1、 硕士学位论文 柴油机低介质密度条件下 壁面液膜燃烧机理研究 姓 名： 学 号： 所在院系：汽车学院 学科门类：工程 学科丏业：动力工程 指导教师： 二 XX 年 X 月 I Study on Liquid Wallfilm Combustion Mechanism under Low Density Environment in Diesel Engines Candidate: Student Number: School/Department: Discipline: Major: Supervisor: 同济大学 硕士学位论文 摘要 摘要 我国高原地区分布较广。其中，海拔高度在 100
2、0m 以上的高原面积超过我国国土面积的三分之一。相比平原，高原地区大气压力低、空气密度低、温度低，导致燃油喷雾撞壁现象加剧，造成附壁燃油堆积及蒸发滞后，导致后燃严重、燃烧恶化，对柴油机动力性、排放性、经济性、可靠性和耐久性能的影响较大，从而不利于柴油机在高原地区的正常工作。基于上述背景，开展低介质密度条件（高原环境）下柴油机壁面液膜燃烧机理研究，具有重要意义。本文以某型柴油机为研究对象，进行了模拟某型柴油机在不同海拔下缸内介质热力状态的定容弹近壁液膜宏观特性可视化试验研究，进行了定容弹壁面液膜特性的数值仿真研究， 研究了海拔和喷油压力对柴油机壁面液膜燃烧特性的影响。本文的主要工作及研究成果如下
3、： 一、开展了模拟不同条件下的定容弹近壁液膜宏观特性可视化试验 通过喷雾撞壁可视化试验研究了海拔、喷油压力、喷孔直径、撞壁角度和撞壁距离等因素对壁面液膜宏观特性（喷雾撞壁扩散直径）的影响作用，拟合了计算喷雾撞壁扩散直径的经验公式，并根据该经验公式分析总结了上述各因素对扩散直径的影响规律。研究结果表明： （ 1）定容弹背压越低（海拔越高）、喷油压力越高、喷孔直径越大、撞壁角度越小及撞壁距离越小，液态燃油发生撞壁的时间越早，最大 扩散直径也越大。 （ 2）喷雾撞壁扩散直径的经验公式比较准确地预测了扩散直径随上述影响因素的变化趋势。 二、开展了定容弹壁面液膜特性的数值仿真研究 利用 FIRE 开展了
4、模拟定容弹撞壁喷雾及壁面液膜特性的三维数值计算研究。研究了海拔（定容弹背压）和喷油压力对空间燃油蒸发量、撞壁燃油的质量、附壁燃油量、附壁液膜面积及厚度的影响规律，并对比分析了喷雾撞壁扩散直径与壁面液膜面积之间的联系。研究结果表明： （ 1）海拔越高（定容弹背压越低），空间燃油蒸发量越少，撞壁燃油的质量、壁面液膜的质量、壁面液膜的面积及壁面液膜厚度越大。 （ 2）喷油压力越高，空间燃油蒸发量越大，撞壁燃油质量、壁面液膜的质量、壁面液膜的面积及壁面液膜厚度越小。 （ 3）同一工况下，喷雾撞壁扩散直径的试验值与壁面液膜面积的变化均保 I 同济大学 硕士学位论文 摘要 持趋势一致。 三、开展了柴油机壁
5、面液膜燃烧机理的数值仿真研究 利用 FIRE 开展了柴油机壁面液膜燃烧机理的三维数值仿真研究。通过分析缸内流场、温度场、油气混合、空间燃油量、附壁燃油量及燃烧放热的特性，研究了海拔和喷油压力这两个重要参数对柴油机壁面液膜燃烧机理的影响，所得结论如下： （ 1）海拔越高，缸内空间油气混合质量越差，空间燃油蒸发量越小，燃油撞壁时刻越提前，撞壁燃油量、附壁燃油量、液膜面积、液膜厚度越大，液膜蒸发速率越慢，第一阶段放热越少、第三阶段放热越多，燃烧恶化越严重。 （ 2）喷油压力越高，燃油蒸发速率越快，空气与燃油的混合越均匀，最大空间燃油蒸发量越少，但喷油压力 80MPa 下最大空间燃油蒸发量和 60MP
6、a 差异 较小，相差 4.8mg。喷油压力越高，燃油开始发生撞壁的时刻越提前，撞壁燃油量、附壁燃油量、液膜面积、液膜厚度越大，但 80MPa 下最大附壁燃油量仅比 60MPa 多 2.2mg，该值约占总喷油量的 0.9%。喷油压力越高，滞燃期越短，燃烧持续时间越长。可见，喷油压力并非越大越好，适当增加喷油压力可以优化燃烧，本文中喷油压力选择 80MPa 可以改善燃烧。 关键词 ：柴油机，燃烧，低介质密度，壁面液膜，海拔 II Tongji University Master of Engineering Abstract ABSTRACT The plateau region in China
7、 is widely distributed, and the area of more than 1000m above sea level accounts for over 1/3 of the national land area. Compared with the atmospheric pressure, air density and temperature in the plain, they are lower in the pleatue, leading to the fuel spray hitting wall, and then resulting in wall
8、 fuel accumulation and evaporation delay, which leads to more serious post combustion. In view of the above problems, it is very important to study the combustion mechanism of liquid film on the wall in the diesel engine under the conditions of low density environment (plateau environment). In this
9、paper, a diesel engine as the research object has been choosed to do both the simulation and test in the constant volume bomb, and to simulate a certain type of diesel engine at different altitudes in the thermal state . And the research on the effects of altitude and fuel injection pressure on the
10、combustion characteristics of liquid film on the side wall of diesel engine has been done. The main work and achievements are as follows: Firstly, the simulation experiments under different conditions of constant volume bomb near-wall liquid film macroscopic characteristics. The effects of altitude,
11、 injection pressure, nozzle diameter, wall angle and the distance of the wall on the macroscopic characteristics of the attached liquid film were studied by means of spray-wall visualization experiment. The influence of the above factors on the diffusion diameter was analyzed quantitatively. The res
12、ults show: (1) The higher the injection pressure, the larger the injection hole diameter, the smaller the wall angle and the smaller the distance, the more time the spray wall hit the wall. The greater the diameter. (2) The empirical formula of the diffusion diameter of the sprayed wall predicts the
