Study On Evaporation Characteristics Of Fuel Film Attached To Wall Under Different Wetting Characteristics

Internal combustion engine is widely used in the field of road traffic and non-road mobile machinery.It is the most important power source in the fields of transportation,construction machinery,agricultural machinery,fishing ships,national defense equipment and so on.However,with the continuous increase of environmental protection pressure worldwide in recent years,the emission problem of internal combustion engines has been further amplified.Among the numerous factors restricting the combustion controllability,one negative factor cannot be fundamentally eliminated due to the working mode of internal combustion engines,that is,the wet wall phenomenon of fuel.Different from external combustion engines,the interaction between fuel/gas and combustion chamber wall is unavoidable because the combustion is confined to a limited space,whether in compression combustion or ignition combustion engines.Although the wet wall of fuel can be reduced to some extent by improving the spray characteristics and organizing the air flow,it can not be completely eliminated.Previous scholars use the alternative fuel,reducing the wall temperature,improvement of bump wall distance,improve combustion chamber shape,air flow movement and other methods to avoid the wet wall or control of wet wall phenomenon and utilization,but few are attached to the wall of fuel film evaporation under different wall wetting property characteristics of research,and research on the process controllability is rarely make the news more.In this paper,the wet-wall phenomenon of fuel in internal combustion engine is studied to explore the influence of different wettability conditions on the spreading and evaporation characteristics of the fuel film attached to the wall after n-butanol fuel impinges on the wall.Mainly set the material surface processing platform,fuel film thickness calibration platform,laser induced fluorescence fuel bump wall test platform,and based on the python-opency image processing software design of the fuel film characteristic parameter handler,the fuel film on the attached wall area,with wall thickness of fuel film,with walls of fuel film quality parameters such as quantitative analysis,mainly in the following aspects of experiments and research work.A test platform for laser induced fluorescence fuel impingement was designed and built.Mainly including: Nd:YAG laser system,laser power meter,laser energy meter,laser homogenizer,band-pass filter,wall intelligent temperature control system,optical test platform,high-speed camera system,complete the construction and debugging of the entire test platform,to ensure the stability,safety and accuracy of the test platform.With laser induced fluorescence of different surface wettability attached to the wall under the condition of fuel film thickness were measured,and its principle is: the other conditions in given conditions,a fluorescence intensity(I)and a linear relationship with oil film thickness h,when the oil film is metal base material surface,the oil film of rhodamine B fluorescence material can fluoresce,by detecting the intensity of the fluorescent agent can realize the measurement of fuel film thickness.The relationship between oil film thickness and fluorescence intensity can be obtained by calibration test.Fuel film thickness of the calibration test choice n-butyl alcohol-rhodamine B liquid mixture for calibration,using the buret to the surface of quartz glass plate fixed area and calibration drops,after being fuel spread completely,with a certain thickness of feeler implementation,form a uniform,fixed thickness of fuel film,using high speed camera calibration test images.In order to reduce the test error as much as possible,the calibration test of each fuel film thickness was repeated for 5 times,and the average value of fluorescence intensity was used to calculate the final fuel film thickness,and the calibration curve of fuel film thickness and fluorescence intensity of fluorescent agent was obtained.The image processing software based on Python-Opency is used to design the pixel processing program,gray value processing program,threshold processing program,image smoothing processing program,Canny fuel film edge detection program,and then the area,thickness and quality of the fuel film attached to the wall are quantified.The influence of wall wettability and wall temperature on the thickness,spread area,quality and evaporation rate of the fuel film was studied by using the laser-induced fluorescent fuel impingement test platform independently built in this paper.