What function does a spark plug serve?

A spark plug plays a crucial role in the operation of an internal combustion engine by igniting the air-fuel mixture within the combustion chamber. This ignition generates the explosion that pushes the piston down, creating the power necessary to drive the engine. The spark plug generates a high-voltage spark that creates a brief arc between its electrodes, which ignites the mixed gases when they are compressed within the cylinder. This ignition is vital for the engine to run efficiently and effectively, making the spark plug an essential component of the ignition system.

Other options, while critical to different functions of the engine, do not describe the role of a spark plug. Regulating coolant flow is managed by components like the thermostat and water pump, supplying fuel is the responsibility of the fuel system, and cooling engine components typically involves oil or coolant circulation. Hence, the primary function of a spark plug is indeed to ignite the air-fuel mixture, making it an indispensable part of the engine operation.