Reformer at 650 C CH4 = 0.12 l/s steam = 0.04 l/s Steam (5%) has no effec
16、t on LSB,2020/6/22,30,Current DLN Gas Turbine Engines Use High-Swirl Injectors (HSI),Centerbody promotes formation of recirculation to entrain and ignite fresh mixture Flame attachment at centerbody rim,2020/6/22,31,LSI can be Configured at Atmospheric Pressure and Low Velocities,Removed centerbody from SoLoNO
