Emissions Acronyms, Decoded

Struggling to stay on top of all the acronyms and technical terms associated with U.S. EPA Tier 4 Final emissions standards? This quick decoder will help you keep the terminology straight.

ACRONYM

DEFINITION

 

DEF

Diesel Exhaust Fluid

DEF is a carefully blended solution of high-purity urea and de-ionized water used in SCR solutions. It’s injected into the exhaust system, where it decomposes into ammonia, then selectively reduces NOx with the help of a catalyst.

 

DOC

Diesel Oxidation Catalyst

A DOC is an aftertreatment device that reduces PM by converting carbon dioxide and hydrocarbons to carbon dioxide and water vapor. It optimizes nitrogen monoxide and nitrogen dioxide ratios for both passive DPF regeneration and the optimal conversion of NOx in SCR.

 

DPF

Diesel Particulate Filter

A DPF is an aftertreatment device that captures PM formed during combustion. It can be regenerated passively or actively and allows for lower fuel consumption and better transient response and performance.

 

EGR

Exhaust Gas Recirculation

EGR reduces the levels of NOx emitted by an engine by recirculating exhaust gas into the engine’s cylinder and replacing some of the air with carbon dioxide. That lowers combustion temperature and reduces the amount of NOx formed.

 

NOx

Nitrogen Oxides

NOx gases are produced from the reaction of nitrogen and oxygen during the combustion of fuels, especially at high temperatures. They’re one of two primary exhaust pollutants covered by emissions standards.

 

NRS

NOx Reduction System

NRS reduces the levels of NOx emitted by an engine by recirculating exhaust gas into the engine’s cylinder and replacing some of the air with carbon dioxide. That lowers combustion temperature and reduces the amount of NOx formed.

 

PM

Particulate Matter

PM is a complex mixture of extremely small particles and liquid droplets that get into the air, including dust, dirt, soot and smoke. It’s the second of two primary exhaust pollutants covered by emissions standards.

 

SCR

Selective Catalytic Reduction

SCR is a catalyzed chemical reaction that reduces NOx to water and nitrogen using diesel exhaust fluid. This fluid is injected into a tube where it mixes with the exhaust, and the reactions take place as the mixture passes through the SCR catalyst.

 

ULSD

Ultra-Low-Sulfur Diesel

ULSD is diesel fuel with substantially lower sulfur content that contributes to PM reductions in non-road engines and equipment. Many advanced emission-control technologies require the use of ULSD.

 

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