Numerical Study Of Gas Flow And Its Influence Factors Of Diesel Engine Scavenging Process

With the shortage of oil resources and environmental problems becoming more serious,peoples’requirement of the performance of diesel engine is higher and higher.With6l21/31Marinemedium-speed diesel engine as an object, The scavenging process was studied by the method ofthree-dimensional numerical calculation. The flow field in cylinder along with the change of thecrankshaft rotation was studied, on this basis， the influence factors of flow field in cylinder ofscavenging process were discussed. For optimizing the gas flow in cylinder of this machine andproviding reference and guidance to improve the machine performance and fuel economy.Specificwork is as follows:(1)The numerical model of6l21/31marine medium speed diesel engine has been built by theAMESim software,and the one-dimensional simulation calculation has been calculated, the initialand boundary conditions for the gas three dimensional flow calculation in cylinder has beenprovided.(2)The6L21/31single cylinder diesel engine entity model has been built by PRO/Esoftware,and it’s divided into grid model.The transient three-dimensional numerical calculation onthe process of diesel engine’s scavenging has been done by FLUENT software, the variation of theflow field inside the cylinder with the different crank angle in the diesel engine of scavengingprocess was obtained.(3)The different factors that influence gas flow inside the cylinder in the process of dieselengine scavenging are analyzed.The flow field in the cylinder of scavenging process wasResearched through changing different valve overlap,revolving speed and the shape of piston top.The results show that:Gas backflow phenomenon of6l21/31was not occurred on the time ofinlet valve opening and exhaust valve closing through scavenging process; The wall near the gasexhaust in the cylinder was not cooled well,The temperature can be further reduced；At the end ofscavenging,the average gas pressure in the cylinder decrease first with the enlargement of theoverlap angle and then increase,while the average temperature is reduced before they are thesame.And airflow velocity inside the cylinder increase along with the enlargement of the overlapangle.The higher the revolving speed,the greater the average flow velocity of the gas.themaximum turbulent kinetic energy of low speed of revolution is lower than that of higher speed ofrevolution and the crank angle is smaller;Gas flows in bowl shape combustion chamber smootherthan that in ω shape combustion chamber,the turbulent kinetic energy is higher,too.ω type ofcombustion chamber forms more whirlpools;From the analysis of influence factors of flow field incylinder, conclusion can be drew that:Increasing this machine valve overlap Angle5°CA,it’s conducive to the machine cylinder scavenging,it’s conducive to improve the efficiency of airintake, it’s helpful to improve economy and power performance of the diesel engine.;Optimizingthe distribution parameters under different rotational speed, which can improve the performance ofthe diesel engine;Piston head shape affect gas flow in cylinder strongly at TDC,This effectdecreases with the increasing of cylinder volume.