# Fuels: Definitions

What is a fuel?

Conventional fuels massively currently used are hydrocarbons (organic body composed solely of carbon atoms and hydrogen).

The chemical formula of the hydrocarbons used in automobile is usually in the form:
CnHm where "n" and "m" represent the number of carbon and hydrogen atoms of the molecule.

Some features employed

- The density:
give the weight of a volume 1 dm3 (or 1 l) of this material relative to water that has a weight of 1 1 kg l.
The essence has a weight of 0,755 kg per liter.

- Flash point:
This is the lowest temperature at which the concentration of emitted vapors is sufficient to produce deflagration in contact with a flame or hot spot but insufficient to produce the propagation of combustion in the absence of the flame " pilot".

- Gross Calorific Value (GCV):
Heat quantity in kWh or MJ, which would be released by the complete combustion of one (1) Cubic meter of gas Normal. The water formed during the combustion is returned to a liquid state and the other products being in the gaseous state.
- The lower heating value (LHV): Calculated by deducting by convention, the PCS condensation heat (2511 kJ / kg) of the water formed during the combustion and optionally water in the fuel.

- Auto-ignition temperature:
This is the minimum temperature at which a fuel mixture, pressure and composition data, spontaneously ignites without contact with a flame.

- Vapour pressure:
The vapor pressure is the pressure under which the single body placed at a given constant temperature, is in equilibrium with its vapor. In other words, it is the pressure at which the liquid boils (or the solid sublimates) at the temperature.

- Vapour density:
This data indicates the number of times the vapors of a product are heavier or lighter than air. This measure is taken to boiling point.
If the vapor density is greater than 1, the vapors of a product will tend to remain near the ground.

- Viscosity: (Wikipedia, the free encyclopedia)
The viscosity refers to the ability of a fluid to flow, in fluid mechanics. In everyday language, it also uses the term fluidity.
With increased viscosity, fluid's ability to flow decreases. The viscosity tends to decrease with increasing temperature.
One class including mechanical oils according to their viscosity, depending on the lubrication needs of the motor and the temperatures at which the oil will be subjected during engine operation.

The different kinds of hydrocarbons:

1) Paraffin or alkanes:

Paraffinic hydrocarbons are presented, according to the number of atoms, at ambient temperature and pressure, in the form:

- Gas with less carbon 5
- Fluid between 5 and 15 atoms
- Paraffin (solid fats) than 15 atoms

They are characterized by an open carbon chain.

We distinguish the normal paraffin and iso paraffin, by assembling their atoms. The two have a general formula: C n H (+ 2n 2)

Some examples :
- CH4: methane
- C3H8: propane
- C4H10: butane
- C8H18: octane

Conventional fuels are therefore part of the family of alkanes.

2) Aromatic

They contain one or more unsaturated rings to 6 carbon atoms of the same type as that which is benzene.

general formula CnH (2n-6)

3) olefin.

unsaturated hydrocarbons with one or several double bonds, and called, alkenes and cyclenes by shape (chains or cycles).

general formula CnH2n (for non-cyclic)

Note: The suffix "ane" is used for saturated hydrocarbons
The suffix "éne" is used for unsaturated double bond hydrocarbons (one or more)
The suffix "yne" is used for triple bond unsaturated hydrocarbons (one or more)

More: Petroleum fuels

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