Definition
A fuel-air mixture in which the proportion of fuel to air is higher than the chemically ideal (stoichiometric) ratio of approximately 1 part fuel to 15 parts air by weight. The excess fuel does not all burn; instead, it cools the combustion process and helps prevent detonation and overheating.
Plain English
A fuel-air blend that has more fuel in it than is strictly needed to burn cleanly. The extra fuel keeps the engine cooler and helps protect it during high-power operations.
Context Anchor
Encountered when using or adjusting the mixture control, especially during engine start, takeoff, climb, cruise, and operations at different altitudes.
Derivation
‘Rich’ comes from Old English ‘rice’ meaning abundant or plentiful. In this context it describes a mixture that is abundant in fuel relative to air — not richer in quality, but richer in fuel content.
Why Pilots Care
Excess fuel absorbs heat and reduces the risk of detonation and overheating at full power.
Intuition Check
Rich does not mean better or more powerful by itself. Here it means the mixture has more fuel relative to air.
Example Sentence 1
The pilot kept the mixture full rich during takeoff and the initial climb to help cool the engine.
Example Sentence 2
With a rich mixture the exhaust gas temperature drops while fuel flow increases.