Effect of piston ring geometries on lubrication and friction in diesel engine

Abstract

Lubrication and friction in piston rings are of a greater importance which has been receiving significant attention from tribologists for a long time. The main subsystems which contribute to friction include the ring-pack/liner, piston-skirt/liner, piston-pin/connecting-rod and connecting rod-crankshaft bearings. Piston rings are used in engines mainly to reduce leakage of gas in the combustion chamber and simultaneously provide a lubrication film in order to reduce friction during its motion. Wear between piston rings and liner is inevitable and therefore in order to reduce it, different types of ring geometries are being used which has its own advantages and disadvantages. Another major problem being faced during operation is that oil from the liner gets transported by pumping, reverse blow by, inertia and squeezing of oil due to ring dynamics into the combustion chamber. The present work focuses on to investigate different ring geometries and their effects on friction and lubrication oil consumption. It was found that Tangential force has an inverse relationship with Oil Film Thickness and Oil filling ratio. Top ring friction is high at Top dead centres due to boundary lubrication. Ring Barrel height has a direct relationship with asperity friction and an inverse relationship with Oil Film Thickness. Axial width is directly proportional to the wear of rings, which is due to the area exposed to back pressure on the rings exerted by gases from combustion chamber. Second ring closed gap has a direct relationship with Inter-ring pressure thus increasing reverse blowby. Rings with a Positive twist are found to be stable during operation. For this analysis, AVL Excite software is being used and results are validated with an experimental model.