Ethanol Content in Different Gasoline Octane Ratings

Ethanol Content in Different Gasoline Octane Ratings

Gasoline nowadays is offered with several different octane ratings depending on the application.

In the US market, specifically, over 98% of sold gasoline comes with a blend of ethanol.

Now, you might be curious as to what ethanol exactly is and how it goes hand-in-hand with the octane rating of gasoline.

In this article, we’ll be discussing how ethanol is used in today’s gasoline and provide you with some specific figures as to how much ethanol is actually used for each octane rating.

How much ethanol is in gasoline?

Gasoline with an 87 to 93 octane rating can have a blend of either 10 (E10) or 15% (E15) ethanol with them. These are the most common ethanol-gasoline blends.

E85, depending on the region or country, has around 50 to 85% ethanol, and is used in gasoline with an octane rating of 94 or higher.

Take note that the three general gasoline-ethanol blends we’ve mentioned above are only the ones most commonly used in the automotive world.

While some places may use other blends like E20 or E30, we will be solely focusing on the three general categories of ethanol-gasoline blends for this specific article.

What is ethanol?

To put it simply, ethanol (also called ethyl alcohol) is a colorless organic chemical used in a lot of consumer and industrial products.

In the oil and gas industry, ethanol is mostly derived from the fermentation of sugar in the starches of corn. Some countries, however, may choose to use sugarcane instead.

What is ethanol

Aside from being mixed with fuel, ethanol is also used in hand sanitizers, vinegar, feedstocks, and, of course, alcoholic beverages.

The Use of Ethanol in Gasoline

Ethanol, in and of itself, has a very high octane rating of 100, which makes it very useful for raising the octane rating of gasoline when they are mixed together.

Now, you might be wondering why gasoline needs its octane rating raised, to begin with. And what even is “octane”?

Octane rating (also called octane number) is a standardized measurement used to see how capable a certain fuel is in going through the compression cycle in an engine without detonating.

Certain types of engines require gasoline with different octane ratings, as the right octane rating essentially prevents engine knocking and ensures your fuel doesn’t detonate too early.

When you add ethanol into the mix, it further decreases the chance of early detonation because of its high octane rating.

The interesting part about blending pure ethanol with an octane rating of 100 with gasoline is that it actually performs as if it has an octane rating of 113.

This is why you can commonly see ethanol being described as having an octane rating of 100 to 113.

The Mandate of Ethanol in Today’s Gasoline

Back before we even started mixing ethanol with gasoline, a fuel additive called MTBE (Methyl Tertiary Butyl Ether) was used to oxygenate gasoline instead.

This resulted in reduced emissions and an improvement in combustion efficiency. The problem was that MTBE was very toxic if it was ever spilled into surrounding water sources.

Since ethanol is organic by nature while still efficiently oxygenating fuel, it’s a lot safer for the water supply.

In the United States, a federal government mandate called the Renewable Fuel Standard (RFS) required a certain level of ethanol to be blended with gasoline in 2005.

However, the first actual use of ethanol in gasoline was way back in 1990, when the US congress made the “Clean Air Act”.

Back then, all ethanol-gasoline blends first started with only the E10 (gasoline with 10% ethanol).

But nowadays, a lot of automobile manufacturers actually make cars that can run on both E10 and E15.

Despite there being inconsistencies regarding the emissions of ethanol-blended gasoline versus pure gasoline, the production of ethanol is undeniably cleaner.

As we’ve discussed, the production of ethanol involves the fermentation of the sugar of plants such as corn, thereby making the process organic.

Thus, if we were to compare the two based on their lifecycle as a whole, ethanol still comes out on top as the one that’s cleaner to produce.

Does ethanol increase engine performance?

Gasoline containing ethanol, especially highly-concentrated ones like E85, is actually known for providing an added boost in performance.

This is especially true in the world of motorsport, wherein engines are designed to run on fuel with higher octane.

Does ethanol increase engine performance

While motorsport applications can definitely make use of gasoline with more than 85% of ethanol, E85 is still the most commonly used blend that doesn’t break the bank.

Ethanol, having a naturally high octane rating, makes a great addition to performance applications.

