Additives
Chemicals added to fuel in very small quantities to improve and maintain fuel quality and/or to lower emissions.

After treatment Devices
Devices which remove pollutants from exhaust gases after the gas leaves combustion chamber (e.g., catalytic converters or diesel particulate filters). The term “exhaust gas after treatment” is considered derogatory by some in the emission control industry, but there is no consensus on the use of such alternatives as “post-combustion treatment” or “exhaust emission control

Air Quality Management District (AQMD)
Administrative districts organized in California to control air pollution. Nationwide in the U.S., AQMDs are parallel to the areas designated for classification against the National Ambient Air Quality Standards (NAAQS). Generally, AQMDs and their national parallel encompass multiple jurisdictions and closely follow the definition of Consolidated Metropolitan Statistical Areas and Metropolitan Statistical Areas.

Air Toxics
Toxic air pollutants, as classified by pertinent regulations. Examples of substances classified as air toxics by the US Clean Air Act include acetaldehyde, benzene, 1,3-butadiene, formaldehyde, and polycyclic organic matter (POM). California air toxics regulations also classify diesel exhaust particulates as a toxic air contaminant.

Alternative Fuel
Fuel other than petroleum diesel or gasoline.

American Society for Testing and Materials (ASTM)
A non-profit organization that establishes specifications and standard test methods for a broad range of materials and products. ASTM standards are recognized as definitive guidelines for quality of motor fuels.

Biodiesel
The mono alkyl esters of long chain fatty acids derived from renewable lipid feedstock, such as vegetable oils and animal fats, for use in compression ignition (diesel) engines. Manufactured by transestrification of the organic feedstock by methanol.

Brake Specific Fuel Consumption (BSFC)
BSFC is the ratio of the engine fuel consumption to the engine power output (as measured at the flywheel). BSFC has units of grams of fuel per kilowatt-hour (g/kWh) or pounds mass of fuel per brake horsepower-hour (lb/bhp-hr). BSFC is a measure of engine efficiency.

California Air Resources Board (CARB)
A state regulatory agency charged with regulating the air quality in California.

Carcinogens
Substances known to cause cancer.

Catalyst
A substance which influences the rate of a chemical reaction but is not one of the original reactants or final products, i.e. it is not consumed or altered in the reaction. Catalysts are used in many processes in the chemical and petroleum industries. Emission control catalysts are used to promote reactions that change exhaust pollutants from internal combustion engines into harmless substances.

Cetane Index
A calculated value, derived from fuel density and volatility, giving a reasonably close approximation to cetane number.

Cetane Number
A measure of ignition quality of diesel fuel. The higher the cetane number the easier the fuel ignites when injected into an engine. Cetane number is determined by an engine test using two reference fuel blends of known cetane numbers. The reference fuels are prepared by blending normal cetane (n-hexadecane), having a value of 100, with heptamethyl nonane, having a value of 15.


Clean Air Act (CAA)
In the U.S., the fundamental legislation to control air pollution. The original Clean Air Act was signed in 1963. The law set emissions standards for stationary sources, such as factories and power plants. Criteria pollutants included lead, ozone, CO, SO2, NOx and PM, as well as air toxics. The CAA was amended several times, most recently in 1990. The Amendments of 1970 introduced motor vehicle emission standards for automobiles and trucks

Cloud Point (CP)
A measure of the ability of a diesel fuel to operate under cold weather conditions. Defined as the temperature at which wax first becomes visible when diesel fuel is cooled under standardized test conditions (ASTM D2500).

Evaporative Emissions
Hydrocarbon vapors that escape from a fuel storage tank or a vehicle fuel tank or vehicle fuel system.

Injection Period
The time, measured in degrees of crankshaft rotation, between the beginning and end of injection. On engines with hydro mechanical injection systems, it is controlled by the opening and closing of ports in the injector body or by the action of a plunger forcing fuel out of a cup. On electronic injection systems, it is determined directly or indirectly by the action of a solenoid valve.

Liquefied Natural Gas (LNG)
Natural gas that has been refrigerated to cryonic temperatures where the gas condenses into a liquid.

Liquefied Petroleum Gas (LPG)
Liquefied Petroleum Gas (LPG) is a mixture of low-boiling hydrocarbons that exists in a liquid state at ambient temperatures when under moderate pressures (less than 1.5 MPa or 200 psi). LPG is a by-product from the processing of natural gas and from petroleum refining. Major components of LPG are propane (min. 85% content in the U.S.), butane and propylene.

Natural Gas (NG)
A mixture of hydrocarbon compounds and small quantities of various non hydrocarbon components existing in the gas phase or in solution with crude oil in natural underground reservoirs. The main component of natural gas is methane.

Nitrogen Oxides (NOx)
Several air-polluting gases composed of nitrogen and oxygen which play an important role in the formation of photochemical smog. Nitrogen oxides are collectively referred to as “NOx”, where “x” represents a changing proportion of oxygen to nitrogen. Internal combustion engines are significant contributors to the worldwide nitrogen oxide emissions. For the purpose of emission regulations, NOx is composed of colorless nitric oxide (NO), and the reddish-brown, very toxic and reactive nitrogen dioxide (NO2). Other nitrogen oxides, such as nitrous oxide N2O (the anesthetic “laughing gas”), are not regulated emissions.

NMHC
Non-Methane Hydrocarbons.

NMOG
Non-Methane Organic Gases.

Ozone (O3)
An oxygen molecule with three oxygen atoms. The stratosphere ozone layer, which is a concentration of ozone molecules located at 10 to 50 kilometers above sea level, is in a state of dynamic equilibrium. Oxygen molecules absorb ultraviolet (UV) light to form ozone which, in turn, decomposes back to oxygen. These processes absorb most of the ultraviolet light from the sun, shielding life from the harmful effects of UV radiation. Ozone is normally present at ground level in low concentrations. In cities where high level of air pollutants is present, the action of the sun’s ultraviolet light can, through a complex series of reactions, produces harmful concentrations of the ground level ozone. The resulting air pollution is known as photochemical smog.

Particulate Matter (PM)
Particles formed by incomplete combustion of fuel. Compression ignition (diesel) engines generate significantly higher PM emissions than spark ignited engines. The particles are composed of elemental carbon, heavy hydrocarbons (SOF), and hydrated sulfuric acid (“sulfate particulates”).

Pour Point
A measure of the ability of a diesel fuel to operate under cold weather conditions. Defined as the temperature at which the amount of wax out of solution is sufficient to gel the fuel when tested under standard conditions (ASTM D97).

Propane (C3H8)
A normally gaseous straight-chain hydrocarbon. Propane is a colorless paraffinic gas that boils at a temperature of -42°C. It is extracted from natural gas or refinery gas streams.

Renewable Energy
Energy obtained from sources that are essentially inexhaustible, unlike fossil fuels. It includes conventional hydro-electric, wood, bio-feedstock, waste, geothermal, wind, photovoltaic, and solar thermal energy.

Selective Catalytic Reduction (SCR)
Term frequently used as a synonym for catalytic reduction of NOx in diesel exhaust or flue gases by nitrogen containing compounds, such as ammonia or urea. Such SCR systems are commercially available for stationary applications and are being developed for mobile diesel engines. Since “selective catalytic reduction” is a generic term which also applies to other reactions, its use may lead to confusion in some situations.