Visualization Characterization And Simulation Research On Cavitation Flow In Fuel Injection System

Internal combustion engine is widespread used in transportation,construction machinery and agriculture machinery fields for its high thermal efficiency,compact structure and small weight and size.With the release of stricter emission regulations,the internal combustion engine face higher demand of performance and emission.High pressure fuel injection system is an effective method to meet the requirements of emission regulations and raise the performance.But with the increase of the injection pressure,the cavitation problems occurred.Cavitation flow not only causes cavitation damage,which affects metallic lifetime and reliability,but also affect the flow capacity of the flow channel,which lead to the decrease of the fuel injection system.Therefore,the research of cavitation flow characteristics in fuel injection systems is of great significance.It is the key point of the process of fuel injection system develop to higher parameters.This paper firstly established the fuel injection system visualization experiment table in order to acquire the cavitation flow pattern based on similarity principle.Designed fuel supply system and data & image acquisition system.Designed a“sandwich” structure visualization model based on a diesel engine high pressure common rail fuel injector fuel channel.Tested the experiment table and validated the results with numerical simulation.The results had shown that the visualization experiment table could acquire clear cavitation flow pattern of complex flow channel.Based on the cavitation flow pattern,applied the visualization experiment to the fuel injector control valve structure flow channel to acquire the cavitation position image and validated the results with numerical simulation.Analyzed the cavitation flow of fuel injector control valve and proposed a theory to separate the cavitation area and key sealing area to avoid the cavitation damage to sealing area.Designed a new control valve structure named convergent model.Compared the origin model and convergent model with experiment and numerical simulation.The results had shown that convergent model could effectively reduce the cavitation intensity near the sealing annulus.To study the effect of cavitation to fuel injector flow capacity,chose a square shape nozzle as research object,defined discharge coefficient and contraction coefficient.Studied the influence of cavitation to flow capacity,especially to contraction coefficient by 3-D CFD simulation with experimental validation.The result has shown different trend with existing research.To follow the development of intelligent manufacturing and intelligent diagnosis system,we would like to use other signal like noise,vibration or pressure fluctuation instead of photos of visualization experiment to represent the cavitation flow status in real fuel injector systems.The cavitation cloud shedding phenomenon was chosen to be put into experiment with high speed photography and image processing using Lab VIEW.Some basic characteristics of cavitation cloud shedding were acquired.The main conclusions are listed below:1.The visualization experiment table based on similarity principle could effectively capture the cavitation flow characteristics and represent the flow pattern of the real fuel injection system.2.The convergent structure design of control valve could effectively reduce the cavitation intensity near seal annulus,which is a feasible optimization method.3.The contraction coefficient value of nozzle depends on the cavitation flow status.There is an optimized L/D ratio of nozzle that has the largest flow capacity.4.The cavitation shedding frequency depends on inlet pressure and the frequency signal could provide method to detect invisible cavitation.