After my post The Hidden Tax on Gasoline, I was asked to provide more information on octane. Here is my attempt at a Dick and Jane.
Gasoline and engines are a system. As engines change so must gasoline. Today’s engines reflect engineering designed for them to meet strict CAFÉ standards, tail pipe emissions standards and to incorporate technology advances. In general, this has led to higher compression engines which provide better performance, greater efficiency, and more horse power but as a result many of these engines require a higher octane gasoline.
Octane measures a gasoline’s knock resistance or the ability to avoid premature ignition. Most cars still run on regular gasoline–85 %–while cars in the class of BMW and Mercedes and many turbocharged engines require premium or 91-93 octane. Race cars burn fuel with 100 octane or higher.
Until the mid 1980s, refiners used Tetraethyl lead to prevent knocking. Lead was phased out for health reasons. Refiners turned to ethanol or ethers to boost octane. Ethanol has an octane rating of 115 but has a number of problems which is why it is limited to a 10% blend for most vehicles. Ethers—MTBE—were banned about a decade ago.
As more refineries began dealing with more light—lower sulfur crudes—from imports and shale oils and stricter fuel specifications, they had to find additional sources of octane because gasoline from light crudes have a lower octane rating.
Gasoline is a complex chemical mixture and various refining processes are used to rearrange hydrocarbon molecules to produce higher octane. These include catalytic reforming, isomerization, and dehydrogenation. Probably most refiners use catalytic reforming to produce reformate which is a high octane blending component. All of these processes add to the cost of producing gasoline.