Private Pilot Private Exam

When does detonation occur in a reciprocating aircraft engine?

1. When fuel ignites before the spark

2. When the fuel/air mixture burns normally

3. When the unburned charge explodes

4. When air density is low

The correct answer is: When the unburned charge explodes

Detonation occurs in a reciprocating aircraft engine when an unburned charge explodes instead of burning smoothly. This phenomenon typically results from a rapid rise in pressure and temperature within the combustion chamber, which can lead to an uncontrolled and explosive reaction rather than the intended, orderly combustion. This explosive reaction can create severe stresses on the engine components, potentially causing damage. Detonation is often associated with factors such as excessive engine heat, high compression ratios, or low-quality fuel that does not withstand the combustion conditions. Understanding detonation and its causes is crucial for pilots because it can significantly impact engine performance and safety. By recognizing what leads to detonation, pilots can better manage engine settings, fuel quality, and operational practices to avoid damaging engine conditions.