Fluent发动机汽缸内燃烧过程数值模拟

摘要车用压缩天然气 CNG（compressed natural gas）与常规石油燃料相比，其化学性质稳定，火焰传播速度较慢，在气缸内燃烧时平均有效压力低，并会产生局部热负荷较高，热效率低下等不良结果。因此，必须对天然气在缸内的燃烧过程进行研究，以期望改善燃烧过程，提高发动机性能。文章利用CFD软件 Fluent对一台改装的 CA20 型天然气发动机缸内的压缩、燃烧和膨胀过程进行了二维的数值模拟，对缸内气体的气相湍流流动模型，缸内火花塞点火模型、燃烧模型在理论上进行具体的分析。在压缩比ε=8 时，对不同点火正时和不同空燃比的燃烧过程进行计算比较，根据各种情况下缸内CH4浓度场和温度场的分布情况，研究点火提前角和空燃比对燃烧过程的影响。研究结果表明：在适当范围内，增大点火提前角火焰传播速度增加，燃烧过程温度增高，气缸内压力变大；增大空燃比可燃混合气燃烧过程速度减慢，缸内温度、压力均下降。 61027
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

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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