Quality of diesel - cetane number

Cetane number is defined as the percentage of cetane in a mixture of cetane and -methyl naphthalene, which has the same ignition quality as the fuel under examination at the same conditions.

Cetane is arbitrarily given a cetane number of 100 as it ignites rapidly while -methyl naphthalene ignites is given a cetane number of zero as it ignites slowly.

Gasoline additive

Gasoline additives are compounds added to gasoline, which improve the octane number of a fuel. Such substances are called antiknock compound that improve the fuels combustion in an internal combustion engine. Tetraethyl lead ((C₂H₅)₄Pb) is a main additive and is a common antiknock compound. A small quantity of tetraethyl lead (TEL) improves the anti-knock quality of the gasoline. Gasoline containing tetraethyl lead is called leaded petrol or ethyl gasoline.

A gasoline-engine (internal combustion engine) discharges various substances into the atmosphere. These are carbon dioxide, water, carbon monoxide, nitrogen oxides, unburnt hydrocarbons from leaded gasoline and certain compounds of lead. About 0.1 g of lead per litre of the gasoline burnt escapes into the atmosphere. Most of it finds its way into the soil.

Steps to reduce pollution due to automobile exhausts

While many compounds present in the exhaust of any automobile are harmful, lead is extremely toxic and poisonous. The increasing emission of such harmful substances into the atmosphere due to the increasing use of automobiles, is a serious pollution problem. Methods adopted to improve this pollution problem are:

•             Removal of lead from gasoline is done by replacing tetraethyl lead in gasoline by certain aromatics and branched-chain hydrocarbons. The gasoline free from tetraethyl lead is called lead-free gasoline (or lead-free petrol).

•             Certain devices such as, catalytic converters are now being used to oxidize the un-burnt hydrocarbons and carbon monoxide to carbon dioxide and to decompose nitrogen oxides into nitrogen and oxygen.