The Energy Evolution - Hydrogen and Fuel Cells: Advances in Transportation and Power - page 18

away from single-fuels to several fuels. This is also true in many power
plants today. Dual-fuel or flexible-fuel vehicles are now used to some de-
gree around the world. A dual-fuel boiler for a turbine generator or an en-
gine to drive a generator might operate on natural gas, fuel oil, gasoline
or an alternative fuel. Typically, boilers or engines will switch between a
liquid or gaseous fuel. Cars, trucks, and buses that use both gasoline and
compressed natural gas have been in use in northern Italy.
Flexible-fuel engines are able to use a variable mixture of two or
more different fuels, as long as they are alike physically, in usually liquid
form.
Vehicles with flexible-fuel engines are not in widespread use. There
are about 15,000 M85 methanol vehicles in operation in the U.S. While
methanol vehicles can provide greater power and acceleration but they
suffer from cold starting difficulties. Cold starting problems can occur
with these fuels in their pure form, but the addition of a small percent-
age of gasoline eliminates this problem. Both methanol and ethanol have
a lower energy density than that of gasoline and thus more alcohol fuel is
needed to provide the same energy.
The costs for near alcohol automobiles will be very close to the cost
of a gasoline automobile. FFVs are expected to cost slightly more. The
EPA estimates that with the necessary adjustments, the savings and costs
will balance out. The increased costs necessary for fuel tank adjustments
and to compensate for cold-start problems could be balanced out by the
smaller, lighter engines that these cars can have because of their increased
efficiency.
CARBON EXCHANGE
When fuels are derived from biomass, the net increase in carbon di-
oxide emitted into the atmosphere is usually considered to be neutral or
even negative since the plants used to produce the alcohol fuel have re-
absorbed the same or more carbon than is emitted from burning the fuel.
The net effect may not be as favorable when the carbon dioxide emitted by
equipment for the harvesting of the biomass feedstocks is considered in
the balance. Much of this depends on the differences in equipment, farm-
ing techniques and other regional factors.