斯特林发动机积碳机理及与振荡流动相互影响机制

Stirling engines are very important for solar dish power systems. Oscillating flows are the core of Stirling cycles, which link the processes of heat absorbing, regenerating, releasing and driving pistons. Carbon deposition in Stirling engines would cause an sharp increase of flow resistance and a great drop of heat-exchange efficiency, and the output power would decrease, or even, the heating tube would be blasted, which is very dangerous. This proposal is to study the processes of thermal cracking of lubricating oil, migration of volatilized products and carbon deposition, and to study the effects of carbon deposition on heat transfer of oscillating flows. Cracking pathways and reaction kinetics will be investigated when lubricating oil is thermally cracked in inert gas and hydrogen atmospheres. Size distributions, physical and chemical properties will be also studied for solid products. It tries to reveal the mechanism of thermal conversion of lubricating oil in Stirling engines. The migrating and accumulating process of volatilized products will be researched, and the mechanism of secondary cracking will also be discussed. Thus, the patterns of cohering and carbon deposition will be summarized. Effects of carbon deposition will be investigated on flow resistance and heat transfer coefficient, and a numerical model will be set up for analysis. The relationships will be discussed between location and amount of carbon deposition and flow resistance, heat transfer coefficient and regenerator's efficiency. A quantitative correlation will be proposed based on the above study, which is expected to provide theoretical guides for design, operation and maintenance of Stirling engines.

太阳能碟式热发电系统的关键在于斯特林发动机。振荡流动贯穿吸热、回热、放热和推动活塞做功整个过程，是斯特林循环的核心。斯特林发动机积碳会增大振荡流动阻力，降低回热效率和换热能力，致使输出功率大幅下降，甚至引发加热器爆管，危害运行安全。本申请针对斯特林发动机的积碳机理及与振荡流动之间的相互影响开展研究。探讨惰性和氢气气氛下润滑油的热转化途径与反应动力学，考察固相产物的粒径分布、物理形貌和化学特性，阐明斯特林循环气氛中润滑油的热转化过程与机理。分析挥发与热转化产物在振荡流动中的迁移和累积过程，探讨挥发性产物的二次转化特性，揭示振荡流动中回热器和加热管上固相产物的粘结和积碳规律。研究积碳对振荡流动阻力和换热系数的影响，建立数值模型，探讨积碳部位与累积量同振荡流动阻力、加热器换热系数、回热效率之间的依变规律，获得定量分析关联式，为斯特林发动机的运行与维护提供理论指导。

斯特林发动机积碳会增大振荡流动的阻力，降低换热能力和回热效率，进而降低循环效率和输出功率。本项目主要研究斯特林循环中的积碳机理及振荡流动的传热传质规律。在氮气、二氧化碳气氛下，分析了不同时间或加热温度下润滑油的质量损失特性，采用傅立叶红外光谱、热重分析、扫描电镜等方法对产物进行物理化学分析，发现PAO油形成的固体残渣表面光滑，能有效抑制污垢层的形成，阐明了斯特林发动机气氛中润滑油的热转化过程与机理。分析了加热管的积碳机理及对换热性能的影响，研究了振荡流在加热管和回热器中的流动与换热特性。在加热管积碳的初级阶段，积碳可以强化加热管的换热性能，随后换热近似线性降低；相同雷诺数下管壁表面温度和主流流体温差先减小后增加。获得了积碳180h内无量纲换热系数变化的拟合关系式，努赛尔数的计算值与试验值的偏差小于9.2%。分析了斯特林循环中加热管和冷却管内的振荡流传热传质特性，研究了回热器对振荡流的影响规律，开发了基于振荡流传热传质特性的改进Simple模型（ISAM），探究了积碳对斯特林发动机性能的影响，进一步完善了ISAM模型。提出了利用ISAM计算的损失信息优化Sage模型的耦合分析方法，提出了一套斯特林发动机除碳的简便装置，为斯特林发动机的优化设计提供重要参考。发表相关学术论文13篇，其中SCI 论文11 篇、EI论文1篇、中文核心论文1篇；录用EI论文3篇、中文核心论文1篇；授权国际发明专利2件、国家发明专利2件，另外还申请国家发明专利4件，获得软件著作权3件；培养与本项目直接相关的研究生15 名，其中毕业7名、在读8名。