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Alternative Fuels and Emerging Fuels

factory producing ethanol from sugar cane

Alternative fuels, also known as advanced fuels, represent today a green alternative to the common fuels used in our cars, and their purpose is to conserve fuel and lower the emissions released by vehicles.

Today, we have more than a dozen alternative fuels that are already in production or under development, and they will become the green fuels of a new series of alternative fuel vehicles using advanced technology. Let’s see what are alternative fuels and emerging fuels.

Alternative Fuels Definition

Alternative fuels represent the fuels created for internal combustion engines that are produced partly or wholly from a source that is different than petroleum and is less harmful for the environment than conventional fuels.

For the moment, the primary users of the alternative fuels (green fuels) are the U.S Government and vehicle fleets of the private-sector, but individual consumers are showing an increased interest in these green alternatives to conventional fuels.

Replacing the vehicles that use conventional fuels (based on oil) with advanced vehicles using alternative fuels will help the U.S. to conserve its fuel reserves and lower the level of emissions released by vehicles in the country.

Types of Alternative Fuels

The list of alternative fuels available today includes biodiesel, ethanol, natural gas, propane, hydrogen, liquid nitrogen, algae-based fuels, electricity, etc.

1. Biodiesel

Biodiesel is an alternative fuel produced domestically from vegetable oils, animal fats, or recycled grease (from restaurants), and can be used in diesel engines or any other equipment that operates with diesel fuel.

The physical properties of the biodiesel are similar to those of the regular diesel fuel obtained from petroleum.

Biodiesel is mostly used as a blend with petroleum diesel fuel, and works well in many diesel vehicles without any engine modification.

The most common biodiesel blends used today are B20 (contains 6% to 20% biodiesel and 80% to 94% regular petroleum diesel), B5 (contains 5% biodiesel and 95% petroleum diesel) and B3 (contains only 3% biodiesel and 97% petroleum diesel).

Fleet vehicles are regular users of the biodiesel blends because the mix of alternative fuel improves the lubricity of the fuel (the diesel engine will live longer) and lowers the emissions.

2. Ethanol

Ethanol is an alternative fuel made from corn and other plants (cellulosic ethanol is made from poplar trees) and is used mixed with gasoline to improve engine’s performance and lower the emissions.

Today, more than 98% of the gasoline used in the U.S. is a mix of regular gasoline and ethanol.

E10 (containing 10% ethanol and 90% gasoline) is the most common blend of ethanol and gasoline (there are blends where ethanol is even lower in share).

E85 also known as flex fuel is an alternative fuel where the share of the ethanol in the mix is between 51% and 83% (depending on geography and season) and can be used only by flexible fuel vehicles (not by regular vehicles).

E15 is another mix of 10.5% to 15% ethanol and gasoline.

Flexible fuel vehicles (FFVs) have an internal combustion engine that is modified to be capable of operating on gasoline and any blend of ethanol and gasoline (ethanol up to 83%).

FFVs can accelerate faster when operating on higher ethanol blends than regular vehicles, but the fuel economy (miles per gallon) will decrease while increasing the level of ethanol in the mix (ethanol has lower energy content compared to gasoline).

3. Natural gas

Natural gas is a gaseous fuel produced domestically and is available through the utility infrastructure because is mostly used for heating and cooking.

To be used in vehicles, this gaseous fuel must be compressed or liquefied (LNG or liquefied natural gas).

Today, more than 160,000 vehicles run on natural gas in the U.S., mostly because is cheaper than gasoline or regular diesel, and because it improves the range of the vehicle.

It is generally used by centrally fueled fleets, but also by individual users because is cheaper than regular fuel.

4. Propane

Propane is known today as liquefied petroleum gas (LPG) or simply autogas, and has been used worldwide to power vehicles for decades.

To be used as alternative fuel, propane is stored in liquid form.

Today, there are more than 200,000 on-road propane vehicles in the U.S. and they use fuel systems that are certified for road use in the country.

Vehicles running on propane have been widely used and refined for several decades.

There are two types of propane vehicles available today: dedicated propane vehicles and bi-fuel propane vehicles.

Dedicated propane vehicles run only on propane, while the bi-fuel propane vehicles rely on separate fueling systems that enable the vehicle to use propane or gasoline.

Power, acceleration, cruising speed and range of a vehicle running on propane is similar to those of conventionally fueled vehicles.

5. Hydrogen

Hydrogen is a clean fuel used today in fuel cells to produce electricity.

The vehicles that run on hydrogen are called fuel cell electric vehicles (FCEVs) and a full tank can provide a range of about 300 miles.

Today, the hydrogen fueling infrastructure is limited in the U.S. and on the planet because producing hydrogen in an expensive process.

However, FCEVs are more efficient than the vehicles running on conventional fuels and they release no harmful emissions into the atmosphere.

6. Liquid Nitrogen

Liquid nitrogen is another alternative fuel that features high efficiency and no emissions.

Nitrogen extracted from air needs to be liquefied and stored in a tank to be used by the engine.

