Numerical Study on Pressure Generation Mechanism of Oil Film under Oil Control Ring

To reduce oil consumption in reciprocating engines, many studies have been conducted on the mechanism and control of the upward transport of oil from the sump to the combustion chamber through the gap between the cylinder liner and compression rings, which is the main cause of oil consumption. Our research group has previously conducted experiments and numerical analysis elucidating the behavior of oil around the piston skirt and oil ring that forms the entrance for the upward transport of oil and is important in optimizing the amount of oil. However, many uncertainties remain regarding the pressure generation mechanism of oil under the oil ring and clarification is essential to establish a high-accuracy prediction method for oil consumption. In the present study, we demonstrated the pressure generation mechanism of oil under the oil ring by reproducing the flow field in the gap between the liner and piston skirt/underside oil ring using computational fluid dynamics (CFD). CFD was conducted with a simplified geometric shape model assuming a viscous two-phase (oil-air) flow and the interface between the oil and air was calculated using the volume of fluid (VOF) method. Mainly, we discussed the influence of an oil film thickness, area size of circumferential direction φ and skirt length on behavior of the oil-air flow and the time-variation of the pressure under the oil control ring (OCR).