【作者】 柏金；

【导师】 李昌烽；

【作者基本信息】 江苏大学 ， 工程热物理， 2014， 博士

【摘要】 微机电系统的发展,无论是对国防军工行业还是人们的日常生活,都产生了巨大的影响,但动力供给部分成为了其进一步发展的瓶颈,随着机电系统逐渐趋向于微型化和功能集成化,越来越迫切需要体积小、能量密度大、供能时间长及能量补给迅速的新型动力系统。近年来由于碳氢燃料能量密度大,基于碳氢燃料燃烧的微动力系统引起了广大学者的关注。随着微动力装置燃烧室体积的急剧变小,燃烧条件和环境发生了改变,混合气体在微尺度空间里的驻留时间缩短,而化学反应时间增加,造成混合气体燃烧不稳定；微燃烧室空间的急剧减小还会造成火焰淬熄现象；同时微燃烧室体积的减小造成大的面容比值,从而产生壁面传热损失,降低了微动力装置的能量转换效率。针对微燃烧面临的困难和挑战,本论文中选择微自由活塞式动力装置作为研究对象,主要是因为微自由活塞动力装置采用均质压缩燃烧方式,燃烧迅速,无火焰扩散现象,整体结构简单,易于向微型化发展,且压缩比可变,同时借助预热及催化等处理方法,可以有效解决微燃烧所存在的问题。目前关于微自由活塞动力装置的研究还处于初步理论研究阶段,还没有成熟的理论用以借鉴,因此本文着重研究微自由活塞动力装置的核心问题,即微压缩燃烧过程。建立单次压缩燃烧过程研究模型,通过数值模拟分析方法及可视化实验研究手段,开展较系统的基础理论研究工作,取得了一些具有学术意义及实用价值的研究结论：为了提高微自由活塞动力装置燃烧过程的稳定性和动力输出性能,首先对微自由活塞动力装置进行了概念设计,将进气管道布置在排气管道中,利用高温废气预热进气管道中的均质混合气,提高均质混合气的初始温度；设计了扫气板与废气腔结构,利用废气腔中的压力差,将燃烧废气最大程度地排出微燃烧室外,使得更多的新鲜均质混合气进入微燃烧室内；在微燃烧室底部添加铂催化剂涂层,通过催化燃烧方式使均质混合气燃烧更加充分和稳定,并可以拓宽燃烧界限,增大微自由活塞动力装置燃料适用范围。针对单次压缩燃烧过程搭建了可视化实验平台,借助高速数码相机拍摄了微压缩燃烧过程图片,证明了均质混合气在微小空间里压缩着火燃烧的可行性；通过图片分析,定义四种典型的燃烧过程,即压缩未着火过程、临界压缩着火过程、完全压缩燃烧过程及超高压缩比燃烧过程；并针对不同活塞初速度、活塞质量及微燃烧室参数开展了实验研究,实验结果表明自由活塞初速度是决定均质混合气能否压燃的重要因素,其它条件不变的情况下,活塞质量越大,燃烧过程越剧烈,微燃烧室长度越长,均质混合气越不容易压缩着火,并通过大量实验数据总结得出,使用二甲醚燃料气体时,压缩比大于18时,均质混合气才能压缩燃烧。根据实验原理建立了单次压缩燃烧过程的数学模型,将燃烧化学反应过程与活塞运动过程相耦合,动态模拟计算了微HCCI燃烧过程,并结合可视化实验结果,对计算模型的正确性进行了验证；对单次压缩燃烧过程开展了多方案变参数数值模拟计算工作,详细研究了活塞压缩初速度、活塞质量、均质混合气当量比、初始温度与初始压力、微燃烧室直径与长度、传热、泄漏以及催化燃烧等因素对微压缩燃烧特性及活塞运动特性的影响。最后通过总结大量计算结果,得出了微自由活塞动力装置关键设计参数的选取原则,自由活塞与微燃烧室内壁面之间的间隙应小于8μm,应尽量提高微燃烧室的密封性,有利于微动力装置输出功率的提高；得到混合气临界压缩着火初动能的计算公式,当自由活塞所获得的压缩动能大于临界压缩着火初动能时,均质混合气才能完全压缩着火,对研究微自由活塞动力装置启动条件具有一定的指导意义；具体分析了活塞质量与压缩初速度的选取准则,相同压缩初动能条件下质量大而压缩初速度小的活塞适用于低速工况,质量小而初速度大的活塞适用于高速工况,工作频率高但微燃烧过程不稳定；对微燃烧室几何结构的设计原则也进行了研究,结论表明,在其它条件相同的前件下,细长型的微燃烧室更加适合。本论文的研究工作可以丰富微燃烧理论,为微自由活塞动力装置的研制提供理论依据,同时对其它类型微动力系统的研究也有一定的参考价值。更多还原

