Gasoline (hydrocarbon)

The gasoline used like Carburant in the thermal engine or spark-ignition Engine with positive ignition is a mixture of Hydrocarbure S, to which other combustible or auxiliary products are sometimes added. One finds there on average:

20 to 30% of Alkane S, hydrocarbons saturated with C_nH_2n+2 formula,
5% of Cycloalcane S, saturated hydrocarbons cyclic,
30 to 45% of Olefinic hydrocarbon S, hydrocarbons unsaturated,
30 to 45% of aromatic hydrocarbons, the family of the Benzene.

These products result, essentially, from the Distillation of the Pétrole. In the event of oil shortage, it was also called upon the distillation of the oil shales, as that was practiced a few decades ago in the exploitation of the mine of Télots, with Autun.

Among alkanes, two play a particular part: the Octane C₈H₁₈ and the Heptane C₇H₁₆.

Indeed, these two alkanes have properties radically different from the point of view of their tendency to auto-ignition (spontaneous lighting of the fuel in the cylinder not requiring the use of the candle). A mixture of Air and vapor of octane with difficulty will ignite spontaneously, it will be thus well the candle which will cause lighting, and will create at the time envisaged a Déflagration, i.e. a flame of premixing which is propagated in the mixture at a speed lower than the Speed of sound. On the contrary, for heptane, auto-ignition is easy: for raised compression ratios, lighting will take place in volume in the cylinder before the candle does not function. This phenomenon characteristic of the driving with positive ignition is called the Cliquetis and causes the formation of shock waves in the cylinder, from where characteristic noise. In the worst of the cases, there can be creation of a Détonation which can go as far as dissolving the piston, moving face of flame the more quickly than the sound while being coupled with the Shock wave. It is thus rather current, in particular in the Anglo-Saxon literature, of speaking improperly about Détonation when one actually speaks only about Cliquetis.

In the actual position of technologies a driving with detonation would have one very short lifespan compared to the engine spark-ignition current. This term of engine to explosion is however not very precise, because the deflagrations just like the detonations are both of the Explosion S. It would be better to employ the internal combustion engine term of .

Octane number

See also: Number octane

The tendencies to the auto-ignition of the mixtures of octane and heptane are different. They are used as reference to determine the Number octane of a fuel to test. If, for example, the compression ratio necessary to the appearance of the Rattling of a mixture of air and this fuel in an engine of reference is the same one as for a mixture comprising iso-octane 95% and heptane 5%, then it is said that this fuel has an octane number of 95. Naturally, this determination must be done under standardized conditions. It is understood in addition that the mixtures made up exclusively of heptane and octane will have all of the octane numbers ranging between 0 and 100

Mixtures with other products make it possible nevertheless to have numbers octane superior to 100, it should then be defined by extrapolation: certain gasolines of competition, known as “gasolines aviation” reach approximately 110. During very many years, one added to the gasoline a certain quantity of tetramethyl Plomb Pb (CH₃) ₄ or better of tetraethyl Plomb Pb (C₂H₅) ₄ in order to decrease the tendency to the gasoline detonation containing a strong percentage of heptane. It was a manner of increasing the octane number artificially (one gained 10 points with 1 g/l of PTE) and to support the Lubrification engines but that resulted in dispersing in the environment of strong quantities of Plomb, metal which one knows toxicity. The gasolines comprising of lead are from now on prohibited. One knows other solutions, not inevitably free from disadvantages, for example to use more aromatic hydrocarbons (much more toxic than alkanes…), to add alcohols (by causing risks of Corrosion engines), etc

A fuel whose octane number is too weak tends to cause a too brutal Combustion, but presents also an annoying tendency to the spontaneous combustion at the time of the Compression in the cylinders of the engine and to the rattling. The higher the compression ratio of the engine is, the more the temperature reached during the compression of gases is raised and the more the octane number must approach 100. As it in addition is known, the increase in the compression ratio improves, in accordance with the laws of the Thermodynamique, the Rendement of the engine, by increasing the variation of the temperatures of the hot source and the cold source. An engine designed to function with a fuel having a certain octane number can without problem being fed with another fuel of higher index, but not the reverse!

Two values of the octane number exist:

the Number Octane Seeks (Research Octane Number, RON ) characterizes the behavior of a fuel with low mode or during accelerations.
the Driving Number Octane (Motor Number Octane, MY ) evaluates the resistance of a fuel to the rattling to high mode.

