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Lean NOx Catalyst (LNC)
Catalyst designed to reduce nitrogen oxides from diesel or spark-ignited engine exhaust gases under net oxidizing conditions, i.e., in the presence of excessive amount of oxygen.
Light Duty Vehicle (LDV)
A passenger car or small truck.
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.
Low Emission Vehicle (LEV)
A vehicle that is certified to meet the LEV emission standards set by the California Air Resources Board (CARB).
National Ambient Air Quality Standards (NAAQS)
Ambient standards for six pollutants including ozone, carbon monoxide, nitrogen dioxide, lead, particulate matter, and oxides of sulfur specifically regulated under the U.S. Clean Air Act of 1990. Urban areas are required to achieve attainment in regards to ambient concentrations of these criteria pollutants.
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.
Nonattainment Area
A region that exceeds the U.S. National Ambient Air Quality Standards (NAAQS) for one or more criteria pollutants. Such regions, or areas, are required to seek modifications to their State Implementation Plans (SIPs), setting forth a reasonable timetable using means that are approved by the Environmental Protection Agency (EPA) to achieve attainment of NAAQS by a certain date. Under the Clean Air Act, if a nonattainment area fails to attain NAAQS, the EPA may superimpose a Federal Implementation Plan (FIP) with stricter requirements. Also, the EPA may impose fines, construction bans, or cut-offs in Federal grant revenues until the area achieves applicable NAAQS.
On-Board Diagnostics (OBD)
A system on board of the vehicle that monitors emission control components and alerts the driver (e.g., by a dashboard light) if malfunctions or emission deterioration occurs. The OBD system involves a number of sensors and a data processor, which is typically integrated with the vehicle’s electronic management system.
Open Frontal Area (OFA)
In monolith catalyst substrates, the part of the total substrate cross-section area which is available for the flow of gas. The OFA is frequently expressed as a percentage of the total substrate cross-section and sometimes also called the substrate void fraction.
Original Equipment Manufacturer (OEM)
Manufacturers of equipment (such as engines, vehicles, etc.) that provide the original product design and materials for its assembly and manufacture. OEMs are directly responsible for manufacturing and modifying the products, making them commercially available, and providing the warranty.
Overhead Cam
A camshaft used for operating both valves and unit injectors, located on top of or within the cylinder head. Such camshafts are driven by a multi-gear geartrain off the crankshaft. They simplify the design of the cylinder head and eliminate pushrods, allowing for much larger, open intake and exhaust ports and better breathing.
Oxygen Storage Capacity (OSC)
A capacity of the catalyst washcoat to store oxygen at lean and to release it at rich condition. Typically provided by cerium oxide (ceria), which oscillates between an oxidized and reduced state, depending on the exhaust gas chemistry. The OSC is an important component of three-way catalysts, used to extend the catalyst window.
Oxygenated Fuel
Any fuel substance containing oxygen, such as ethanol, methanol, or biodiesel. Oxygenated fuel tends to give a more complete combustion of its carbon into carbon dioxide (CO2), thereby reducing emissions of hydrocarbons and carbon monoxide. Oxygenated fuels may result in increased nitrogen oxides emissions.
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”).
Petroleum
A generic term applied to oil and oil products in all forms. Examples include crude oil, lease condensate, unfinished oil, refined petroleum products, and natural gas plant liquids.
Polycyclic Organic Matter (POM)
A class of air toxics defined in the US Clean Air Act as compounds with more than one benzene ring and a boiling point of 100°C and higher. Includes practically all of diesel PAH material.
Polynuclear Aromatic Hydrocarbons (PAH)
Aromatic hydrocarbons with two or more (up to five or six) benzene rings joined in various, more or less clustered forms.
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).
Precombustion Chamber
A small, auxiliary combustion chamber connected by a narrow orifice with the main chamber. Fuel is injected into the prechamber and ignites there, causing hot gases to expand into the main chamber (cylinder).
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.
Pump-Line-Nozzle Fuel System
A fuel system using a single injection pump driven off the geartrain on the front of the engine that also drives the camshaft. The central injection pump feeds a separate injection nozzle located in the cylinder head above each cylinder. Lines which must be of exactly equal length link each pump plunger with the associated nozzle. Each nozzle incorporates a needle valve and the orifices which actually handle atomization.
Purge Test
A test used to determine if fuel vapors are properly drawn from the evaporative canister and the fuel tank into the engine for combustion. If the purge system is not working properly, the evaporative canister can become saturated and vent hydrocarbons into the atmosphere.
Reformulated Gasoline (RFG)
Gasoline whose composition has been changed, from that of gasolines sold in 1990, to (1) include oxygenates, (2) reduce the content of olefins, aromatics and volatile components, and (3) reduce the content of heavy hydrocarbons to meet performance specifications for ozone-forming tendency and for release of toxic substances (benzene, formaldehyde, acetaldehyde, 1,3-butadiene, and polycyclic aromatic hydrocarbons) into the air from both evaporation and tailpipe emissions.
Renewable Energy
Energy obtained from sources that are essentially inexhaustible, unlike fossil fuels. It includes conventional hydro-electric, wood, bio-feedstocks, waste, geothermal, wind, photovoltaic, and solar thermal energy.
Respirable Combustible Dust (RCD)
A method of measuring ambient DPM exposures using a combustion process. Used in underground mines in Canada.
Rotary Injection Pump
A lower-cost injection pump used with pump-line-nozzle systems. The pump has a central plunger system (usually consisting of two opposing plungers) that provides fuel to every cylinder during the required injection period. A plate located near the top of the pump rotates, opening an appropriate orifice at the right time for distribution to each cylinder’s injection nozzle through a separate line. It is usually used with automotive or agricultural engines that have lower performance and durability requirements than the heavy-duty truck diesels.

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