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THE NATIONAL
CLEAN BUS NETWORK
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FUELS
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technologies
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Diesel and gasoline have
been used to power vehicles for more than
100 years. They are
cheap and abundant, but without emission control devices, they produce harmful pollutants like carbon monoxide, nitrogen oxides, air toxins and
the greenhouse gas, carbon dioxide. Besides, the transportation
sector drives more than sixty percent of petroleum consumption in
the United States. This has important implications for national
energy security.
The Diesel Option
Because the nation's
bus fleets rely to such an extent on diesel, this will continue to
be an option for fleet managers with tight budgets and complicated
access to alternatives.
But there are transit
planners, local government officials, public interest groups and
others searching
for alternative ways to reduce petroleum consumption and improve air
quality. One way of
accomplishing this is by using a different fuel altogether. Here are
some options.
The Natural
Gas Option
Natural gas is the most
widely-used alternative fuel in transit buses today. Many large
transit agencies deployed natural gas buses in the 1990s to reap
immediate clean air benefits. Major transit agencies in Los Angeles,
Seattle, Dallas, Atlanta, Washington, DC, New York and Boston
currently operate large natural gas fleets. If and when hydrogen
fuel becomes a feasible alternative for transportation applications,
natural gas is expected to be the primary feedstock.
The Biodiesel
Option
Interest in biodiesel is
growing rapidly for its benefits as a renewable,
domestically-produced fuel. Biodiesel can be used directly in diesel
engines with practically no engine modification. This is important
because other fuels require large capital investments in refueling
infrastructure and engine conversions. Refiners can use waste feedstocks
like animal fats and used frying oil, keeping these from entering
landfills. Refiners can also use agricultural commodities like soybeans
and mustard seed that provide incomes to American farmers. Biodiesel is
especially good for its reduction of carbon dioxide emissions that
contribute to global warming.
The Liquid Petroleum
Gas (LPG) Option Also
known as Propane, LPG is a common fuel found in barbecues and indoor
vehicles like forklifts because of its clean-burning properties.
Deployment of propane-powered buses was widespread in the 1980s in
school bus fleets and national park bus fleets. But as natural gas has
grown in popularity among heavy-duty vehicle alternatives, propane bus
deployment has waned. Though there are one or two commercial propane
buses on the market, engine conversion kits are currently the more
common form of propane bus deployment.
The Hydrogen
Option In
contrast to the fuels listed above, hydrogen is not available for
commercial use. This is because no vehicle technologies have been fully
developed to use the fuel. There are two potential hydrogen technologies
under development. These are hydrogen fuel cells and hydrogen internal
combustion engines. Fuel cells are much more efficient than the internal
combustion engine, but may not be commercially available for at least
ten to fifteen years. The internal combustion engine, however, is a
well-developed propulsion system that can meet or even exceed emissions
performance of natural gas engines when fueled with hydrogen. This
system may be available sooner than the fuel cell, but must first
undergo some field demonstrations and testing.
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