Question 41 MODE01 - Chief MODU Engineer

The Correct Answer is B **Why option B is correct:** The process of removing sulfur from distillate fuels (hydrodesulfurization) also removes or alters the naturally occurring polar compounds (like heteroatoms containing oxygen and nitrogen) that provide boundary lubrication properties. When sulfur levels are significantly reduced to meet modern emission regulations (creating "low sulfur distillate fuel"), the resulting fuel often exhibits poor lubricity. This lack of lubrication is a critical issue in high-precision fuel system components, such as fuel pump plungers, barrels, and injector nozzles, which rely on the fuel itself for cooling and lubrication. Poor lubricity leads to excessive friction, resulting in wear, sticking, scuffing, and eventual failure of these components, causing significant operational difficulties. **Why the other options are incorrect:** * **A) Lower heat content results in higher fuel consumption.** While low sulfur distillate fuels can have slightly lower energy density (heat content) compared to high sulfur fuels (due to the hydrotreating process changing the hydrocarbon composition), this is typically a manageable efficiency consideration, not a direct cause of immediate operational **difficulties** (like component failure). The primary operational issue associated with these fuels is component wear due to poor lubricity. * **C) Higher zinc content precipitates out sludge.** Low sulfur distillate fuels are hydrocarbon products; they do not inherently contain high levels of metallic additives like zinc. Zinc is typically found in lubricating oils, not in the fuel itself. Sludge formation in fuels is usually associated with oxidation, contamination, or instability, not high zinc content. * **D) Increased viscosity requires additional heating.** Low sulfur distillate fuels (like marine gas oil or diesel) are generally characterized by a **low** viscosity compared to heavy fuel oils. In fact, compared to older high-sulfur diesel, the hydrotreating process can sometimes slightly decrease the viscosity. These fuels are designed to be used without requiring heating for pumping or injection. Requiring additional heating is a characteristic of high-viscosity fuels (like Heavy Fuel Oil), not low sulfur distillates.