Tractor & Construction Plant Wiki

A jug of diesel exhaust fluid on a Canadian Tire store shelf

Diesel Exhaust Fluid (DEF) is an aqueous urea solution used in Selective Catalytic Reduction (SCR) to lower NOx concentration in the exhaust emissions from diesel engines. The solution may also be referred to[by whom?] as AUS32, shorthand for Aqueous Urea Solution, 32.5%, or as AdBlue, a trademark held by the German Association of the Automobile Industry (VDA), who ensure quality standards are maintained in accord with ISO 22241 specifications. Initially the specification was described in DIN 70070.[1] In 2006 the worldwide ISO 22241 standard was introduced, which also stipulates analytical test protocols to verify adherence to specifications, as well as requirements for storage, transport and handling of the fluid.

SCR systems are sensitive to potential chemical impurities in the urea solution, therefore the solvent is demineralised water. The solution is clear, non-toxic and safe to handle. However, it can corrode some metals and so must be stored and transported in vessels made of materials not so affected. DEF is stored in a tank onboard the vehicle, and injected into the exhaust stream by a metering system at a rate of 3–5% of diesel consumption volume. This low dosing rate ensures long fluid refill intervals . An Electronic control unit adjusts the addition of fluid in accord with such parameters as engine operating temperature and speed to ensure that the emmisions levels are with permitted limits.

These systems are required on trucks, modern high power tractors and construction plant under the Tier 4 emissions standard that were introduced in 2011 ? in most major countries. From 2012 smaller delivery vehicles will also have to meet this standard in some areas (i.e. within the "London Low Emission Zone").

See also

Alternative systems to meet the standards are available using catalytic converters and Particle filters which need replacing at intervals.


  1. Trautwein, Wolf-Peter (2003), AdBlue as a Reducing Agent for the Decrease of NOx Emissions from Diesel Engines of Commercial Vehicles, DGMK Deutsche Wissenschaftliche Gesellschaft für Erdöl, Erdgas und Kohle e.V.. 616-1, 

External links

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