Question 43 MODE01 - Chief MODU Engineer

The Correct Answer is D **Explanation for Option D (Correct Answer):** Option D describes the widely accepted and practical "Spot Test" or "Blotter Test" used onboard ships to quickly assess the compatibility of different fuel oils (specifically heavy fuel oil, HFO). Fuel compatibility is primarily determined by whether the mixing of the two fuels causes the asphaltenes (heavy, paraffinic components) to precipitate out of the mixture. The procedure involves placing a single drop of the resulting fuel mixture (or placing a drop of the new fuel concentrically inside a drop of the old fuel) onto a piece of standard filter or blotter paper. * **If the fuels are compatible**, the asphaltenes remain stable and dissolve evenly, resulting in a single, uniform, homogeneous stain on the paper. * **If the fuels are incompatible**, the asphaltenes will precipitate out and coagulate. When the lighter components of the fuel wick away from the center, the precipitated asphaltenes leave a distinct, dark, concentric ring or spot pattern (often described as a 'fried egg' appearance) in the center, indicating incompatibility and the high risk of sludge formation if bunkered together. **Explanation for Incorrect Options:** **A) Take equal samples of both fuels, elevate their temperature, and mix them vigorously. If no frothing occurs, they are compatible.** This is incorrect. Compatibility is about the stability of asphaltenes, not the potential for frothing. Frothing is usually related to water content, entrained air, or volatile components, which are separate issues from chemical compatibility. **B) Perform a running viscosity test of both fuels, at the same temperature, if the viscosities are equal, they should be compatible.** This is incorrect. Viscosity is a measure of a fluid's resistance to flow and is a key parameter for engine injection, but it has no direct bearing on the chemical stability or compatibility of the asphaltenes in two different fuel oils. Fuels of the same viscosity can still be highly incompatible due to differences in their paraffinic/aromatic ratios. **C) Mix two equal samples of the two fuels at elevated temperatures and determine if they become a homogeneous mixture.** This is insufficient and vague. While a homogeneous appearance is the goal, visual inspection alone, even at elevated temperatures, cannot reliably detect the minute precipitation and destabilization of asphaltenes that leads to sludge formation. The Blotter Test (Option D) is specifically designed to visually exaggerate this precipitation effect onto the paper substrate, providing a definitive result.