【作者】 李小粉；

【导师】 王铁；

【作者基本信息】 太原理工大学 ， 动力机械及工程， 2010， 硕士

【摘要】 二甲醚作为一种清洁的汽车代用燃料已经越来越多的应用在压燃式发动机上。本文对二甲醚作为压燃式发动机燃料的特点进行了分析,对二甲醚的研究现状进行了总结,并且对内燃机的缸内流动以及燃烧模拟研究现状进行了研究。内燃机的燃烧是关系到内燃机动力、经济以及排放性的重要因素,由于试验条件的限制,无法对缸内燃料分布与排放之间的关系和缸内燃烧过程的实际状态进行研究。但借助于计算机技术和相关流体知识,可对缸内的燃烧过程进行数值模拟。本文利用AVL公司的FIRE软件对4100柴油发动机的燃烧室进行了建模和网格划分,模拟了从进气门关闭到排气门打开这段时间内燃料的燃烧排放情况,对仿真所得数值与燃烧分析仪所测得的台架试验值进行了分析,验证了模型的正确性,并对4100发动机缸内的喷雾流场、温度场、燃料浓度场、排放物的浓度场等三维结果以及缸压、缸内温度、排放物的质量分数等二维结果进行了研究。研究表明:当膨胀行程中缸内温度达到一定值之后,NOx的生成会进入“冻结”阶段,而碳粒的生成则是先生成后氧化的。研究还表明,油束对缸内的流场有一定的影响。在此基础上,选取了D65、D75、D85三种高比例的二甲醚柴油,对三种比例的二甲醚柴油与纯柴油在缸内的平均压力、平均温度、燃料的质量分数以及排放物的质量分数等规律进行了研究,还对燃料缸内的温度场、燃料浓度场以及排放物的浓度场进行了对比。结果表明:高比例的二甲醚柴油燃料的缸内最高压力是低于柴油的,但是其缸内最高温度和累积放热量相互接近并且是高于柴油的,说明高比例二甲醚柴油混合燃料可以降低缸内的机械负荷,同时还有很高的热效率。随着二甲醚比例的增大,缸内NOx的生成越晚并且生成的质量分数越小。除此之外,三种比例的混合燃料的碳粒生成都远低于柴油的,D85在碳粒生成上最低。本文还研究了喷油提前角和喷油持续期对对高比例的二甲醚柴油的影响。研究表明:喷油提前角加大,缸内的压力、温度以及累积放热率都会增加,同时NOx和碳粒的生成也有所增加;喷油持续期的加大则会造成缸内压力的过多降低。更多还原

【Abstract】 As a clean alternative fuel of vechiles, DME has been increasingly applied in compression-ignition engines. This paper analyses the characteristics of DME as the fuel of compression-ignition engines, sums up the current research of DME at home and abroad, and makes a research on the in-cylinder turbulence flow and the current research of combustion simulation to an extent. The combustion of engine is an important factor which relates to the power and economic as well as emission performance. Limited to the experiment condition, it is impossible to study the relation between the fuel distribution and the emission, and also the actual condition of in-cylinder combustion. But with computer technology and related knowledge of fluid, it is possible to study the combustion process through numerical simulation.By using the FIRE software, this paper sets up the combustion chamber model of 4100 diesel engine and carries on the grid partition. Also, the paper simulates the combustion and emission from the inlet valve closed to the outlet valve opened. Through the comparison between the simulation results and the results from the combustion analyzer in the test stand, the paper verifies the correctness of the model. What’s more, this paper makes a research on the 3D results such as velocity distribution, temperature field, emission field, fuel concentration, and the 2D results such as mean pressure, mean temperature, emission mass fraction and so on. The results show that NOx growth will come to a“freezing period”when it comes to a certain temperature during the expansion stroke, while soot growth is growing first and oxygenated later. The results also appear that the fuel spray influences the velocity distribution.Based on this, this paper selects three high proportional DME-diesel fuels such as D65, D75 and D85, and makes a research on the rule of diesel and the three kinds of fuels in the in-cylinder mean pressure, mean temperature, fuel mass fraction and emission mass fraction. What’s more, this paper makes a comparison of combustion process, temperature distribution and emission distribution. The result shows that the maximum pressure of high proportion DME-diesel fuel is lower than diesel’s, but maximum temperature and accumulated heat release is close to each other while higher than diesel’s. It appears that high proportion DME-diesel fuel can reduce the mechanical load in cylinder with high efficiency. With the increase of the proportion of DME, NOx grows later and NOx mass fraction is lower. Besides, the mass fractions of soot of three kinds of mixed fuels are far below diesel’s, D85’s is the lowest.This paper studies the influence to high proportion DME-diesel fuel through the changes of injection advance angle and injection duration, and provides a theory basis for the high proportional DME-diesel fuel. The results show that mean pressure, mean temperature and accumulated heat release will increase with advance of injection angle, but at the same time NOx and soot mass fraction will increase too; the extended injection duration will result in mean pressure lower too much.更多还原