Ethanol is a renewable fuel made from various plant materials collectively known as "biomass." More than 98% of U.S. gasoline contains ethanol to oxygenate the fuel. Typically, gasoline contains E10 (10% ethanol, 90% gasoline), which reduces air pollution.
Ethanol is also available as E85 (or flex fuel), which can be used in flexible fuel vehicles, designed to operate on any blend of gasoline and ethanol up to 83%. Another blend, E15, is approved for use in model year 2001 and newer light-duty vehicles.
There are several steps involved in making ethanol available as a vehicle fuel:
- Biomass feedstocks are grown, collected, and transported to an ethanol production facility.
- Feedstocks are converted to ethanol at a production facility and then transported to a fuel terminal or end-user by rail, truck, or barge.
- E10 is sourced from fuel terminals whereas E85 is sourced from a terminal or directly from an ethanol production facility.
- E15 is available from fuel terminals or through a blender pump dispenser that draws from E10 and E85 tanks at a station.
Fuel Properties
Ethanol (CH3CH2OH) is a clear, colorless liquid. It is also known as ethyl alcohol, grain alcohol, and EtOH (see Fuel Properties search.) Ethanol has the same chemical formula regardless of whether it is produced from starch- or sugar-based feedstocks, such as corn grain (as it primarily is in the United States), sugar cane (as it primarily is in Brazil), or from cellulosic feedstocks (such as wood chips or crop residues).
Ethanol has a higher octane number than gasoline, providing premium blending properties. Minimum octane number requirements for gasoline prevent engine knocking and ensure drivability. Lower-octane gasoline is blended with 10% ethanol to attain the standard 87 octane.
Ethanol contains less energy per gallon than gasoline, to varying degrees, depending on the volume percentage of ethanol in the blend. Denatured ethanol (98% ethanol) contains about 30% less energy than gasoline per gallon. Ethanol’s impact on fuel economy is dependent on the ethanol content in the fuel and whether an engine is optimized to run on gasoline or ethanol.
Ethanol Energy Balance
In the United States, 94% of ethanol is produced from the starch in corn grain. Energy is required to turn any raw feedstock into ethanol. Ethanol produced from corn demonstrates 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 improves the energy balance of ethanol because the feedstocks are either waste, coproducts of another industry (wood, crop residues), or dedicated crops—such as switchgrass and miscanthus—with lower water and fertilizer requirements compared to corn. When biomass is used to power the process of converting non-food-based feedstocks into cellulosic ethanol, the amount of fossil fuel energy used in production is reduced even further. Another benefit of cellulosic ethanol is that it results in lower levels of life cycle greenhouse gas emissions.
For more information on the energy balance of ethanol, download the following documents:
FAQs
Ethanol has a higher octane number than gasoline, providing premium blending properties. Minimum octane number requirements for gasoline prevent engine knocking and ensure drivability. Lower-octane gasoline is blended with 10% ethanol to attain the standard 87 octane.
What are the disadvantages of ethanol as an alternative fuel? ›
One of the primary disadvantages of ethanol is that it is not as energy-dense as gasoline. This means that it has a lower energy content and is less efficient than gasoline. As a result, vehicles that use ethanol as a fuel source may not get as many miles per gallon as those that use gasoline.
What are the benefits of using ethanol as a fuel? ›
Because of its high oxygen content, ethanol burns more completely than ordinary unleaded gasoline and reduces harmful tailpipe emissions. Ethanol prevents gas line freeze-up. It suspends moisture in your fuel system, so you don't need to add expensive anti-freeze in cold weather.
Why is ethanol not used as fuel? ›
Ethanol: Contains significantly less energy per gallon than gasoline. Is hygroscopic, meaning it absorbs water out of the air, which means it can damage engines due to excess water content if not handled carefully.
Can you use 100% ethanol as fuel? ›
Ethanol is more difficult to ignite than gasoline, especially in cold temperatures. Thus, for an engine to operate on 100 percent ethanol, the ignition and fuel systems may need modifications. Ethanol is energy-intensive to produce and therefore could affect the total energy-cost cycle.
Why is the use of ethanol as a fuel controversial? ›
Critics believe that widespread production of ethanol will result in more land being used to grow corn for fuel rather than for food. They also believe that producing and using ethanol actually does more harm to the environment than good.
What are 2 disadvantages of ethanol? ›
There would have to be a large infrastructure change to provide ethanol refueling stations. Ethanol also absorbs water easily giving it a high tendency to corrode materials. Pure ethanol is difficult to vaporize meaning starting a car in cold weather could be more difficult that a car that runs on petrol.
Why is ethanol bad for the environment? ›
State of play: Ethanol produces more carbon emissions than gasoline because of the amount of farmland that's required to grow the corn crops and the tillage associated with it, Reuters reports.
What are the pros and cons of ethanol fuel? ›
Ethanol. Pros: Reduces demand for foreign oil, low emissions, high octane, and can potentially be produced from waste materials; existing cars can use 10-percent blends (called E10), and more than 8 million cars already on the road can use E85. Cons: Twenty-five percent lower fuel economy on E85 than gasoline.
What are two pros and cons of ethanol? ›
Ethanol has both pros and cons as a renewable fuel source. While it is renewable, domestically produced, and produces fewer greenhouse gas emissions than non-renewable sources of energy, it is less energy-dense, expensive to produce, and can have negative impacts on the environment.
India plans to start using 20% ethanol blended petrol from 2025. Currently, most petrol pumps give 10% ethanol blended petrol. Economists argue that ethanol production in the future will have to rely more on maize and less on sugarcane and rice.
What are the problems with ethanol? ›
Ethanol is corrosive. Ethanol reacts naturally with oxygen in the air to form acidic compounds which lead to corrosion of fuel system components and engine wear. With the presence of both water and ethanol, corrosion is accelerated in all metal types.
What octane is pure ethanol? ›
In addition to having lower lifecycle greenhouse gas emissions than conventional gasoline, ethanol is an excellent octane provider, with neat (pure) ethanol having an octane rating of over 100. Currently, refiners create 'sub-octane gas,' which has a lower octane rating than required.
What are the negative effects of ethanol? ›
Chronic ingestion of ethanol may cause liver cirrhosis, affect the nervous system and affect the glands in humans. Ethanol may cause mutations (genetic changes). Ethanol is rapidly oxidised by the body to carbon dioxide and water, with no cumulative effect.
What is a disadvantage of alternative fuel? ›
The Initial Cost of Renewable Energy Is High
Considering the energy we can get from renewable technologies, their initial cost is high and sometimes unaffordable.
