| Summary: | With an influx of new propulsion technologies and increasingly stringent emission standards on the horizon, the internal combustion engine (ICE) faces more hurdles than ever before to remain competitive in a rapidly changing social and market environment. Due to the distinct advantages of the ICE—namely the existing energy supply infrastructure and long driving range combined with the ability to replenish the energy supply in a short matter of time—it remains, however, yet to be seen how fast these new technologies will be adopted. Therefore, further developing ICE is critical if we are to succeed in reducing overall greenhouse gas and pollutant emissions. Understanding lubricant transport in the piston-cylinder unit is essential to this mission, due to its direct impact on both types of emissions.
The first part of this thesis focuses on the development of an experimental system which allows us to visualize liquid oil transport under realistic engine operating conditions. To achieve this, a one-cylinder gasoline research engine equipped with a sapphire window for optical access is utilized in combination with the Laser Induced Fluorescence (LIF) measurement technique. This novel system is capable of capturing oil transport phenomena at various time- and length-scales synchronized with engine operation.
The second part of this thesis provides an analysis of the images acquired by the system, with the primary points of interest being the piston skirt area and oil control ring (OCR). Within the skirt area, we were able to characterize oil addition and transport, as well as and most especially, the influence of piston secondary motion on the latter. These key findings enable us to design a better, more efficient piston in the future—in fact, one recent design iteration of the piston skirt has already revealed the benefits of this approach.
The OCR is at the crucial interface between skirt and ring pack. As a result of the high resolution in time and space made possible by this system, we were also able to expand our understanding of known transport mechanisms in the ring pack, as well as discover new avenues of oil transport. Another considerable finding is the interplay between oil supply through the Twin-Land oil control ring (TLOCR) gap and gas pressure enhanced bridging—a discovery which finally offers a conclusive explanation as to how oil is transported into the severe contact areas of the ring pack in engines without reverse flow. Lastly, this thesis contains a summary of avenues for transport in the ring-pack, avenues which were observed in this research. This summary will inform how we approach new designs that will achieve a healthy oil transport system in the next generation of combustion engines.
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