The various types of currently available gasolines are:

unleaded gas 95 or “Eurocarburant” (octane number 95),
unleaded gas 98 (octane number 98, available in Italy only in some stations, because too much polluting),
the “super one” (index 98, in the process of disappearance). It does not contain any more lead but a Potassium for the “anti-recession of the valves” and poses of this fact of the problems of operation.

The unleaded gas 98 is more detergent than the unleaded gas 95 and appears more corrosive, in particular for the parts in elastomer S (rubber S). These two fuels contain strong quantities of aromatic components which are very toxic. It is thus necessary to avoid breathing the vapors of them and not to make use of it like agent of cleaning or degreasing.

Gasoline aviation

It is containing hydrocarbon specific used in the engines of planes with pistons. It is with very high number octane and treated in order to be less volatile than the regular gas in particular for the altitude flight. The most used in light aviation is the AVGAS 100LL (Low Lead). It is of blue color.

This gasoline always contains tetraethyl lead although it is removed for the cars. Taking into account the price reached by this fuel for light aviation, a certain number of attempts are made to develop engines diesel aviation. But of many engines with positive ignition using of the automobile gasolines are used, in particular the Rotax engines and Jabiru. One finds them in particular for the low powers and the ULM.

However, for the jets, it is the Kérosène which is at the base of the fuel. Obtained directly by the distillation of crude oil, it is used amongst other things for the production of the fuel, THREW and JET-B.

Others

One finds in hardware store the gasoline C, the gasoline F, the “White spirit”, the gasoline G (oil ether), etc which are mixtures of more or less volatile hydrocarbons and little poisons. These are obviously very flammable products that it is advisable to handle far from any source of heat and in quite ventilated places.

In addition to the filling of the lighters which represents a very marginal use (one spoke formerly about gasoline with lighters), the oil gasolines are used especially as Solvant S which are used to eliminate the spots from greasy substance or thinners for paintings.

Price of the gasoline

Because of an important dependence of many Western countries near the countries of OPEC, the hydrocarbons are strongly taxed. The European policy consists in taxing energy with an aim of:

To restrict energy consumption (safeguard of the planetary resources and in particular of the atmosphere);
To ensure a margin of price which could absorb and/or temporize a too brutal increase in the course of oil;
To reduce the dependence near the exporting countries;
To ensure of the considerable incomes the State.

In France, TIPP accounts for 400% of the price of the gasoline net of tax, which represents a share of 80% of the final price. For better informing the Consuming and fighting against the Inflation, the government opened on January 2nd, 2007 the site price-carburants.gouv.fr which makes it possible to know everywhere the tariffs of the fuels France updated at each evolutions of price, by the owners of the service stations. For the moment only the principal fuels are listed. In the long term of other types of fuel as bio-ethanol will be taken into account.

These prices increased until exceeding the bar of: 8.00$ on September 10th, 2005.

In the United States and Canada, the policy is opposite, because weak taxation makes it possible to offer a cheap gasoline; the respective governments privilege " the standard of living of American, which is not négociable" (sic. George W Bush, president of the the United States) to the planetary resources.

Although the United States has oil resources (the USA were the first world oil producer in 1920, ensuring 80% of its production), they are mainly importers (export: 20,000 barrels per day mainly towards Canada, importation: 10,000,000 barrels per day). The United States is thus dependant énergétiquement on other countries like the Saudi Arabia, the Venezuela or the Canada. Following the intervention of the American army in Iraq and with the new possibility to import resources since this country, the United States imports approximately 4% of Iraqi oil.

Consumption

Since the Years 1970 and the 2 oil crises, the policies of state and manufacturers were to reduce overall the consumption of the principal automobile models.

In France, the average consumption of the car fleet thus passed from 8,3 liters to the 100 km to 7 liters in 2004. The consumption of the " convey nine moyen" marketed in France in 2005 of 6 liters/100km is. Moreover for the 4th year of continuation, annual total consumption the super one and of Gazole moved back in France to return on the level of 1996 is 29 million cubic meters. That is due to the rise in the price of the gasoline which involves a reduction in traversed mileage (398 billion km in 2005 against a peak to 404 billion in 2003) supported by the ageing of the French population, tendency so noted in Germany and Great Britain - and to a reduction speed (helped by controls radar speed in clear increase).

On average in the world, consumption is of 10 liters/100 km by particular vehicle.

References

External bonds

See a diagram detailed on a gasoline distributer for car.

Simple: Gasoline

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