Investigation Oil Transport In Piston Assembly-cylinder Liner Based On SPH Method

The green transportation system is limited by material science,production process and supporting service facilities,so it is difficult to achieve real popularization in a short time.The internal combustion engine(ICE)using liquid fuel will probably continue to play a major role in the next few decades while reducing energy losses caused by the friction is still the most practical method at present to improve the efficiency of ICEs.Therefore,it is of great significance to study the oil transport mechanism of ICEs.In the ICE,the friction loss between the piston assembly and the cylinder liner accounts for the highest proportion,and the lubricating oil transport process piston assembly-cylinder liner is an extremely complex transient process,therefore,it is difficult to obtain effective test data by experiments.The numerical simulation provides an effective means for the study of the oil transport process in these regions.The oil transport process is accompany with complex multi-phase interaction,large deformation and free surface of fluids in the cylinder liner and piston skirt,on the piston land and between the cylinder liner and the piston rings.It is difficult to calculate the oil transport process with these behaviors based on Reynolds equation with multiple solutions or numerical oscillations.Smoothed particle hydrodynamics(SPH)is becoming an attractive method to investigate the lubrication issues due to its ability to handle large deformation problems and complex fluid,such as fluid problems with free surface,multiphase or moving boundary.In this paper,the Navier Stokes equation is used to describe the oil transport process,and for the first time,the weakly compressible SPH method is used to solve the oil transport process in different parts between piston assembly and the cylinder liner.The Couette flow is first simulated to validate that the accuracy of our proposed numerical approach.The mechanical friction losses of the piston assembly-cylinder system that can be reduced by the fully flooded hydrodynamics lubrication during the oil film developed between the piston skirt and the cylinder liner.The improved SPH method is then used to study such oil transport process with the piston reciprocating motion.The effects of the viscosity of lubricating oil,inertia force of oil film,the velocity of piston reciprocating motion,oil film thickness on oil transport are studied systematically.A surface tension model of inter-particle force is constructed with the characteristics that the absolute value of the maximum value and the minimum value of the coefficient equation is equal.A wetting model of solid surface is proposed which is combined with the improved coupled dynamic solid boundary and inter-particle force model.The oil transport process on the piston land is studied under the action of inertia force.The effects of the surface tension,viscous force and solid surface wettability and whether there is oil film on the piston land in advance on oil transport are studied systematically.The hydrodynamic behavior that is occurred by surface tension,viscous force and solid surface wettability of pressure distribution and particle distribution in different regions are discussed in detail.The coupling effects between piston ring and oil,cylinder liner and oil are described by the improved coupled dynamic solid boundary.Considering the second-order motion of piston ring,the oil transport process driven by piston ring motion is explored.The effects of inertia force and viscosity force on the distribution of oil,pressure and velocity field are systematically studied.The results are compared with Moving least squares in terms of the distribution of oil,the shape of free surface and the movement of vortices.The hydrodynamic behavior of the movement of vortices,the separation,fusion and accumulation of oil around the piston rings are discussed thoroughly.The pressure distribution around the piston ring,the pressure change with time at the designated monitoring points around the piston ring,the pressure distribution near the cylinder liner are studied systematically.The evolution process of the free surface of oil film is studied in comprehensively.We provide an effective calculation method for the lubrication of internal combustion engine.This method overcomes the difficulties of numerical oscillation and interface tracking in traditional methods.Based on the study on the transport mechanism of oil film,it can guide the designation and development of new engine oil,guide the shape optimization of various components of internal combustion engine,then to provide better lubrication conditions for internal combustion engine.