E85 Bioethanol - What's All The Fuss?

by L.J. Martin

There has been a movement in countries such as the United States towards using bioethanol as a fuel in the form of E85, with the aim of reducing the carbon footprint of transport. E85 is simply a mixture of 85% ethanol with 15% gasoline. However, this has caused a great deal of controversy. In this guide we will look at the good points and bad points of using bioethanol to fuel cars.

gas pumps
©André di Lucca
(Some rights reserved)

Ethanol as a fuel

The first question you might ask is why add 15% gasoline? The main reason is to make sure the engine starts in cold weather. Ethanol has a lower vapor pressure than gasoline, which essentially means that it evaporates more slowly at a given temperature. Adding gasoline to ethanol increases the amount of vapor produced at low temperatures, helping the engine start from cold

Apart from possible trouble starting some cars in cold snaps, does ethanol make a good fuel for cars? Yes, ethanol is fundamentally a good fuel. Its biggest selling point is that it can be used in a normal gasoline engine with relatively small modifications. E85's octane rating is lower than that of 100% ethanol, but still better than normal pump gasoline. However, an engine designed to run well on gasoline cannot take advantage of E85's high octane rating. Flex fuel vehicles are those designed to run on either ethanol, gasoline or a mixture of both. The energy content of E85 is lower than that of gasoline, meaning that vehicles achieve fewer miles per gallon of fuel. This reduction can be up to 30% compared to gasoline, meaning that it may be more expensive to run a car on E85 unless it is substantially cheaper than gasoline.

The other main issue with ethanol as a fuel is corrosion. Ethanol is corrosive to some materials used in fuel tanks and pipes which were designed to hold gasoline. Ethanol is also hygroscopic, which means that it tends to absorb water. If ethanol is left sitting exposed to air for a long time, it will tend to absorb water vapor from the atmosphere, which can act to increase corrosion. While flex fuel vehicles are designed to withstand this, using a gasoline/ethanol mix can damage some older engines.

Ethanol and CO2

What about fossil carbon reductions, which are the main reason given for switching to E85 use? When bioethanol is burned, the carbon dioxide released does not add to the amount of CO2 in the biosphere. This is because the carbon locked up in the ethanol came from a plant, which absorbed CO2 from the atmosphere during photosynthesis. Therefore the CO2 released from burning bioethanol is merely continuing its way through the carbon cycle. In other words, burning bioethanol is a carbon neutral process. The main sources of plant material for bioethanol production are currently sugar cane in Brazil, and corn (maize) in the United States. Most U.S. bioethanol production is in the "corn belt" in the Midwest. It has been suggested that switchgrass could be an alternative source of biomass for ethanol production in the United States. Of course, E85 contains 15% gasoline, which is a fossil fuel. This means that E85 is not carbon neutral, but releases a certain amount of fossil CO2 when burned. Bear in mind that the lower fuel economy of E85 results increases the fossil carbon emissions from its gasoline content.

While the bioethanol content of E85 might be carbon neutral when burnt, the process by which this ethanol is produced is not, and this is one of the most controversial aspects of the push for E85. Refining gasoline from crude oil releases less CO2 than turning corn into bioethanol with an equivalent energy content. Bioethanol still has the advantage of being carbon neutral when burnt, while gasoline releases fossil CO2 when burnt. However, when the total amount of fossil CO2 released in the production and burning of E85 are added together, the gap between E85 and gasoline shrinks dramatically. Part of the problem is that farmers rarely use biofuels to power machines such as tractors and combine harvesters. This is because biofuels are fundamentally more expensive to produce, and as farmers pay low tax rates on fossil fuels, it is simply uneconomic for them to run machinery on biofuels. Fertilizers are also energy-intensive to produce. (The Haber-Bosch process used to turn nitrogen and hydrogen into ammonia for fertilizer production requires a temperature of 500 degrees Celsius and a pressure of 200 atmospheres.) When fertilizer is applied to a field, oxides of nitrogen are released, which are greenhouse gases and are therefore equivalent to releasing a certain amount of fossil CO2.

Some recent studies have claimed that the difference in fossil CO2 and equivalents released in the production of E85 is so close to that of gasoline as to render E85 pointless. More optimistic studies have said that substituting bioethanol for all gasoline use would reduce CO2 emissions by up to 30 percent. Using the current processes, it is not economically possible for large scale bioethanol production to approach carbon neutrality.

Food for fuel

Another of the main criticisms of ethanol is that its production from food crops will inevitably increase the price of food due to competition for the same crops. Increased demand for a limited resource such as corn will inevitably lead to price increases. This is a particular problem for third world countries, where using food crops for fuel could lead to food shortages. Cynics have suggested that the agriculture industry in the Western world are using bioethanol as a route to increased subsidies and profits. Regardless of motivation, many people are uneasy at the idea of having food and fuel production in direct competition.


Ethanol is fundamentally a good fuel, which makes it attractive to people who are trying to cut down on fossil fuel use. However, there are problems which must be tackled before bioethanol becomes a realistic substitute for gasoline on a large scale. The two main issues are that current bioethanol production methods save much less fossil carbon than some proponents suggest, and that using intensively-farmed food crops as a fuel source must inevitably lead to food price increases and shortages unless very carefully managed, simply due to the laws of supply and demand. In the future, bioethanol may well become an important carbon-neutral fuel, but only when new methods of production come online. For instance, producing ethanol from algae is a promising technology that is still in its infancy, and using sustainably produced, carbon-neutral energy sources in the production of ethanol is also in its early stages. For now, E85 cannot produce a major reduction in fossil CO2 emissions.


Related articles: