摘 要

经济的发展，汽车的广泛普及导致能源的枯竭和日益严峻的环境污染问题，高寿命、低油耗的柴油机则成为了解决这些问题的关键。而作为决定柴油雾化质量、燃烧质量的喷油嘴，其结构直接影响柴油机的燃烧和排放。为了提高这些性能，喷油嘴的结构优化则成了重中之重。随着对高压喷射的需求不断提高，传统的实验测试很难了解高压、高速柴油流经喷嘴的流动性能.因此，FLUENT的数值模拟分析成了主要研究方式。通过对比方案的数值模拟分析，提供了喷油嘴结构优化的研究思路。

本文理论分析了喷孔形状、压力室容积大小对柴油机性能的影响。结合喷油嘴当前的研究现状与存在的问题，确定了结构优化的原则与具体方案。利用SolidWorks创建不同方案喷油嘴的三维模型，然后在Workbench中对简化的模型抽取流道，并利用ICEM-CFD划分结构化网格，最后导入FLUENT中进行流动特性的数值模拟分析。方案主要是通过在针阀运动距离分别为h=0.1mm、h=0.2mm、h=0.3mm时将针阀双锥面的角度由60°、95°改为60°、80°来减小0.21的压力室容积以及将喷孔入口直径D'=0.24mm、出口直径D"=0.24mm改为入口直径D'=0.24mm、出口直径D"=0.22mm来改变喷孔形状进而对比研究喷油嘴的流动特性，得出结论：

（1）理论分析可知，在一定范围内，减小压力室容积、减小喷孔出口直径有利于提高经济性能和排放性能。

（2）FLUENT的数值模拟分析结果与理论分析一致，说明了本文的计算模型是正确有效的。

（3）数值模拟分析表明，在针阀运动距离为h=0.1mm、h=0.2mm、h=0.3mm时分别改变喷孔形状，减小压力室容积都能使喷孔整体压力提高，压力分布更均匀，喷孔入口处局部压力更低，空穴紊乱更严重，出口速度分别提高34%、7%、6.25%、27%、4%、1.5%，这都有利于提高柴油的雾化质量。

关键词：柴油机；喷油嘴；压力室；喷孔形状；流动特性。

Abstract

The development of economy, the widespread popularity of cars leads to the energy depletion and increasingly severe environmental pollution, high life, low fuel consumption of the diesel engine has become the key to solve these problems. As decided atomization of diesel quality, combustion quality of the fuel injectors, which structure directly affect the combustion and emissions of diesel engine. In order to improve these properties, the optimization of the structure have become a top priority. With the increasing demand for high-pressure injection, the traditional experimental tests is difficult to understand the flow performance about the high-pressure、high-speed diesel fuel flow through the nozzle. Therefore, FLUENT numerical simulation analysis has become the main research methods. By comparing the scheme of numerical simulation analysis, provides a research way of thinking in optimizing the structure of the nozzle.

This paper theoretical analysis the impact of the shape of the orifice, pressure chamber volume size on diesel engine performance. Combined with the nozzle of the current research status and existing problems, determine the principles and concrete scheme of the structure optimization. establish the three-dimensional model of the different scheme  nozzle by using SolidWorks, and then extraction flow channel of the simplified model in the Workbench , and use the ICEM-CFD to divide structured grid, Finally import the FLUENT software to carry on the numerical simulation analysis about the flow characteristics. Program is mainly through needle movement distance is h = 0.1mm, h = 0.2mm, h = 0.3mm when the needle double cone angle from 60 °, 95 ° to 60 °, 80 ° reduced 0.21 pressure chamber volume and the inlet orifice diameter D '= 0.24mm, outlet diameter D "= 0.24mm to inlet diameter D' = 0.24mm, outlet diameter D" = 0.22mm to change the shape of the nozzle holes and then comparative study nozzle flow characteristics, draw a conclusion:

（1）Theoretical analysis shows that within a certain range, decreasing the pressure chamber volume, reduced diameter nozzle exit help to improve economic performance and emissions performance.

（2）FLUENT numerical simulation analysis results are in agreement with the theoretical analysis results, indicating reduced pressure chamber volume, changing the shape of the injection hole help to improve the overall performance of the diesel engine.

（3）FLUENT numerical simulation analysis shows that the needle movement distance of h = 0.1mm, h = 0.2mm, h = 0.3mm respectively When change the nozzle shape, reduce the pressure chamber volume  can make the whole nozzle hole pressure increase, the pressure distribution is more uniform, lower partial pressure of the injection hole entrance ，hole disorder is more serious, the exit velocity increased 34%、7%、6.25%、27%、4%、1.5%，which are conducive to improving the quality of atomization of diesel.

Key Words：Diesel engine; Nozzle; Pressure chamber; Orifice shape; flow characteristics.

目 录

摘要.......................................................................................................................................... I

Abstract..................................................................................................................................... II

第1章 绪论……………………………………………………………………………………..1

1.1设计的背景与目的及意义……………………………………………………………...1

1.2 国内外喷油嘴结构的研究现状………………………………………………………..1

1.3喷油嘴存在的问题……………………………………………………………………...2

1.4 研究的基本内容………………………………………………………………………..3

第2章 喷油嘴结构优化设计…………………………………………………………………..4

2.1喷油嘴部分结构参数对柴油机性能的影响…………………………………………...4

2.1.1 喷孔形状对柴油机性能的影响…………………………………………………4

2.1.2压力室容积对柴油机性能的影响……………………………………………….4

2.2 喷油嘴结构优化的原则与目标………………………………………………………..5

2.2.1结构优化的原则………………………………………………………………….5

2.2.2 结构优化的目标…………………………………………………………………5

2.3 结构优化设计的技术方案……………………………………………………………..7

2.4 结构优化设计的技术路线……………………………………………………………..9

2.5本章小结………………………………………………………………………………...9

第3章 流动特性数值模拟分析………………………………………………………………10

3.1简化后的流道模型…………………………………………………………………….10

3.2 求解器的选择…………………………………………………………………………11

3.3 物理模型的选择………………………………………………………………………11

3.4 定义流体的物理性质………………………………………………………………....12

3.5 边界条件设置…………………………………………………………………………12

3.6 求解算法的设置与控制………………………………………………………………12

3.7 松弛因子的设置………………………………………………………………………13

3.8 本章小结……………………………………………………………………….……...13

第4章 流动特性结果分析…………………………………………………………………....14

4.1喷孔形状对流动的影响……………………………………………...………………..14

4.1.1 针阀运动处于最大值时，改变喷孔形状……………………………… …….14