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Master Dissertation of Chongqing University Numerical Simulation on Premixed Catalytic Combustion of Methane in Micro-combustor
Master Candidate: Qiu Yun
Supervisor: Prof. Zhang Li
Major: Thermal Engineering
College of Power Engineering
Chongqing University
Oct. 2007
摘要
医用材料与应用
随着微电子机械系统技术的迅速发展，微器件对许多领域的影响日趋明显，装置的微型化与微型系统已成为当今研究的重要课题。近几年发展起来的体积在1cm3量级上，能产生约10-100W功率的微型发动机已引起了世界各国的普遍关注。微型发动机具有能量密度高、寿命长、体积小、重量轻、结构简单等优点，将对微电子、信息、生物等各个行业产生巨大的积极影响。
甲烷燃料容易获得、价格低廉，在未来数十年内将是微型气体发动机的主要燃料。微型燃烧器的尺寸较小、散热速率较大，使常规空间反应无法稳定进行，因此，有必要研究微型燃烧器内甲烷预混催化燃烧，为微型发动机碳氢燃料燃烧技术打下基础。 微型燃烧器由四层不锈钢材料采用电火花技术加工而成，主要包括预混腔和燃烧腔两个腔室。采用连续介质层流有限速率模型二阶离散的方法，对三维微型燃烧器内各微小复杂流道内的催化燃烧、流动和传热进行了详细的数值模拟计算。研究了预混腔结构、甲烷质量流量、过量空气系数及壁面边界条件等因素对甲烷-空气混合物在微型燃烧器内催化燃烧的影响。
数值模拟计算结果表明，气体流动为层流，催化燃烧主要在燃烧腔的下壁面进行，表面催化燃烧不同于常规燃烧，没有火焰区域，火焰的温度分布为层状。预混腔结构对预混效果有较大影响，但预混腔结构对甲烷转化率的影响不大。
随着甲烷质量流量的增大，甲烷转化率减小，当壁面温度较低时，热负荷先增大后减小，当壁面温度较高时，热负荷增大。 过量空气系数是微型燃烧器内催化燃烧的重要影响因素，甲烷转化率随过量空气系数的增大先增大后减小，存在一个最佳过量空气系数。当催化壁面温度增大时，最佳过量空气系数随之增大；当甲烷质量流量增大时，最佳过量空气系数随之减小。
催化壁面温度是微型燃烧器内甲烷催化燃烧的主要影响因素。随着催化壁面温度的升高，催化反应速率增大，甲烷转化率迅速提高。
当通入甲烷-氢气混合燃料时，混合气体中的氢气催化反应速率很快，在微型燃烧器燃烧腔内基本上完全反应。随着甲烷转变为氢气的百分数的增大，甲烷组分的转化率减小，甲烷-氢气整体转化率增大，热负荷迅速增大。
关键词：微型燃烧器，甲烷，预混，催化燃烧，数值模拟，转化率
ABSTRACT
With the technology development of micro-electro-mechanical system, the influence of micro-apparatus on many realms is gradually obvious. Researches on micromation and micro-systems have been an important study subject now. The micro-engine capability of producing 10-100W of power in a volume about 1cm3 has brought prevalent attention of world countries in recent years. With the advantages of high power density, longevity, small volume, light weight and simple fabric, micro-engine will have immense positive influence on micro-electronics, communication, biology and so on.
电伴热带温控Methane，which has the advantages of high power density and cheap cost， will be the main fuel of micro-gas-engine in next decades. Because of small dimension and high rate of heat loss, traditional homogeneous reaction can not carry through steadily. The research of methane premixed catalytic combustion in micro-combustor lays the foundation for the technology of hydrocarbon-fueled combustion in micro-engine.
牧草割草机Micro-combustor was made up of four stainless steel pieces by using electro discharge machining technology, and it was composed of premixing-chamber and combustion-chamber. Numerical simula
tion of catalytic combustion, flow and heat transfer in micro-channels of three-dimensional micro-combustor was done in detail by using laminar finite-rate and second-order upwind discretization model. Catalytic combustion of methane/air mixture in micro-combustor was studied by changing the fabric of premixing-chamber, mass flow rate of methane, coefficient of excess air and wall boundary condition.
The results indicate that gas flow is laminar flow. Catalytic combustion is mostly happened on the downside wall of combustion-chamber. Surface catalytic combustion is different from homogeneous combustion. There is no flame area, and temperature distribution is laminar. Fabric of premixing-chamber has influence on premixing effect, but it has little influence on conversion rate of methane.
Conversion rate of methane increases while mass flow rate of methane decreases. While wall temperature is low, heat load firstly increases and then decreases. While wall temperature is high, heat load increases.
Coefficient of excess air is the important influence factor of catalytic combustion in micro-combustor. While coefficient of excess air increases, conversion rate of methane firstly increases and then decreases. There is an optimal coefficient of excess air. Optimal
coefficient of excess air increases, while catalytic wall temperature increases and mass flow rate of methane decreases.
Catalytic wall temperature is the primary influence factor of catalytic combustion in micro-combustor. Catalytic reaction rate and conversion rate of methane increases immediately, while catalytic wall temperature increases.
While methane/hydrogen mixture is injected into micro-combustor, catalytic reaction rate of hydrogen is high, and the combustion of hydrogen is complete. While hydrogen ratio increases, conversion rate of methane decreases. Conversion rate of methane/hydrogen increases, and heat load increases immediately.
Keywords：Micro-combustor, Methane, Premix, Catalytic Combustion, Numerical Simulation, Conversion rate
目录
摘要..............................................................................................................................II
1 绪论 (1)
1.1 课题的背景和意义 (1)
1.2微型燃烧器发展状况 (2)
1.2.1 国内外研究进展 (2)
1.2.2 存在的问题 (6)
1.3 催化燃烧研究进展 (9)
1.4 本文主要研究内容 (11)
2 微型燃烧器的物理模型和数学模型 (12)
2.1 物理模型 (12)
2.2 数学模型 (13)
3 反应机理和计算方法 (16)
集装箱内衬袋
3.1 反应机理 (16)
3.2 计算方法 (16)
4 催化燃烧影响因素的数值模拟结果和分析 (19)
4.1 预混腔结构 (19)
4.1.1 燃料入口位置 (19)小便冲洗阀
4.1.2 燃料入口直径 (21)
4.1.3 小结 (23)
4.2 甲烷质量流量 (24)
4.3过量空气系数 (30)
4.3.1 甲烷质量流量为3g/h (31)
4.3.2 甲烷质量流量为7g/h (35)
4.3.3 小结 (37)
4.4 壁面边界条件 (37)
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