Definition
A piston ring positioned on the lower part of an aircraft engine piston whose function is to wipe excess oil from the cylinder wall and return it to the crankcase, preventing oil from passing into the combustion chamber.
Plain English
A ring around the piston that scrapes used oil off the cylinder wall so it can drain back into the engine, instead of being burned with the fuel.
Context Anchor
Seen in piston-airplane exhaust, cabin heat, and carbon monoxide safety discussions.
Derivation
From the verb 'scavenge,' originally meaning to clear away or collect waste. In engine use, 'scavenging' refers to clearing or collecting spent oil or exhaust gases. The ring 'scavenges' oil from the cylinder wall.
Why Pilots Care
Proper scavenging prevents oil from pooling inside the engine, which could lead to overheating, increased drag on rotating parts, or loss of lubrication pressure.
Grounding Statement
As exhaust rushes past the area, the scavenging ring helps pull nearby unwanted fumes outward instead of letting them linger near the cabin heat path.
Intuition Check
Scavenging here does not mean searching for something useful. It means removing unwanted gases from an area where they could become dangerous.
Example Sentence 1
Excessive oil consumption in a reciprocating engine often points to worn scavenging rings allowing oil into the combustion chamber.
Example Sentence 2
If the scavenging ring becomes blocked, oil can accumulate in the lower cylinders and cause hydraulic lock on startup.