论文总字数：17264字

摘 要

随着低碳环保的推行和重工业的发展进步，内燃机工作性能有了更高的要求，HCCI技术的产生很好的解决了这个难题，但随着重型柴油机的广泛应用，HCCI技术在高负荷工作状态下存在着运行范围有限、着火时点控制困难、热效率难以把控等技术性难题，并伴随柴油本身固有的粘度大，挥发困难，难以形成混合气等弊端，研究进展缓慢^[1]，因此本课题针对高负荷要求下（背景温度达1100K，背景密度达60kg/m³）对柴油混合气形成的影响进行研究。

使用STAR-CD软件建立定容燃烧弹，模拟燃油可燃混合气温度场和浓度场及贯穿距离物理和数学模型，实验中背景温度为800-1100K，背景密度为20-100kg/m³，喷油压力为100-220MPa，喷孔直径为0.10-0.18mm，共划分为9种工况，来探究柴油喷雾形成形状、延伸和放散方向，从而探究柴油混合气的形成和演变，得到最高做功效率和最低污染物排放。

计算结果表明背景密度对于柴油液滴蒸发速度的影响最为显著，背景密度的增大加快了柴油液滴的破碎，使其与环境气体的接触面积增大，加速了液滴蒸发，因此柴油喷雾浓度总体随背景密度的增大而减小；柴油喷雾温度场主要由背景温度影响，柴油喷雾最高温大致恒等于环境温度，且最低温随环境温度的升高而升高；背景密度和温度的提高使柴油液滴升温，液体表面张力减小而破碎，液滴数增多同时液滴直径减小，受到的空气阻力增加，因而贯穿距离减小；喷射压力的增加和喷孔直径的增大提分别提高了液滴的初速度和质量，使其获得更大动能，运动距离更远，因而贯穿距离增加。

关键词：柴油机 喷雾 定容弹 混合气形成 数值模拟

Numerical simulation of diesel concentration field and temperature

field of heavy diesel engine under similar environmental conditions

Abstract

With the implementation of the low carbon environmental protection and the development of heavy industry progress, the performance of the internal combustion engine had higher requirements, the generation of HCCI technology well solved the problem. But HCCI technology has disadvantages such as limited operation scope, difficulty in control of ignition timing and difficulty in controlling thermal efficiency under high load condition with the wide application of heavy duty diesel engines. And the diesel oil is large, not volatile and difficult to form a mixture., so the research is progressing slowly^[1].This topic studied on the formation of diesel mixture under high load requirements (background temperature of 1100K, the influence of the background density of 60kg/m³ ) .

I built a combustion chamber model on STAR-CD to simulate physical and mathematical models of the concentration field, temperature field and penetration distance of combustible mixture. The background temperature of the experiment was 800-1100K, the background density was 20-100kg/m³, the injection pressure was 100-220MPa, and the diameter of the nozzle was 0.10-0.18mm.I divided them into nine working conditions to explore the formation and development of diesel fuel mixture, and finally get the best combustion state.

The results showed that the background density has the most significant effect on the evaporation rate of diesel droplet. The increase of environmental density increased the speed of the breakdown of diesel oil droplets, which increased the contact area with the environmental gas and accelerates the evaporation of the droplet. Therefore, the diesel spray concentration decreases with the increase of environmental density. The diesel spray temperature field was mainly influenced by ambient temperature. The highest temperature of diesel spray was approximately equal to the ambient temperature, and the lowest temperature increased with the increase of ambient temperature. The increase in background density and temperature increases the diesel oil droplets. Raising the ambient density and temperature increased the temperature of the diesel droplets. The droplets are broken and the air resistance increases, so the spray penetration got shortened. The increase of injection pressure increased the initial velocity of the droplet and the increase of the hole diameter increases the drop weight, so they got more kinetic energy. So the spray penetration got longer.

Key Words: The diesel engine; Diesel spray; Combustion chamber; Mixture formation; Numerical simulation

目 录

摘 要 I

Abstract II

第一章 绪论 1

1.1 引言 1

1.2 HCCI简介 1

1.3 HCCI燃烧机理 2

1.4 HCCI特点 3

1.5 STAR-CD简介 4

第二章 燃油喷射雾化数学模型及物理模型 5

2.1 数学模型 5

2.1.1 控制方程的理论基础 5

2.1.2 湍流模型 6

2.1.3 微分方程的数值求解 7

2.1.4 离散液滴的守恒方程 8

2.2 物理模型 10

2.2.1 Reitz- Diwakar破碎模型 10

2.2.2 蒸发模型 10

2.2.3 Huh雾化模型 11

第三章 定容燃烧弹的设计 15

3.1 定容燃烧弹的物理模型 15

3.2 试验工况设置 15

3.4 本章小结 18

4.1 环境温度对柴油喷雾的影响 19

4.2 环境密度对柴油喷雾的影响 23

4.3 喷油压力对柴油喷雾的影响 27

4.4 喷孔直径对柴油喷雾的影响 31

4.5 本章小结 34

第五章 全文总结 36

5.1 经济性分析 36

5.2 全文总结 36

参考文献 38

绪论

引言

柴油机由于其高效、经济等特点而广泛应用于实际生产生活中，在产业链处于相对核心的位置上，随着科学的进步，柴油机在许多方面都有了很大的提升和改进，并促进了人类文明的发展进程。

内燃机的燃烧质量直接会影响其做功效率、燃油消耗量和污染物排放量，主要受可燃混合气形成过程影响。优秀的雾化过程造就了良好的燃烧，能发挥出更高效的功率，并能更好的做到低碳减排。因此，我们需要探究混合气形成过程，研究雾化原理，优化燃烧质量，从而提高发动机性能^[2]。

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