If oil discharges are detected when the scavenging air receiver drains are blown on a slow-speed, two-stroke, turbocharged, aftercooled engine, what is the most likely oil source?

Correct Answer: Option D — Cylinder lubricating oil

Large two-stroke crosshead diesel engines use mechanical lubricators to inject specialized cylinder oils directly onto the sliding liner walls. Excess oil scraped downward by piston rings accumulates within the scavenging air receiver drains.