Performance Analysis And Optimization Of Natural Gas Engine Valve Train

Valve train is one of the most important devices that affect the engine performance. The power performance, emission performance, noise and vibration of engine are mostly affected by its stability and accuracy. The rational valve train could ensure good volumetric efficiency, meanwhile, it would guarantee the stability of the engine, reduce abrasion of the components and parts, decrease the noise and vibration, and prolong service time of the engine. The optimization of cam profile is one of the most valuable methods to ensure the excellent performance of valve train.In this paper, the author researched the irrationality of valve train of a four-valve natural gas engine, and imitated the kinematics and dynamics of original valve train, and then found out the existing problem, Finally, optimize the cam profile while meet the requirement of engine performance. Details as follow:(1) The kinematics and multi-mass dynamics model of valve train was established based on the AVL Excite Timing Drive software. The stiffness and other parameters required for the model have been obtained by Mathematic calculation method and finite element method.(2) The below problems of original valve train were summarized after simulating analyzed: The maximum contact stresses between charging, exhausting cam and tappet exceeded the allowable value; The greatest jerk value of intake valve was oversize and intake valve crash impact was big; the rebound phenomenon and flying-away phenomenon existed in cam follower.(3) The influence factor of polydyne cam was analyzed. An optimization solution for charging and exhausting cam profile was proposed based on original valve train problem. The intake and exhauste cam profile was confirmed after compared different solution of kinematics and dynamics performance.(4) The optimized valve train performance was compared with the original one and the conclusion as follow: the ample factor of cam profile on intake and exhauste valve increased 2.7%, 7.5% respectively after optimized, the maximum contact stresses between cam and tappet reduced 38.6%, 15.5% respectively, the lubrication performance was improved, and the phenomenon of big valve crash impact, rebound and flying-away as well.(5) The working process model of natural gas engine was built, the volumetric efficiency of optimized engine improved 0.7% at the rated speed, the flow of combustible mixture increased 4.44kg/h, the torque enhanced 6.6Nm, the power rose 1.8kw.