Alternative Fuels Summary
 Alternative fuels are being used worldwide in a variety of vehicle applications. Using
these alternative fuels in vehicles can generally reduce harmful pollutants
and exhaust emissions. In addition, most of these fuels can be domestically
produced and derived from renewable sources.
Biodiesel
Biodiesel is a domestically produced, renewable fuel that can be manufactured from
vegetable oils, animal fats, 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 generally be used in unmodified diesel engines; however, users
should consult their OEM and engine warranty statement. Biodiesel can also be used
in its pure form (B100), but it may require certain engine modifications to avoid
maintenance and performance problems and may not be suitable for wintertime use.
Users should consult their engine warranty statement.
Pure biodiesel (B100) is considered an alternative fuel under EPAct. Lower-level
biodiesel blends are not considered alternative fuels, but covered fleets
can earn one EPAct credit for every 450 gallons of B100 purchased for use
in blends of 20% or higher. Biodiesel (fatty acid alkyl esters) is a cleaner
burning diesel replacement fuel made from natural, renewable sources such
as new and used vegetable oils and animal fats. Just like petroleum diesel,
biodiesel operates in compression-ignition engines. Blends of up to 20%
biodiesel (mixed with petroleum diesel fuels) can be used in nearly all
diesel equipment and are compatible with most storage and distribution equipment.
These low-level blends (20% and less) generally do not require any engine
modifications, however, users should consult their OEM and engine warranty
statement. Biodiesel can provide the same payload capacity and as diesel.
Higher blends, even pure biodiesel (100% biodiesel, or B100), may be able
to be used in some engines (built since 1994) with little or no modification.
However, engine manufacturers are concerned about the impact of B100 on
engine durability. Additionally, B100 is generally not suitable for use
in low temperature conditions. Transportation and storage of B100, however,
require special management.
Using biodiesel in a conventional diesel engine substantially reduces emissions
of unburned hydrocarbons, carbon monoxide, sulfates, polycyclic aromatic
hydrocarbons, nitrated polycyclic aromatic hydrocarbons, and particulate
matter. These reductions increase as the amount of biodiesel blended into
diesel fuel increases. The best emission reductions are seen with B100.
The use of biodiesel decreases the solid carbon fraction of particulate
matter (since the oxygen in biodiesel enables more complete combustion to
CO2) and reduces the sulfate fraction (biodiesel contains less than 15 ppm
sulfur), while the soluble, or hydrocarbon, fraction stays the same or increases.
Therefore, biodiesel works well with emission control technologies such
as diesel oxidation catalysts (which reduce the soluble fraction of diesel
particulate but not the solid carbon fraction).
Emissions of nitrogen oxides increase with the concentration of biodiesel
in the fuel and the increase is roughly 2% for B20. Some biodiesel produces
more nitrogen oxides than others, and some additives have shown promise
in reducing the increases. More R&D is needed to resolve this issue.
Biodiesel has physical properties very similar to conventional diesel.
Electricity
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 their electricity
must be replenished by plugging the vehicle into an electrical source. 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.
Electricity is unique among the alternative fuels in that mechanical
power is derived directly from it, whereas the other alternative fuels release
stored chemical energy through combustion to provide mechanical power. Motive
power is produced from electricity by an electric motor.
Electricity used to power vehicles is commonly provided by batteries, but
fuel cells are also being explored. Batteries are energy storage devices,
but unlike batteries, fuel cells convert chemical energy to electricity.
Ethanol
Ethanol is an alcohol-based alternative fuel produced by fermenting and
distilling starch crops that have been converted into simple sugars. Feed
stocks 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.
Ethanol can be blended with gasoline to create E85, a blend of 85%
ethanol and 15% gasoline. E85 and blends with even higher concentrations
of ethanol, E95, for example, qualify as alternative fuels under the Energy
Policy Act of 1992 (EPAct). Vehicles that run on E85 are called flexible
fuel vehicles (FFVs) and are offered by several vehicle manufacturers.
In some areas of the United States, lower concentrations of ethanol are
blended with gasoline. The most common low concentration blend is E10 (10%
ethanol and 90% gasoline). While it reduces emissions, E10 is not considered
an alternative fuel under EPAct regulations.
Ethanol (ethyl alcohol, grain alcohol, EtOH) is a clear, colorless liquid.
In dilute aqueous solution, it has a somewhat sweet flavor, but in more
concentrated solutions it has a burning taste. Ethanol (CH3CH2OH) is made
up of a group of chemical compounds whose molecules contain a hydroxyl group,
-OH, bonded to a carbon atom. Ethanol made from cellulosic biomass materials
instead of traditional feed stocks (starch crops) is called bioethanol.
The Clean Air Act Amendments of 1990 mandated the sale of oxygenated
fuels in areas with unhealthy levels of carbon monoxide. Since that time,
there has been strong demand for ethanol as an oxygenate blended with gasoline.
In the United States each year, approximately 2 billion gallons are added
to gasoline to increase octane and improve the emissions quality of gasoline.
Blends of at least 85% ethanol are considered alternative fuels under
the Energy
Policy Act of 1992 (EPAct). E85, a blend of 85% ethanol and 15% gasoline,
is used in flexible fuel vehicles (FFVs) that are currently offered by most
major auto manufacturers. FFVs can run on gasoline, E85, or any combination
of the two and qualify as alternative fuel vehicles under EPAct regulations.
