| With the improvement of product performance requirements and the need for national low-carbon economic development,the internal combustion engine,as one of the main power plants in modern society,has a significant increase in power density,which brings the challenge of high thermal load and high explosion pressure.The piston as one of the core parts of the internal combustion engine,whose top is affected by the high temperature and high pressure working medium in the combustion chamber directly,its reliability has been a target of numerous scholars and experts.The three-dimensional simulation is used to analyze the combustion in the cylinder to deal with some issues remained,and the stress distribution of the piston is obtained by the finite element method in this paper.The life of the piston in rated condition is estimated by the simulation results of different accelerating conditions to evaluate the reliability of the piston.At first,there are some research on boundary conditions of the piston top with the empirical formula.In contrast,3D CFD software is used to simulate the situation of the combustion chamber in a cycle in this paper,which not only can assess conditions of flow,heat transfer and combustion in cylinder,but also gain the more accurate temperature and the heat transfer coefficient distribution of the piston top surface from simulation results compared with empirical formula method.Then cylinder pressure curve is calibrated with the results of 1D simulation to ensure that 3D simulation model is basically accurate and the simulation results are regarded as the boundary conditions of the piston top.Secondly,the temperature field and the stress distribution of the piston in the condition of thermal load,mechanical load and thermal-mechanical coupling load are calculated in Abaqus using simulation results from the CFD software combined with the experimental data,experience setting.The simulation results show that the temperature of the exhaust side is generally higher than that of the inlet side due to the turbulence and the intake air cooling in the cylinder,so that the thermal stress is larger and the maximum value is reached on the inner edge of the second ring of the exhaust side.The mechanical stress has a maximum value in the upper part of the piston pin because of the contact with the piston pin boss.The maximum stress value of the piston appears in the second ring,which is the result of the stress superposition of the two loads under coupling load.In consequence of the piston pin material,the two stresses are offset,and the stress is relatively small.Finally,the fatigue life of the piston under different accelerated conditions calculated by using the simulation results is used to fitted in Matlab combined with the appropriate acceleration models which are chosen according to the relevant theory of the accelerated test.By comparing the simulation values and the fitting values,it can be seen that the fitting effect is good,and the fatigue life of the piston under the rated working condition is estimated by the fitting curve.Compared with the simulation values,the relative errors were 4.11%,2.66%and 7.91%respectively under the thermal load,mechanical load and coupled load,which are relatively small.It is consistent with the requirements of engineering use,thus the feasibility of Arrhenius model,inverse power law model and Eyring model is proved as the acceleration model under these three loads respectively.When there is actual fault data,it is necessary to analyze the distribution model to obtain the corresponding characteristic life,and then the life of the rated condition is estimated by using the appropriate acceleration model according to the situation.In conclusion,the way has a high prediction accuracy of the piston fatigue life using the piston top boundary conditions obtained from 3D CFD and the accelerated test theory in this paper,which is suitable for the project to assess the reliability of the piston. |
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