Optimization Design And Simulation Study Of The Valve Mechanism Of Coal-bed Methane Engine

Under the background of energy crisis and environmental problems,coal-bed methane(CBM),as an alternative fuel,has attracted more and more attention.Coalbed methane(CBM)is a kind of energy with low environmental pollution.It mainly consists of methane,heavy hydrocarbon gas,nitrogen and carbon dioxide.Coalbed methane resources in Shanxi Province have large reserves,which can be exploited and utilized,reduce transportation costs and direct discharge pollution,and have a good resource and market base.In the process of retrofitting the spark plug ignition coal bed methane engine based on diesel engine,due to the problems of large valve impact and serious wear in the process of retrofitting the valve train of the original 396 diesel engine,the dynamic optimization of the cam profile of the coal bed methane engine is realized by dynamic calculation of the valve train of the original engine and reverse analysis of its cam profile.Valve cam is the key component of engine valve train,which can drive the valve to open and close at the same time,and complete regular movement.Therefore,it is particularly important to optimize the cam profile design of valve train.On the one hand,it can improve the seat impact of valve.on the other hand,it can effectively improve the valve time,increase the filling coefficient,and obtain larger power with a small amount of fuel consumption.In this paper,AVL-Excite Timing Drive software is used to establish the kinematics and dynamics simulation model of valve train,and the stiffness parameters,damping parameters and mass parameters of the model are calculated.Combining with the kinematics and dynamics evaluation indexes of valve train,the simulation analysis of the original valve train is carried out,including spring margin,valve jump,lubrication characteristics and valve seat force,etc.The causes of valve cam and valve wear of the original valve train are summarized,including the non-smooth acceleration curve of intake and exhaust valves,the excessive maximum jump value of intake and exhaust valves,and the cam type of intake and exhaust valves.The maximum contact stress between intake camand tappet exceeds the allowable stress of material.Aiming at the problems in kinematics and dynamics simulation of the original valve train,according to the design theory of cam profile,the optimal design of the original cam is carried out,including the equal acceleration-equal speed buffer section of the optimized rear intake and exhaust cams,the sectional acceleration section of the working section,and the asymmetric form of the opening and closing sections.Kinematics and dynamics simulation of the optimized cam profile valve train are carried out and compared with the original machine,and the wear of the valve seat is calculated and analyzed.Due to the limitation of time,the engine bench test is not used to verify,so the AVL-Boost software is used to analyze and simulate the working process of the optimized intake and exhaust cam profile.Compared to the original machine,the kinematics and dynamics performance of the optimized valve train are optimized and improved,the valve seating force and valve seat wear are reduced,and the economy and power of the valve train are improved through the simulation analysis and verification.