Performance Prediction In Dry And Wet Composite Air Filter For Diesel Engine

Air filter is an air filtration components of diesel engine air intake system,its purpose is to filter dust and other impurities in the air entering the engine,so as to reduce the wear between piston group and cylinder,ensure adequate and clean air in the cylinder,and prolong the service life of the diesel engine.The filter resistance and filter efficiency directly affect the power,the fuel consumption and the reliability and durability of the engine.This thesis intends to make a research on the performance of dry and wet composite air filter,which mainly analyzes the pressure drop of the filter,in order to provide correlative theoretical direction to the designers.This thesis uses theoretical approach,combining with CFD numerical simulation method.The filter paper in the fine filter is simplified as pleated filter and the filter resistance of the filter paper is studied.Based on FLUENT,the simulation of the flow field in the pleated filter is carried out more detailed.The flow field visualization is done with the pressure atlas and velocity vector,the pressure and velocity distributions are gotten.The results show that when the air flows through the filter paper,the pressure is larger,and the pressure drop in the fine filter is mainly caused by the filter paper.The classical filtration theory of fiber is applied to the filter paper,filter mechanism of the filer paper is analyzed,and the main influential factors of the fiber filter resistance are summed up as: fiber media fill rate,filter media thickness,fiber diameter,filtration velocity and so on.In thesis,a method is proposed to calculate pressure drop in the dry and wet composite air filter,the filter is simplified into a series of different diameter pipes,a new series model is established in the dry and wet composite air filter.The non-circular cross section pipeline is simplified into a circular cross section pipeline,with the equivalent diameter of non-circular cross section pipeline to replace the pipeline diameter;the steel wire mesh and filter core in the air filter are simplified into porous media.The total pressure drop is the sum of the friction head loss and local pressure loss along the flow paths.This model is expressed as a function of the frictional resistance coefficient ?,local resistance coefficient ?,penetration rate K,fluid density ?,fluid velocity v and so on.The conclusion of this thesis,especially the calculation method of pressure drop across dry and wet composite air filter can offer available instruction to the designers,the semi-empirical formula for the pressure drop of dry and wet composite air filter can be used to predict the service life of the filter.