Having a high octane rating also means that you’ll have high resistance to knocking, which is pretty important when you’re pushing your engine to the limit of its performance.

Does this mean that you should be adding E85 to your regular engine to boost its performance? Not exactly, we’re afraid.

As we’ve discussed earlier, not all engines are built to accommodate the same type of gasoline and octane rating.

In the case of a normal non-performance-oriented engine, you’re not going to get much benefit from putting E85 in it unless it’s in a “flex-fuel” vehicle.

You can read more about flex-fuel vehicles and how E85 factors into them a bit further down.

Going back to the whole topic of ethanol and performance, the engine (or the car model) itself will determine whether or not you will get any benefit from putting more ethanol in your tank.

To give a recap, only an E10 or E15 blend is used in most of the gasoline sold out there. These blends are commonly used for gasoline with 87 to 93 octane ratings.

Most of the cars that you see on the road should already be within this octane range in terms of fuel, with the average needing at least 91.

We still recommend that you check your specific car’s owner’s manual, as the minimum octane rating that your car needs can also be dependent on its engine’s compression ratio.

Engine Compression Ratio and Octane Rating

In general, lower compression engines (around 9.3 to 1) can safely make use of 87 octane gasoline. This type of gasoline is usually labeled as “Regular”.

In the case of engines with higher compression ratios ( over 10.5 to 1), higher octane gasoline is usually required. This is usually labeled as “Premium” gasoline.

When you start to enter E85 territory that has a much higher octane rating, the list of vehicles that can you can safely use it in gets a lot shorter.

Flex-fuel vehicles, as we’ve discussed, are part of that list. 

A lot of motorsports enthusiasts also commonly modify their car’s fuel system. That, paired with a lot of careful tuning, allows them to safely make use of E85 to boost their performance as well.

Flex-Fuel and E85

Flex-fuel vehicles are manufactured with engines that can use both regular gasoline and ethanol-gasoline blends with up to 85% (51 to 83% in the US) ethanol.

Such flex-fuel vehicles don’t necessarily have to be sports cars or race cars. Some examples of these can be pickup trucks such as certain models of the Ram 1500.

The term “flex-fuel” is actually interchangeable with E85, as both essentially refer to the same type of ethanol-gasoline blend used in flex-fuel vehicles.

One easy way of telling if your car is a flex-fuel vehicle is by checking the markings on its fuel cap. It will usually have the text “E85/Gasoline” printed on it.

In the US, there are more than 3900 gas stations across 42 states that offer E85 at their pump. You’ll also commonly see them marked with a “for flex-fuel vehicles/FFV only” reminder.

Flex-Fuel and E85

However, just as the percentages we’ve mentioned above suggest, the actual ethanol content that they contain can vary depending on the geographical location and even the season.

The Cons of Ethanol in Gasoline

Ethanol, judging by how we’ve presented its plethora of benefits above, seems to have been a big success in terms of being a renewable fuel. But it’s still not without its downsides.

For one, gasoline blended with ethanol isn’t exactly the best way to save money per mile in the long run.

Ethanol, especially E85, may be cheaper to buy on the pump, but it also contains about 1/3 less energy than ethanol-free gasoline.

This means that it’s going to take a bit more ethanol-blended gasoline to achieve the same mileage that you can get with a lesser amount of ethanol-free gasoline.

The general consensus is that the higher the ethanol content, the more noticeable the impact it has on your fuel economy.

While this isn’t exactly that much of an issue in high-performance applications such as motorsports, it can definitely be one for the average motorist.

Another downside that’s more on the preparation side of things is that ethanol requires a lot of land for crop-growing.

Not only that, but it has also caused a shift in the usage of crops such as corn from food to fuel production instead, racking up the demand and prices of such crops in the process.

Due to the nature of ethanol’s production, it’s also reliant on how good the quality of the growing season is.

This means that if there were ever to be any natural calamities that can cause the destruction of such crops, then it could certainly take a toll on the usual production of ethanol-blended fuel.

Ultimately, the use of ethanol-blended gasoline is up to each individual car owner’s discretion and due diligence.

With modern automotive technology allowing even more cars to accept higher amounts of ethanol in their tanks, ethanol seems to be here to stay as one of the world’s top biofuels.