A
aftermarket conversion - A standard, conventionally fueled, factory-produced vehicle to which
equipment has been added that enables the vehicle to operate on an alternative fuel; also, the process of
converting such a vehicle.
alcohol - The family name of a group of organic chemical compounds composed of a hydrocarbon
plus a hydroxyl group (OH). The two simplest alcohols are methanol and ethanol.
alternative energy source - An environmentally friendly source of energy not traditionally used for a
particular application.
alternative fuel - Any fuel for vehicles other than the petroleum-based fuels now in conventional use;
for cars, trucks, and buses, conventional fuels are considered to be gasoline and diesel. Generally,
alternative fuels are alcohols, natural gas, propane, hydrogen, and electricity. A more stringent
definition is set forth in the federal Energy Policy Act of 1992: methanol, denatured ethanol, and other
alcohols, separately or in mixtures of 89% by volume or more (or other percentage not less than 70%
as determined by U.S. Department of Energy rule) with gasoline or other fuels; compressed natural gas;
liquified natural gas; propane (liquefied petroleum gas); hydrogen; coal-derived liquid fuels; other than
alcohols derived from biological materials; electricity; or any other fuel determined to be substantially
not petroleum and yielding substantial energy security and environmental benefits.
alternative-fuel vehicle - A vehicle designed and manufactured or converted to operate in dedicated or
multi-fuel modes on fuels other than gasoline or diesel as defined by EPAct.
atmosphere - The envelope of air surrounding the earth and bound to it by the earth’s gravitational
attraction.

B
barrel - A unit of measure (volume) for crude oil and petroleum products, equivalent to 42 U.S. gallons.
bi-fuel vehicle - A vehicle with two separate fuel systems designed to run on an alternative fuel and
gasoline, using only one fuel at a time.
biodiesel - A biodegradable transportation fuel for use in diesel engines that is produced through
transesterification of oil from plants such as soybeans, rapeseed, or sunflowers; animal fat; or agricultural
byproducts such as rice hulls.
biogas - A mixture of carbon dioxide and methane produced from the anaerobic decomposition of
organic material; typically a low-quality gas with numerous contaminants.
biomass - Organic matter such as plant materials and animal waste used for the production of energy.
Examples include agricultural crops; crop-waste residues; wood, animal, and municipal wastes; aquatic
plants; and fungal growth.
British thermal unit - A standard unit for measuring heat energy. One Btu is the amount of heat
required to raise one pound of water 1EF at sea level.

C
CNG - Compressed natural gas. CNG has been pressurized to between 2,000 and 3,600 psi in a
container and expands when released for use as a fuel.
carbon dioxide - A colorless, odorless, non-poisonous gas normally present in air. One source of
carbon dioxide is fossil-fuel combustion. Although CO2 does not directly impair human health, it is a
greenhouse gas that traps the earth’s heat and contributes to the potential for global warming. It is vital
to plants, which absorb it from the air.
carbon monoxide - A colorless, odorless gas, slightly lighter than air, produced by the incomplete
combustion of fuels with a limited oxygen supply, as in automobile engines. Carbon monoxide is
poisonous if inhaled, entering the bloodstream through the lungs and forming a compound that inhibits
the blood’s capacity to carry oxygen to organs and tissues. Carbon monoxide can impair exercise
capacity, visual perception, manual dexterity, and learning functions. Severe CO poisoning can result in
death.
carcinogenic - Known to cause cancer.
coal - A black or brownish-black solid combustible substance formed by the partial decomposition of
vegetable matter without access to air. See also anthracite, bituminous coal and lignite.
combustion - Burning; a chemical change, usually oxidation, accompanied by the production of heat
and light.
compressed natural gas - Natural gas that has been pressurized to between 2,000 and 3,600 psi. It is
held in a container and expands when released for use as a fuel.
compressor - A machine that compresses a gas into a smaller volume of space.
crude oil - A mixture of hydrocarbons that exists in liquid phase in underground reservoirs and remains
liquid at atmospheric pressure after passing through a separating facility. Includes liquid hydrocarbons
produced from tar sands, oil shale, and other sources.

D
dedicated vehicle - A vehicle designed to operate solely on one alternative fuel.
denatured alcohol - An alcohol that otherwise could be safely consumed by humans that contains a
small amount of a toxic substance, such as methanol or gasoline, which cannot be removed easily by
chemical or physical means. Alcohols intended for industrial use, including ethanol, must be denatured
to discourage abuse by ingestion and to avoid alcoholic beverage regulation and taxation.
dispenser - A machine that dispenses a fuel. A dispenser may include more than one pump. Today,
many filing station dispensers have six pumps - three on each side.
dual-fuel vehicle - A vehicle designed to run on a combination of alternative fuel and conventional
fuel at the same time. Dual-fuel systems have separate fuel tanks, and both fuels are injected into the
combustion chamber simultaneously.

