What does octane do?
Compression & Octane
Unless you drove high-performance engines, spending more on expensive high-octane gasoline used to be unnecessary. But in recent years, octane has made a comeback.
Automakers are building smaller, higher-compression engines to reduce weight and meet more stringent fuel economy standards. *Compression, or pressure inside internal combustion engine cylinders, translates to thermal efficiency and work from a volume of fuel. Higher-octane fuels allow for optimization of performance and emissions in high-compression engines.
We have two primary sources of octane. One is renewable ethyl alcohol (ethanol) derived from the bio-based materials like starch in field corn and sugarcane. The other is carcinogenic BTEX toxins (benzene, toluene, ethylbenzene, and xylene) produced from crude oil.
Ethanol is Clean Octane
Good Ol’ Regular: Today, E10 gasolines are used in all gasoline engines. They represent nearly all gasoline sold in the United States and have been used for decades. Regular 87 octane gasoline contains 10% ethanol blended into a “sub-octane” petroleum base that has a rating of 84 octane. Ethanol boosts the resulting octane by at least three points, achieving the 87 regular gasoline. Midgrade and premium fuels, such as 91 or 93 octane, are simply 10% ethanol mixed with gasoline and higher-octane (and more expensive) petroleum compounds.
Unleaded 88 E15: Over the last several years, we’ve seen the rise in popularity of E15, often advertised as Unleaded 88 to reflect its 88.5 midgrade octane rating. Back in 2011, the U.S. Environmental Protection Agency approved E15 use in all 2001 and newer on-road gasoline vehicles. This blend simply has more ethanol than regular E10 we’ve all been using. When sub-octane is the starting base, adding 15% ethanol raises the octane rating by about 4.5 points to 88.5.
Premium and midgrade gasolines have always cost more than regular. However, Minnesota Unleaded 88 E15 has been priced lower than regular 87. That attractive pricing and extra octane have caught the attention of consumers — particularly during recent gasoline price shocks when using Unleaded 88 has provided dramatic cost savings.
E85 Flex Fuels: E85 “flex fuel” is a higher ethanol content alternative fuel intended for use in flexible fuel vehicles (FFVs). Like traditional gasoline and diesel fuel suppliers, E85 producers follow specifications to ensure proper performance at differing temperatures and elevations. Depending on season and location, E85 contains 51% to 83% ethanol and has high octane ratings varying from the upper 90s to 100-plus. Presently, the U.S. is home to 20 million FFVs and 3,300 E85 stations. FFVs and high-level ethanol fuels are also popular in other countries including Brazil and Sweden.
More Ethanol Octanes: Pure ethanol has an estimated octane rating of approximately 114. That’s more than our sedan, SUV, and pickup engines can utilize today. But when engines are optimized for biofuel blends, as is done in both Indy and NASCAR racing, those ethanol-powered engines achieve impressive performance and horsepower.
Automakers have advocated for a universal high-octane fuel that would allow them to optimize new engine technologies. Ethanol could be the path to a future renewable-based and cleaner higher-octane fuel.
*Knock-knock! It’s Octane! The U.S. Energy Information Administration defines “octane rating” as a measure of fuel stability. It is based on the pressure at which a fuel spontaneously combusts (pre- or auto-ignites , “knocks” or “pings”) in a test engine. The name “octane” is shorthand for iso-octane, a knock-resisting hydrocarbon with a 100 octane rating.