摘要高原环境严重影响发动机的燃烧过程以及性能，主要表现其动力性、经济 性和排放性能明显下降。因此高海拔下柴油机想要达到高效清洁燃烧需要克服 更多的困难。

多次喷射技术已成为柴油机降低排放、获得良好性能的重要手段。多次喷 射是将每循环固定喷射的燃油总量分为两次或多次进行分步喷入，这样能够合 理的控制燃烧过程，达到在对NOx排放不产生明显影响的情况下降低颗粒排放， 以满足严格的排放法规。84398

预喷射引发的初期燃料的引燃现象，使得着火延迟期的缩短，降低了预混 合阶段的燃烧总量；同时初期缸内燃烧温度升高、放热始点前移且靠近TDC附 近。在全工况范围内，采取预喷射的喷油策略对降低柴油机的燃烧噪声与油耗 效果显著；而预喷阶段的燃烧产物会被主喷射油束卷吸，抑制其最大瞬时放热 速率，主燃期缸内平均温度降低，有效减少NOx生成。

本文利用CFD软件对海拔4500m环境下高海拔下柴油机缸内的燃烧过程进 行了模拟计算，详细研究了主预喷间隔对高海拔下柴油机排放的影响。

毕业论文关键词：柴油机、高原条件、主预喷间隔、燃烧数值模拟

Abstract High altitude environment affects the combustion process and performance of the engine, the main performance of its power, economy and emission performance significantly decreased。 Therefore, the high altitude of the diesel engine to achieve high efficiency and clean combustion need to overcome more difficulties。

Multiple injection technology has become an important means to reduce emissions and achieve good performance of diesel engine。 Multiple injections per cycle fixed injection fuel amount will be pided into two or several step by step  injection, which can reasonably control combustion process, reached in the emission of NOx does not produce obvious influence on the reduce particulate emissions to meet stringent emissions regulations。

Pre injection caused the initial fuel ignition phenomenon, the ignition delay is shortened, reducing the total premixed combustion; and early in cylinder combustion temperature, exothermic starting point forward and close to the near TDC。 In the full range of operating conditions, take pre injection fuel injection strategy to reduce the effect of diesel engine combustion noise and fuel consumption significantly, and pre injection combustion products will is the main oil injection beam entrainment, inhibition of the maximum instantaneous heat release rate and burning period in cylinder mean temperature decreased, effectively reduce the total NOx generation。

In this paper, CFD software is used to simulate the combustion process of a diesel engine cylinder at an altitude of 4500m, and the effect of the main pre injection interval on the emission of diesel engine at high altitude is studied in detail。

Keywords:Diesel engine, plateau condition, main-pre injection interval, combustion numerical simulation

目 录

第 1 章 绪 论 1

1。1 课题研究的背景及意义 1

1。2 国内外研究现状及发展趋势 1

1。2。1 内燃机燃烧过程数值模拟的研究现状 2

1。2。2 高原条件下柴油机工作过程与燃烧机理的研究现状与趋势 3

1。2。2。1  国内外研究现状 4

1。2。2。2  发展趋势 5

1。3 研究内容与方法 6

第 2 章 柴油机缸内燃烧数值模拟与模型建立