Americans are becoming increasingly concerned about the condition of our nation's air quality and our dependence on foreign oil. Yet the vehicles we drive on a daily basis, mostly powered by petroleum-based fossil fuels, are a major source of air pollutants. The good news is that alternative fuels are readily available. Some businesses, government agencies, individuals, and school corporations are choosing to drive alternative fuel vehicles (AFVs). Most major automakers produce AFVs, including cars, light and heavy-duty trucks, shuttle and transit buses, and off-road vehicles. Many AFVs are sold as fleet vehicles, but many models are also available to the public to purchase as well. AFVs come in three basic configurations: flexible-fuel, bi-fuel or dual fuel, and dedicated-fuel. Flexible-fuel vehicles have one tank and can run on a mixture of petroleum fuel and alternative fuel. Bi-fuel or dual-fuel vehicles have two fuel tanks for two separate fuels. Dedicated-fuel vehicles use one alternative fuel full-time.
Most of the alternative fuels we use are produced domestically. They can be instrumental in our efforts to reduce our nation's dependence on foreign oil. AFVs generally release fewer harmful air pollutants to our environment than petroleum-powered vehicles. Many fleet operators are required by law to purchase AFVs because of Congress passing the Energy Policy Act in 1992 that requires certain types of vehicle users, including fleets operated by state and federal government agencies, to acquire specific proportions of light-duty AFVs.
Alternative Fuel Choices for Vehicles
Ethanol
Ethanol is an alcohol-based alternative fuel produced by fermenting and distilling starch crops (such as corn, barley, and wheat) that have been converted into simple sugars. Ethanol is most commonly used to increase octane and improve the emissions quality of gasoline. Ethanol can be blended with gasoline to create E85, a blend of 85% ethanol and 15% gasoline. Vehicles that run on E85 or traditional gasoline blends are called flexible fuel vehicles and are offered by several vehicle manufactures.
| Pollutant | E85 Approximate Reductions |
| NOx | 10% |
| PM | 20% |
| SO2 | 80% |
| VOC | 15% |
*Actual emission values vary with engine make and model.
Biodiesel
Biodiesel is a domestically produced, biodegradable, renewable fuel that can be used in unmodified diesel engines with the current fueling infrastructure. Biodiesel is made by chemically reacting alcohol with vegetable and soybean oils and animal fats. It is most often used in blends ranging from 2% to 20% (B20) biodiesel. It may also be used as pure biodiesel (B100 or sometimes referred to as "neat" biodiesel). Biodiesel is a sulfur free lubricant that aids in loosening and dissolving sediments throughout the diesel engine system. Performance, storage requirements, and maintenance are similar for biodiesel blend fuels and petroleum diesel. Biodiesel is also readily available throughout the country and can be ordered through a number of companies and delivered anywhere in the country. Although biodiesel can cost more than petrodiesel, diesel drivers can transition to biodiesel without purchasing new vehicles. In the case of fleets, managers can transition to biodiesel without acquiring new spare parts inventories or updating refueling stations.
| Pollutant | B20 Approximate Reductions |
| NOx | +2% |
| PM | 12% |
| SO2 | 20% |
| VOC | 20% |
*Actual emission values vary with engine design.
Compressed Natural Gas (CNG)
Compressed Natural Gas (CNG) is a high-pressure form of natural gas that is used as a common energy source in homes, businesses, and vehicles. CNG is odorless, colorless, and tasteless and is mostly composed of methane. Although CNG is a flammable gas, it is inherently safe since the flammability range of methane is so small. CNG is used for its clean burning qualities and the general reduction of emissions associated with its use. Currently there are vehicles that run solely on CNG as well as those that run on either CNG or gasoline. The cost of CNG is more stable than that of gasoline and generally costs significantly less per the equivalent of one gallon of gasoline. CNG only contains about a quarter of the energy by volume of gasoline and therefore CNG fueled vehicles require more frequent refueling. In addition, CNG vehicles cost $2,000 to $4,000 more than their gasoline counterparts. Heavy-duty natural gas engines cost approximately twice as much as that of a comparable diesel engine.
| Pollutant | CNG Approximate Reductions |
| CO | 97% |
| HC | 75% |
| PM | 97% |
| NOx | 60% |
*Actual emission values vary with engine design.
Propane/Liquefied Petroleum Gas
Propane is a byproduct of natural gas processing and petroleum refining. In its natural state, propane is colorless, nontoxic, has good luminosity, and does not have to be stored at extremely high pressure or low temperatures. As a motor vehicle fuel, propane is referred to as liquefied petroleum gas (LPG), which is combination of hydrocarbons such as propane, ethane, and butane. An odorant is added to the LPG so it can be detected for safety reasons. Under moderate pressure, propane gas turns into a liquid mixture, making it easier to transport and store in vehicle fuel tanks. In the U.S., about half of the LPG is obtained as a by-product of natural gas processing and the remainder comes from crude oil refining. Approximately 92 percent of the nation's LPG supply is domestically produced. Propane in its liquid state has the lowest flammability range of any alternative fuel, but when a leak occurs, it becomes a gas and is more likely to ignite than gasoline and other liquid fuels. LPG use in medium and heavy-duty vehicles is a popular application. According to the U.S. EPA, in 2002, there were more than 350,000 LPG vehicles on the road in the United States, including taxicabs, school buses, and police cars. LPG is used for its clean burning qualities and the general reduction of emissions associated with its use. Currently there are vehicles that run solely on LPG as well as those that run on either LPG or gasoline. Propane refueling stations are currently located in all 50 states. Converting vehicles from gasoline to propane typically costs between $1,000 to $2,000 and that usually requires adding a special fuel tank that takes up some trunk space and adds approximately 100 pounds to the weight of the vehicle. Converting diesel engines to LPG operation is possible but not economically feasible at this time. Propane-powered vehicles bought new from the manufacture cost $3,000 to $4,000 more than their gasoline counterparts. Propane fuel cost is comparable to gasoline in price per gallon equivalent, but propane cost tends to fluctuate with oil prices and spike during periods of increased demand, such as harsh winters. LPG contains less energy than gasoline and therefore LPG-powered vehicles require more frequent refueling.
| Pollutant | LPG Approximate Reductions |
| CO | 32% |
| HC | 30% |
| PM | 88% |
| NOx | 57% |
*Actual emission values vary with engine design
Ultra-Low Sulfur Diesel (ULSD)
Ultra-low sulfur diesel (ULSD) is a cleaner diesel fuel that enables the performance of aftermarket treatment technologies such as diesel particulate filters. The emissions levels of ULSD alone will vary depending upon the individual vehicle. ULSD is currently available nationwide.
| Pollutant | ULSD Approximate Reductions |
| CO | 6% |
| HC | 13% |
| PM | 13% |
| NOx | 3% |
*Actual emission values vary with engine design