Fuels: Definitions

What is a fuel?

The conventional fuels used massively at present are hydrocarbons (an organic body composed only of carbon and hydrogen atoms).

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

Some characteristics used

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

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

- Higher Calorific Value (PCS):
Quantity of heat expressed in kWh or MJ, which would be released by the complete combustion of one (1) Normal Cubic Meter of gas. The water formed during combustion being returned to the liquid state and the other products being in the gaseous state.
- The lower calorific value (PCI): Calculated by deducting by convention, from the PCS the heat of condensation (2511 kJ / kg) of the water formed during combustion and possibly of the water contained in the fuel.

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

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

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

- Viscosity: (Wikipedia, the free encyclopedia)
Viscosity refers to the ability of a fluid to flow, in fluid mechanics. In everyday language, we also use the term fluidity.
As the viscosity increases, the ability of the fluid to flow decreases. Viscosity tends to decrease with increasing temperature.
Mechanical oils are classified in particular according to their viscosity, according to the engine lubrication requirements and the temperatures to which the oil will be subjected during engine operation.

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The different kinds of hydrocarbons:

1) Paraffinics or alkanes:

Paraffinic hydrocarbons are present, depending on their number of atoms, at ambient temperature and pressure, in the form:

- gaseous with less than 5 atoms
- liquid between 5 and 15 atoms
- paraffinous (fatty solid) greater than 15 atoms

They are characterized by an open carbon chain.

Normal paraffins and iso paraffins are distinguished by the assembly of their atoms. Both have a general formula: CnH (2n + 2)

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

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Conventional fuels are therefore part of the alkane family.

2) Aromatics

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

General formula: CnH (2n-6)

3) Olefinic.

Hydrocarbons unsaturated with one or more double bonds, and called alkenes or cyclenes, according to their form (chains or cycles).

General formula: CnH2n (for non cyclic)

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

More: Petroleum fuels

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