Fluent发动机汽缸内燃烧过程数值模拟
毕业论文关键词 发动机 数值模拟 点火提前角 空燃比 Title Numerical Simulation Of Combustion Process nside of The Engine Cylinder
Abstract Compared with traditional oil fuel, compressed natural gas (CNG) used in vehicle has Chemical properties of stability, its flame has a slow speed of spread, and the mean effective pressure is low in the cylinder. High heat load in some parts of the space and low heat efficiency can be caused. Study on the combustion process of the CNG in cylinder is needed. It is expected to improve the combustion process and the performance of engine.The CFD software Fluent is used for 2D and 3D numerical simulation for the process of compression, combustion and expansion in the cylinder of a modified CA20 natural gas engine in the thesis. The gas phase turbulent flow model, the spark ignition model in cylinder and combustion model are analysed in theory. When the ratio of the compression is 8, different combustion process in different spark ignition time and different air-fuel ratio are Compared with each other. The distribution of concentration field of CH4 and the distribution of temperature field in cylinder in different conditions are displayed to find the influence of the spark ignition time and air-fuel ratio to combustion process. The results show that: in appropriate range, with the increase of ignition advance angle, speed of flame propagation can be increased, the combustion temperature and the pressure in the cylinder can be higher; with the increase of the air-fuel ratio, combustion process is slowed down, temperature and pressure in cylinder is decreased.
Keywords engine numerical simulation ignition advance angle air-fuel Ratio
目次
1绪论..1
1.1课题背景.1
1.2天然气发动机简介.2
1.3本文主要研究内容4
2发动机汽缸建模..6
2.1发动机物理模型6
2.2基本控制方程...9
2.2.1质量守恒方程....9
2.2.2动量守恒方程....9
2.2.3能量守恒方程....9
2.2.4组分守恒方程..10
3数值模拟分析....11
3.1数值模拟技术的发展....11
3.2Fluent计算条件设置...12
3.3计算模型选择.13
3.3.1湍流模型13
3.3.2化学反应模型..15
3.3.3点火模型16
3.4动态网格设置.16
3.4.1动态网格更新方法....17
3.4.2计算步长19
4模拟结果分析....21
4.1点火提前角对燃烧过程影响...21
4.2空燃比对燃烧过程的影响.24
结论....28
致谢....29
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