【Abstract】 The development of Micro Electro Mechanic System (MEMS) brings profound iMPact not only on daily life but also on national military. However, with the development of technology, these devices gradually tend to miniaturization and function integration, and require a power source to have characteristics of small size, high energy density, long life span and quick charge technology. The power supply section has become the bottleneck of MEMS further development. In recent years, due to the advantage of high energy density of hydrocarbon fuels, micro power system based on burning hydrocarbon fuels has aroused public concern of scholars.The combustion condition and environment change with the rapidly reducing in size of micro power device, residence time of mixture gas in micro scale space is shortened and the reaction time increases, resulting in combustion instability. It also will cause flame quenching phenomenon, and heat transfer loss will happen because of large area to volume ratio, it will reduce the energy conversion efficiency of micro power device. For micro combustion difficulties and challenges, micro free-piston power device is selected as the research object in this paper. Mainly because that homogeneous charge compression ignition (HCCI) combustion mode is used in micro free-piston power device, the combustion is rapid and without flame spread phenomenon. The compression ratio is variable, and this power device is easy to miniaturization because of its simple structure. At the same time, the micro combustion problems mentioned above can effectively be resolved through preheating and catalytic method.At present, research about micro free-piston power device is still in the initial theoretical research stage, and there is no mature theory for reference, so this paper firstly focuses on the research of micro free-piston power device core part, micro compression combustion process. By establishing single compression combustion model, numerical simulation and visualization experimental study on basic theory research were carried out, and some achievements with academic significance and practical value have been acquired: Firstly, the micro free-piston power device is conceptual designed, in order to improve its combustion stability and power output performance. The intake pipe is arranged in the exhaust pipe, using the exhaust gas heat to preheat the intake pipe, aiming to increase the initial temperature of homogeneous gas. Air sweeping plate and exhaust gas chamber are designed, and the special structures can make the burned gas exhaust much more effectively, more fresh homogeneous gas into micro combustion chamber by utilizing pressure difference. Adding catalyst coating at the bottom of micro combustion chamber, micro combustion will be more complete and stable and the combustion limit could be broaden through HCCI catalytic combustion, and catalytic combustion can also expand the scope of fuel application.A visual experimental platform was set up according to the single compression combustion process, and the pictures of micro compression combustion process were captured by means of high speed digital camera, the result proved that homogeneous gas could be compressed combustion in micro space. According to the analysis of experimental images, four typical types of HCCI combustion process in micro-combustor were defined: compression process without ignition, critical compression ignition process, complete compression combustion process and high compression ratio combustion process. Variable parameter experiments were carried out under different conditions of piston initial velocities, piston mass and micro combustion chamber length, and the experimental results show that piston initial velocity is an important factor deciding whether the homogeneous gas could be compressed ignition or not. Heavier the piston is, stronger the combustion is, and longer the micro combustion chamber is, more difficult to be compressed ignition when other conditions remain unchanged. And a conclusion could be obtained through a large number of experimental data that the homogeneous gas could not be compressed ignition until the compression ratio is greater than18when using dimethyl ether.Mathematical model of single compression combustion process was established according to experiment principle, coupling the chemical reaction process and the motion of piston, and the micro HCCI combustion process was simulated. CoMParing to the experimental results, the calculation model was verified. Subsequently, variable parameter simulation for single compression combustion process were conducted to analyze the iMPact factors on micro combustion and piston motion characteristics, such as piston compression initial velocity, piston mass, homogeneous gas equivalence ratio, initial temperature and pressure, micro combustion chamber length and diameter, heat transfer model, leakage model, catalytic combustion and so on.Finally, by summing up the calculation results, principle of parameter design of micro free-piston power device was obtained. The gap between micro combustion chamber inner surface and free piston should be less than8μm, improving the sealing performance benefits the power output of the micro power device. Formula of critical compression ignition initial kinetic energy value is obtained by statistical calculation, homogeneous gas could not be compressed combustion completely until the compression initial kinetic energy obtained by piston is greater than critical compression ignition initial kinetic energy, which has a certain guiding significance to the study on start-up condition of micro free-piston power device. The piston mass and compression initial velocity selection principle was analyzed, the piston with great mass and low compression initial velocity suits for low speed engine, and the piston with light mass and high compression initial velocity suits for high speed engine under the same condition of compression initial kinetic energy, but the micro combustion is not stable when the working frequency is too high. The structure design of micro combustion chamber was also studied, and the results show that slender combustion chamber is more suitable for micro free-piston power device when other parameters are the same.This work could enrich the micro combustion theory and also could be the basic theories for designing the micro free-piston power device, and all the research result could also be applied to other micro power systems.更多还原