Mandating alternative fuels
At present, about 80% of the world's demand for transportation fuels -- road, rail, air and sea -- are met by derivatives from the fossil fuel, petroleum.Petrol, one of the major derivatives of petroleum, is used throughout the world as a motor vehicle fuel.When there is enough oxygen, hydrocarbons can be burnt to form CO If insufficient oxygen is available, incomplete combustion occurs, forming carbon monoxide CO, nitrogen oxides and carbon, as well as carbon dioxide and water. Environmental considerations Exhaust emissions from petrol-driven cars include, in addition to CO and water vapour, hydrocarbons, nitrogen oxides and CO.These latter emissions may be effectively reduced by fitting a three-way catalytic converter that converts these three types of exhaust components into less reactive substances.The hydrocarbon constituents are those that have 4 - 12 carbon atoms in their structure and fall into three general types: Petrol consists of a blend of more than 200 such hydrocarbons either occurring naturally in petroleum or manufactured from it.
Concerns also about atmospheric 'smog' pollution have led to the desire to remove up to 90% of the smog precursors present in engine exhaust gases by the use of catalytic converters.Volatile organic compounds are also emitted into the atmosphere through evaporation from fuel tanks, carburetors and refuelling stations.These emissions can be reduced by using carbon canisters containing activated charcoal which absorbs these vapours.This change is not without its disadvantages, since a lower octane fuel results in a less efficient engine, and an overall increase in carbon dioxide emissions.Some additional CO emissions also arise from the changed refining processes.
They are 'heavier' than the components of petrol and thus it is a less volatile fuel.