What is Difference between main engine and aux engine?

The main engine, typically found in ships and large vehicles, is responsible for providing the primary source of propulsion, enabling movement and navigation. In contrast, the auxiliary engine serves secondary functions, such as generating electricity for onboard systems, powering pumps, and supporting other machinery when the main engine is not in operation. While the main engine is larger and more powerful, the auxiliary engine is generally smaller and designed for efficiency in supporting various operational needs.