Study On Mechanism Of Oil Flow On Piston Land Region Of Internal Combustion Engine

In this article, the main purpose is to study the lubricant oil transport on the piston land and related regions. By the driven mode of oil flowing on the piston land, here made two aspects to analyze the oil transport on the piston land, one is inertia force driven and the other is shear stress driven created by the gas flow.The lubricant oil inertia force results from the piston alternative accelerations and decelerations. Firstly, we introduced the momentum conservation Navier-Stokes equation of the viscous incompressible fluid to describe the oil flow pattern on the piston land. Then, the N-S equation was simplified according to the actual working conditions of the engine and the differential equation of the oil flow on the piston land driven by the inertia force was obtained as the parameters were determined. Finally, combined with the dimensional analysis method, a numerical model of the oil flow distance on the piston land was established. Through the qualitative and quantitative analysis, we find that the distance of the oil motion on the piston lands driven by the inertia force is determined by five parameters:the structure of the piston pack, the thickness of the uniform oil layer covering the land, the rate of oil supplying, the viscosity of the oil and the engine speed. Moreover, we also discussed the change of oil transport on the land with the different rate of oil supplying, engine speed and oil film thickness.The shear stress created by the gas flow at the surface of the oil layer is another driven force of oil flow on the land. According to the flow direction, the blow-by gases can be divided into circumferential and axial gas flow, they drive the oil flowing along the circumferential and axial direction of the piston. In this article, the gas flow model was firstly discussed. Then, we established an oil flow mode on the piston lands driven by the shear stress, and quantitatively calculated and discussed the oil motion on the land. As a result, we find that the factors that influence the oil flow on the land driven by the gas flow are the relative position of the gaps of the adjacent rings, the oil film thickness covering on the land, the land/liner clearance, the engine speed and load, etc. Moreover, when the piston rings move up and down along the internal wall of the liner, the effect of the oil scraping is inevitable, and it is also a main cause of oil transport and redistribution inside the cylinder which has certain influence for the oil flow on the land. In this article, we studied on the effect of the oil scraping, considering the influence of ring pack, and established a numerical model of oil scraping based on the calculation of minimum oil film between piston ring and cylinder. In addition, we also calculated the amount of oil scraped by the rings for a specific engine, and this provides not only an important reference to the oil transport in the cylinder, but also a clear basis of the oil supplying boundary status to calculate the more true oil film the piston rings and the liner friction pair.