Question 27 AEL01 - Assistant Engineer - Limited

The Correct Answer is B **Explanation for Option B (Sludge) being correct:** Centrifuging is a mechanical separation process that works by exploiting the differences in density between components in a liquid mixture. A centrifuge rapidly spins the fuel, generating a high centrifugal force. This force causes denser, solid particulate matter (like rust, dirt, and microbial growth, which collectively form **sludge**) and immiscible liquids (like water) to be thrown outward to the periphery of the spinning bowl, separating them from the lighter, cleaner diesel fuel. Sludge is a macroscopic contaminant with a density significantly greater than diesel fuel, making its removal by centrifugation highly effective and satisfactory. **Explanation for why the other options are incorrect:** * **A) Lube oil:** Lube oil (motor oil) is miscible (mixable) with diesel fuel and has a density very similar to diesel fuel. Centrifuging separates materials based on density and insolubility. Since lube oil mixes thoroughly with the fuel and does not form a distinct, denser phase, it cannot be separated by standard mechanical centrifugation. * **C) Gasoline:** Gasoline is highly miscible with diesel fuel and has a density even lower than diesel fuel. It dissolves completely into the fuel and therefore cannot be mechanically separated by density differentiation using a centrifuge. Separation would require fractional distillation or another chemical/physical process. * **D) Fuel oil:** Fuel oil (if referring to a similar grade like marine diesel or heavy fuel oil) is entirely miscible with diesel fuel and is primarily composed of similar hydrocarbon chains. While heavy fuel oil is denser than diesel, if mixed, it typically forms a uniform solution and does not separate into distinct, discrete phases under centrifugal force suitable for purification. Fuel oil is a hydrocarbon fuel, not a contaminant designed for mechanical removal.