Question 67 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is A. ### Explanation for Option A (Correct Answer) Option A, **"The operating oil temperature range of the governor,"** is the primary factor that determines the recommended oil viscosity for a speed control governor. 1. **Viscosity Definition:** Viscosity is a measure of a fluid's resistance to flow. For lubricating oil, it dictates how easily the oil can circulate and how well it maintains a protective film between moving parts. 2. **Temperature Dependence:** Oil viscosity is highly dependent on temperature. As oil heats up, its viscosity decreases (it becomes thinner); as it cools down, its viscosity increases (it becomes thicker). 3. **Governor Operation:** Hydraulic governors, like those used on main propulsion engines, rely on oil not only for lubrication but also as the hydraulic fluid that transmits power to make adjustments to the fuel rack. The oil must maintain a specific viscosity range at the typical operating temperature to ensure the hydraulic passages are properly filled and the governor responds accurately and rapidly without excessive internal leakage or sluggishness. The manufacturer specifies the correct oil weight (viscosity grade, e.g., SAE 20, 30, or a specific ISO grade) based on the expected ambient and operating temperatures of the unit. ### Explanations for Incorrect Options **B) The output power of the governor as expressed in inch-pounds.** While the power output (work capacity) of the governor actuator is related to its physical size and the forces it must overcome, the power output itself does not directly dictate the *viscosity* of the hydraulic fluid. The viscosity is determined by the internal tolerances and the required stability across the operating temperature range, not the magnitude of the final output force. **C) The maximum rated power output of the engine.** The maximum engine horsepower determines the size and torque capacity required for the governor's actuator, as a larger engine requires a stronger governor to move the fuel racks. However, the viscosity of the oil used *inside* the governor is governed by the governor's specific design tolerances and its operating temperature, not the engine's total output power. **D) The speed range (from idle to maximum governed speed) of the engine.** The speed range is a critical operational parameter for engine control and determines the settings and adjustments necessary for the governor (such as droop and speed settings). However, the specific speed range does not determine the optimal oil viscosity. The viscosity is determined by the physical characteristics of the fluid required to operate the precision hydraulic components at temperature.