Certified Flight Instructor - Flight Instructor Airplane Practice Exam

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

1. Combustion.

2. Detonation.

3. Pre-ignition.

4. Spontaneous ignition.

The correct answer is: Pre-ignition.

The scenario described refers to pre-ignition, which is the condition where the fuel/air mixture ignites too early in the cycle, prior to the arrival of the spark plug's ignition. This can happen due to excessive heat or pressure in the cylinder, leading to a situation where spontaneous combustion occurs. Pre-ignition is detrimental to engine performance because it can cause knocking, reduce efficiency, and potentially damage engine components. In the context of aircraft engine operation, understanding the timing and sequence of ignition events is crucial for optimal performance and safety. Pre-ignition can harm the engine if not managed, making it important for pilots and flight instructors to recognize and address its potential occurrence during flight operations. Combustion, while part of the overall process that occurs in the engine, refers specifically to the actual burning of the fuel/air mixture initiated by the spark. Detonation denotes a different phenomenon altogether, where the combustion wave travels through the cylinder explosively rather than smoothly. Spontaneous ignition is more closely related to fuel ignition occurring without a spark due to extreme conditions but does not specifically relate to the timing problem described. Understanding these distinctions is vital for proper engine management and flight operations.