Clarification of Fuel and Oil Flow Behavior Around the Piston Rings of Internal Combustion Engines – Simultaneous analysis of oil flow behavior and oil emissions during transient operation

Future demands for modern emission free drivetrains using hydrogen or liquid e-fuels also necessitate a fundamental reduction in oil emissions. Entry of lubrication oil into the combustion chamber can lead to pre-combustion phenomena (LSPI) in downsizing or hydrogen engines and is a cause of particle emissions, which play a significant role especially if fuel related particle emissions are already low. A fundamental understanding of the oil film behavior on the piston assembly and cylinder liner surface are crucial to avoid oil ingress into the combustion chamber. The processes involved take place mainly around the piston group. In particular, the area of the piston rings with the prevailing pressure and temperature conditions as well as the component geometries has a high influence on the exchange of media between the crankcase and combustion chamber.

The objective of this paper is to increase the understanding of the processes leading to oil ingress into the combustion chamber. In addition, the resulting oil emissions are to be analyzed and put into perspective. An optical accessible “glass-liner” SI- engine is used as a test bench for simultaneous measurements of the oil film by LIF and the oil emission by mass spectrometry to connect and correlate the information gathered into a more profound understanding of the processes involved and their influence on emission behavior.

The focus of this paper lies on transitional behavior from fired to motored operation and back to fired operation. The temporal course of the oil flow and its influence on oil-borne emissions in transient phases could be visualized. A non-deterministic behavior of the oil emissions was observed and validated optically.