What is the function of a spark plug in a gasoline engine?

The function of a spark plug in a gasoline engine is to ignite the air-fuel mixture by producing a spark. When the engine's piston compresses the air-fuel mixture in the combustion chamber, the spark plug creates a high-voltage spark at its electrode. This spark provides the necessary energy to ignite the mixture, resulting in a rapid combustion that expands gases and drives the piston down, creating mechanical power. The reliability and timing of this spark are crucial for efficient engine performance, engine efficiency, and to minimize harmful emissions.

In the context of the other options: regulating fuel flow into the engine is managed by fuel injectors or carburetors, controlling engine temperature is the role of the cooling system, and compressing the air-fuel mixture occurs during the piston's upward stroke in the cylinder. Thus, the primary and essential role of the spark plug is specifically to initiate combustion.