In some areas, ethanol is blended with gasoline to form an E10 blend (10%
ethanol and 90% gasoline). Chemical properties: Ethanol is ethane
with a hydrogen molecule replaced by a hydroxyl radical.
Hydrogen
Hydrogen (H2) will play an important role in developing sustainable transportation
in the United States, because in the future it may be produced in virtually
unlimited quantities using renewable resources. Hydrogen has been used effectively
in a number of internal combustion engine vehicles as pure hydrogen mixed
with natural gas.
In addition, hydrogen is used in a growing number of demonstration fuel
cell vehicles. Hydrogen and oxygen from air fed into a proton exchange membrane
(PEM) fuel cell "stack" produce enough electricity to power an
electric automobile, without producing harmful emissions.
The simplest and lightest fuel is hydrogen gas (H2). Hydrogen is in
a gaseous state at atmospheric pressure and ambient temperatures. Hydrogen
may contain low levels of carbon monoxide and carbon dioxide, depending
on the source.
Hydrogen is being explored for use in combustion engines and fuel cell
electric vehicles. On a volumetric basis, the energy density of hydrogen
is very low under ambient conditions. This presents greater transportation
and storage hurdles than for liquid fuels. Storage systems being developed
include compressed hydrogen, liquid hydrogen, and physical or chemical bonding
between hydrogen and a storage material (for example, metal hydrides).
The ability to create hydrogen from a variety of resources and its clean-burning
properties make it a desirable alternative fuel. Although there is no significant
transportation distribution system currently for hydrogen transportation
use, we can transport and deliver hydrogen for early market penetration
using the established hydrogen infrastructure; for significant market penetration,
the infrastructure will need further development.
Methanol
Methanol, also known as wood alcohol, can be used as an alternative fuel
in flexible fuel vehicles that run on M85 (a blend of 85% methanol and 15%
gasoline). However, it is not commonly used because automakers are no longer
supplying methanol-powered vehicles.
Methanol can be used to make methyl tertiary-butyl ether (MTBE), an oxygenate
which is blended with gasoline to enhance octane and create cleaner burning
fuel. MTBE production and use has declined because it has been found to
contaminate ground water.
Methanol (CH3OH) is an alcohol fuel. Today most of the world's methanol
is produced by a process using natural gas as a feedstock. However, the
ability to produce methanol from non-petroleum feedstocks such as coal or
biomass is of interest for reducing petroleum imports.
Chemical Properties: As engine fuels, ethanol and methanol have similar
chemical and physical characteristics. Methanol is methane with one hydrogen
molecule replaced by a hydroxyl radical (OH).
Natural Gas
Natural gas is domestically produced and readily available to end-users
through the utility infrastructure. It is also clean burning and produces
significantly fewer harmful emissions than reformulated gasoline or diesel
when used in natural
gas vehicles. In addition, commercially available medium- and heavy-duty
natural gas engines have demonstrated over 90% reductions of carbon monoxide
(CO) and particulate matter and more than 50% reduction in nitrogen oxides
(NOx) relative to commercial diesel engines. Natural gas can either be stored
onboard a vehicle as compressed natural gas (CNG) at 3,000 or 3,600 psi
or as liquefied natural gas (LNG) at typically 20-150 psi. Natural gas can
also be blended with hydrogen.
Natural gas is a mixture of hydrocarbons—mainly methane (CH4)—and
is produced either from gas wells or in conjunction with crude oil production.
Natural gas is consumed in the residential, commercial, industrial, and
utility markets.
The interest in natural gas as an alternative fuel stems mainly from its
clean burning qualities, its domestic resource base, and its commercial
availability to end users. Because of the gaseous nature of this fuel, it
must be stored onboard a vehicle in either a compressed gaseous state (CNG)
or in a liquefied state (LNG).
Chemical Properties: The main constituent of natural gas is methane, which
is a relatively unreactive hydrocarbon. Natural gas as delivered through
the pipeline system also contains hydrocarbons such as ethane and propane;
and other gases such as nitrogen, helium, carbon dioxide, hydrogen sulfide,
and water vapor.
Propane
Propane or liquefied petroleum gas (LPG) is a popular alternative
fuel choice for vehicles because there is already an infrastructure of pipelines,
processing facilities, and storage for its efficient distribution.
Besides being readily available to the general public, LPG produces fewer
vehicle emissions than gasoline. Propane is produced as a by-product of
natural gas processing and crude oil refining.
According to the Gas Processors
Association HD5 specification for LPG as a transportation fuel, LPG
must consist of 90% propane, no more than 5% propylene, and 5% other which
is primarily butane and butylene. It is produced as a by-product of natural
gas processing and petroleum refining. The components of LPG are gases
at normal temperatures and pressures.
P-Series
P-series fuel is a unique blend of natural gas liquids (pentanes plus),
ethanol, and the biomass-derived co-solvent methyltetrahydrofuran (MeTHF).
P-Series fuels are clear, colorless, 89-93 octane, liquid blends that are
formulated to be used in flexible fuel vehicles (FFV's). P-Series are designed
to be used alone or freely mixed with gasoline in any proportion inside
the FFV's gas tank. These fuels are not currently being produced in large
quantities and are not widely used.
Since 1992, when the Energy
Policy Act (EPAct) was passed, only one new fuel has been recognized
as an alternative fuel under the EPAct petitions provision. P-Series fuels
were added to the list of alternative fuels in 1999. |
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