Write note on Leaded Petrol

Petrol or gasoline which contains tetraethyl lead (TEL) is known as leaded petrol or leaded gasoline.
Compounds such as tetraethyl lead, greatly reduces knocking and they are added up to 0.01% in the gasoline.
The action of tetraethyl lead increases the octane number by any one of the following ways :
(i) Tetraethyl lead dissociates into ethyl radicals which prevents the explosive burning of the fuel.
(ii) Tetraethyl lead. decomposes and forms fine lead particles which acts as a shield between the unburnt and burning portions.
(iii) The finely divided lead particles act as an oxidation centres, thereby making the combustion homogeneous and uniform.
But lead compounds are poisonous and also contribute to air pollution.
In order to prevent the deposition of lead in the cylinder, ethylene dibromide is added to the gasoline.
Ethylene dibromide breaks down into ethylene and bromine in the internal combustion engine.
Bromine reacts with lead to form lead bromide. Lead bromide is volatile in nature and can be removed along with the exhaust gas