Definition
A reciprocating-engine system that injects a water-methanol mixture into the induction airflow during high-power operation to suppress detonation. The added fluid cools the fuel-air charge and lowers combustion temperatures, allowing the engine to safely produce takeoff or emergency power that would otherwise risk detonation damage.
Plain English
A system that sprays a water and alcohol mixture into the engine's air intake during high power settings. The fluid cools things down inside the cylinders so the fuel burns smoothly instead of exploding in a way that could damage the engine.
Context Anchor
Seen in powerplant maintenance, high-power piston engine operation, and aircraft operating instructions for takeoff, emergency, or maximum-power settings.
Derivation
Anti- (Latin: against) plus detonation (Latin detonare, to thunder down). The system is literally named for what it prevents: the sharp, thundering knock of uncontrolled combustion inside the cylinder.
Why Pilots Care
It protects the engine from detonation damage while permitting maximum safe power output.
Grounding Statement
At very high power, the system helps keep combustion under control by cooling the mixture before it burns.
Intuition Check
Do not confuse this ADI with an attitude direction indicator. In this powerplant context, ADI is an engine system, not a flight instrument.
Example Sentence 1
Before takeoff, the flight engineer confirmed the ADI tank was full and the system armed for maximum power.
Example Sentence 2
Before the flight, the mechanic topped off the ADI system reservoir with the correct water-alcohol mixture.