What Are Alternative Fuels?

Alternative fuels are typically not based on petroleum and are desirable because they help provide energy security and environmental benefits. As legislated by the Energy Policy Act of 1992, the U.S. Department of Energy (DOE) currently recognizes the following as alternative fuels:

Alcohols: ethanol and methanol
Compressed natural gas (CNG): natural gas under high pressure
Electricity: stored in batteries for use by electric motors
Hydrogen: a clean-burning type of gas
Liquefied natural gas (LNG): natural gas that is kept very cold, compressed to a liquid
Liquefied petroleum gas (LPG, also known as "propane"): hydrocarbon gases kept under low moderate pressure as a liquid
Liquids made from coal: gasoline and diesel fuel that are not made from petroleum
Biodiesel: a transportation fuel for use in diesel engines that is produced from similar to diesel fuel, but made from plant oils, or animal fats, or agricultural by-products (often blended with conventional diesel fuel)

Biodiesel

Biodiesel is an alternative fuel that can be used in conventional diesel engines, so it was used by some of the FutureTruck teams with diesel-driven vehicles. The fuel is typically combined with petroleum-based diesel fuel in a 20% blend, called "B20," although other blend levels can be used, depending on the cost of the fuel and the desired benefits.

Biodiesel can be manufactured from vegetable oils, animal fats, and recycled greases. U.S. producers typically use recycled cooking oils and soy oil. Through a process called transesterification, the organic oils are combined with alcohol (ethanol or methanol) and chemically altered to form fatty esters, such as ethyl or methyl ester. The biomass-derived ethyl or methyl esters can then be blended with conventional diesel fuel or used as a "neat" fuel (100% biodiesel).

Ethanol

Ethanol is a high-octane, domestically produced, renewable liquid fuel, made by the fermentation of plant sugars. Typically produced from corn and other grain products, ethanol can also be made from other biomass resources, such as agricultural and forestry wastes, or specially grown energy crops.

When used as a motor fuel, ethanol is commonly used in a blend of 85% ethanol and 15% gasoline, called "E85," which is an alternative fuel as defined by DOE. E85 burns cleaner than gasoline, has an octane of approximately 105, sells for about the same price as unleaded gasoline, is biodegradable, and does not contaminate water.

Hydrogen

Fuel-cell-powered vehicles require hydrogen, an alternative fuel, to power the fuel cell. These vehicles usually do very well in the events that measure emissions and greenhouse gas impact because hydrogen is a very clean fuel and hydrogen production generates very few greenhouse gases as calculated by the GREET model. (As a non-carbon-based fuel, the exhaust is free of carbon dioxide, a greenhouse gas that some scientists believe may be building up in the atmosphere and contributing to changes in the world's climate.)

The hydrogen is compressed and stored in onboard cylinders. A key problem faced by the fuel cell vehicle is that hydrogen storage tanks must be fairly large because compressed hydrogen contains less energy per volume compared with liquid fuels, such as gasoline. Hydrogen can also be cooled to produce liquid hydrogen, but it is costly and presents other technical challenges.