Question 9 QMED03 - Oiler

The Correct Answer is C ### Why Option C (Cylinder lubricating oil) is correct: On a slow-speed, crosshead-type diesel engine, the cylinder lubricating oil is injected directly onto the cylinder liner wall, separate from the main system oil (which lubricates the bearings and cools the pistons). This oil is designed to lubricate the piston rings and liner, neutralize acidic combustion products (sulfur), and control wear. Crucially, the cylinder oil is burned or consumed during the normal combustion process and exits the engine with the exhaust gases or as deposits. Therefore, it must be continuously replenished, making it a **consumable** item. ### Why the other options are incorrect: * **A) Main circulating oil:** This oil is part of a closed, pressurized circulation system (the sump system) that lubricates the crosshead, bearings (main, thrust, and crankpin), and cools the pistons (in most modern designs). While some small losses occur (e.g., leakage, vaporization), the vast majority is continuously filtered, cooled, and reused, making it a system oil, not a regularly consumed lubricant like the cylinder oil. * **B) Turbocharger lubricating oil:** On large, slow-speed engines, turbochargers are typically lubricated by the main circulating oil system. Even if a separate system is used, this oil is filtered and reused in a closed loop, meaning it is a system oil, not a consumable that is intentionally lost or burned during operation. * **D) Piston cooling oil:** In crosshead engines, the pistons are usually cooled by the main circulating oil (Option A). The oil passes through the piston crown and returns to the sump. Its primary function is heat transfer, not lubrication of the cylinder walls, and it operates within a closed system.