Research And Structure Optimization On Internal Flow And Atomization Performance Of Diesel Injection Nozzle

The number of motor vehicles in China is increasing,and the environmental pollution caused by vehicle exhaust is becoming more and more serious.In order to meet the requirements of strict emission regulations and implement the "carbon peak and neutrality" strategic goals,it is necessary to take scientific and technological innovation as the guide,reduce exhaust emissions pollution and improve energy efficiency,reduce carbon emissions.Fuel injection nozzle is a key structural component of diesel injector.Its internal flow performance and atomization performance determine the quality of engine fuel injection system,and affect the combustion and emission of diesel engine.Therefore,it is of great significance to study the flow performance of diesel in nozzle and fuel atomization performance to reduce exhaust pollution and carbon emission.However,it is very difficult to conduct experimental research because of the small size of the injection nozzle and the large velocity and pressure of diesel in the nozzle.Therefore,the Computational Fluid Dynamics(CFD)software Fluent is used to numerically simulate the injection nozzle,which can easily and effectively study the internal flow and spray process of diesel.In this thesis,CFD software Fluent is used to simulate the internal flow,cavitation phenomenon and spray process of the injection nozzle of high pressure common rail diesel engine,and the structural parameters of the nozzle are optimized.The Mixture multiphase flow model,Schnerr-Sauer cavitation model and Realizable k-ε model were used to build the vapor-liquid two-phase flow model in the nozzle.The flow parameters at the nozzle outlet were taken as the initial conditions of spray simulation and discrete phase model was used to build spray calculation model.Then,the numerical model coupled the diesel injection nozzle flow and the spray was established.The influence of different structure parameters and working parameters on internal flow characteristics and syray characteristics was studied.Results showed that with the increase of orifice diameter,the thickness and volume of cavitation micelle inside the nozzle increase,cavitation intensity is enhanced,outlet mass flow rate increases with the increase of effective circulation area,due to the inertia to the increase of jet,spray penetration is also increasing,the diameter of the first continuous jet increases,resulting in a larger droplet diameter after the outlet crushing;Reducing the orifice length can improve the atomization performance,but at the same time,the cavitation phenomenon in the nozzle is intensified and the flow performance is affected.The existence of the round radius of the entrance can effectively weaken the cavitation phenomenon in the orifice and improve the atomization performance.The higher the inlet pressure is,the larger the volume of fuel vapor in the nozzle will be.The development of cavitation can be inhibited by increasing back pressure.Central Composite Design(CCD)is used to extract sample points within the given range of nozzle structure parameters.Response surface methodology(RSM)was used to construct the surrogate model of the internal flow and spray process of the nozzle,and the nozzle structure was optimized by multi-objective genetic algorithm NSGA-Ⅱ.After optimization,Both the flow performance and the atomization performance are improved.