| In recent years,with the gradual development of diesel engines in the direction of high strengthening and high power density,the piston ring-cylinder liner working environment as a key component of diesel engine has become more and more demanding;At the same time,with the deepening of various advanced fuel injection technologies,as well as the application of fuel injection strategies such as the increase of injection pressure,the advance and delay of fuel injection timing,the phenomenon of lubricating oil dilution has gradually attracted attention.Lubricating oil dilution refers to the phenomenon that part of the fuel oil that is not involved in combustion and the exhaust gas generated by incomplete combustion are mixed into the oil pan along the cylinder wall,resulting in the dilution of lubricating oil,which will worsen the lubrication environment of the cylinder liner and affect its tribological properties.Therefore,it is necessary to study the tribological properties of piston rings and cylinder liners under the influence of different factors,and to analyze the reliability of cylinder liners and predict wear life based on the lubricating oil dilution phenomenon.Firstly,this paper adopts a simulated test method,using the previous complex friction and wear testing machine as the platform,taking the piston ring-cylinder liner interception of diesel engine as the sample,extracting the friction coefficient,wear amount and wear surface morphology as the characterization parameters,and exploring the influence of different proportions of fuel mixed with different speeds and loads on the tribological properties of piston rings and cylinder liners.The test results show that the introduction of a small amount of fuel oil in the lubricating oil will reduce the anti-friction and anti-wear performance of the lubricating oil,and the more fuel is mixed,the more significant the adverse effect,and the friction coefficient and wear amount of the cylinder liner increase with the increase of the working load,and decrease with the increase of the speed.Therefore,the engine is conducive to reducing the frictional wear between the piston rings and cylinder liners under the conditions of low load and high speed and low lubricating oil dilution rate.Secondly,in order to avoid the problems of long time,large workload and high cost of traditional life test,the accelerated degradation test is used to evaluate the reliability of cylinder liner and predict the wear life of the cylinder.Based on the failure form and wear mechanism of the liner,the accelerated degradation model of the liner based on the Gamma random process and the polynomial acceleration equation is established,and the wear degradation data and the failure threshold of the liner are combined to obtain the wear life characteristics and reliability indicators of the liner under different lubricating oil dilution rates.The results show that the failure process of cylinder liner under high dilution rate level is more rapid,and the wear life is smaller,taking a certain model of medium-speed cylinder liner working in the environment of6% lubricating oil dilution rate as an example,its average life is 32700 hours,90% reliability life is 32400 hours,and 75% reliability life is 32600 hours.For this model of medium-speed machine,it is recommended to monitor the working state of the cylinder liner when it reaches32600 hours to avoid excessive wear to ensure the normal operation of the engine.Finally,the AD test and t-test method are used to test the goodness-of-fit test and parameter consistency test of the normal distribution of parameters to verify the rationality of the cylinder liner accelerated degradation model.The area ratio method is used to verify the consistency between the life prediction value obtained by accelerated stress extrapolation and the test standard value,so as to verify the validity of the cylinder liner life prediction results based on the accelerated degradation test. |
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