Research Of Cam Optimization And Influence To In-cylinder Flow Field For Small High-speed Gasoline Engine

As an important mechanism of engine, valve-train makes a great influence topower performance and economy performance of engine, and the camshaft is corecomponent of valve-train, design of camshaft is more important particularly. Theoptimization of intake cam is an effective solution for the low power performanceproblem of a150mL motorcycle engine, and this thesis analyzed the intake camprofile of this engine at the kinematics and dynamics perspective. This paperdiscussed cam profile design、CFD simulation、performance forecasting and testvalidating, and so on in detail.This paper introduced evaluation standard of valve-train and the points of camdesign, and valve-train model of a150mL motorcycle engine was built based on AVLTYCON. Through the kinematics and dynamics calculation, it is found that theoriginal valve-train prefers stability and reliability to intake capability, but the fullnessratio is0.49. A new cam profile for intake ability improvement purpose was designed,the fullness ratio increased to0.55, and other target all meet the requirement at thesame time.In this thesis,3D model of engine intake and compression stroke are built, andcalculation of two cam profile were finished with AVL FIRE. The results of the CFDsimulation demonstrate that law of flow filed in cylinder doesn’t change almost, butthe maximum tumble ratio and average turbulence energy increased16%and13.4%respectively, and the mass of circulating intake air increased1.5%, which mean thenew cam make a good influence to engine.Model of engine was built with AVL BOOST, and the engine performance withtwo cam profile projects were accomplished, the result indicates that the powerperformance have a great improvement after the cam profile optimization, and theresults of dynamometer test with two camshafts validate the forecast, the power andtorque curve have a obvious improvement during the whole rotate speed range. Themaximum power and torque of the engine increase3.8%and4.4%respectively, andthe effects at low speed are more remarkable, the power and torque have5.8%and5.7%improvement at4000rpm.