Rajan Wilcox
Ethanol is a type of alcohol that can be used as fuel for cars. It is most commonly used as a biofuel additive for gasoline. Ethanol is produced through the fermentation of sugar solutions, and in the US, it is primarily made from corn starch. While ethanol is a popular fuel choice in countries like Brazil and the United States, there are some considerations regarding its production costs, environmental impact, and compatibility with different types of engines. The use of ethanol in cars offers both advantages and challenges, and its suitability as a fuel depends on various factors, including the availability of resources and the specific requirements of the vehicles.
| Characteristics | Values |
|---|---|
| Ethanol fuel composition | Fuel containing ethyl alcohol, the same type of alcohol found in alcoholic beverages |
| Use as automotive fuel | One of the first automotive fuels in the US; consumption increased in 2002 as states banned the gasoline oxygenate MTBE due to groundwater contamination concerns |
| Current use | Ethanol is blended with gasoline in most petrol stations; nearly all gasoline sold in the US contains ethanol |
| Ethanol blends | E10, E15, E85, and flex fuel (up to 100% ethanol) |
| E10 | A blend of 10% ethanol and 90% gasoline; the primary source of US ethanol consumption |
| E15 | Motor gasoline with up to 15% ethanol content; approved for use in 2001 and newer light-duty vehicles |
| E85 | A gasoline-ethanol blend containing 51-83% ethanol, depending on geography and season; defined as an alternative fuel |
| Flex fuel vehicles | Can operate with ethanol mixtures up to E100 (hydrous ethanol with up to 4% water) |
| Fuel efficiency | Ethanol has a "gasoline gallon equivalency" (GGE) value of 1.5, i.e., 1.5 times the volume of ethanol is needed to replace the energy of 1 volume of gasoline |
| Cost | Ethanol is usually less expensive than gasoline, but in GGE, it is rarely cheaper due to the higher volume required |
| Engine compatibility | Engines designed or modified to use pure ethanol or high ethanol blends; some flexible-fuel vehicles can use up to 100% ethanol |
| Environmental impact | Reduces air emissions compared to MTBE; Brazilian ethanol from sugarcane refining is more efficient than American ethanol made from corn |
| Production process | Fermentation of sugars, distillation, dehydration, and denaturing (optional); second-generation processes use enzymes, yeast fermentation, or pyrolysis |
| Feedstocks | Corn kernels, cellulosic ethanol from waste, coproducts, or dedicated crops like switchgrass and miscanthus |
| Benefits | Reduces water and fertilizer requirements, lowers life cycle greenhouse gas emissions, and improves knock resistance |
| Drawbacks | Hygroscopic nature, higher production cost, potential engine issues with small engines and older machinery |
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What You'll Learn
Ethanol blends
Ethanol is available in several different blends for use in conventional and flexible fuel vehicles. The most common blends are E10, E15, and E85. E10 is a mixture of 10% ethanol and 90% gasoline, and it is approved by the U.S. Environmental Protection Agency (EPA) for use in any conventional, gasoline-powered vehicle. E15 is a blend of 10.5% to 15% ethanol and gasoline, and it is approved for use in model year 2001 and newer light-duty conventional vehicles. E85 is a blend of 51% to 83% ethanol, depending on geography and season, and it is considered an alternative fuel under EPAct.
In Brazil, the government has mandated the blending of ethanol with gasoline since 1976, and the current legal blend is around 25% ethanol and 75% gasoline (E25). Brazilian flex-fuel vehicles can operate with ethanol mixtures up to E100, which is hydrous ethanol with up to 4% water. However, during cold starts, pure gasoline is injected to avoid starting problems at low temperatures.
Other common ethanol blends include E5 and E7, which are considered safe for recent engines that should run on pure gasoline. Additionally, some countries have mandates for blending specific percentages of ethanol into vehicle fuels. For example, India achieved a target of 10 percent ethanol blending in June 2022, while Argentina approved an E12 minimum in June 2021.
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Flex fuel vehicles
Flexible-fuel vehicles (FFVs) are designed to run on gasoline or a blend of gasoline and ethanol. They are equipped with internal combustion engines and can operate on any blend of gasoline and ethanol up to 85% ethanol (E85). FFVs have been in production since the 1990s, and there are now over a hundred models available. In the United States, FFVs are commonly referred to as "E85 vehicles".
