Katerina Swanson
Ethanol is a renewable fuel made from plant materials such as grains, sugarcane, and corn. It is a common additive in gasoline, as it oxygenates the fuel, making it safer for the water supply and boosting its octane number. The amount of ethanol in fuel varies by region and season, but in most states in the USA, it is standard practice to include 10% ethanol in gasoline. This mixture, known as E10, is the primary source of US ethanol consumption and is used in all light-duty vehicles in the country. Other blends include E15, which contains 15% ethanol, and E85, which can contain up to 85% ethanol and is used in flexible-fuel vehicles.
| Characteristics | Values |
|---|---|
| Percentage of ethanol in gasoline in the US | 10% |
| Gasoline with 10% ethanol content | E10 |
| Gasoline with 15% ethanol content | E15 |
| Gasoline with up to 85% ethanol content | E85 |
| Ethanol's energy compared to gasoline | 33% less |
| Ethanol's impact on fuel economy | Depends on ethanol content and engine type |
| Ethanol production feedstocks | Corn grain, sugarcane, grains |
| Ethanol's impact on water supply | Safer than gasoline |
| Ethanol's impact on octane rating | Boosts octane number |
| Ethanol's impact on engine performance | May cause overheating in older engines |
| Ethanol's impact on fuel prices | Debated by economists |
| Ethanol's impact on the environment | Reduces need for oxygenates and octane boosters |
| Ethanol's impact on the farm economy | Billions of dollars and thousands of jobs |
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What You'll Learn
- Ethanol blends: E10, E15, E85, and E25
- Ethanol production: corn, sugarcane, and biomass
- Ethanol's benefits: oxygenates fuel, boosts octane, and reduces air pollution
- Ethanol's drawbacks: less energy than gasoline, higher consumer cost, and engine overheating
- Ethanol in the US: history, usage, and impact on fuel economy
Ethanol blends: E10, E15, E85, and E25
Ethanol is a renewable fuel made from plant materials collectively known as biomass. In the United States, 94% of ethanol is produced from the starch in corn grain. Ethanol blends have "E" numbers that indicate the percentage of ethanol in the mixture by volume. For example, E85 contains 85% anhydrous ethanol and 15% gasoline.
E10 is a common ethanol blend, with 10% ethanol and 90% gasoline. It is sometimes called gasohol and can be used in the internal combustion engines of most modern automobiles and light-duty vehicles without the need for modifications. E10 blends are typically rated as being 2 to 3 octane numbers higher than regular gasoline and are approved for use in all new US automobiles. They are also mandated in some areas for emissions and other reasons. As of 2011, blends of E10 or less are used in more than 20 countries around the world. E10 can reduce carbon monoxide (CO) emissions by 20 to 30% under the right conditions and decrease emissions of CO and greenhouse gases such as CO2 by an estimated 2% over regular gasoline. However, it can also cause increases in evaporative emissions and some pollutants, depending on factors such as the age of the vehicle and weather conditions.
E15 is another ethanol blend that contains 15% ethanol and 85% gasoline. This is generally the highest ratio of ethanol to gasoline recommended for vehicles that run on E10 in the US. E15 is approved for use in model year 2001 and newer light-duty vehicles. In October 2010, the EPA granted a waiver to allow up to 15% of ethanol to be blended with gasoline for cars and light pickup trucks with a model year of 2007 or later. This waiver was expanded in January 2011 to include model year 2001 through 2006 passenger vehicles. According to Consumer Reports, ethanol has worse fuel economy than regular gasoline, so E15 gas may not be as energy-dense.
E85 is an ethanol blend with 85% anhydrous ethanol and 15% gasoline. It is commonly used in the US and Europe for flexible-fuel vehicles, which are designed to operate on any blend of gasoline and ethanol up to 83%.
Low-ethanol blends typically range from E5 to E25, although the term can also refer to E10 blends. E20 to E25 blends have been used in Brazil since the late 1970s. In 2010, due to supply shortages and high ethanol fuel prices, the Brazilian government temporarily reduced the blend from E25 to E20. As of 2007, the mandatory blend in Brazil has been set at 25% anhydrous ethanol (E25).
