Lubrication Modeling Method And Optimization Of Lubricating Oil Supply Strategy For Low-speed Diesel Engine Piston Ring Pack

Piston ring-cylinder liner friction pair was one of the key parts of high-power marine low-speed diesel engine,and the safety,reliability and economy of low-speed diesel engine was directly affected by its lubricating properties.In this study,the piston ring-cylinder liner friction pair of low-speed diesel engine was taken as the research object.Based on the coupling modeling of dynamics and tribology,the lubrication modeling research under the given lubricating oil supply condition was carried out,and comprehensively considering the loading characteristics of the lubricating medium,the thermal effect of the low-speed diesel engine and the influence of the lubricating oil supply strategy,established the piston ring pack lubrication model under dynamic flow boundary conditions and optimization research of the lubricating oil supply strategyBased on the force balance equation of the piston ring,combined with the piston ring kinematics model,fluid lubrication model,blow-by model,asperity contact model and friction calculation model,a coupling model of piston ring dynamics and tribology was established with sufficient oil supply.The reciprocating friction test machine was used to carry out friction force test,and the ultrasonic test technology was used to measure the oil film thickness on the diesel engine test bench,and the accuracy of the established coupling model was verified by the measured data.This model was applied to the piston ring-cylinder liner friction pair of low-speed diesel engine,and the results of the calculated gas pressure distribution,minimum oil film thickness,surface bearing capacity,friction force and friction loss were analyzed.Aiming at the problem of low-speed diesel engine injection lubrication,based on the coupling model of piston ring dynamics and tribology,a piston ring lubrication model considering the given lubricating oil supply condition was established with insufficient oil supply.Based on the conservation law of oil quality,the discretized explicit expression of the oil film thickness in the lubrication area was derived,and the lubrication solving area was determined in conjunction with the average Reynolds equation.The processing method of the squeeze lubrication term in the average Reynolds equation was discussed in different cases when the lubrication solving area changed.The minimum oil film thickness/average minimum oil film thickness and instantaneous friction loss power were selected to evaluate the effect of surface roughness and ring profile on the lubrication performance under different lubricating oil supply conditions.According to the supply of lubricating oil,a method to reduce the friction power loss was proposed by reducing the surface roughness of the cylinder liner by regions.Under the condition of given lubricating oil supply,the solid particle load theory was used to modify the force balance equation and friction force calculation equation of the piston ring,and a piston ring lubrication model considering the bearing characteristics of the solid particle was established.The effectiveness of the established model was verified by conducting a small sample test containing Si O₂micropowder in lubricating oil.This model was used to study the effect of solid particle properties on the lubrication performance of piston rings,and it was learned that as the solid particle equivalent diameter,mass concentration and yield strength increased and density decreased,the minimum oil film thickness,solid particle bearing capacity and total friction gradually becomed grown,when the solid particle equivalent diameter was greater than the minimum oil film thickness.By establishing the heat transfer analysis model of the water-cooled cylinder liner,the temperature field and thermal deformation of the cylinder liner were obtained,and the thermal boundary of the piston ring lubrication model was determined.Using the measured data of the viscosity of the lubricating oil and the predicted values of four empirical formulas of viscosity-temperature characteristics of the lubricating oil,the ASTM formula was finally selected for the characterization of the viscosity-temperature characteristics of the lubricating oil in the cylinder of the low-speed diesel engine.Based on the established lubrication model,the effects of the thermal boundary of the lubrication model and the viscosity-temperature effect of the lubricating oil on the lubrication properties of the piston ring were explored respectively.The results showed that the thermal effect of the low-speed diesel engine leads to a decrease in the minimum oil film thickness and the bearing capacity of the lubricating oil film,and an increase in the bearing capacity of asperities and solid particles;the effect of viscosity-temperature characteristics of lubricating oil on piston ring lubrication performance was greater than the effect of thermal deformation of cylinder liner on piston ring lubrication performance.Based on the relationship between the lubricating oil supply strategy of the low-speed diesel engine and the oil film thickness at the inlet of the lubrication area of the piston ring pack,combined with the above research,a lubrication model of the piston ring pack under dynamic flow boundary conditions was established,and the model was developed to be a lubrication performance simulation software of low-speed diesel engine piston ring group-cylinder liner friction pair.Using this software to carry out the optimization study of the lubricating oil supply strategy,it was found that the initial oil supply had the most significant effect on the lubrication performance of the piston ring pack;the influence order of various factors of the circulating lubricating oil supply strategy on the lubrication performance of the piston ring pack was the position,width,oil supply rate,and ratio.This conclusion was used to optimize the lubricating oil supply strategy of a low-speed diesel engine.