摘 要

柴油机是用过燃烧柴油燃料来获取能量的相关发动机，随着全球化石燃料的紧张，柴油机在日常生产生活中的运用越来越广泛。但是柴油燃料燃烧所产生的氮氧化物，可入肺烟尘颗粒等对人体及环境有害的物质也随之产生。各国各省市也都相继出台了相关法规法案，对柴油机排放的尾气处理做出了严格的规定。因此也推动了柴油机尾气处理相关技术的发展。选择性催化还原技术SCR作为一个相对成熟的技术，可以有效处理柴油机尾气排放中的氮氧化物（NOx），其被广泛应用于国内外商业生产之中。

SCR系统中非常重要的一个部分即为尿素喷雾及喷嘴，本文对喷雾的特性以及存在的问题进行了研究，同时也探究了柴油发动机尾气处理系统的工作原理与存在的问题。在建立流场模型以及喷雾模型的基础上，完成喷雾水解条件的理论与仿真分析，并得出结论。

关键词：柴油机；SCR系统；尿素喷雾；CFD计算 Abstrict

Diesel engines are related engines that use diesel fuel to obtain energy. With the shortage of global fossil fuels, diesel engines are increasingly used in daily production and life. However, the nitrogen oxides produced by the combustion of diesel fuel can be produced by substances such as lung dust particles that are harmful to the human body and the environment. Various provinces and cities have also issued relevant laws and regulations, and strict regulations have been imposed on the exhaust gas treatment of diesel engines. Therefore, it has also promoted the development of technologies related to diesel exhaust gas treatment. As a relatively mature technology, SCR is widely used in commercial production at home and abroad.

A very important part of the SCR system is the urea spray and nozzle. This paper studies the characteristics of the spray and the existing problems, and also explores the working principle and existing problems of the diesel engine exhaust gas treatment system. Based on the establishment of the flow field model and the spray model, the theoretical and simulation analysis of the spray hydrolysis conditions was completed and the conclusions were drawn.

Keywords: Diesel engine；SCR system；Urea spray；CFD calculation

目录

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

1.1引言...............................................................1

1.2 NOx生成的机理.....................................................1

1.2.1 温度型NOx...................................................1

1.2.2 燃料型NOx...................................................1

1.2.3 瞬时型NOx...................................................2

1.3 关于我国柴油机后处理排放的标准....................................2

第2章 研究柴油发动机尾气处理系统的工作原理与存在的问题...................4

2.1 柴油机排放的尾气成分分析..........................................4

2.2 有关颗粒状物质与氮氧化物产生的相互影响............................4

2.3 目前柴油发动机尾气后处理的主要技术路线............................4

2.3.1 废气再循环技术...............................................5

2.3.2 选择性催化还原技术...........................................6

2.3.3 SCR技术优势分析.............................................7

第3章 完成SCR系统中喷雾的特性与存在的问题调研 ..........................8

3.1 国内外SCR系统发展趋势............................................8

3.2 SCR系统中影响催化效率的主要因素..................................8

3.3 柴油机SCR系统中影响喷雾特性的因素................................9

3.3.1 柴油机SCR喷嘴对喷雾特性的影响..............................9

3.3.2 排气流量对尿素分解的影响....................................10

3.3.3 温度对SCR反应的影响........................................11

第4章 完成喷雾水解条件的理论与仿真分析...................................12

4.1 排气通道模型的建立................................................12

4.2 流场内部流动条件及喷雾特性的仿真分析..............................12

4.2.1 流场内部网格的划分..........................................13

4.2.2 求解器参数的设置............................................13

4.2.3 仿真过程的计算..............................................15

4.3 喷雾仿真的结果分析................................................15

4.3.1 观测点2D结果的观测分析.....................................16

4.3.2 喷雾2D计算结果观测.........................................18

4.3.3 流场内3D切片分析...........................................19

4.3.4 流场中喷雾模型的分析........................................21

第5章 结论...............................................................28

参考文献................................................................29

致谢....................................................................30

第1章 绪论