Question 61 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is D **Explanation for Option D (High jacket water temperature) being correct:** The jacket water system is responsible for cooling the critical internal components of the main propulsion engine (cylinder liners, cylinder heads, etc.). Excessive heat buildup is directly indicated by the temperature of this cooling medium. Engine protection systems (safety trips) are designed to prevent catastrophic failure, such as seizure or major cracking, caused by overheating. A dangerously high jacket water temperature signifies a breakdown in the primary cooling function, often due to coolant loss, pump failure, or a clogged heat exchanger. Because this condition directly threatens the structural integrity and operation of the entire engine, it is universally monitored as the primary parameter for initiating an automatic, solenoid-actuated safety trip shutdown on commercial marine propulsion engines. **Explanation of why other options are incorrect:** * **A) High charge air temperature:** While indicative of a potential problem (e.g., turbocharger fouling, intercooler malfunction), high charge air temperature primarily affects combustion efficiency and NOx emissions. It will often lead to a reduction in engine power (de-rating) and an alarm, but usually not an immediate, catastrophic safety shutdown unless it rapidly and severely affects other critical parameters (like exhaust temperature or jacket water temperature). * **B) High fuel temperature:** Fuel temperature is monitored for operational efficiency (viscosity control, especially with heavy fuel oil), but high fuel temperature alone is not typically a trip condition on a conventional diesel engine unless it exceeds manufacturer limits severely enough to cause vaporization or pump damage. * **C) High exhaust temperature:** High exhaust temperature is a key indicator of poor combustion (e.g., overloading, injector problems) and thermal stress on the turbine, but modern marine engines are often run near their maximum exhaust limits. While a high exhaust temperature alarm is critical, the engine safety trip is usually tied to temperatures that cause immediate engine component destruction, making jacket water temperature the more direct trip initiator for general overheating failures. (Note: Exhaust temperature is sometimes used as a trip for fire-risk conditions in specific machinery spaces, but not typically as the primary indicator for engine overheating shutdown.)