Numerical Study Of Binary Diesel Droplet Collision Process

Drop collision is a physical phenomenon widely existing in nature and industrial production.In the actual working process of the engine,a series of collision processes will occur after the diesel droplets are ejected from the injector,causing the droplet size and velocity to change,affecting the combustion performance of the engine,and thus affecting its emission performance.Through detailed research on the physical process of diesel droplet collision,revealing its physical laws and collision mechanism,it can provide a useful reference for the optimization and improvement of the engine atomization system,and has important theoretical significance and industrial value.This article uses OpenFOAM open source computing platform,based on VOF(fluid volume method)method and adaptive grid technology,to conduct a detailed numerical study of the collision process of binary diesel droplets.First,in order to verify the feasibility and accuracy of the calculation model,the centripetal and eccentric collision processes of n-tetradecane droplets were simulated and compared with the existing experimental results;subsequently,different Weber numbers We and collision parameters B were developed.Under the study of the collision process of diesel droplets,three types of collision results of polymerization,separation and crushing were obtained.The physical process and formation mechanism of various types of collision results were analyzed.The statistical results of all working conditions were statistically analyzed to obtain The We-B diagram of the regional distribution of binary diesel droplet collision results is presented.Finally,the effects of droplet size,size ratio,bubbles and ambient pressure on the collision process are studied.The main research contents and conclusions of this article are as follows:(1)Concentric and eccentric collisions of binary diesel droplets of the same size:We:10-160;u0:0.8-8.48m/s;D0=200μm;Oh=0.0078.Three types of results of polymerization,separation and crushing were obtained.Among them,the critical Weber number We for the center collision polymerization and separation was 17.3,and the critical Weber number We for separation and crushing was 92.The difference between the eccentric collision of droplets and the collision of centripetal is that the deformation process is accompanied by obvious rotational movement.The energy conversion mechanism in the process of eccentric collision is also different from that in the process of centripetal collision.In addition to the conversion of surface kinetic energy into droplet energy and viscous consumption,a part of the kinetic energy is converted into the rotational energy of the droplet.(2)It can be seen from the regional distribution map of the collision results that with the increase of the collision parameter B,the critical Weber number We of aggregation and separation increases first and then decreases;the critical Weber number We of separation and fragmentation decreases first.The later increasing trend shows that within a certain range,eccentric collisions are more likely to cause droplet breakage.(3)Diesel droplets with diameters of D0=80μm,200μm,and 400μm,corresponding to Oh=0.025,0.0076,and 0.0039.The critical Weber numbers We are 28,17.3,and 13.It shows that as the diameter of the droplet increases,the Oh number decreases,the critical Weber number We of the polymerization and separation of the droplet decreases,and the droplet is more likely to separate.(4)When the droplet size ratio γ=1,2,and 3,the maximum Weber number We of the diesel droplet polymerization area is 17.3,48,and 80,respectively.It shows that as the droplet size ratio γ increases,the polymerization area increases significantly.In other words,within a certain range,the larger the droplet size ratio,the easier the polymerization will occur.(5)The collision law of bubble-containing droplets is significantly different from that of solid droplets.The critical Weber number We for the collision polymerization and separation of bubble-containing droplets with a diameter of 200μm is 65,which is higher than that of two solid droplets under the same conditions The critical Weber number We number 17.3 is obviously increased,which indicates that the presence of bubbles will cause the critical Weber number We of the polymerization and separation after the two droplets collide to increase,and the droplets are more likely to polymerize.(6)The influence of environmental pressure on the droplet collision process was studied.When the environmental pressure was 6 MPa,9 MPa and 12 MPa,the critical Weber numbers of polymerization and separation after droplet collision were 17.3,17.7,and 17.5,respectively.Under the environment,the change of pressure does not affect the critical Weber number of droplet separation.