贫燃条件下甲烷着火的动力学机理研究

发布时间：2018-06-12 20:43

本文选题：甲烷 + 贫燃　；参考：《中国科学技术大学》2015年博士论文

【摘要】：甲烷是煤层气和天然气的主要成分。高浓度煤层气和天然气作为优质燃料,在锅炉、燃气轮机等各种燃烧设备中得到了广泛应用。甲烷也是很强的温室气体,在煤矿开采过程中,为控制井下甲烷浓度,常常通过大量通风将甲烷直接排入大气中。煤矿安全事故,常常是低浓度甲烷的爆炸所引起的,控制甲烷浓度可有效防止矿难的发生。为了控制燃烧温度,燃气轮机常常运行于贫燃状态。废气处理等场合,存在大量的低浓度甲烷氧化过程。对于贫燃甲烷着火过程的研究,具有重要的理论意义和实用价值。作者建立了一套包含激波管及对应的配气、压力控制、光学测量系统的实验平台。利用激波与反射激波的压缩效应,将甲烷/空气混合物瞬间加热至高温工况,对其着火过程的OH发射谱进行了测量。在甲烷浓度10%-0.5%,温度1500K-2000K,压力约0.9atm的工况范围内以OH发射谱峰值为着火标志测量了甲烷/空气混合物的着火延迟。在实验过程中通过达到缝合条件来延长有效的测量时间。对于激波管内的缝合条件运行工况,采用层流模型、k-ω模型、k-ε模型、RSM模型,Spalart-Allmaras模型进行了数值模拟, k-ω模型以外的模拟结果都比较符合理想激波关系。考察了不同模型对网格的适应性,结果发现,S-A模型对网格的适应性最强,其次为RSM模型,k-ε模型的适应性比较差。在考虑边界层网格后发现：只有对网格适应性强的湍流模型,进行边界层网格局部加密后,得到的计算结果会比较接近密网格效果。通过数值模拟及实验结果,表明虽然完美的缝合条件很难达到,但是在靠近激波管低压段端面的实验测量区域,可以在甲烷着火的时间尺度内保持反射激波形成的温度压力工况的稳定,足以满足实验需要。对甲烷／空气混合物着火延迟的测量和与GRIMECH 3.0详细反应动力学机理模拟值的对比表明：低温时着火延迟会随甲烷浓度的降低而缩短,但是在1900K以上的高温工况,各种浓度工况的甲烷着火延迟差距非常小,GRIMECH3.0预测的着火延迟普遍比实验测量值短。实验数据显示本文研究的工况全部为弱点燃工况,甲烷的着火延迟在同一温度范围内存在一定的变化,用阿累尼乌斯关系式,即温度倒数项与着火延迟对数项的线性关系拟合后,实验测量的着火延迟体现出来的随甲烷浓度与温度的变化趋势与详细机理模拟值基本一致。由于我们采用OH生成速率达到峰值作为着火标志时,反应机理模拟难以体现从着火启动到测量信号达到峰值的过程所需的时间,所以模拟值的计算结果要比实验测量值更小。以实验测量值为基础,在前人研究的基础上给出了修正表观活化能和指前因子后的着火延迟经验公式。以GRIMECH 3.0详细反应动力学机理为基础,计算了各个基元反应对关键中间组分的生产与消耗贡献,并利用敏感性分析的方法研究了甲烷氧化过程中各基元反应对整体反应速率的贡献程度。分析表明,贫燃条件下甲烷氧化速率主要取决于CH3的转化,CH3+O2=CH3O+O主导了整体反应速率,CH3转化为CH2(s)与两个CH3复合为C2H5、C2H6为主反应路径之外的主要CH3转化分支反应路径。H+O2=O+OH为主要的活性氧化剂产生反应。在确定主反应路径的前提下,构建了包含16种组分,31步反应的贫燃甲烷氧化的简化反应动力学机理。该简化机理主要适用于当量比0.2以下的极端贫燃工况。
[Abstract]:Methane is the main component of coal bed gas and natural gas. High concentration coal bed gas and natural gas are widely used in all kinds of combustion equipment, such as boiler and gas turbine. Methane is also a very strong greenhouse gas. In the process of coal mining, to control the concentration of methane in the underground, methane is often drained directly into the large amount of methane through large amount of ventilation. In gas. Coal mine safety accidents are often caused by the explosion of low concentration methane. Controlling the methane concentration can effectively prevent the occurrence of mine disaster. In order to control the combustion temperature, the gas turbine often runs in the poor combustion state. There are a large number of low concentration methane oxidation processes in the waste gas treatment. The author established a set of experimental platform including shock tube and corresponding gas, pressure control, optical measurement system. Using the compression effect of shock wave and reflected shock wave, the methane / air mixture was heated to the high temperature condition at a moment, and the OH emission spectrum of the ignition process was measured. The methane concentration was 1. 0%-0.5%, temperature 1500K-2000K, the ignition delay of methane / air mixture is measured by the peak of OH emission spectrum in the range of pressure about 0.9atm. In the experimental process, the effective measurement time is extended by suturing conditions. The laminar model, the k- Omega model, the k- epsilon model are used for the suture conditions in the shock tube. The model, the RSM model and the Spalart-Allmaras model are simulated, and the simulation results other than the k- Omega model all conform to the ideal shock relation. The adaptability of the different