论文总字数：20201字

摘 要

随着石油等不可再生资源的过量消耗，世界自然环境造到巨大的破坏，环境污染越来越严重，节能减排的呼声越来越响亮，国家相关机构对于汽车尾气排放的标准越来越高，对车辆的平均燃油消耗率的限制也越来越严格。由于直喷式汽油机具有良好的燃烧效率和更低的尾气排放，其受到越来越多的追捧和关注。国内外许多学者都把改善发动机的性能的目光和重点放在这里，对燃油燃烧过程的研究也越来越深入，为了缩短研发周期和降低研发成本，广泛采取计算机模拟、实验验证的方法。为了探究对燃油燃烧有影响的因素及其影响效果。本课题利用流体分析软件STAR-CD设计、生成和使用定容燃烧弹系统，通过计算机数值模拟的方式模拟直喷式汽油机燃油喷射和燃烧的过程，并对得到的气相燃油喷雾的温度场、浓度场和喷雾贯穿距进行分析。以此为基础，探究相似环境下缸内背压、缸内温度、燃油喷射压力和喷孔直径对直喷式汽油机喷雾特性的影响，由此寻得提高内燃机燃烧效率的有效措施。

研究结果表明:降低环境背压能够促进液相的蒸发，促进气相的形成，有利于喷雾的发展形成，使得燃油分布更加均匀，并增加喷雾的贯穿距，获得较为宽阔的喷雾空间构型，提高燃油利用率；提高环境温度有利于燃油的蒸发和气相的形成，提高浓度的最大值，加速燃烧速率，增加燃油利用率；较大的喷射压力有利于油滴的破碎，能够获得更高的喷油贯穿距，促进气相喷雾的形成和发展，使得燃油与空气混合的更加均匀，提高燃烧质量；减小孔径能够促进气相喷雾的形成和发展，但是扩散速率会下降，减小喷雾贯穿距。增加喷孔直径能够增加喷雾的质量流率，提高喷雾动能，增加喷雾与环境热量的交换。提高燃油喷射压力、降低背压和提高环境温度可以与减小喷孔直径互补，能够有效减小因缩小喷油空而带来的喷雾贯穿距较短的劣势并保留小喷孔直径原有的优势。由此可得，一台燃烧效率高且排放低的直喷式汽油机必定要具有较高的燃油喷射压力，较高的环境温度，尽可能低的环境背压和合适的喷孔直径这几个特征。

关键词：直喷式汽油机　数值模拟　喷雾特性　温度场　浓度场　贯穿距

Numerical simulation of spray characteristics of Di gasoline engine (GDI)

Abstract

With the excessive consumption of non renewable resources such as oil, the world's natural environment has caused great damage, environmental pollution has become more and more serious, the voice of energy conservation and emission reduction has become more and more loud, the relevant national institutions have higher and higher standards for vehicle exhaust emissions, and the restrictions on the average fuel consumption rate of vehicles have become more and more strict. Due to its good combustion efficiency and lower exhaust emissions, direct injection gasoline engine has attracted more and more attention. Many scholars at home and abroad focus on the improvement of engine performance, and the research on fuel combustion process is more and more in-depth. In order to shorten the research and development cycle and reduce the cost of research and development, computer simulation and experimental verification methods are widely used. In order to explore the factors that affect fuel combustion and their effects. This project uses the fluid analysis software STAR-CD to design, generate and use the constant volume combustion bomb system, simulate the fuel injection and combustion process of the direct injection gasoline engine by means of computer numerical simulation, and analyze the temperature field, concentration field and spray penetration distance of the gas fuel spray obtained. Based on this, the influence of cylinder back pressure, cylinder temperature, fuel injection pressure and nozzle diameter on the spray characteristics of Di gasoline engine under similar environment is explored, and effective measures to improve combustion efficiency of internal combustion engine are found.

The research results show that reducing the ambient backpressure can promote the evaporation of liquid phase, promote the formation of gas phase, facilitate the development of spray, make the fuel distribution more uniform and increase the penetration distance of the spray, obtain wider spray space configuration, improve fuel utilization rate, and improve the ambient temperature, which is conducive to the evaporation of fuel and the formation of gas phase, and to increase the maximum concentration and speed up. The combustion rate and fuel utilization rate are increased. The larger injection pressure is conducive to the breakup of oil droplets, the higher fuel injection penetration distance, the better formation and development of gas phase spray, the more uniform fuel and air mixture and the higher combustion quality. The smaller pore size can promote the formation and development of vapor phase spray, but the diffusion rate will decrease and the spray penetration distance will be reduced. Increasing the diameter of the nozzle hole can increase the mass flow rate of the spray, increase the kinetic energy of spray, and increase the exchange of spray and environmental heat. Increasing fuel injection pressure, reducing back pressure and increasing ambient temperature can complement each other with reduced nozzle diameter, which can effectively reduce the disadvantage of shorter spray penetration due to narrowing of fuel injection and retain the original advantage of small nozzle diameter. Therefore, a direct injection gasoline engine with high combustion efficiency and low emissions must have the characteristics of high fuel injection pressure, high ambient temperature, as low as possible ambient back pressure and appropriate orifice diameter.

Keywords: direct injection gasoline engine；numerical simulation；spray characteristics ；temperature field ；concentration field ；penetration

目录

摘要 I

Abstract II

第一章 绪论 1

1.1 引言 1

1.2 国内外研究进展 1

1.3 STAR-CD 简介 3

1.4 本课题要研究的问题及研究手段 3

第二章 GDI喷雾特性数学模型和物理模型介绍 4

2.1数学模型 4

2.1.1 控制方程的理论基础 4

2.1.2 湍流模型 5

2.1.3 微分方程的数值求解 6

2.2 物理模型 7

2.2.1 Reitz-Diwakar破碎模型 7

2.2.2 Huh雾化模型 8

2.2.3 蒸发模型 11

2.3本章小结 12

第三章各种因素对汽油喷雾贯距及其浓度场、温度场的影响 13

3.1 实验参数设定 13

3.2结果分析与讨论 15

3.2.1 背压Pa的影响 15

3.2.2 环境温度T的影响 20

3.2.3 喷射压力P_inj的影响 24

3.2.4 喷孔直径的影响 27

第四章全文总结 30

4.1论文总结 30

4.2经济性分析 30

参考文献 31

致谢 33

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