Ethylene dibromide

A chemical compound added to aviation gasoline to convert some of the deposits left by the tetraethyl lead into lead bromides. These bromides are volatile and will pass out of the engine with the exhaust gases.

Aviation Maintenance Technician Handbook — Airframe, p. G-14

Also defined in 1 more source

A colorless, poisonous liquid BrCH2CH2Br that is blended with leaded gasoline to help scavenge lead oxides.

Aviation Maintenance Technician Handbook — Powerplant, p. G-11