The main use for octane is as an ingredient in car fuel.
Octane and its isomers make up most of the composition of gasoline, which is an engine fuel refined through the fractional distillation of petroleum.
Petroleum, obtained by drilling, is produced through the decomposition over time of organic matter that has been compressed into layers in the earth's crust.
Petroleum is drilled in the ocean using oil platforms or on land with regular drills.
The crude fuel is then refined into four fractions (or levels): diesel, kerosine, gasoline, and refinery gas.
The size of the hydrocarbons gets progressively larger from refinery gas on up.
Therefore, the majority of octanes (C8) are found in gasoline (40-180 degrees C).
Gasoline fractions make up 15-30% of petroleum through the refining process.
The refining process for engine fuels is also known as "cracking" (History).
The two main categories of cracking are thermal (high temp.) and catalytic (low temp.) decomposition.
In thermal decomposition, fractions are seperated through boiling the petroleum: the lighter hydrocarbons are burned off to leave behind the heavier ones, which are most useful for fuel.
Catalytic decomposition is cracking at low temperatures using a catalyst, which is quite often a silica-alumina product (SiO2-Al2O3).
Other forms of catalytic cracking are catalytic synthesis of hydrocarbons from carbon monoxide and hydrogen, and catalytic high-pressure hydrogenation of soft coal (adding hydrogen atoms to coal).
When you go to a gas station and pull your car up in front of the pumps, you will notice (along with the "Regular Unleaded", "Premium", and "Super Premium" names) different numbers labeling the choices for gas.
These numbers are the octane ratings for your gas choices. Octane rating is a performance rating of petrol in internal-combustion engines.
An octane rating defines that level of petrol's capability of limiting "knocking" (premature ignition of the fuel) in an engine.
Knocking causes noise and, if let to progress, will do damage to the car engine.
A fuel's ability to prevent knocking is based on its ratio of branched-chain to straight-chain hydrocarbons.
Higher levels of branched-chains in a fuel are more efficient for high-performance engines (engines that burn alot of fuel, i.e. sports cars and race cars) because branched-chain hydrocarbons have weaker bonds and, therefore, burn faster (Structure).
Additives, such as tetraethyl lead, are put in gasoline to limit knocking as well (History).
A fuel's octane rating is determined by comparing it to a mixture of isooctane and heptane. The octane-rating scale goes from 0 to 100, where heptane is 0 and isooctane is 100. Therefore, this mixture is a mean, and all other mixtures of gasoline will fall somewhere within the scale. The higher its octane rating, the greater ability that gas has to reduce "knocking." It is more practical and economic for the average car owner to use lower-octane fuel because the average car does not require high-efficiency "Super Premium" fuel, which is much more expensive than the "Regular Unleaded."