FAA Ground School Practice Test

What is known as the uncontrolled firing of the fuel/air charge in advance of normal spark ignition?

1. Backfiring

2. Pre-ignition

3. Afterburning

4. Flameout

The correct answer is: Pre-ignition

Pre-ignition refers to the phenomenon where the fuel/air mixture ignites prematurely, prior to the engine’s intended spark firing from the spark plug. This can happen due to various reasons including excessive heat in the combustion chamber or hot spots caused by carbon deposits, leading to spontaneous combustion of the fuel/air mixture. In essence, pre-ignition can cause a number of operational issues, such as engine knock, rough running, or even engine damage, due to the pressure and temperature not being optimized for the intended combustion timing. Understanding pre-ignition is crucial for maintaining engine performance and preventing potential failures. Other terms in the question relate to different combustion issues. Backfiring typically refers to an explosion in the intake system, afterburning refers to the igniting of unburnt fuel in the exhaust stream to increase thrust, and flameout signifies the complete loss of the flame in the combustion chamber, particularly in a jet engine.