Question 33 DDE04 - Designated Duty Engineer - 1000-4000 HP

The Correct Answer is D **Explanation of why Option D ("Winter operations with prolonged idling on station.") is correct:** 1. **Condensation Formation:** Water (H₂O) is a major byproduct of hydrocarbon combustion (diesel fuel). If the temperature of the exhaust gas drops below its dew point (the temperature at which the water vapor turns into liquid water), condensation will occur inside the exhaust system components (like mufflers, silencers, and piping). This liquid water, especially when mixed with sulfur combustion products (even ultra-low sulfur content fuels still produce some sulfuric acid), is corrosive and must be drained frequently. 2. **Cold Ambient Temperatures (Winter Operations):** In winter, the ambient air temperature is significantly lower. This cold air rapidly cools the external surfaces of the exhaust system, causing the internal temperature of the exhaust components to drop faster and more severely, making it much easier for the exhaust gas to fall below the water's dew point. 3. **Low Engine Load (Prolonged Idling):** Harbor tugs often spend extended periods waiting or holding station at very low engine loads (idling). At low loads, the engine produces much less heat and the flow rate of the exhaust gas is low. This insufficient heat and low flow volume mean the exhaust system (especially the parts further from the engine, like the stack) will not be hot enough to effectively vaporize and push the water vapor out, guaranteeing that condensation forms and pools rapidly. The combination of extreme external cooling (Winter) and insufficient internal heating/flow (Idling) maximizes condensation formation. **Explanation of why the other options are incorrect:** * **A) Winter operations with lengthy ship escort transit times:** While winter operations increase cooling (a factor for condensation), lengthy escort transit times imply the engine is operating under a higher, sustained load. A sustained load generates high exhaust temperatures and high flow rates, which effectively keep the exhaust components above the dew point, minimizing condensation pooling. * **B) Summer operations with lengthy ship escort transit times:** This scenario has high exhaust temperatures (due to high load/transit) and high ambient temperatures (Summer). Both factors work strongly against condensation formation, leading to the least frequent need for draining. * **C) Summer operations with prolonged idling on station:** Prolonged idling (low load) encourages condensation, but the warm summer ambient temperatures significantly reduce the cooling effect on the exhaust components compared to winter. The exhaust components are less likely to fall below the dew point, resulting in less condensation than in Option D.