13、 variation trend of diffusion diameter with the above factors. Secondly, the numerical simulation study on the liquid film characteristic of the constant volume bomb was carried out. The numerical simulation was carried out by using the three - dimensional simulation software AVL FIRE. The influence
14、s of the altitude (back pressure of constant volume bomb) and the injection pressure on the amount of fuel vaporization, III Tongji University Master of Engineering Abstract the fuel quality of the wall, the quality of the liquid film, the area of the liquid film and the thickness of the liquid film
15、 were studied. And the telationship between the surface area of the liquid film and the diffusion diameter was studied. Research indicates: (1) The higher the altitude (the lower the back pressure of constant volume bomb), the less the space fuel evaporation, the quality of the wall fuel, the qualit
16、y of the film attached, the area of the liquid film and the film thickness. (2) the higher the injection pressure, the more space the amount of fuel evaporation, the quality of wall fuel, the quality of liquid film attached to the liquid membrane attached to the wall area and the thickness of the fi
17、lm attached to the smaller. (3) Under the same operating conditions, the experimental values of the diffusion wall diameter of sprayed impingement and the liquid film area of the attached membrane keep the same trend. Thirdly, the numerical simulation research of the liquid film combustion mechanism
18、 of the diesel engine is carried out. The numerical simulation of the combustion mechanism of liquid film on diesel engine with FIRE was carried out. By analyzing the characteristics of the flow field, the temperature field, the oil and gas mixing, the space fuel quantity, the wall fuel quantity and
19、 the combustion heat release, the influence of the two parameters of the altitude and fuel injection pressure on the liquid film combustion mechanism.The conclusions are as follows: (1) The higher the altitude, the worse the mixing quality of the oil and gas in the space, the smaller the amount of s
20、pace fuel evaporation, the more the fuel hit the wall ahead of time, the amount of wall fuel, wall fuel, liquid film, The slower the rate of liquid film evaporation, the less heat the first stage, the third stage more heat, the mor e serious deterioration of combustion. (2) The higher the fuel injec
21、tion pressure, the better the mixture quality of the oil and gas in the cylinder space, the faster the fuel evaporation speed, the less the maximum space fuel evaporation. But the difference of the maximum space fuel oil evaporation is small, Part of the crank angle fuel injection pressure 80MPa spa
22、ce than the 60MPa fuel evaporation is greater, the maximum up to 68.4mg. The higher the fuel injection pressure, the higher the fuel wall thickness at the time of 80MPa, the higher the wall thickness of fuel injected, the wall fuel quantity, the amount of wall fuel, the film area, and the maximum wa
23、ll fuel quantity of 2.2MPa. Accounting for about 0.9% IV Tongji University Master of Engineering Abstract of the total fuel injection. The higher the injection pressure, the shorter the ignition delay, the longer the combustion duration. Visible, the fuel injection pressure is not the bigger the better, the appropriate increase in fuel injection pressure can be optimized combustion. Key words: diesel engine, combustion, low working medium density, wall liquid film, altitude V