E
E10 - Ethanol/gasoline mixture containing 10% denatured ethanol and 90% gasoline, by volume. See
also gasohol.
E85 - Ethanol/gasoline mixture containing 85% denatured ethanol and 15% gasoline, by volume.
efficiency - The ratio of the effective or useful output to the total input of any system.
electric vehicle - Vehicle powered by electricity, whether stored in batteries or produced within a fuel
cell.
28
electrical energy - Energy generated by moving electrons.
emissions - Substances discharged into the air, especially by an internal-combustion engine.
energy - As defined in physical science, the capacity to do work and change matter. Energy is neither
created nor destroyed, but can change from one form into another.
energy source - A supply of energy that can be used for a particular application.
ethanol - Otherwise known as ethyl alcohol, alcohol, or grain-spirit. A clean, colorless, flammable
oxygenated hydrocarbon. It is used in the United States as a gasoline octane enhancer and oxygenate
(up to 10 percent concentration). It is commonly derived from biomass sources such as corn. See also
E-10, E-85, gasohol.
evaporative emissions - Hydrocarbon vapors that escape from a gasoline storage tank, from a vehicle
tank during refueling, or from a vehicle fuel system. See also exhaust emissions.
exhaust emissions - Sometimes called tailpipe emissions. Any substances, gases, or particles, that
result from fuel combustion, e.g., water vapor, carbon monoxide, and soot particles. See evaporative
emissions.

F
fast fill - A type of natural gas refueling, requiring a compressor and a storage tank that allows quick
dispensing of fuel.
flexible-fuel vehicle - A vehicle designed to operate on methanol or ethanol, gasoline, or any
combination thereof.
fossil fuel - Fuel derived from materials formed over millions of years from organic debris. Fossil fuels
include coal, distillates of petroleum, and natural gas and its components.
fuel cell - A system that converts the chemical energy of a fuel, such as hydrogen and oxygen, directly
to electricity. The principal components of a fuel cell are catalytically activated electrodes for the fuel
(anode) and the oxidant (cathode) and an electrolyte to conduct ions between the two electrodes.

G
gaseous fuel - A combustible mixture that has neither independent shape nor volume; unless contained,
it would expand indefinitely. Gaseous fuels used for transportation, such as propane and natural gas,
have an advantage over liquid fuels, which must be vaporized for efficient ignition. Their disadvantage
is that they must be stored in pressurized tanks.
gasification - Any chemical or heat process used to convert a feedstock to a gaseous fuel; especially,
a method for turning coal into a gas. This can be accomplished by burning the coal or extracting and
gasifying the coal at a plant.
gasohol - In the United States, gasohol refers to gasoline that contains 10% ethanol by volume. This
term was common in the late 1970s and early 1980s. Future gasohol will contain 5.7% and 7.7%
ethanol.
gasoline - A mixture of volatile hydrocarbons used to operate an internal-combustion engine, produced
through the distillation and other chemical transformation of petroleum.

H
hybrid vehicle - A vehicle that can run on electricity and another fuel.
hydrocarbon - An organic chemical compound of hydrogen and carbon in either gaseous, liquid, or
solid phase. The molecular structure of hydrocarbon compounds varies from the simple (e.g., methane,
a constituent of natural gas) to the heavy and complex (e.g., benzene, a constituent of gasoline).
hydrogen - The simplest and lightest of the elements; exists as a colorless, odorless, diatomic gas as well
as in combination with other elements.

I
internal-combustion engine - A heat engine in which the combustion that generates the heat takes place
inside the engine instead of in an external furnace.

L
liquefaction - The process of making, or state of being, a liquid.
liquefied natural gas - Natural gas that has been condensed to a liquid, typically by cooling the gas to
-259EF.
liquefied petroleum gas (LPG) - Several gases extracted from natural gas or petroleum that liquefy under
pressure. The term is often used to substitute for the name of an individual gas, especially propane. See
also butane and propane.

M
M85 - 85% methanol and 15% unleaded gasoline by volume; used as a motor fuel for light-duty
applications.
M100 - 100% (neat) methanol, used as a motor fuel for heavy-duty engines.
methane (CH4) - The simplest of the hydrocarbons and the principal constituent of natural gas. Also,
the principal gas derived from landfills. Pure methane has a heating value of 1,012 Btu per cubic foot.
methanol (CH3OH) - Also known as methyl alcohol, wood alcohol. A colorless, poisonous liquid with
essentially no odor and very little taste. The simplest alcohol, it is extremely flammable, burning with
a nearly invisible blue flame. Methanol is produced commercially by catalytically combining carbon
monoxide (CO) with hydrogen (H2) under high temperature and pressure or by steam-reforming natural
gas.
miles per gallon equivalent - The average number of miles a vehicle can travel on a gallon equivalent
of an alternative fuel, i.e., an amount of fuel equal in energy content to one gallon of gasoline.
mobil-source emissions - Emissions of pollutants from cars, trucks, buses, and other motor vehicles.
This category includes both exhaust and evaporative emissions.

