The division of gasoline into different categories is carried out depending on the value of its octane number. This is the main indicator that determines not only the actual quality of gasoline, but also its chemical properties.
The concept of the octane number of gasoline
As a result of fractional distillation of oil under the influence of different temperatures, all kinds of fuels (including gasoline), lubricants, and products for petrochemical synthesis are obtained. This, no doubt, is known to everyone who has been to chemistry lessons at school. However, driving up to a gas station, you probably more than once paid attention to the mysterious numbers that divide gasoline into different types. What is their real difference?
These same numbers in the markings of gasoline indicate its octane number. This is the main criterion by which various types of gasoline are classified. The term "octane" characterizes the ability of a fuel to burn freely in an engine under a variety of conditions. The higher this number, the more resistant the gasoline is to autoignition when compressed. However, it is somewhat more difficult to obtain high-octane gasoline during production, in addition, it must be sufficiently pure.
Determination of anti-knock properties of gasoline
Each engine is designed to run on fuel with a specific octane rating. In Russia, most car owners use Ai92. Such types of gasoline as Ai95 and Ai98, as a rule, are afforded to the owners of a "premium" class car. Diesel fuel and Au80 are in even less demand.
Determination of the resistance of gasoline to detonation is carried out using standard mixtures. The fact is that gasoline is equivalent to a mixture of isooctane and heptane. Accordingly, if the octane number of gasoline is 92, it will self-ignite as a composition of 92% isooctane and 8% heptane.
Increasing the octane number of gasoline
In the production of various types of gasoline, a method of mixing fuel components is used. This process is otherwise called "compounding". As a result of all the necessary processes, products should be obtained that fully comply with state standards and have an accurate octane value.
Primary fractional distillation of oil produces gasoline with an octane index of 70. The quality of gasoline is improved not only with the use of compounding, but also thanks to the use of special antiknock additives. Previously, tetraethyl lead was used to improve the detonation properties of the fuel. For all that for a person, this substance is a strong poison. Currently, ferrocene or methyl tertiary butyl ether are used as high-octane additives, which do not have such a huge toxicity.