Investigation On The Internal Flow And Spray Characteristics In A GDI Engine Injector With Elliptical Orifice

As the actuator of the fuel injection process of GDI,the injection nozzle's internal flow characteristics and atomization performance directly determine the formation quality of the incylinder mixture,which is the key to achieve efficient clean combustion of the engine.The existing research shows that the elliptical orifice has the potential to improve the atomization characteristics of jet and the mixing quality of oil and gas.Therefore,in this paper,the injector of the direct injection gasoline engine in the cylinder is taken as the research object,and the flow and spray characteristics of the elliptical injector of GDI engine are studied by combining numerical simulation and experimental research,which provides a theoretical basis for the application of elliptical injector in GDI engine.In terms of the flow in the elliptical orifice,the cavitation flow model in the elliptical orifice was established by using the VOF(Volume of Fluid)multiphase flow model,the Schnerr-Sauer cavitation model,and RANS(Reynolds-averaged Navier-Stokes)turbulence calculation method.Through the numerical simulation of the flow process in the elliptical orifice,the flow characteristics in the elliptical orifice and its influence on the flow characteristic parameters were studied.The results show that: compared with the circular jet hole,the cavitation distribution in the elliptical jet hole is asymmetrical,the length of the cavitation distribution in the long axial plane is shorter than that in the short axial plane,and the unique horseshoe-shaped cavitation pattern appears on the outlet section.The cavitation intensity in the elliptical orifice increases with the increase of the injection pressure and the decrease of the ambient backpressure.The volume fraction of the gas phase in the elliptical orifice is 20.2% smaller than that in the circular orifice,and decreases first and then increases with the increase of the length-axis ratio of the elliptical orifice,which reaches the minimum value when the length-axis ratio is 4.The turbulent vorticity,mass flow rate,flow coefficient and area coefficient at the outlet of the elliptical orifice are larger than that of the circular orifice,and all of them increase first and then decrease with the increase of the axial ratio of the elliptical orifice,and reach the maximum value when the axial ratio of the elliptical orifice is 4,in which the flow coefficient of the elliptical orifice is more than 2.7% larger than that of the circular orifice.In terms of the spray characteristics of the elliptical nozzle,based on using the femtosecond laser micro-drilling method to realize the fine elliptical nozzle processing,the spray characteristic test platform of the GDI nozzle based on the principle of Mie scattering was built,and the development of the elliptical nozzle spray through the acquisition and analysis of historical images,the influence of elliptical orifice shape parameters on the macroscopic characteristics of the spray was studied.The research results show that the spray penetration distance of the elliptical nozzle is shorter than that of the circular nozzle,and the maximum gap is 18.9%.The spray cone angle,spray projection area,and air suction volume is larger;compared to the elliptical nozzleE3,the spray penetration distance of the elliptical nozzle E4 is shorter,the maximum gap is 10.2%,the spray cone angle,the spray projection area,and the air suction volume is larger;As the injection pressure increases,the spray projection area and air entrainment volume also increase.Compared with the elliptical orifice E3,the elliptical orifice E4 has a lower frequency of axis changes,but the amplitude of the axis changes larger the spray projection area of the elliptical nozzle E4 and the larger the volume of air suction,it indicates that the use of the elliptical nozzle E4 can improve the quality of oil and gas mixing.In a word,the elliptical orifice can effectively inhibit the generation of cavitation in the orifice,enhance the flow performance of the orifice,improve the volume of air entrapment of the spray,and enhance the mixing characteristics,indicating that the elliptical orifice of the GDI nozzle can effectively improve the mixing quality of oil and gas.