Study On Near Field And Full Field Characterization Of Diesel Spray

The atomization characteristic of diesel directly affects the combustion process and emission characteristic of diesel engine.In order to understand the memory relation between the characteristics of near field spray and full field spray with the spraying environment during injection,the spraying process under different experimental conditions are studied with the help of micro-amplification and Schering-Mie scattering technology,and the characteristic parameters of the spraying were extracted with the self-made spray image processing program.The main conclusions are listed as follows:In the initial stage of injection,the near field spray penetration is accelerated,the spray head and liquid column area are broken.Among them,the breakup time of liquid column area is later than that in the head and then an increased umbrella-shaped head is formed,coupling with stripped fuel filaments during injection.The larger the injection pressure is,the larger the area of fuel droplets distributes at the same injection timing.With the outflow of the cavitation area in the nozzle hole,the width of the spray bunches increases obviously,the columnar shape disappears gradually,and the near field spray cone angle increases rapidly.At the ambient pressure of 4.5MPa,the time of the liquid column breakup is advanced from 72?s to 36?s when the injection pressure is increased from 80 MPa to 140 MPa.At the injection pressure of 120 MPa,the time of the liquid column breakup is delayed and the penetration and spray area are reduced obviously when the ambient pressure is increased from 2.5MPa to4.5MPa.When the aspect ratio of the nozzle hole decreases from 6 to 5,the penetration of the initial spray increases,the breakup time of the spray liquid column is advanced,the cone angle of the near field spray increases,and more symmetrical distribution of fuel droplets relative to the center line of the spray.At the end stage of injection,the near field spray cone angle decreases rapidly.With the increase of oil injection pressure,the number of fuel wire decreases and the particle size of fuel droplets after breakup becomes smaller.In the high temperature environment,the gas and liquid phase fuel flow downstream simultaneously in the initial stage of injection.When fuel evaporation enters the quasi-steady state stage,liquid phase penetration reaches its maximum value and does not increase.Under high injection pressure,the liquid phase fuel is more likely to deviate from the axis and produce unstable fluctuation.With the increase of time after injection,the growth rate of gas phase penetration decreases gradually.When the ambient pressure is 3MPa and the injection pressure is increased from 120 MPa to180MPa,the cone angle and penetration of gas and liquid phase spray are increased,but the spray cone angle is slightly increased,and the average difference of the stabilization stage is within 2°.The spray area of gas and liquid phase increases with the increase of injection pressure,but the liquid phase spray area changes slightly.When the injection pressure is 150 MPa and the ambient pressure is increased from 3MPa to5 MPa,the spray shape is gradually transformed from the fine and long type to the coarse and short type,and the cone angle of gas and liquid phase spray increases,but the spray area and penetration decrease.With the increase of ambient temperature,the cone angle and area of liquid phase spray decrease,but the effect of gas phase spray is very small.When the ambient temperature increases from 550 K to 750 K,the liquid phase penetration decreases from 40 mm to about 23 mm,and the higher the ambient temperature is,the less sensitive the liquid phase penetration is to the temperature.