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 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. Consequently, a thorough experimental characterization of oil transport processes is critical to 1) reduce lead-time and cost of new piston ring pack development, 2) provide the physically based oil transport models needed to develop analytical tools for oil consumption prediction.
In this work, a two-dimensional multiple-dye Laser-Induced Fluorescence (LIF) visualization system was successfully implemented in a diesel and a spark-ignition engine. Real time high resolution images of the ring pack oil distribution were acquired and analyzed for the entire range of operating conditions typically encountered by passenger car engines. Based on experimental observations, major oil flow patterns in the piston ring pack were identified and their mechanisms were characterized. Physically based models were proposed to describe each individual oil transport process, such as, oil flows on the piston lands in both axial and circumferential directions and oil flows through the ring grooves and gaps.
On the piston lands, oil was observed to move in both axial and circumferential directions. The axial oil displacements were found to be driven by the inertia force resulting from the piston alternating motion. The circumferential flow appeared to result from the dragging action of the blow-by gases. Two major mechanisms were found to be responsible for oil flows from the piston lands to the ring grooves: the ring pumping, which was observed experimentally, and the lateral motion of the piston relative to the rings. The oil flow from the ring grooves to the piston lands appeared to be governed by the ring squeezing action and the dragging effect of the gases flowing through the ring groove clearances, this latter mechanism being only significant when ring flutter occurs. Eventually, the onset of oil transport from the piston to the liner via the rings was investigated.