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Diesel Exhaust Fluid (DEF)

Today, cars and trucks and other applications using diesel engines sold in the United States must meet stringent U.S. Environmental Protection Agency (EPA) emissions requirements. To meet these requirements, many diesel engine manufacturers use Selective Catalytic Reduction (SCR), an emissions aftertreatment technology that converts nitrogen oxides (NOx) in the diesel-engine exhaust stream into nitrogen and water vapor, two natural components in the air we breathe. 

Diesel exhaust fluid (also referred to as DEF or AUS 32) is injected into the diesel exhaust stream and the heat from the exhaust, the fluid, and a catalyst convert the NOx into the harmless gases.

Diesel exhaust fluid is a 32.5% solution of technically pure urea in purified water. For the SCR unit to operate properly, the DEF must meet an exacting purity standard. This standard, published by the International Organization for Standardization (ISO), is intended to ensure that the diesel exhaust fluid used in SCR-equipped cars and trucks provides the purity required by diesel engine manufacturers and the quality to preserve the emissions control system and the environment.

The API Diesel Exhaust Fluid (DEF) Certification Program is a voluntary program designed to certify and monitor the quality characteristics of diesel exhaust fluid intended for use in motor vehicles with diesel engines. Diesel exhaust fluid marketers that have demonstrated that their products satisfy the requirements of the most recent and applicable edition of ISO 22241, Diesel engines – NOx reduction agent AUS 32, may be licensed to display the API Diesel Exhaust Fluid Certification Mark. 

API Diesel Exhaust Fluid Certification has many benefits:  

  • Identifies for consumers diesel exhaust fluids that meet diesel engine manufacturer requirements.
  • Helps consumers find those fluids.
  • Gives consumers a choice of quality brands from which to choose.
  • Helps reduce Nitrogen Oxide emissions.
  • Provides rigorous monitoring of fluids in the marketplace.
  • Tests licensed fluids to ensure that they meet program requirements.

To view a real-time Directory of DEF licensees, click the button at the top of this section or simply click here.

Please download the Diesel Exhaust Fluid Program Overview for additional information and program requirements.

Please direct any questions or comments regarding licensing to apidef@api.org.

To login and manage a license, please visit http://dieselexhaust.api.org.

Proceed to the Applications & Fees section.  

API has launched the Marine Diesel Exhaust Fluid Certification Program

Marine DEF, or AUS 40, is an aqueous high-purity urea solution at a concentration of 40% that is needed to operate converters with SCR in applications with large combustion engines. As the name implies, Marine DEF is used in many marine applications but is increasingly used in rail and other land-based applications.

The Marine Diesel Exhaust Fluid Certification Program will certify brands of Marine DEF offered by marketers that have demonstrated that their products satisfy the requirements of the most recent and applicable edition of ISO 18611, Ships and marine technology – Marine NOx reduction agent AUS 40. Licensed marketers may use the API Marine Diesel Exhaust Fluid Certification Mark in conjunction with their licensed products and marketing materials.

The program has been integrated into the existing Diesel Exhaust Fluid Certification Program licensing portal and is designed to operate exactly as the original Diesel Exhaust Fluid Certification Program.  An existing licensed marketer may easily apply for licensing of their Marine DEF products at no additional charge simply by logging in and adding the new product.

To view a real-time Directory of DEF licensees, click the button at the top of this section or simply click here.

Please download the Diesel Exhaust Fluid Program Overview for additional information and program requirements.

Please direct any questions or comments regarding licensing to apidef@api.org.

To login and manage a license, please visit http://dieselexhaust.api.org.

Proceed to the Applications & Fees section.