What is
Diesel Exhaust Fluid (DEF)?

What is DEF?

DEF (diesel exhaust fluid) is the trade name for an aqueous solution of urea. It is commonly used in diesel engines with integrated Selective Catalytic Reduction (SCR) technology to meet stricter emission standards for diesel engines.

DEF is known by several names depending on the country: in America it’s known as Diesel Exhaust Fluid (DEF for short), in Brazil, ARLA32. AUS32 is the technical name for this liquid that is used as the reducing agent in an SCR system, converting harmful nitrogen oxide into innocuous nitrogen and water.

Back in 2005, changes were made to legislation on diesel vehicles across the world demanding a drastic reduction of NOx emissions (nitrous oxides) that are a major cause of atmospheric pollution which leads to smog in many cities. And in 2011, the off-road sector was also included in this new legislation.

All of these changes to legislation have led to vehicle manufacturers having to take another look at their exhaust systems, particularly for large goods vehicles. This redesign led to the introduction of the SCR system that is now commonly found in off-road vehicles, cars, trains and commercial vehicles. 

What Does DEF do? DEF Storage & Handling Requirements

DEF is not the most difficult to store, but there are certain conditions that users should be aware of. Ideally, DEF needs to be stored between 0 and 30 degrees Celsius and should always be protected from direct sunlight. DEF also freezes at -11 degrees, so it is important to ensure you use a DEF tank that can handle temperature fluctuations in order to protect your DEF - though it is possible to use DEF again once it has thawed and returned to its original state.

A key factor to keep in mind when it comes to DEF storage is ensuring that it is protected from contamination at all times. Even the smallest amount of dust, fuel, dirt, water etc. can seriously damage an SCR system and have serious implications on your fleet. For this reason it is recommended that you only store DEF in a dedicated DEF tank.

DEF needs to remain pure from production through to storage and handling and ultimately, end use. If your DEF becomes contaminated at any point, you risk serious damage to the SCR system within your vehicle. This can lead to the vehicle not operating correctly and at worst, it could potentially incur expensive repair costs. Damage to the catalyst can happen over time, but this would depend on the severity of the contamination. It is worth noting that incorrect storage of DEF could possibly effect any related insurance, so care should always be taken when looking for a DEF tank.


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