What is defined as detonation in an aircraft engine?

Detonation in an aircraft engine refers to a phenomenon where there is an instantaneous combustion of the unburned fuel/air charge in the cylinder, which is characterized by a rapid increase in pressure and temperature. This occurs due to the auto-ignition of the fuel mixture, typically caused by excessively high temperatures or pressures within the combustion chamber. When detonation occurs, it can result in a knocking sound and can cause damage to engine components due to the rapid and uncontrolled nature of the combustion event.

In contrast, the other options describe different processes within an aircraft engine. The preparation of the engine for start involves various pre-flight checks and functions, gradual burning refers to the desired combustion process that occurs under normal operating conditions, and the formation of carbon deposits typically happens over time due to incomplete combustion, which is a separate issue from detonation. Understanding the concept of detonation is crucial for pilots, as it can significantly impact engine performance and safety.