Question 39 QMED01 - Junior Engineer

The Correct Answer is D ### Explanation of Why Option D (Diesel fuel oil) is Correct A centrifugal purifier separates components based primarily on differences in **specific gravity (density)**. It efficiently removes substances that are heavier than the lubricating oil (e.g., water, sludge, metals). **Diesel fuel oil (or Marine Gas Oil/MGO)** is inherently lighter than standard marine lubricating oil (LO). * **Lube Oil SG:** Typically 0.88 – 0.92 * **Diesel Fuel SG:** Typically 0.82 – 0.86 Because the density difference is small, and the contaminant (diesel) is lighter than the oil being purified, the diesel will remain mixed with the lubricating oil flow (the light phase) and cannot be separated effectively by density differences at normal operating speeds and temperatures. The diesel acts as a diluent, reducing the viscosity and flash point of the lubricating oil, but not forming a separate phase that can be spun out. ### Explanation of Why Other Options are Incorrect **A) Carbon particles:** These are solid combustion byproducts (soot). They are significantly denser than the lubricating oil and typically aggregate with heavier inorganic ash components. They are efficiently removed by the centrifugal purifier as part of the solid sludge phase. **B) Metal particles:** These are solid wear materials (e.g., iron, copper). Metals have a very high specific gravity (much higher than water or oil). They are extremely dense and are easily removed by the centrifugal purifier, forming a key component of the solid sludge phase. **C) Water:** Water (fresh or saltwater) has a specific gravity near 1.0 to 1.03. Since water is significantly denser than lubricating oil (SG ~0.90), it forms a separate heavy liquid phase. Water is the most common liquid impurity removed by a centrifugal purifier.