Anti knocking Agents

The Octane number of Internal combustion fuel can be raised by the addition of such extremely poisonous materials as tetraethyl lead(C₂H₅)₄Pb) and diethyl telluride

Knocking is the outcome of an early ignition of fuel (in gasoline engines) before the timed ignition spark occurs. It drastically increases the pressure inside the engine cylinder. which results in destructive effects to the engine

Adverse effect of using leaded petrol
Lead oxide vapours are formed on using leaded petrol as a fuel.These vapours are poisonous and may contaiminate the atmosphere. This can be stopped to some extent by adding ethylene dibromide to the leaded petrol.
Pb + Br--CH2---Br  --------- PbBr2 + CH2=CH2

Other anti-knocking agents which can be used are teriary butyl acetate,diethyl telluride,benzol,alcohol.
Factors reducing the Knock
Using high Octane fuel
Using Lower compression ratio
Designing suitable compression chamber

Pollution Reduce way

Lead is poisonous and is extremely toxic.Increasing use of automobile increase the harmful substances in the atmosphere.To improve the pollution problem following methods are used.

Many devices such as, Catalyst converters are used to oxidize the un-burnt hydrocarbons and carbon monoxide to carbon dioxide and to decompose nitrogen oxide into nitrogen and oxygen.

Tetraethyl lead in gasoline is replaced by certain aromatics and branched -chain hydrocarbons. The gasoline is free from tetraethyl lead is termed as leaded free gasoline.