Which device is used to ignite the fuel-air mixture in a gasoline engine?

• A. Glow plug
• B. Spark plug
• C. Fuel injector
• D. Ignition coil

Answer: (B)

Gasoline engines use spark-ignition. The spark plug is the component that creates a spark across its gap to ignite the compressed air–fuel mixture at the right moment in the cycle. It receives a high-voltage pulse from the ignition coil, and that spark starts the combustion that drives the piston.

Glow plugs heat the chamber for starting in some engines (more common in diesel) and are not the normal ignition method for gasoline engines. A fuel injector delivers fuel but does not ignite it. The ignition coil provides the high voltage needed, but the spark plug is the part that actually generates the flame that starts combustion.