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Ethanol production: corn, sugarcane, and biomass
In the United States, ethanol is most commonly produced from corn grain starch. The process involves dry- or wet-mill processing. Dry milling grinds corn into flour, which is then fermented into ethanol, with distillers grains and carbon dioxide as coproducts. Wet-mill plants separate starch, protein, and fiber in corn before processing these components into products like ethanol, corn sweeteners, corn oil, and starch.
The production of ethanol from corn has a positive energy balance, meaning the process of producing ethanol fuel does not require more energy than the amount of energy contained in the fuel itself. This is because ethanol produced from corn requires energy to turn the raw feedstock into ethanol, and corn demonstrates a positive energy balance. Cellulosic ethanol, on the other hand, improves the energy balance of ethanol because the feedstocks are either waste, coproducts of another industry (like wood or crop residues), or dedicated crops with lower water and fertilizer requirements compared to corn.
Sugarcane is another feedstock used in ethanol production, particularly in Brazil, where it is a well-established industry with relatively simple operations and high yield. The sugarcane juice is fermented, and the fermented juice is processed into an ethanol stream and a liquid-rich byproduct called vinasse. Vinasse is a residue from the sugar-ethanol industry, characterized by its acidic suspension, high COD values, unpleasant odours, and dark brown colour. It is mostly used in fertirrigation practices, acting as a liquid fertilizer for crops and reducing water input for plant growth.
Biomass, or plant materials, are also used to produce ethanol. The process of converting non-food-based feedstocks into cellulosic ethanol using biomass power reduces the amount of fossil fuel energy used in production. There are two primary pathways to produce cellulosic ethanol: biochemical and thermochemical. The biochemical process involves a pretreatment to release hemicellulose sugars, followed by hydrolysis to break cellulose into sugars. These sugars are then fermented into ethanol, and lignin is recovered and used to produce energy to power the process. The thermochemical conversion process involves adding heat and chemicals to a biomass feedstock to produce syngas, a mixture of carbon monoxide and hydrogen.
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Ethanol's benefits: oxygenates fuel, boosts octane, and reduces air pollution
Ethanol, a renewable fuel made from plant materials, is a common addition to gasoline. In the United States, more than 98% of gasoline contains ethanol, typically in a blend of 10% ethanol and 90% gasoline, known as E10. This fuel blend helps to oxygenate the fuel, improving combustion and reducing air pollution.
Oxygenates Fuel
The addition of ethanol to gasoline serves as an oxygenating agent, promoting more complete combustion. Oxygenates are fuel additives that contain at least one oxygen atom, ensuring a more efficient burning process. Without oxygenates, fuel combustion can be incomplete, leading to the release of harmful pollutants such as carbon monoxide, soot particles, and various hydrocarbons into the air.
Boosts Octane
Ethanol blends can also improve a fuel's octane rating. Octane rating refers to the fuel's resistance to combustion under compression, and higher octane ratings generally indicate higher-quality fuel.
Reduces Air Pollution
The use of ethanol in fuel blends has been touted as an environmentally friendly option, with proponents arguing that it can reduce harmful particulate pollution and lower greenhouse gas emissions. The argument for ethanol blends is linked to the perception that federal mandates requiring an annual increase in the amount of ethanol blended with gasoline will lead to improved environmental outcomes.
However, there is also criticism of ethanol blends. Some argue that increasing the amount of ethanol in gasoline will lead to higher levels of air pollution, reduced fuel efficiency, and potential damage to engines. Additionally, the environmental impact of growing corn for ethanol production and the potential impact on food prices are further points of contention.
While the debate continues, it is clear that ethanol plays a significant role in today's fuel landscape, and its benefits and drawbacks are carefully considered by various stakeholders.
