Ethanol Engines
Corn generated ethanol biofuel with test tubes on white background ©U.S. Green Technology

Ethanol Engines vs. Traditional Engines: Understanding the Difference

Ethanol Engines Could Pack Big Punch

95 percent of all petroleum-based gasoline sold in the United States is now blended with 10 percent ethanol, according to the U.S. Energy Information Administration. In 2015, ethanol biorefineries located in 29 states set a record by producing 14.7 billion gallons of high-octane renewable fuel, the Renewable Fuels Association reported. Oak Ridge scientists’ recent discovery that ethanol can be produced from carbon dioxide and the hope that U.S. ethanol imports can help countries such as Japan reduce greenhouse gas emissions are likely to affect demand for ethanol in the near future. Ethanol is in demand because ethanol and ethanol engines differ from traditional gasoline and gas engines in the way they are manufactured, their fuel efficiency and their affordability. Here’s a closer look at how ethanol engines differ from traditional engines.


Traditional gasoline comes from petroleum, which is a mixture of many different hydrocarbons. It is found in underground rock formations underlying oil fields, from which it must be drilled, pumped and refined into gasoline. When used in gasoline engines, fuel and engines differ according to how much the engines compress the fuel and air in their cylinders. High-compression engines squeeze fuel and air more than low-compression engines do. This can cause premature ignition and wasted power, called engine knock, which can damage an engine. To operate efficiently, high-compression engines need gasoline with more knock resistance than low-compression engines. A gasoline’s ability to resist knock is expressed in its octane number. The higher the octane number, the more resistant to engine knock the gasoline is.

Ethanol comes from ethyl alcohol, the same type of alcohol found in alcoholic beverages. It is a natural byproduct of yeast and can be produced by fermenting sugars with yeast or by hydrating ethylene. When used for fuel, it is typically produced from organic matter called biomass, which can consist of starch- and sugar-based feedstocks, such as corn, or from cellulosic feedstock, such as crop residues or wood chips. There are two main production processes for converting biomass into ethanol, known as dry milling and wet milling, which differ in their initial treatment of the grain being used. In dry milling, the grain is initially ground into flour meal, while in wet milling, it is soaked in water and dilute sulfurous acid.

Ethanol delivers less energy per gallon than gasoline, but it has a higher octane number. Because of this, ethanol is often blended with low-octane gasoline to improve its knock resistance. However, ethanol can cause problems for engines that were designed purely for gasoline. Ethanol is a strong solvent that can absorb water and it can be corrosive to plastic and rubber compounds of traditional engines, as well as brass, copper and aluminum unless these are specially treated. Ethanol can also raise the temperature and pressure in ethanol engines.

Fortunately, most vehicles built after 2005 have on-board computers that make air/fuel mixture and spark timing adjustments to accommodate up to 15 percent ethanol mixes. Engines designed to run on ethanol blends use different materials for their rubber sealants and o-rings. Some auto enthusiasts have modified their engines to run on pure ethanol.

Fuel Efficiency

Ethanol is not as fuel-efficient as gasoline. Ethanol engines deliver approximately one-third less energy per gallon than gasoline. Consequently, a mixture of 85 percent gasoline and 15 percent ethanol is approximately 30 percent less powerful than pure gasoline, and ethanol gets less miles per gallon than gasoline. However, ethanol is comparable to gasoline for acceleration, power and cruising capability.


Ethanol is less expensive than gasoline, especially in regions that grow corn such as the U.S. Midwest. For instance, in July 2016, the national average price for E85 ethanol was $1.99 per gallon, compared to $2.26 per gallon for gasoline. However, the savings from this difference can be offset by the fact that ethanol gets fewer miles per gallon. For instance, for a 2014 Ford Focus, the price of E85 would need to be 30 percent cheaper than gasoline to translate into real savings after the difference in miles per gallon is factored in. To determine whether ethanol is more cost-efficient for your vehicle, see the Department of Energy’s website

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  • Erocker

    Shelf life of E10 is: only 3 months
    Shelf life of gasoline is: 2 years
    Shelf life of ethanol not exposed to the air is: unlimited

    Mixing gasoline with ethanol is a bad idea. Ethanol when mixed at 10% in gasoline has a reactivity which causes the vapor pressure to increases by one point results in higher VOC and results in increased ozone. Reactivity from the mix of ethanol and gasoline also results in the ethanol turning the sulfur normally found in gasoline into sulfuric acid. When water gets into this mixture it causes it to separate. The water and ethanol combines and drops to the bottom of the tank causing great corrosion damage to the tank. I have seen this water ethanol mix after separation from 6 month old e10 and it is not like the original ethanol, it is milky and feels a little waxy. It appears to have changed chemically and combined with some of the gasoline mixture.