Question 40 DDE04 - Designated Duty Engineer - 1000-4000 HP

The Correct Answer is C **Explanation for Option C (High jacket water temperature) being correct:** In marine diesel engines, particularly those used for critical functions like main propulsion on a harbor assist tug, the engine's core operational temperature is primarily regulated by the jacket water (coolant) system. A rapid or sustained increase in jacket water temperature indicates a major cooling failure or severe internal issue (like excessive combustion temperature or lubrication breakdown). Engine safety systems are designed to protect the most vulnerable components—the pistons, liners, and cylinder head—from catastrophic thermal damage. Therefore, high jacket water temperature is the standard, primary parameter monitored by engine safety trip systems to automatically initiate an emergency shutdown (safety trip) when the temperature exceeds safe operational limits, preventing total engine failure. **Why the other options are incorrect:** * **A) High fuel temperature:** While high fuel temperature can cause operational issues (like vaporization or viscosity changes) and may trigger an alarm, it is not typically the primary parameter used to initiate a full, emergency engine safety trip shutdown, which is reserved for direct threats to the engine's mechanical integrity. * **B) High charge air temperature:** High charge air temperature (air delivered from the turbocharger/cooler to the cylinders) primarily reduces engine efficiency and power and can increase cylinder temperatures, potentially triggering a high-temperature alarm. However, the direct measurement of the resulting **high jacket water temperature** is the protective parameter that initiates the final safety trip shutdown. The charge air temperature itself is generally a secondary, less immediate risk factor compared to a lack of core cooling. * **D) High exhaust temperature:** High exhaust temperature indicates a heavy engine load or potential combustion issue (e.g., injector failure, turbocharger problems) and will certainly trigger an alarm. Engine management systems often reduce fuel rack settings (de-rate) in response to high exhaust temperature to protect the turbine blades. However, like charge air temperature, it is a symptom of a thermal issue, whereas the direct measurement of **high jacket water temperature** is the most reliable and direct indicator of critical, imminent thermal failure requiring a safety trip.