| In order to meet the requirements of strict emission regulations and fuel economy standards,the injection pressure of gasoline direct injection engine(GDI)continues to increase,and the spray impingement phenomenon is difficult to avoid,resulting in the deterioration of particulate matter and unburned hydrocarbon emissions.Previous studies have found that elliptical orifice can reduce the spray penetration and improve the atomization quality.Aiming at the problem of spray impingement in gasoline direct injection engine,this paper takes the elliptical nozzle of GDI engine as the research object,and adopts the method of combining experiment and numerical simulation to study the spray impingement characteristics of elliptical nozzle with different shapes and under different impingement conditions,which provides theoretical support for the application of non-circular nozzle and the improvement of spray impingement process in GDI engine.In this paper,the GDI elliptical spray impingement test platform was built based on the principle of shadow method,and the elliptical spray impingement experiment was carried out.The numerical simulation model of elliptical nozzle spray impingement on GDI engine was established by Converge software.By comparing the test and simulation results of elliptical nozzle spray impingement,the verification of numerical model was completed.The geometric models of elliptical nozzles with different aspect ratios of 2,3,4 and 5 were defined as E2,E3,E4 and E5,respectively.The influence of GDI nozzle shape on spray impingement characteristics was studied.The results show that: compared with circular spray,the surface area of elliptical spray increases,the speed of spray development slows down and the time of impingement delays with the increase of the aspect ratio of elliptical nozzle.The spreading radius of the circular spray is the largest.Compared with circular spray,elliptical spray has stronger entrainment ability,resulting in obvious wall vortex structure and stronger momentum exchange,which promotes the upward movement of fuel droplets.The entrainment height of elliptical spray is higher than that of circular spray.The wall film mass and wall film area of elliptical spray were smaller than those of circular spray.The wall film mass of elliptical spray E2,E3,E4 and E5 decreased by 6.01 %,11.3 %,15.79 % and18.5 % respectively compared with circular spray.With the increase of the aspect ratio of the nozzle,the average thickness of the wall film of the elliptical spray decreases first,and then increases.The average thickness of the wall film of the elliptical spray E4 is the smallest,which is 9.34 % lower than that of the circular spray.The effects of impingement conditions(injection pressure,impingement distance,wall inclination angle and the wall temperature)on the impingement characteristics of GDI circular spray C and elliptical spray E4 were studied.The results show that with the increase of injection pressure,the momentum of circular spray and elliptical spray increases,and results in the increase of the spreading radius and entrainment height.The increase of injection pressure leads to the decrease of wall film mass and average wall film thickness.When the injection pressure increased from 20 MPa to 30 MPa,the average film thickness of circular spray C and elliptical spray E4 decreased by 35.34 % and 36.83 %,respectively.The film mass of elliptical spray E4 is always less than that of circular spray.With the increase of impingement distance,the momentum of circular spray and elliptical spray decrease,which lead to the reduce of the spreading radius and entrainment height.With the increase of impingement distance,the average thickness of wall film keeps increasing.When the impingement distance increases from 30 mm to 70 mm,the wall film average thickness of circular spray increased by 22.46 % and the wall film average thickness of elliptical spray E4 increased by 18.2 %.With the increase of wall inclination angle,the downward velocity of circular spray C and elliptical spray E4 increase,and the entrainment ability and momentum of the spray are enhanced.The spreading radius and entrainment height of circular spray and elliptical spray increase,and the wall film mass and average thickness decrease.When the wall inclination angle increases from 0° to 30°,the average film thickness of circular spray decreases by 21.82 %,and that of elliptical spray E4 decreases by 19.6 %.Increasing wall temperature can promote the development of impinged spray,improve the evaporation of wall film,and reduce the mass and average thickness of wall film.When the wall temperature increased from300 K to 420 K,the wall film mass of the circular spray decreased by 43.92%,and the average thickness of the wall film decreased by 20.7%;the wall film mass of the elliptical spray E4 decreased by 46.87%,and the average thickness of the wall film decreased by 18.73%. |
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