N
natural gas - A mixture of gaseous hydrocarbons, primarily methane, occurring naturally in the earth,
used principally as a fuel in the production of heat, electricity, or in transportation. For vehicular use,
natural gas is compressed in special tanks to a pressure of 2,000-3,600 psi. It can also be liquified by
cooling to -259EF.
nitrogen - A non-metallic element that occurs naturally as a colorless, odorless, diatomic gas (N2).
Nitrogen constitutes nearly 4/5 of the volume of the earth’s atmosphere.
non-attainment area - A region that exceeds minimum federal air-quality standards for certain
pollutants. See also Clean Air Act of 1970, criteria pollutants.
non-renewable fuel - Fuel that takes millions of years to make, such as a fossil fuels. At current rates of
consumption, these sources will be depleted long before more are available for use.

O
octane rating - Also called octane number; a numerical representation of the anti-knock properties of
motor fuel.
original equipment manufacturer - Manufacturer that provides the original design and materials for
making a product. OEMs include the major U.S. auto manufacturers. In the context of alternative fuels,
OEM refers to a manufacturer that produces a vehicle that leaves the assembly line ready to use an
alternative fuel without further conversion.
oxygenated gasoline - Gasoline with an oxygen content of 2.7% by weight. Oxygenated fuel tends to
burn more completely, converting its carbon into carbon dioxide rather than carbon monoxide. This
reduces air pollution from exhaust emissions.
ozone (O3) - A molecule consisting of three oxygen atoms that occurs naturally at both ground level and
high in the atmosphere. It is a blue, pungent-smelling gas at room temperature. Ground-level ozone
if formed naturally when water vapor reacts with lightning. It is formed in greater quantities when
sunlight acts on nitrogen oxides and volatile organic compounds emitted by fuel combustion. Ozone is
the principal component of the brownish haze called smog. Ozone is a lung irritant, causing particular
health problems for growing children, some elderly people, and people with lung conditions such as
asthma.

P
particulates - Small particles of polluting compounds.
parts per million - A measurement of the concentration or density of one substance compared to
another. If 50 ml of carbon monoxide is present in 1 million ml of air, the concentration of CO is 50
ppm by volume.
petroleum - See crude oil.
photovoltaic cell - Device that converts sunlight directly into electric current.
pollution - The contamination of soil, water, or air by the discharge of harmful substances.
propane - Colorless, gaseous simple hydrocarbon extracted from natural gas or crude oil, used as a fuel
and as a raw material in chemical manufacturing. One of the alternative fuels specified in the Energy
Policy Act of 1992. Also called liquefied petroleum gas (LPG).

R
rapeseed - The seed of the rape plant, a European plant. Oil is extracted from the rape seed and used
as a lubricant and in food products.
reactive emissions - Compounds emitted by evaporation or combustion of fuels that react with the
atmosphere to form harmful pollutants, such as ozone. Includes reactive hydrocarbons, e.g., benzene,
and other compounds such as sulfur dioxide.
refinery - An industrial plant that manufactures finished products from crude oil, natural gas, natural gas
liquids, other hydrocarbons, and oxygenates.
reformulated gasoline - Gasoline whose composition includes oxygenates and reduced content
of olefins, aromatics, volatile components, and heavy hydrocarbons. The goal is to reduce ozone
formation and the release of toxic substances into the air from both evaporation and tailpipe emissions.
In cities that do not meet air-quality requirements for ozone set forth in the 1990 amendments to the
federal Clean Air Act, only reformulated gasoline can be sold during months when ozone pollution is
most serious.
refueling station - A facility that sells or distributes fuels to motor vehicles.
renewable fuel - Fuel that is created naturally, or by human intervention at a relatively rapid rate, and
therefore does not run out.
reserves - Identified deposits or reservoirs of natural resources, such as coal, forests, or water.

S
smog - A brownish haze seen over polluted cities. The name was coined as a combination of “smoke”
and “fog,” both of which it resembles. A principal component is ozone.

T
toxic - Poisonous or harmful to human life.
toxicity - The degree to which a substance is poisonous.

V
volatile - Describes a substance that readily turns to vapor at normal temperatures.