Antiknocking agents are used to increase the octane number. This reduces the tendency of a fuel to knock. Most popular antiknocking agent is tetraethyl lead. This is added in the form of ethyl fluid and petrol containing ethyl fluid which is known as leaded petrol or ethylated petrol. Ethyl fluid contains 63% tetraethyl lead, 26% dibromoethane and 9% dichloroethane. Dibromomethane and dichloroethane are added to remove lead as volatile lead halides which escape with other gases through the exhaust. Use of leaded petrol in automobiles is being phased out because of the hazardous effects of lead compounds discharged through the exhaust. Another method to enhance octane number is the addition of unleaded petrol. This is methyl tertiary butyl ether which contains oxygen in the form of ether group and supplies oxygen for the complete combustion of the petrol in the internal combustion engines. This reduces the formation of peroxy compounds. Major advantage here is that we can use catalytic converters.
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