Research On Influencing Factors And Mechanism Of Seal Performance Of Piston-Ring Group-Cylinder Hole Friction Pair In Diesel Engine

With the enhancement of the diesel engine,the accompanying sealing problems such as oil consumption of piston-ring group-cylinder friction pair and gas leakage in cylinder are also becoming more and more significant.Sealing performance has become one of the severe problems faced by the research and development of high-efficiency and clean diesel engines.To this end,an in-line four-cylinder four-valve high pressure common rail diesel engine is taken as the research object,and the sealing performance of the piston-ring group-cylinder liner friction pair is systematically studied by the combination of theoretical analysis,simulation and experimental research.It provides certain theoretical and technical support for the improvement of sealing performance and independent design of high-efficiency and clean diesel engine.The main research contents are as follows:(1)Study on heat distribution and working deformation of aluminum piston in diesel engineThermal barrier coating technology can effectively solve the problem of excessively high temperature in the aluminum alloy piston head.The temperature field of the piston is analyzed by experimental testing and simulation.The analysis shows that as the thickness of the ceramic layer increases,the thermal barrier coating’s thermal insulation effect gradually increases,and the temperature of the top surface of the piston body decreases in the range of 3.7℃～5.3℃.The radial working deformation showed a decrease of 0.004～0.006 mm.The radial thermal deformation of the piston in the direction parallel to the axis of pin hole is greater than in the direction per-pendicular to the axis of pin hole,and the difference in the magnitude of the change results in uneven thermal deformation of the piston,which can provide boundary conditions for further research on the influence of piston working deformation on sealing performance of piston-ring group-cylinder liner friction pair.(2)Study on working deformation and influencing factors of diesel engine cylinder linerAiming at the influence of bolt pre-tightening force,thermal load and working load on cylinder liner deformation,combined with cylinder head fire surface and cylinder liner test test and numerical simulation,the coupled model of assembly was analyzed by using the method of fluid-solid-thermal multi-field coupling heat transfer.Research shows that under assembly conditions,the deformation of the cylinder liner gradually decreases from the top of the cylinder liner to the bottom of the cylinder liner,and the comprehensive deformation of the cylinder liner after the application of interference increases nearly twice.Under the action of thermal load,the maximum comprehensive deformation of the cylinder liner increased by about0.005 mm after the interference was applied.Under the coupling action of multiple loads,the deformation trend of the cylinder liner during the explosion of different cylinders was almost the same as that of the bolt pre-tightening force and thermal load applied separately.From the top to the bottom of the cylinder liner,the deformation was gradually decreas,the deformation of the second and third cylinders was smaller,and the deformation of the first and fourth cylinders near the free end was larger on both sides.(3)Experimental research and model validation of piston-ring group seal performance of diesel engineThe sulfur tracer method was used to measure the oil consumption of the researched diesel engine under different loads in the speed range of 1000-2400r/min.The results show that engine oil consumption is closely related to operating conditions.Increasing engine load will directly lead to an increase in oil consumption,especially when the load rate exceeds 90%.The maximum percussion energy of the piston appears at 12℃A after the top dead center of the work stroke;among the four cylinders,the fourth piston has the largest percussion energy,and the maximum percussion energy reaches 0.23N·m.In the entire working cycle of the engine,each cylinder has two air leakage peaks,the main peak is between 60℃A and 90℃A,and the secondary peak is between 450℃A and 480℃A.Of the total oil consumption in the engine’s cylinder,the wall evaporation accounted for the highest proportion,reaching 86.4%;the top ring oil rejection was the second,reaching 13.2%.(4)Study on influencing factors and mechanism of seal performance of diesel engine piston assemblyThrough the establishment of a piston-ring group-cylinder liner friction pair oil consumption and air leakage simulation model,the working deformation of the thermal barrier coating piston,the working deformation of the cylinder liner,and the relationship and change law of the structural parameters of the piston and piston ring on the sealing performance of the piston assembly are studied.The results show that the heat distribution of the piston has a great influence on the oil consumption in the cylinder,and the piston with thermal barrier coating can effectively reduce the oil consumption in the engine cylinder.The deformation of the cylinder liner directly affects the second-order movement of the piston,the amount of air leakage and the oil consumption,which need to be considered during the design.Piston pin offset has a greater impact on piston knocking energy,and has less impact on engine air leakage and oil consumption.The piston radial displacement,piston inclination angle,piston striking energy,air leakage and oil consumption increase with the increase of the cylinder clearance.The position of the convex point in the piston has an obvious influence on the second-order motion of the piston.The change of the piston head clearance changes the volume of gas in the fire bank area,and increases the contact time between the ring and the lower side of the ring groove,which can reduce the amount of air leakage.The piston ring closed gap has a greater impact on the engine air leakage.The top ring and the second ring closed gap have a more obvious impact on the air leakage,and the oil ring closed gap has a smaller effect on the air leakage.With the increase of the radial elastic force of the top ring,the engine air leakage and oil consumption show a gradual decrease trend.When the radial elastic force of the top ring is 32.7N,the air leakage reaches the minimum value,and the minimum value is14.6L/ min,the radial elastic force of the oil ring increased from 41.6N to 73.6N,and the total oil consumption in the engine cylinder was reduced by 3.7%.