Traditional nitrogen engines work by heating the liquid nitrogen inside a heat exchanger, the heat is then extracted and the pressurized gas resulted will operate a piston or a rotary motor.

Today, the vehicles that run on liquid nitrogen are not used commercially.

7. Algae-based fuels

Biofuels based on algae represent alternative fuels that have been considered by many people a good alternative to fuels made of crude oil to lower the emissions.

Algae are very productive because they can produce about 2,000 gallons of fuel per acre each year.

Today, the algae-based fuels are successfully tested by the U.S. Navy.

8. Electricity

Electricity is already used today to power plug-in electric vehicles (PEVs), which includes both the all-electric vehicles (EVs) and the plug-in hybrid electric vehicles (PHEVs).

The EVs store in their batteries, electricity drawn from the grid or another source of power (preferably clean).

The PHEVs are slightly different because they are usually powered by liquid fuels such as gasoline, and they use their batteries to recapture the energy otherwise lost during braking.

This way, the plug-in hybrid electric vehicle manages to save fuel, and also to lower the emissions.

Emerging Alternative Fuels

Besides the regular alternative fuels listed above, there are also emerging alternative fuels that are under development or already available in the U.S.

These emerging green fuels can increase energy security, reduce the level of harmful emissions produced by the transportation sector, improve the performance of the vehicle, and can stimulate the U.S. economy in the long term.

We can include here emerging renewable fuels that are considered alternative fuels under the Energy Policy Act of 1992, and may qualify for federal and state incentives and laws such as Biobutanol, Dimethyl ether, Methanol and biofuels obtained from renewable hydrocarbon.

1. Biobutanol

Butanol is an emerging alternative fuel obtained (exactly like ethanol) from corn grain and other forms of biomass.

Biobutanol is the name of the butanol obtained from renewable energy sources (biomass feedstocks).

Biobutanol is considered a better alternative fuel than ethanol because it has higher energy content and is less miscible with water.

Exactly like ethanol, biobutanol is mixed today with gasoline.

The accepted biobutanol blends in the U.S. consist of 12.5% biobutanol and 87.5% gasoline, but the EPA granted a 16% biobutanol blend which is equivalent with the E10 (ethanol 10% and gasoline 90%).

Compared to regular fuels or with ethanol, biobutanol features the following benefits:

Higher energy content

The energy content of the biobutanol is higher than the energy content of the ethanol, but lower by 10% to 20% than the energy content of the gasoline.

Lower Reid vapor pressure

Compared to ethanol, biobutanol features a lower vapor pressure, which means lower volatility and less emissions.

Fewer emissions

Biobuthanol is cleaner (less emissions) compared to regular fuels.

Increases energy security

Biobutanol can be produced domestically in the U.S. from a variety of biomass feedstocks, which means that it creates jobs and improves the energy security of the country.

2. Dimethyl Ether

Dimethyl Ether or simply DME is a synthetically obtained alternative fuel that can replace the diesel fuel.

This alternative fuel can be used in specially designed compression ignition diesel engines.

Dimethyl ether can be produced from biomass, methanol, and fossil fuels such as natural gas or coal.

Exactly like propane, dimethyl ether requires about 75 pounds per square inch (psi) of pressure to become liquid, and can be stored in pressurized tanks at ambient temperature.

Dimethyl ether has a very high cetane number, but half the energy density of the regular diesel, which means that it will use a fuel tank that is twice as large as the fuel tank used by regular diesel engines.

3. Methanol

Methanol is known today as wood alcohol and is considered an emerging alternative fuel because it has similar physical and chemical fuel properties to ethanol.

Due to the fact that ethanol is now produced from poplar trees (cellulosic ethanol), the use of methanol has been decreased, and automakers are no longer manufacturing vehicles running on methanol in the U.S.

Methanol could be a good alternative to conventional fuels used in the transportation sector because it features several benefits such as:

Is cheaper to produce

Methanol has low production costs because is produced from wood not from food crops.

Improves safety

Methanol is less flammable than gasoline, which means that is safer to use.

Increases energy security

Methanol can be manufactured from wood, and also from fossil fuels such as natural gas and coal.
The use of methanol as an alternative fuel for the transportation sector would help reduce the use of conventional fuels and would lower the emissions.

4. Renewable Hydrocarbon Biofuels

Renewable hydrocarbon biofuels known today as sustainable or advanced hydrocarbon biofuels, represent alternative fuels produced from biomass using several biological, thermal, and chemical processes.

The chemical and physical properties of the renewable hydrocarbon biofuels are similar to the properties of the conventional fuels (gasoline, diesel and jet fuel).

Scientists consider that the renewable hydrocarbon biofuels can be used in the current vehicles without making any changes to the engines.

For fuel transportation and retail, renewable hydrocarbon biofuels can use the existing petroleum fuel pipelines and the current network of fuel stations.


Alternative fuels along with the emerging green fuels will slowly replace the conventional fuels based on crude oil to improve the performances of the vehicles and to lower the emissions.

Article written by:

I am a writer and reporter for the clean energy sector, I cover climate change issues, new clean technologies, sustainability and green cars. Danny Ovy

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