|Clean School Bus|
The U.S. Energy Policy Act defines alternative fuels as: Clean Diesel, Liquefied Petroleum Gas (LPG), Compressed Natural Gas (CNG), Liquefied Natural Gas (LNG), Biodiesel (B20), Electricity, and Hydrogen. This page provides links and information on the four alternative fuels for school buses: Compressed Natural Gas, Clean Diesel a.k.a. Low Sulfur Diesel (also known as Ultra-Low Sulfur Diesel or ULSD), Propane, and a recent addition, Biodiesel.
Governmental vehicle emission standards began in 1959 in California. The federal government became involved eight years later as Congress passed the Air Quality Act of 1967, which designated air quality regions throughout the country and gave states the responsibility for adopting and enforcing pollution control standards in those regions. In 1970, President Richard Nixon brought those responsibilities under one umbrella with the establishment of the Environmental Protection Agency. Since then, the EPA has regulated diesel fuel emissions on an almost annual basis. The most recent updates have been in 2004, 2007 and 2010 aimed at drastically cutting oxides of nitrogen and particulate matter.
The current alternative fuels for diesel-powered school buses are compressed natural gas (CNG) and clean diesel, or as it is sometimes known as ultra-low sulfur diesel. Biodiesel which is made from vegetable oils, such as soybeans, or animal tallow, such as grease. It is usually blended with petroleum diesel, but can be used purely with certain engine modifications. In April 2002, Minnesota became the first state to mandate at least a 2 percent blend of biodiesel. CNG is a mixture of hydrocarbons, mainly methane, extracted from gas wells or crude oil. It must be stored in either a compressed gaseous state or in a liquefied state (LNG). Ultra-low sulfur fuel is "cleaned" as extra oxygen is added to the combustion air supply, which causes it to burn more completely, substantially reducing emissions. However, the extra oxygen will destroy conventional catalytic converters, so special engines are needed with clean diesel-compatible catalytic converters. In addition, sulfur is extracted by refiners during the cracking process. Efforts to introduce battery-powered electric buses in the late 1990s floundered due to battery problems. Since then, hybrid-electric buses have gained steam, but they remain generally cost-prohibitive. IC Bus produces hybrids using Enova drivetrains, and the companies hoped to produce 300 vehicles in 2009. Thomas Built Buses is also developing its own hybrid school bus. Collins Bus Corporation, manufacturer of the Collins Bus and Mid Bus Type A small school bus lines in the United States and Corbeil in Canada, announced in April 2009 that it would be offering a gasoline hybrid bus using an Azure Dynamics hybrid-electric drive train on a Ford E-350 chassis. Those buses were expected to be ready for market by the summer of 2009.
Each of the alternative has significantly lower emission levels than traditional diesel. The debate over which fuel reduces emissions the most is ongoing. See the National Biodiesel Board, Natural Gas Vehicle Coalition and BP for the specific claims of each. Biodiesel reduces PM and HC emissions, but it is similar to diesel fuel in NOx emissions. CNG consists of 90 percent methane. While methane is a more intense greenhouse gas than carbon dioxide, it is not a volatile organic compound, which combines with NOx and sunlight to form ground level ozone, and therefore contributes less to greenhouse gas formation. Ultra-low sulfur fuel contains approximately 90 percent less sulfur than regular diesel and releases 90 percent less sulfur dioxide emissions. A 2002 California Air Resources Board study found buses equipped with a diesel particulate filter running on low sulfur diesel fuel produced fewer PM and HC emissions than a CNG bus.
The U.S. General Accounting Office reported in 2000 that the high cost of purchase, operation and maintenance of alternative-fueled public transit buses is greater than the marginal improvements in air quality from alternative fuels. The report said CNG buses cost 15-25 percent more than diesel buses, not including the high maintenance and fuel costs. This matters little, however, as the EPA set stringent emission rules in December 2002 that will require a 97 percent decrease, from 500 parts per million to 15 ppm, in the sulfur content of diesel fuel for trucks and buses by 2007. Because of the heavy financial burden of this mandate, a bill before Congress would authorize a grant program to offset the purchase of alternative-fueled school buses. Both CNG and low sulfur diesel are included. The Department of Education would appropriate $40 million for fiscal year 2002, with per year increases of $10 million thereafter, to provide up to 10-15 percent of the purchase price of an alternative-fueled school bus. California created a program in 2000 to distribute $50 million to the state's 15 air quality management districts to fund the purchase of low-emission school buses.
Standard No. 2 diesel exhaust releases particulate matter (PM), nitrogen oxide (NOx) and hydrocarbons (HC), which contribute to air pollution, but determining the health effects in regard to children riding school buses depends upon whom you ask. Recent studies by the Natural Resource Defense Council, the Union of Concerned Scientists and Environment and Human Health claimed diesel exhaust was particularly harmful to children. The UCS study asserted that school buses emit as much soot in a year as 125 cars, while the EHH study said its research showed school bus exhaust levels 5 to 10 times higher, during short periods, than government standards. The NRDC study has been discredited as it tested only four older buses of a model no longer in use. Moreover, critics point out that UCS did not actually do any scientific tests, rather it conducted a national survey of diesel buses and extrapolated as to their pollution effects. In the EHH study, the "short periods" were mere 10 second intervals. By contrast, a regarded 2001 study by Fairfax County (Va.) Public Schools said the air on school buses "poses no health risks to students." To date, this is the only study countering adverse health claims by environmentalists.
Diesel fuel has a higher boiling range than gasoline. Since engines create power by converting fuel to heat, the higher boiling range allows diesel engines to provide more horsepower than gasoline engines. Diesel provides greater fuel efficiency than gasoline because of the increased energy produced. Diesel engines emit 40 percent less carbon dioxide than gasoline, and produce lower amounts of hydrocarbon and carbon monoxide.
The first diesel engine was built by German inventor Rudolf Diesel (1858 - 1913) in 1893. By 1898, diesel engines were widely used. Diesel demonstrated mechanical efficiency of his engine to be 75.6 percent. More commonly used steam engines achieved an efficiency of 10 percent or less. Diesel demonstrated his engine at the World Exhibition in Paris in 1900 using peanut oil as fuel.