Definition
A chemical compound (C2H4Br2) added to leaded aviation gasoline as a scavenging agent. It combines with lead during combustion to form lead bromide, which can be carried out of the engine with the exhaust gases instead of depositing on valves, spark plugs, and cylinder walls.
Plain English
An additive in leaded avgas that helps the engine get rid of lead deposits by turning them into something that exits with the exhaust, instead of building up inside the cylinders.
Context Anchor
Seen in aviation fuel, engine maintenance, and discussions of lead deposits in engines that burn leaded aviation gasoline.
Derivation
From 'ethylene' (a simple hydrocarbon, C2H4) and 'dibromide' (containing two bromine atoms). The name simply describes the molecule's makeup, but the key idea is the bromine: bromine is what bonds with the lead during combustion to make a removable compound.
Why Pilots Care
Without it, lead deposits quickly foul spark plugs and valves in engines using 100LL, leading to power loss or engine damage.
Example Sentence 1
Ethylene dibromide is added to 100LL avgas so that lead deposits can be carried out through the exhaust rather than coating the inside of the engine.
Example Sentence 2
During overhaul, the technician noted reduced lead fouling thanks to proper ethylene dibromide levels in the fuel.