Study On Dropplet Size Distribution Of Diesel Spray Based On Laser Sheet Drop-sizing

As for diesel engine,spray characteristics determine the mixing process of fuel and air in chamber,which is an important factor to determine the combustion quality,and combustion quality directly determines the quality of the fuel economy and emissions,so the research on the characteristics of spray is very important.PLIF(planar laser induced fluorescence)and LSD(planar laser dropsize)technology as means of optical testing technology,can provide various macroeconomic and microeconomic parameters about spray,such as spray tip penetration,distribution of fuel concentration in spray,this paper will research the influence of injection pressure,ambient pressure and diameter of the nozzle on diesel spray characteristics basising of those two technologies.First,in order to get the concentration and SMD distribution of diesel spray,this paper built PLIF and LSD test platform.The relationship of spray concentration and fluorescence intensity was calibrated basing on the characteristic of diesel solution and spray,and the coefficient of Kc was got which can establish the contact of spray concentration and fluorescence intensity.The relationship of SMD and LIF/MIE intensity was calibrated basing on the data from PDA,and the coefficient of K was got which can establish the contact of SMD and LIF/MIE intensity.Secondly,macro spray characteristic parameters is studied in this paper.The influence of injection pressure,ambient pressure and diameter of nozzle on spray tip pentration,spray angle and spray volume was studied,which was found that the increase of injection pressure and nozzle diameter can promote the growth of the volume and improve the ability of the spray diffusion within the space,and the ambient pressure will limit the development of the spray in the axial direction leading to reduce of spray volume.Combining with the liquid jet breakup theory,the change of injection pressure and aperture will influence the flow state inside the orifice,while the change of ambient pressure will change aerodynamic force around the oil column at the outlet,so the crushing process oil column was changed.And then,the droplet was influenced by inertial force and aerodynamic force.At last,microscopic characteristics parameters of spray is studied in this paper.The influence of injection pressure,ambient pressure and diameter of nozzle on spray concentration and SMD distribution,which was found that the concentration distribution is more uniform and SMD is smaller,along with the increase of injection pressure,at the same time the maximum equivalence ratio of spray is decreased,that is to say the atomization of diesel is batter with the increase of injection pressure.With the increase of ambirnt pressure spray equivalent ratio decreases,which is mainly because the environment density increases,causing the mass ratio of fuel and air in spray decreased.While the SMD increased,for the spray volume becomes smaller,the droplet number density of spray increases and leads to the collision probability of oil droplets increasing,and oil droplets make polymerization SMD becomes larger.With the increase of nozzle diameter,spray concentration increases,as the nozzle diameter increases the mass flow at nozzle exit and decreases the spray cone angle,so spray the equivalent ratio increased.At the same time,the corresponding SMD increases with the increase of nozzle diameter,that is to say,the increasing of nozzle diameter can improve the spray equivalence ratio but poor quality of atomization.