What are speed-regulating governors used for in machinery?

Speed-regulating governors play a crucial role in controlling the speed of engines, particularly in marine machinery. Their primary function is to maintain a desired engine speed by regulating the amount of fuel injected into the engine. When the engine speed deviates from the preset level—either increasing or decreasing—the governor adjusts the fuel supply accordingly to bring the speed back to the desired range. This precise control is essential for optimal engine performance, stability of operation, and ensuring that the engine runs at efficient levels.

The other choices do not accurately reflect the primary function of speed-regulating governors. Increasing engine temperature or disconnecting the drive mechanism from the propeller are not relevant to the governor's role in speed regulation. While enhanced fuel efficiency can be a byproduct of maintaining optimal engine speeds, it is not the direct purpose of speed-regulating governors. Hence, the correct choice emphasizes the governor's direct responsibility for controlling engine speed through fuel injection management.