E85 Octane Rating – Important Information about Ethanol Fuel

E85 is a blend of ethanol fuel that consists of 85% ethanol fuel plus 15% gasoline. It is used for flex fuel vehicles and is now widely used in the US and in Europe.

E85 has many advantages over traditional gasoline because it reduces dependence on petroleum imports and localizes the production of fuel. It also has a significantly reduced level of emissions, especially of carbon dioxide. However, many experts are expressing concerns about the fuel economy of the E85 fuel since it has a lower amount of energy than regular gasoline.

The performance of a motor or aviation fuel, fortunately, is not only measured in terms of how much fuel it uses. It can also be measured in terms of its octane rating.

A fuel with a high octane rating is more capable of powering up high-compression engines found in high performance vehicles. A high octane rating means that the fuel can stand more compression before it detonates. In simpler terms, a fuel with a high octane rating can make the engine perform better. On the other hand, low octane fuels are ideal for engines that run on diesel.

Ethanol Octane Rating

Ethanol is known to have a higher octane rating than regular gasoline. Pure ethanol may have lower energy content than regular gasoline, but it has a higher octane rating of 113, which is far above the 86 to 94 rating range of gasoline. In fact, even methanol has a lower octane rating of just 107.

So what does the high ethanol octane rating mean for you? Due to the low energy content, you will need to make more trips to the gas station to fill up, but there will be no decrease in the performance of the engine. Its higher octane rating also allows ethanol fuel to be used in high-compression engines.

Octane Rating of Ethanol Fuel Blends

However, once ethanol fuel blends are created by mixing ethanol and gasoline, the octane rating of the end product changes. Thus, E85 octane rating is calculated to be within the range of 94 to 96, which is still higher than that of gasoline. This range was calculated and confirmed by actual octane engine tests conducted by The Renewable Fuels Foundation. This is considered to be the more accurate e85 octane rating as opposed to the 105 rating that is often cited.

According to The Renewable Fuels Foundation’s Changes in Gasoline IV manual, the 105 octane rating of ethanol e85 blend was calculated using the blending octane value of ethanol in gasoline, which is not the correct manner of calculating the octane rating of ethanol fuel blends like E85.

However, the octane rating of E10 fuel is close to the octane rating of regular gasoline. Typically, E10 fuel is rated at 2 to 3 octanes higher. This is because E10 contains only 10% of ethanol, which is an amount not significant enough to cause a major increase in the resulting fuel blend’s octane rating. Nevertheless, the higher octane rating of ethanol fuel still gives it a major advantage over regular gasoline and adequately compensates for its lower energy content.