The octane number (octane) of a fuel represents the percentage of isoctane (Ç8 H18 ) and heptane (Ç7 H16 ) contained in it. The resistance of a fuel to self-ignite is measured through the octane number, which is related to the quality of combustion of the fuel. The higher the index, the more resistant the fuel to detonation.
What would the detonation be? Gasoline detonation happens in the cylinders of internal combustion engines, it corresponds to premature combustion during the compression exerted by the piston. Since good quality combustion occurs with a smooth progression of the flame through the combustion chamber, this process takes place as the fuel is burned.
Gasoline detonation process: is when a mixture of air and fuel spontaneously explodes in the chamber before the flame, this phenomenon is also known as “raters”. These engine knocks lead to reduced performance and can even severely damage the engine. Raters are heard more often when the vehicle is operating under more difficult conditions, such as when climbing a slope or when accelerating.
According to studies, a scale was established to measure the tendency of a gasoline to detonate. On this scale, isoctane (2,2,4-trimethyl-pentane), which detonates only at high compressions, is rated as 100; n-heptane, which triggers very low comprehension, was assigned the index zero. Therefore, an 80-octane gasoline has the same detonation characteristics as a mixture of 80% isoctane and 20% n-heptane.
The compression that the gasoline-air mixture supports in the engine is proportional to the octane rating. The most important of the additives that increase the octane of gasoline is tetra-ethyl lead [Pb (C2H5 )4 ].
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By Líria Alves
Graduated in Chemistry
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Would you like to reference this text in a school or academic work? Look:
SOUZA, Líria Alves de. "Octane number of fuels"; Brazil School. Available in: https://brasilescola.uol.com.br/quimica/numero-octanagem-combustiveis.htm. Accessed on June 27, 2021.
