【作者】 李政；

【导师】 宋崇林；

【作者基本信息】 天津大学 ， 动力机械及工程， 2012， 硕士

【摘要】 由于燃烧过程中产生的碳烟颗粒危害人类健康和污染环境,碳烟颗粒的形成机理始终是燃烧科学研究中的中心课题之一。通过利用缸内取样和各种分析检测技术,我们对柴油机缸内碳烟的演化过程已有一定的认识。但由于缸内高温高压和不稳定非均质的燃烧过程,对于其实际形成机理和工况对其影响还需要进一步的基础性研究和量化分析。因此本文在国外文献调研基础上,建立了一套预混燃烧分析系统,可以实现对预混燃烧产物进行全面的实验分析;并利用建立的燃烧分析系统研究了预混甲烷火焰温度和燃空当量比对基本碳烟颗粒粒径、团聚颗粒分形维数和基本碳烟颗粒纳米结构的影响。论文主要研究工作和结论如下:1,建立了以Mckenna燃烧器为目标火焰源的燃烧系统。可以实现稳定的预混层流燃烧火焰;可以精确的调节燃空当量比和稀释比;可以精确的调节取样火焰高度。并建立了可以对火焰各位置温度进行精确测量的高温热电偶测温系统。2,建立了一套新型的Thermophoretic Sampling Particle Diagnostic(TSPD)系统。该TSPD系统可以水平多点定位,而且定位更精确,动态响应速度、加速度和速度更为优越。建立了毛细管稀释取样系统并且对火焰各位置点的燃烧产物进行了稀释取样初步实验。3,不同发展阶段的碳烟颗粒呈现不同的形貌特征;团聚态碳烟颗粒随着火焰高度增加尺寸增大,分形维数减小。不同高度取样观察到的初生碳烟颗粒粒径基本不变;基本碳烟颗粒粒径随火焰高度增加从～10nm增加到～30nm。随着碳烟成熟的过程,碳烟颗粒的纳米结构变得更为有序,微晶长度明显加长。4,随着火焰温度升高,基本碳烟颗粒粒径减小,团聚态碳烟颗粒分形维数减小,表明高温环境下碳烟颗粒团聚的更松散。随着火焰温度升高,碳烟微晶加长且更直,层间距减小。这说明随着火焰温度的升高,碳烟颗粒的纳米结构组织趋向于变得更有序和氧化活性更低。5,随着燃空当量比增加,基本碳烟粒子粒径增大,团聚形成的团聚碳烟颗粒包含基本粒子数目增多,团聚态碳烟颗粒分形维数减小。随着燃空当量比增大,碳烟颗粒的微晶加长,曲率减小,层间距减小。这些结果表明,相同的高温环境中,大燃空当量比产生的碳烟颗粒的纳米结构更加有序和趋向石墨化。更多还原

【Abstract】 The reaction mechanism of soot formation has become one of the central themes of research activities in the area of combustion, mostly due to environmental and health concerns on pollutant emission from combustion devices. The need to provide a better physical and chemical understanding of soot formation in the high-pressure and high-temperature and inhomogeneous engine combustion chamber requires the development of combustion analysis systems and further fundamental combustion researches. Therefore, combustion analysis systems have been developed to conduct comprehensive experimental investigation of soot formation in premixed flames. The effects of temperature and fuel-air equivalence ratio on nanostructure, fractal dimension and size of soot have been investigated for laminar, atmospheric-pressure premixed methane flames. The major research work and results of this dissertation are listed as follows:1. Combustion system has been developed to investigate flame-formed soot in premixed laminar flames produced on a commercial McKenna burner, with precisely adjustable equivalence ratio and sampling height above burner. For precise temperature measurement of different flame locations, a high-temperature thermocouple temperature measurement system has also been designed.2. A thermophoretic sampling particle diagnostic (TSPD) system and an in-situ probe sampling system have been developed to obtain combustion products for physical and chemical investigation of soot formation. The TSPD system has been further developed on the basis of an advanced electric cylinder, with a freely positionable and accurate linear motor and very high dynamic response.3. Different sizes and morphology of soot are found depending upon the aging of soot formation. With the increase of height above burner, primary particle size increases from ~10nm to ~30nm, and the value of aggregate fractal dimension decreases. Fringe length extends and soot nanostructure becomes more ordered during the maturation process.4. With the increase of flame temperature, both of the primary particle size and aggregate fractal dimension value decrease, signifying that soot particles are more loosely clustered in higher temperature environment. It is revealed that both the fringe tortuosity and separation distance decrease as temperature increases, while the mean fringe length increases distinctly, indicating the soot evolution toward a more graphitic structure and higher resistance toward oxidation. 5. With the increase of fuel-air equivalence ratio, both of the primary particle size and the number of primary particles in aggregates increase. Aggregate fractal dimension value decreases, implying more soot particles with chain-like structure in higher fuel-air equivalence ratio environment. The mean fringe length increases, while the fringe tortuosity and separation distance decrease as fuel-air equivalence ratio increases, indicating the tendency of soot nanostructure toward a more ordered state.更多还原