Fatigue Life Study On The Valve Of A Certain Marine Diesel Engine Based On Multibody Dynamics

Valve-Valve seat is an important friction pairs for the valve train system of diesel engine.The wear and fatigue facture on valve is one of the main factors affecting engine performance.The valve,especially the exhaust valve is working under the impact of alternating load,high temperature and combustion atmosphere.Due to the severe working conditions,the problems of valve failure is increaseing and the degradation of dynamic performance is becoming worse.So it`s of great importance to study the dynamic and wear of valve.The research of this paper is based on a certain type of marine diesel engine,in this paper we establish the flexible multi-body model of the valve using the theory of finite element analysis(FEA).ANSYS is used to do dynamic analysis for the valve at different speeds and offset seat situations.The peak stress has been observed at the maximum cylinder pressure,meanwhile the velocity of the valve also has some contributes to the stress.Offset seat causes the valve stem bend and the valve stress increases rapidly.The temperature of the exhaust valve is higher than the inlet valve,and the stress of the exhaust valve is double of the inlet valve.After the dynamic analysis,the fatigue life of the valve is analysed by using Designlife.The analysis shows that the fatigue facture is focused on the head of the valve.The distribution of fatigue hot spots also explains the cause of the crack on the valve.The fatigue life of the exhaust valve is about half of the inlet valve,meanwhile the ultimate tensile strength(UTS)of the material has a great influence on the fatigue life.In this paper,we also do the modal calculation and dynamic analysis for valve springs.The modal calculation shows that the spring won`t resonate during the working process.Vibrating is observed in the dynamic calculation,and the spring strength meets the design requirement.The flexible multibody model we used in this paper provide some references for the research of valve dynamics.The fatigue life results has given some suggestions to the maintenance of this diesel engine.