Petrol/gasoline
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Description
Petrol (UK English) or gasoline (N. American English) is the most usual fuel used in spark ignition internal combustion engines. It is a major volatile organic compound (VOC)
Detailed description
Generally, petrol is the lightest liquid fraction commercially used after the distillation of cracked petroleum. It is very variable in composition, being a mixture of alkanes and cyclic hydrocarbons with various additives. The producers vary the composition deliberately according to the season, preferring lighter fractions in winter and heavier ones in summer, to reduce losses due to evaporation.
Because of this variability between manufacturer, grades, composition and additives, the amount of thermal energy available from one litre of commercial petrol at 20 °C may be anything between about 32 MJ and 36 MJ. Internal combustion engines must be able to work efficiently over this range of fuels but it is obvious that the mechanical power output will change accordingly. If the engine is in a vehicle, it is evident that a given amount of power is require to drive the vehicle under a given set of conditions; as this power will be a constant and the energy in the fuel is not, it becomes evident that the fuel consumption will vary according to the quality of the fuel. This variation may be expected to be about ±6%. This tends to make a manufacturer's (or EPA) figure for consumption (or mileage) or even individuals' figures rather meaningless, quite apart from differences between individual cars and drivers.
