Visualization Test And Image Processing Of Multi Hole Spray For Marine Diesel Engine

In order to upgrade the performance of marine diesel engine,improve combustion efficiency and reduce pollutant emission,it is of great significance to study the characteristics of multi-hole spray and shock wave of marine diesel engine.A visual experimental platform for multi-hole spray of marine diesel engine was established based on double-path high-speed shadow method.The image processing algorithm of multi-hole spray of marine diesel engine under dynamic background is developed.The spray tip penetration distance,spray far field cone angle and spray near field cone angle were obtained.Specifically,the algorithm includes three parts: image preprocessing,image noise reduction,spray feature recognition and parameter calculation.Bi Cubic interpolation algorithm and OTSU algorithm are μsed to correct image distortion,foreground and background image segmentation in image preprocessing stage,thus more real multi-hole spray image can be obtained.At the stage of image noise reduction,using image filtering and corrosion expansion algorithm,the salt and pepper noise,island noise and peninsula noise in the target area are removed in multiple steps,and the non-target region in the image is removed by Boolean operation.As a result,the target image with clear features and smooth boundary is obtained.In the stage of spray feature recognition and parameter calculation,10 target sub-regions are segmented under angular coordinate system by using image pixel depth difference to identify different spray and background,and the macroscopic parameters of spray are solved in each interval respectively.A clear image of multi-hole spray and shock wave of marine diesel engine is obtained,as well as the spray front end penetration distance,spray far field cone angle and spray near field cone angle.The analysis of multi-hole spray characteristics of marine diesel engine shows that the spray penetration distance and spray cone angle in individual injection holes can be different with the same working conditions under the spray conditions of marine diesel engine with large aperture,multiple injection holes and high background density.When the injection pressure is the same,increasing the background density will not change the average spray penetration distance,the average far field cone angle and the average near field cone angle in the initial stage of spray development.However,in the middle and late stage of spray development,the average spray penetration distance decreases,the average far field cone angle increases and the average near field cone angle increases.Under the same background density,the higher the injection pressure,the greater the average spray penetration,whilst the average far field cone angle and the average near field cone angle are getting smaller.The analysis of the shock induced by multi-hole spray shows that the high flow rate and high background density condition make the multi-hole spray produce strong multilayer shock wave,and the shock wave produced by different spray will interfere and superposition each other,and hit the wall,reflect and oscillate in the constant volume projectile,thus forming a complex flow field in the constant volume projectile.