FFVs are similar to their gasoline-only counterparts, except for some engine and fuel system modifications. They experience no loss in performance when using E85, and some models even demonstrate improved acceleration, generating more torque and horsepower. However, due to ethanol's lower energy content per volume compared to gasoline, FFVs typically achieve 15-27% fewer miles per gallon when fuelled with E85 blends.
The most common commercially available FFVs are ethanol flexible-fuel vehicles. By March 2018, about 60 million FFVs had been manufactured and sold worldwide, with the largest markets being Brazil, the United States, Canada, and Europe. Brazilian FFVs, also known as "total flex" or simply "flex" cars, are optimised to run on blends of E20-E25 gasoline and up to 100% hydrous ethanol (E100). Brazilian flex vehicles are constructed with a small secondary gasoline reservoir located near the engine to facilitate cold starts during low temperatures.
In the United States, nearly all gasoline sold contains some amount of ethanol. The primary source of ethanol consumption in the country is E10 gasoline, which contains 10% ethanol. Higher ethanol blends, such as E15 (up to 15% ethanol) and E85, are also available but are less commonly used. FFVs in the US are often identified by a yellow gas cap labelled "E85/Gasoline".
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Ethanol production
Ethanol is a domestically produced alternative fuel most commonly made from corn in the United States. It is also made from cellulosic feedstocks, such as crop residues, grasses, and wood, although this is less common. The production method of ethanol depends on the type of feedstock used.
The basic steps for large-scale production of ethanol are microbial (yeast) fermentation of sugars, distillation, dehydration, and denaturing (optional). The process is shorter for starch- or sugar-based feedstocks than with cellulosic feedstocks. Nearly 90% of ethanol plants are dry mills due to lower capital costs. Dry milling is a process that grinds corn into flour and ferments it into ethanol with co-products of distillers grains and carbon dioxide. Wet-mill plants primarily produce corn sweeteners, along with ethanol and several other co-products (such as corn oil and starch).
Wet mills separate starch, protein, and fiber in corn prior to processing these components into products, such as ethanol. Making ethanol from cellulosic feedstocks is a more involved process than using starch-based crops. 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. Sugars are 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.
Second-generation processes for the production of ethanol from corn are also under development. The first type uses enzymes and yeast fermentation to convert the plant cellulose into ethanol, while the second type uses pyrolysis to convert the whole plant to either a liquid bio-oil or a syngas.
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Environmental impact
Ethanol is a renewable fuel that can be blended with gasoline to power vehicles. It is mostly produced from corn, although other sources such as switchgrass, wood, soybeans, and sunflowers can also be used. The use of ethanol as a vehicle fuel has been the subject of much debate, with various environmental impacts to consider.
One of the key benefits of ethanol is its potential to reduce greenhouse gas (GHG) emissions. Life cycle analyses have shown that ethanol delivers significant GHG savings compared to fossil fuels. The carbon dioxide (CO2) released when ethanol is burned in vehicles is offset by the CO2 captured when the crops used to produce it are grown. This closed carbon cycle means that ethanol and other renewables simply recycle atmospheric carbon. Studies by Harvard, the USDA, and the Department of Energy's Argonne National Laboratory have found that corn-based ethanol reduces GHG emissions by around 40-50% compared to regular gasoline. The use of ethanol in gasoline in 2024 reduced CO2-equivalent GHG emissions from transportation by 54.3 million metric tons, which is the equivalent of taking 30 million cars off the road. Additionally, ethanol has been found to decrease tailpipe emissions of CO2 and harmful toxins such as benzene, a known carcinogen.
However, there are also concerns about the environmental impact of ethanol production, particularly when it comes to corn-based ethanol. Firstly, there is the issue of land use and food security. Growing enough crops to meet the demands of ethanol production can take away land from food production, leading to higher food prices and potentially requiring the conversion of forests and open spaces into farmland. This is especially true for corn-based ethanol, as corn is a staple food crop. Additionally, while ethanol production can support farmers and create domestic jobs, industrial corn farming can have a harmful impact on the environment. It is important to note that ethanol production's impact on food prices and cropland expansion has been disputed, with some data showing that overall US cropland has declined and corn acreage has remained stable.
