What are the fuels?
Ethanol is an alcohol-based alternative fuel produced by fermenting and distilling starch crops that have been converted into simple sugars. Feedstocks for this fuel include corn, barley and wheat. Ethanol can also be produced from “cellulosic biomass” such as trees and grasses and is called bioethanol. Ethanol is most commonly used to increase octane and improve the emissions quality of gasoline. In some areas of the United States, ethanol is blended with gasoline to form an E10 blend (10% ethanol and 90% gasoline), but it can be used in higher concentrations such as E85 or E95. Original equipment manufacturers produce flexible-fuel vehicles that can run on E85 or any other combination of ethanol and gasoline.
Biodiesel is a domestically produced, renewable fuel that can be manufactured from vegetable oils or recycled restaurant greases. Biodiesel is safe, biodegradable, and reduces serious air pollutants such as particulates, carbon monoxide, hydrocarbons, and air toxics. Blends of 20% biodiesel with 80% petroleum diesel (B20) can be used in unmodified diesel engines, or biodiesel can be used in its pure form (B100), but may require certain engine modifications to avoid maintenance and performance problems.
CNG domestically produced and readily available to end-users through the existing utility infrastructure, natural gas has become increasingly popular as an alternative transportation fuel. Natural gas is also clean burning and produces significantly fewer harmful emissions than reformulated gasoline. Natural gas can either be stored on board a vehicle in tanks as compressed natural gas (CNG) or cryogenically cooled to a liquid state, liquefied natural gas (LNG).
Electricity can be used as a transportation fuel to power battery electric and fuel cell vehicles. When used to power electric vehicles or EVs, electricity is stored in an energy storage device such as a battery. EV batteries have a limited storage capacity and must be replenished by plugging the vehicle into a recharging unit. The electricity for recharging the batteries can come from the existing power grid, or from distributed renewable sources such as solar or wind energy. Fuel cell vehicles use electricity produced from an electrochemical reaction that takes place when hydrogen and oxygen are combined in the fuel cell “stack.” The production of electricity using fuel cells takes place without combustion or pollution and leaves only two byproducts, heat and water.
Propane or liquefied petroleum gas (LPG) is a popular alternative fuel choice because an infrastructure of pipelines, processing facilities, and storage already exists for its efficient distribution. Besides being readily available to the general public, LPG produces fewer vehicle emissions than reformulated gasoline. Propane is produced as a by-product of natural gas processing and crude oil refining.
Hydrogen gas (H2) will play an important role in developing sustainable transportation in the United States, because it can be produced in virtually unlimited quantities using renewable resources. Pure hydrogen and hydrogen mixed with natural gas (hythane®) have been used effectively to power automobiles. However, hydrogen’s real potential rests in its future role as fuel for fuel cell vehicles. Hydrogen and oxygen fed into a proton exchange membrane (PEM) fuel cell “stack” produces enough electricity to power an electric automobile, without producing harmful emissions.