Which device runs the motor on electric power until the engine fuel ignites?

The device that runs the motor on electric power until the engine fuel ignites is the starter. This component is essential in the starting process of internal combustion engines. When you turn the key or push the start button, the starter engages with the engine’s flywheel and uses electrical power from the battery to crank the engine. This cranking action generates enough movement for air and fuel to mix and eventually ignite within the cylinders, allowing the engine to start running on its own.

The other options do not serve this function. A slow motor does not specifically pertain to the engine starting process, and an ignition coil is responsible for providing the high voltage necessary to spark the fuel-air mixture in the combustion chamber, not for cranking the engine. The vent fan's purpose is unrelated, as it usually pertains to ventilation and cooling systems, not engine ignition or starting. Thus, understanding that the starter is pivotal for initiating the engine's operation helps clarify why it is the correct choice.