Optical investigation of cylinder oil sprays in slow-speed marine diesel engines

Whilst modern cylinder lubricant delivery systems claim to provide the ability to reduce oil consumption in marine engines, and offer a more efficient control of liner wear and corrosion, there is a need to better understand the effect of physical properties on oil spray formation and liner coverage. To this end, we built an optical spray chamber and applied optical diagnostics to characterise the sprays produced by a modern, commercial, high-pressure lubricant spray system. We used high-speed video to visualise: the lubricant flow inside a custom-built optical nozzle; the near-nozzle jet; the far-field spray; and the subsequent coverage of a transparent liner. We found that the lubricant injection system showed evidence of internal cavitation. Further investigation of this cavitation was carried out through the use of an optical nozzle, replicating the internal geometry of the lubricant injector. The optical nozzle's refractive index was matched to that of the lubricant, allowing vapour pockets to be clearly visible. The transparent cylinder liner enabled the measurement of liner spreadability and coverage patterns. Changes in these patterns were linked to lubricant viscosity. Our preliminary results demonstrate the possibility to relate the internal nozzle flow to lubricant atomisation and, ultimately, to liner coverage