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Ethanol's drawbacks: less energy than gasoline, higher consumer cost, and engine overheating
In the United States, most gasoline sold today contains 10% ethanol, known as E10. Higher blends, such as E15 and E85, are also available in some locations. While ethanol is a renewable fuel with certain benefits, it also has several drawbacks when compared to gasoline.
Less Energy than Gasoline
Ethanol contains less energy per gallon than gasoline, with the exact difference depending on the volume percentage of ethanol in the blend. Denatured ethanol (98% ethanol) contains around 30% less energy than gasoline per gallon. Consequently, a 10% ethanol-gasoline blend will have approximately 97% as much energy as pure gasoline. This means that vehicles using ethanol blends may experience slightly reduced performance.
Higher Consumer Cost
The addition of ethanol to gasoline has been criticized for leading to higher prices for corn, a staple food crop. Since corn is also used as animal feed, allocating more of it towards ethanol production can impact the prices of meat, eggs, and dairy products. Therefore, increasing the percentage of ethanol in gasoline blends can have a direct effect on consumer costs for food items.
Engine Overheating
Some users have reported engines overheating when using ethanol blends, suggesting that ethanol burns "hotter" than gasoline. However, this is somewhat counterintuitive since ethanol has a lower energy content and a significantly cooler flame temperature than gasoline. The likely explanation for the overheating lies in the air/fuel ratio. Ethanol blends tend to run leaner due to the higher oxygen content in the fuel-air mixture. If the engine cannot compensate by adjusting the airflow, the combustion conditions in the cylinder may be less than ideal, potentially leading to overheating. Newer vehicles are generally designed to handle this, but older engines may require manual adjustments to optimize the air-fuel mixture.
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Ethanol in the US: history, usage, and impact on fuel economy
Ethanol has been used as a fuel in the US since the 19th century. In 1826, Samuel Morey experimented with an internal combustion chemical mixture that used ethanol, but his discovery was overlooked due to the popularity of steam power. Ethanol fuel gained attention again in 1860 when Nicholas Otto began experimenting with internal combustion engines. Henry Ford designed his first car, the "Quadricycle", to run on pure ethanol in 1896. The Ford Model T, released in 1908, was capable of running on gasoline, ethanol, or a combination of both. Despite Ford's advocacy for ethanol fuel, the lower prices of gasoline made it a more popular choice.
The demand for ethanol produced from field corn increased in the 1970s due to federal policies promoting ethanol through tax credits. Gasoline containing up to 10% ethanol began a decades-long growth in the United States during this time. Federal tax credits ended on December 31, 2011, but The Energy Policy Act of 2005 and Energy Independence and Security Act of 2007 mandated annual ethanol use levels, which remain in effect today. The first ethanol mandate law was signed by the President in early August 2005.
In the US, ethanol is primarily produced from the starch in corn grain, with corn accounting for 37% of total US corn use during the 2018 market year. Ethanol is a renewable fuel made from various plant materials collectively known as "biomass". Typically, gasoline in the US contains E10 (10% ethanol, 90% gasoline), which helps to reduce air pollution. Higher blends such as E15 and E85 are also available but are less commonly used due to a lack of fueling infrastructure.
The impact of ethanol on fuel economy is dependent on the ethanol content in the fuel and the type of engine. Vehicles typically experience a reduction in miles per gallon when using E10 and E15 blends due to ethanol's lower energy content compared to gasoline. However, proponents of higher ethanol blends, such as E30, argue that this can be offset by using high-compression engines tuned to use the fuel. Additionally, ethanol produced from corn has a positive energy balance, meaning that the process of producing ethanol fuel does not require more energy than the amount of energy contained in the fuel itself. Cellulosic ethanol further reduces the amount of fossil fuel energy used in production and results in lower levels of life cycle greenhouse gas emissions.
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Frequently asked questions
Normal fuel in the US usually contains 10% ethanol, known as E10.
E10 fuel contains 10% ethanol and 90% gasoline.
Other blends include E15 (15% ethanol) and E85 (up to 85% ethanol).
E10 is the primary source of ethanol consumption in the US.
All models of vehicles sold in the US can use E10.
