CFD Analysis of Oil/Gas Flow in Piston Ring-Pack

The oil consumption and blow-by are complex phenomena that need to be minimized to meet the ever changing modern emission standards. Oil flows from the sump to the combustion chamber and the blow-by gases flow from the combustion chamber to the crank case. There are several piston rings on the piston, which form a ring-pack. The ring pack has to be efficiently designed to minimize the oil consumption and blow-by. Since it is difficult and extremely costly to conduct experiments on every series of engines to check for the blow-by and oil consumption, a CFD analysis can be performed on the ring pack to study the blow-by and oil-consumption characteristics. In the CFD analysis described here, the region considered is between the compression chamber and the skirt, between the piston (including the rings) and the cylinder liner. The 3D CFD analysis was conducted for the engine running conditions of 5000 rpm and load of 13.5 kPa, for a 2.4L gasoline engine. The inertia force was provided as a body force term for the fluid domain to simulate the effects of the direction change of the piston. The effects of the position of the rings in the grooves and the position of the end gaps on blow-by and oil consumption were studied using commercially available CFD software. The position of the rings is assumed either at the bottom, at the top or at the middle of the ring groove. Due to the complexity of CFD dynamic meshing, ring motion is not modeled. The studies for ring position is intended to bound the flow behavior, and provide an estimate, along with 2D ring dynamics analysis, to the flow path. The final results of the study helped in a better understanding of blow-by and oil consumption mechanism in the ring pack.