Oil Transport in the Piston Ring Pack (Part II): Zone Analysis and Macro Oil Transport Model 2003-01-1953
Engine oil consumption is one of the primary interests for the automotive industry in controlling emissions and reducing service cost. Due to a lack of understanding of the mechanisms and flow patterns of oil transport along the piston, reducing oil consumption from the ring pack of internal combustion engines has been extremely challenging for engine manufacturers and suppliers. In work prior to this study (see Part I ), individual oil transport processes such as oil flows on the piston lands in both axial and circumferential directions, oil flows through the ring grooves and gaps and oil flows between the piston and the liner have been identified and characterized. One of the major difficulties remaining for oil transport analysis was the lack of description of how the oil transport mechanisms previously investigated affect, through the multitude of flow paths, the oil balance in the various sub-regions and the net oil flow toward the combustion chamber.
In this work, in order to have a comprehensive description of the routes of oil transport through the entire piston ring pack, a unique two-dimensional Laser-Induced Fluorescence (LIF) visualization system was used to examine the oil flow patterns in the upper piston region under a wide range of engine operating conditions. All major flow paths and mechanisms of oil transport along the piston were integrated into a macro oil transport model. It appeared that the rate at which oil is lost to the combustion chamber is mostly determined by the competing oil transport processes occurring on the piston lands. While the inertia force carries oil across the lands and through the ring grooves toward the top of the piston, the dragging action of the blow-by gases removes oil from the piston lands and recycles it to the crankcase. Additionally, dividing the ring pack in three zones, oil transport processes were analyzed region by region, emphasizing the effect of ring designs and engine operating conditions on the control of the oil supply to the most critical areas, namely, the top ring groove and the crown land. Eventually, the region by region analysis showed that there are three main locations where the rate of oil transport to the combustion chamber can be controlled:
The oil control ring which determines the oil supply to the third land and the part of the liner located between the scraper ring and the OCR (Oil Control Ring).
The second ring and its groove where the rate of oil transport from the third to second land can be controlled by detailed geometrical features and/or second ring flutter.
The second land where the balance between the oil supply and the gas-driven oil removal determines the total amount of oil accumulated on the second land and thus the rate of oil supply to the top ring groove.