Another concern is the energy efficiency of ethanol. While ethanol has a higher octane number than gasoline, providing increased power and performance, it has lower energy content per gallon. This means that ethanol impacts fuel economy, with vehicles optimized for gasoline experiencing reduced efficiency when using ethanol blends. However, this can be mitigated by optimizing engines to run on higher ethanol blends, which would likely increase engine efficiency and improve fuel economy.
Furthermore, while ethanol can reduce certain tailpipe emissions, it may increase others. For example, while E85 (a blend of 85% ethanol and 15% gasoline) decreases CO2 emissions, it increases acetaldehyde emissions, which are "reasonably anticipated" to be carcinogenic and can contribute to ground-level ozone formation. Additionally, low-level ethanol blends can increase evaporative emissions due to the higher volatility of ethanol compared to gasoline. However, vapor pressure can be adjusted to meet the same volatility standards as gasoline, and E85 is less volatile than low-level ethanol blends, resulting in lower evaporative emissions.
Overall, while ethanol has the potential to reduce GHG emissions and provide a renewable alternative to fossil fuels, it is not without its environmental impacts. The benefits of ethanol must be weighed against concerns such as land use, food security, energy efficiency, and tailpipe emissions to determine its role in a sustainable energy future.
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Ethanol vs petrol
Ethanol is a renewable fuel that can be blended with petrol to reduce a car's reliance on petroleum. It is produced by converting starch or plant cellulose into alcohol, which is then blended with petrol. The most common way to produce ethanol is through fermentation. Brazilian ethanol, for instance, is made from the leftovers of sugarcane refining, while American ethanol is primarily made from corn.
Ethanol has a higher "gasoline gallon equivalency" (GGE) value than petrol, meaning that more ethanol is needed to generate the same amount of energy as petrol. A blend of 10% ethanol and 90% petrol (by volume) is known as E10. Most cars on the road in the US can run on blends of up to 15% ethanol, and nearly all gasoline sold in the US contains ethanol. However, ethanol has a lower stored energy value than petrol, with about 30% less energy per unit volume. As a result, a 10% ethanol-petrol blend will have slightly less energy than pure petrol.
Ethanol has been touted as a greener alternative to petrol, with some studies claiming that it reduces greenhouse gas emissions by up to 50%. However, critics argue that the production of ethanol from corn requires a significant amount of energy, and in some cases, the energy input may even be greater than the energy output. Additionally, the demand for ethanol may drive up the price of feed corn and other crops, leading to higher food prices.
Despite these concerns, ethanol has several advantages over petrol. It is usually less expensive than petrol, and it is safer for the water supply as it is not as toxic as other fuel additives like MTBE. Ethanol also boosts the octane number of fuel, helping to prevent pre-ignition knock. Furthermore, ethanol-blended fuel is widely used in countries like Brazil, the US, Canada, and Europe, and many vehicles are designed to run on ethanol blends or even pure ethanol.
In conclusion, ethanol and petrol have their own advantages and disadvantages. Ethanol is a renewable and cleaner fuel option, but it may be less energy-efficient and more expensive than petrol in certain cases. On the other hand, petrol may be more energy-dense and convenient, but it is derived from non-renewable fossil fuels and may have a larger environmental impact. The choice between ethanol and petrol depends on various factors, including vehicle compatibility, availability, and personal preferences regarding cost, performance, and environmental impact.
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Frequently asked questions
Ethanol, or ethyl alcohol, is the same type of alcohol found in alcoholic drinks. It is produced by fermenting sugar solutions, such as corn starch or sugarcane refining by-products.
Ethanol is most often used as a biofuel additive for gasoline. It can be blended with petrol or gasoline to create a fuel mixture. In the US, petrol from the pumps is mixed with up to 10% ethanol.
Ethanol is a renewable energy source that can be produced from plants. It is also quasi-renewable as it is made from plants that get their energy from the sun. It can reduce greenhouse gas emissions and tailpipe emissions.
Ethanol is not as energy-dense as gasoline and is more expensive to produce. It also has issues with cold-starting as it doesn't burn as quickly as gasoline. It can also cause corrosion in older car models.
Ethanol is used as a fuel for cars in several countries, including the United States, Brazil, Canada, and Europe. In Brazil, the government has mandated the blending of ethanol with gasoline since 1976.
