【作者】 张航；

【导师】 段树林；

【作者基本信息】 大连海事大学 ， 轮机工程， 2011， 硕士

【摘要】 二冲程船用柴油机的扫气过程在很大程度上影响了柴油机可燃混合气形成的质量,进而决定了柴油机在燃烧等方面的性能。扫气口作为二冲程直流扫气柴油机的重要组成部分,其结构直接影响了扫气过程中新鲜空气的充入量和燃烧废气排出的干净程度,另外,柴油机的转速也对扫气过程的进行有重要影响。本文针对6S50MC-C二冲程船用柴油机,运用CFD(计算流体力学)方法,应用大型CFD软件Fluent,首先改变扫气口数目、扫气口仰角、径向倾角的大小以及扫气口的结构,对该模型的扫气过程进行数值模拟,然后改变柴油机的转速,再进行上述模拟。可以得出流场关于压力、温度、湍流强度、进出口质量流量、速度等参数以及这些参数的分布情况。通过分析其流动状况后,找到较为合理的结构参数和运转参数。本文首先对扫气口、气缸内部和上部一段排气道的流体空间进行建模,得到物理模型；接着使用GAMBIT对模型划分网格,并设定压力进出口等边界条件；然后导入Fluent中,设定参数,启用动网格模型,开始计算；最后应用后处理程序得到大量数据、云图、矢量图、流线图等,对流场进行分析。通过研究发现,对于6S50MC-C大型低速船用柴油机,在适当的范围内以较低转速运行,增加扫气口数目、使用0°的仰角以及20°的径向倾角比较有利于扫气过程和可燃混合气形成。并发现当转速较低或较高时,仰角大小对扫气过程的影响会变得更小。本文可以为优化柴油机结构和参数,进而解决燃烧与排放等问题提供理论依据,具有一定的现实意义。更多还原

【Abstract】 Scavenging process of two-stroke marine diesel engines largely determines the formation quality of fuel mixture, and then determines the performance of combustion etc. As an important part of the two-stroke uniflow scavenging diesel, the scavenging port’s structure directly affects the intake flux of fresh air and the exhaust cleanliness of combustion gas. In addition, the diesel’s rotational speed, also affect the process of scavenging.6S50MC-C diesel engine is studied by using the method of CFD (Computational Fluid Dynamic), and CFD software Fluent is applied. First, the number, the elevation/radial angle and the structure of scavenging port are changed, and the scavenging process is simulated. Then the simulation is carried out like above mentioned at different diesel’s rotational speed. Some parameters like pressure, temperature, turbulence intensity, mass flow of inlet, velocity etc. and the distribution of these parameters can be obtained. By analyzing its flow status, some reasonable structural and operating parameters can be found.Firstly, the fluid space of port, in-cylinder part, and exhaust passage above the cylinder is modeled. Then, GAMBIT is used to mesh the model, meanwhile, pressure inlet/outlet boundary condition is set. Afterwards, the mesh is imported to Fluent, parameters are set, the dynamic mesh model is enabled, and then calculate begins. Finally, with the help of post-processing procedure, lots of data, contours, vector, path lines etc. can be obtained, so analysis can be done. It can be found with the appropriate range, operating in low rotational speed, increasing the number of scavenging ports, using 0°elevation angle and 20°radial angle may benefit scavenging process and the formation of oil and air. Meanwhile, when operating in lower or higher rotational speed, the influence of elevation angle becomes smaller on the scavenging process. So it can provide theoretical basis for diesel’s structural optimization and solving problem of combustion, emission etc., therefore there is a certain practical significance.更多还原