models to the grid is investigated. The results show that the S-A model has the strongest adaptability to the grid, followed by the RSM model, and the k- e model has a poor adaptability. The results of the numerical simulation and experimental results show that although the perfect suture conditions are difficult to reach, the experimental measurement area near the face of the shock tube low pressure section can be in methane. The stability of the temperature and pressure condition of the reflected shock wave in the time scale of the fire is sufficient to meet the experimental needs. The measurement of the ignition delay of the methane / air mixture and the simulation value of the dynamic mechanism of the GRIMECH 3 reaction show that the ignition delay will be shortened with the decrease of the methane concentration at low temperature, but it is above the 1900K. The gap of methane ignition delay in various concentration conditions is very small. The ignition delay predicted by GRIMECH3.0 is generally shorter than that of the experimental measurement. The experimental data show that the working conditions of this paper are all weak ignition conditions, the ignition delay of methane in the same temperature range is fixed, with the formula of the Arrhenius relationship, that is, the temperature. After the reciprocal term is fitted to the linear relation of the ignition delay logarithm term, the variation trend of the methane concentration and temperature measured by the experimental measured ignition delay is basically the same as the simulation value of the detailed mechanism. Because when we use the OH generation rate to reach the peak value as the ignition symbol, the reaction machine is difficult to reflect from ignition to the measurement letter. The time required for the process to reach the peak value is needed, so the calculation results of the simulated values are smaller than the experimental measurements. Based on the experimental measurements, the empirical formula of the ignition delay after the modification of the apparent activation energy and the pre finger factor is given on the basis of the previous research. Based on the GRIMECH 3 detailed reaction kinetics mechanism, the various bases are calculated. The contribution of the element reaction to the production and consumption of the key intermediate components, and the contribution degree of each element reaction to the overall reaction rate in the process of methane oxidation is studied by the method of sensitivity analysis. The analysis shows that the rate of methane oxidation mainly depends on the transformation of CH3, the CH3+ O2=CH3O+O dominates the overall reaction rate and CH3 is converted to CH under the condition of lean combustion. 2 (s) and two CH3 are combined with C2H5, and the main CH3 conversion path.H+O2=O+OH is the main active oxidant outside the main reaction path of C2H6. Under the premise of determining the main reaction path, the simplified reaction kinetics mechanism containing 16 components and 31 step reaction of Lean Methane oxidation is constructed. The simplified mechanism is mainly applicable. At the extreme lean burn conditions under the equivalent ratio of 0.2.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ038.1

【参考文献】