Addition of ethylene dibromide to petrol

Ethylene dibromide is added to leaded petrol to act as a 'scavenging agent' [2]. When tetraethyl lead (TEL) is used as an antiknock agent to increase octane ratings, its combustion naturally produces lead oxide. Lead oxide is a solid at engine operating temperatures (up to 900°C), which can lead to harmful deposits on spark plugs and combustion chambers [4]. Ethylene dibromide reacts with this lead oxide to form lead bromide (PbBr2) [1]. Lead bromide has a significantly higher vapor pressure and a lower volatility temperature (around 200-250°C), allowing it to remain in a gaseous state and be easily eliminated through the exhaust system [1]. Therefore, the primary function of ethylene dibromide is to help in the elimination of lead oxide deposits from the engine [2].

Sources

1. [1] https://ntrs.nasa.gov/api/citations/19930083302/downloads/19930083302.pdf
2. [2] https://downloads.regulations.gov/EPA-HQ-OPPT-2018-0488-0029/attachment_1.pdf
3. [4] https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=9101KHJA.TXT