Definition
Two methods of temporarily increasing the thrust output of a turbofan engine beyond its normal rated thrust. Water injection sprays water (or a water-alcohol mixture) into the engine's compressor inlet or combustion section, cooling the airflow and increasing its density so that more mass flows through the engine, producing greater thrust. Afterburning (also called thrust augmentation) injects and burns additional fuel in the exhaust stream aft of the turbine, where unused oxygen remains; the resulting expansion of hot gases through the exhaust nozzle significantly increases thrust. Both techniques are used for short periods, typically during takeoff or for military performance demands, because they consume fuel or water at high rates and add thermal stress to the engine.
Plain English
Two ways to temporarily boost a turbofan engine's power. Water injection sprays water into the engine to make the air denser, so more of it flows through and pushes harder. Afterburning sprays extra fuel into the hot exhaust and burns it again, giving a big extra shove out the back. Both are used briefly because they burn through fuel or water quickly and stress the engine.
Context Anchor
Seen in turbine-engine performance, military jet operations, takeoff performance discussions, and older jet aircraft systems that use thrust augmentation.
Derivation
Water injection is literal -- water is injected into the engine. Afterburning means burning fuel after the main combustion stage, in the exhaust section behind the turbine. The 'after' refers to its position downstream of the normal burner.
Why Pilots Care
Provides the extra thrust needed for short runways, hot-day takeoffs, or rapid climb without requiring a larger engine.
Grounding Statement
Both methods are ways of getting a short burst of extra thrust from a turbofan engine, not normal continuous engine operation.
Intuition Check
Water injection does not mean the engine is running on water; the water helps the engine make more thrust for a short time. Afterburning does not mean the engine is overheating; it means extra fuel is intentionally burned in the exhaust to add thrust.
Example Sentence 1
Early Boeing 707s used water injection on takeoff to meet thrust requirements on hot days or from short runways.
Example Sentence 2
During the military transition course the instructor demonstrated how the turbofan engine by water injection or afterburning delivers the acceleration needed for a go-around with heavy stores.