Electricity can be used to power all-electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEV’s) directly from the power grid using battery storage, or from electricity generated on-board through fuel cells (see hydrogen fuel cells).
Electric vehicles were developed in Europe over a century ago, and in 1899 were the most popular vehicle type sold in the United States before being overtaken by petroleum-based engines. However, when air quality and energy independence emerged as top priorities at the turn of the 21st century, electric vehicle propulsion has been gaining popularity yet again.
Hydrogen (H2) is the simplest and most abundant element in the universe. It exists in water, hydrocarbons (such as methane), and organic matter. Hydrogen fuel is a colorless, odorless gas at ambient temperature and atmospheric pressure. In nature hydrogen bonds with other elements, therefore pure hydrogen gas must be produced by separating it from other compounds.
Ethanol is a renewable fuel made from corn and other plant materials. The use of ethanol is widespread, and more than 98% of gasoline in the U.S. contains some ethanol. The most common blend of ethanol is E10 (10% ethanol, 90% gasoline). Ethanol is also available as E85 (or flex fuel)—a high-level ethanol blend containing 51% to 83% ethanol, depending on geography and season—for use in flexible fuel vehicles. E15 is defined by the Environmental Protection Agency as a blend of 10.5% to 15% ethanol with gasoline. E15 is an approved ethanol blend for use in model year 2001 and newer light-duty conventional gas vehicles.
Natural Gas is a hydrocarbon mixture predominantly composed of methane (CH4). Lesser components of this gaseous mixture include ethane, propane, butane, nitrogen, helium, carbon dioxide, hydrogen sulfide and water vapor, which are removed prior to use. It is a nontoxic, non-corrosive, non carcinogenic fuel with significantly less harmful tailpipe emissions.
A majority of natural gas is a fossil fuel that is drawn from wells or extracted in conjunction with crude oil production. Natural gas can also be mined from subsurface porous rock reservoirs through extraction processes, such as hydraulic fracturing. Natural gas from renewable sources (biogas) is an emerging fuel, produced from decaying organic materials (waste from plants, landfills, wastewater and livestock).
Propane, also known as liquefied petroleum gas (LPG) or “autogas,” is a three-carbon alkane hydrocarbon (C3H8). It is a nontoxic, odorless gas at ambient temperature and pressure. It can be stored as a liquid at moderate pressures (300 PSI) or at temperatures below -44oF. In its liquid form, the energy density of propane is 270 times greater than in its gaseous form. However, a gallon of liquid propane has approximately 25% less energy content (BTUs) than a gallon of gasoline.
Propane is a byproduct of natural gas processing and crude oil refinement, and therefore it is not a renewable energy source. Propane fuel used for vehicles must be 90% propane. Butane (C4H10) is a common minor component, as well as propylene and butylene. Commercial propane also contains the odorant Ethyl mercaptan, which aids in leak detection.
Biodiesel is a liquid fuel derived from vegetable oils, or animal fats, which consists of mono-alkyl esters of long chain fatty acids (or fatty acid methylesters). It has fueled diesel engines since they were invented by Rudolph Diesel in the late 1800’s.