Vibration Fatigue Analysis Of Exhaust Manifold Of A Marine Diesel Engine

The exhaust header is an important part of the marine diesel engine.It is installed on the diesel engine frame and connected to the exhaust hole of the marine diesel engine head.The exhaust manifold collects the combustion chamber exhaust gas and participates in the diesel engine booster system work,so the stability of the exhaust manifold is directly affects the working performance of marine diesel engines.The research object of this paper is the exhaust manifold on a marine diesel engine.The main research content is the vibration fatigue failure of the exhaust manifold.Exhaust manifolds are hardly structurally damaged under dead load conditions.However,diesel engine moving parts,such as crankshafts,pistons,connecting rods,camshafts,etc.,make the diesel engine vibrate during the trial operation of the marine diesel engine.The header is subjected to a cyclical impact load in this vibration environment and is prone to fatigue failure.Therefore,only static strength analysis of the exhaust manifold can not guarantee its stability,and it needs to conduct additional research on dynamic response,vibration fatigue and other aspects.The main research contents and conclusions of this article are as follows:(1)Modal analysis of the exhaust manifold is performed using finite element software.Three-dimensional model and finite element model of the exhaust manifold of a marine diesel engine are constructed.The free-mode and constrained modes of the exhaust manifold are calculated using ABAQUS software.The structural vibration of the exhaust manifold is analyzed under unconstrained and working conditions.Intrinsic characteristics,from the results of free modal calculations,it can be seen that the stiffness of each bracket of the exhaust manifold is poor,and the overall torsional stiffness of the exhaust manifold is poor from the results of the constraint modal calculation.(2)Harmonic response analysis of exhaust manifolds was performed by using ABAQUS software.The theoretical basis of the harmonic response analysis is studied;the finite element model of the marine diesel engine is constructed to calculate the excitation load of the harmonic response analysis;the harmonic response analysis of the exhaust manifold is performed using the modal method and the results are calculated from the middle row.The response shape of the gas manifold analyzes the structural defects of the exhaust manifold;the structure is optimized based on the results of the harmonic response analysis,and compared with the original model to analyze the optimization of the structure to improve the structural stability of the exhaust manifold.(3)Vibration fatigue analysis of the exhaust manifold.The fatigue analysis theory and the current fatigue analysis methods and theoretical basis were studied;the vibration fatigue of the marine diesel engine exhaust manifold was performed through the power spectral density function of the excitation load,the S-N curve of the exhaust manifold and the related parameters.Describes the exhaust fatigue failure of the header manifold.The cause of fatigue failure is analyzed.The exhaust manifold generates cyclic deformation in the low-order mode shape and causes the vibration fatigue failure of the contact between the support plate and the base of the exhaust manifold support.