【作者】 李楠；

【导师】 简林莎；

【作者基本信息】 长安大学 ， 车辆工程， 2020， 硕士

【摘要】 为了研究二甲醚代用燃料在发动机上的燃烧特性,本文根据团队前期进行的喷雾实验,从大量喷雾图片中筛选出质量较好的喷雾图像用于研究,利用图像处理及参数测量程序得到喷雾油束宏观特性参数,为后续二甲醚代用燃料的研究提供理论依据。本文重点在于图像处理算法分析及参数测量方法的研究。首先在图像增强方面,引入图像客观评价指标,对比几种图像增强算法,本文选择背景差分法结合对比度线性展宽来更好的增强图像对比度。其次,在滤噪方面,分别比较了中值、均值滤波等四种滤波方法,最终选取对油束边界保护较好的改进的中值滤波来进行滤波去噪。接着,在阈值分割方面,根据喷雾油束的实际特征,喷雾前期图像采用OTSU法,喷雾后期图像采用局部分块阈值分割算法。同时,对分块的方法进行了详细实验验证,结果表明将图像分成4*2的小块时,阈值分割的效果最优。而后,在测量喷雾锥角方面,分析霍夫变换与最小二乘法各自的优缺点设计本文的油束边界数据拟合算法。结果表明,本文算法测量得到的喷雾锥角对称性更好,精度更高。再次,利用编写的程序测量不同背压、不同启喷压力和不同孔径下的宏观特性参数,并分析其变化情况,得到如下结论:(1)提高喷孔直径,喷雾锥角、横向贯穿距离以及喷雾面积都增大,但对轴向贯穿距离影响不大。喷雾前期,喷雾油束面积与喷油时间呈线性关系,随着喷油时刻的推进,孔径越小,则越早脱离线性关系。(2)增加定容弹背压,有利于喷雾锥角的增加,但环境背压提高到一定值后,喷雾锥角的增加将不显著。同时,提高背压,会降低油束前端的发展速度,并且背压越高油束前端越早的到达最大速度。(3)增大喷油压力,将促进喷雾锥角、贯穿距离及喷雾面积的发展,喷雾面积随时间近似呈线性提高。最后,基于MATLAB/GUI模块,开发喷雾宏观特性参数测量系统,方便用户测量、分析、保存数据,节省了大量人力物力。更多还原

【Abstract】 In order to study the combustion characteristics of dimethyl ether substitute fuel on the engine,this article based on the spray experiment conducted by the team in the early stage,selected a good quality spray image from a large number of spray pictures for research,using image processing and parameter measurement procedures to obtain spray oil The macroscopic characteristic parameters of the beam,providing a theoretical basis for the subsequent research of dimethyl ether substitute fuel.This article focuses on the analysis of image processing algorithms and the study of parameter measurement methods.First,in terms of image enhancement,the objective evaluation index of the image is introduced,and compared with several image enhancement algorithms,this paper chooses the background difference method combined with contrast linear broadening to better enhance the image contrast.Secondly,in terms of noise filtering,four filtering methods such as median and mean filtering are compared respectively,and finally,an improved median filter with better protection for the boundary of the oil bundle is selected for filtering and denoising.Then,in terms of threshold segmentation,according to the actual characteristics of the spray oil bundle,the OTSU method is used for the early spray image,and the partial block threshold score algorithm is used for the late spray image.At the same time,detailed experimental verification of the block method was performed,and the results showed that the effect of threshold segmentation was the best when the image was divided into 4 * 2 small blocks.Then,in terms of measuring the spray cone angle,the advantages and disadvantages of the Hough transform and the least square method are analyzed to design the oil bundle boundary data fitting algorithm in this paper.The results show that the spray cone angle measured by the algorithm in this paper has better symmetry and higher accuracy.Thirdly,the program was used to measure the macro characteristics parameters under different back pressures,different initiation pressures,and different apertures,and the changes were analyzed to obtain the following conclusions:(1)Increase the nozzle diameter,spray cone angle,lateral penetration distance,and The spray area is increased,but it has little effect on the axial penetration distance.In the early stage of spraying,the area of the spray oil bundle and the injection time have a linear relationship.As the injection time advances,the smaller the aperture,the sooner the linear relationship is released.(2)Increasing the back pressure of the constant volume bomb is conducive to the increase of the spray cone angle,but after the environmental back pressure is increased to a certain value,the increase of the spray cone angle will not be significant.At the same time,increasing the back pressure will reduce the development speed of the front of the fuel bundle,and the higher the back pressure,the sooner the front of the fuel bundle reaches the maximum speed.(3)Increasing the injection pressure will promote the development of spray cone angle,penetration distance and spray area,and the spray area will increase approximately linearly with time.Finally,based on the MATLAB / GUI module,a spray macro characteristic parameter measurement system was developed to facilitate users to measure,analyze,and save data,saving a lot of manpower and material resources.更多还原