Question 14 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is B **Explanation for Option B (Sulfur):** Sulfur is a naturally occurring contaminant in crude oil, which is the source material for diesel fuels. When diesel fuel is combusted in the engines of tugboats, the sulfur content is oxidized, primarily forming sulfur dioxide ($\text{SO}_2$). Sulfur dioxide is a major air pollutant and a precursor to acid rain and secondary particulate matter. To limit atmospheric emissions, particularly in highly regulated areas like harbors (Emission Control Areas or local regulations), marine diesel fuels are subject to strict regulations limiting the maximum allowable **sulfur content** (often expressed as a percentage mass/mass). Lower sulfur limits require additional refining and hydro-treatment processes. Therefore, sulfur is the correct soluble contaminant applicable for limiting atmospheric emissions. **Explanation of Incorrect Options:** * **A) Asphaltenes:** Asphaltenes are large, complex hydrocarbon molecules present in some heavy residual fuels. While they contribute to combustion residues (soot/particulate matter) and can affect engine performance, they are primarily studied as insoluble or semi-soluble macro-constituents affecting fuel stability and storage, not regulated primarily as a soluble atmospheric *contaminant* in the same way sulfur is for gaseous emissions. Furthermore, high-speed diesel used in tugboats typically has very low asphaltene content. * **C) Total sediment:** Total sediment (potential or existent) refers to solid, insoluble matter that can clog filters, cause abrasion, and deposit in engines. It affects engine performance and maintenance, but it is not a *soluble contaminant* whose limitation is directly aimed at controlling major gaseous atmospheric emissions ($\text{SO}_x$, $\text{NO}_x$). * **D) Water:** Water is a common contaminant found in fuel due to condensation or storage issues. It can cause corrosion, promote microbial growth, and interfere with combustion stability (potentially leading to $\text{NO}_x$ reduction, but this is not the primary purpose of its limitation). However, water is a physical contaminant (immiscible with fuel), not the primary *soluble chemical contaminant* that must be limited to control sulfur oxide ($\text{SO}_x$) atmospheric emissions as described in the context of the question.