Diesel Exhaust Fluid is the trade name for an aqueous solution of urea (technical name AUS 32), commonly used as an additive in diesel powered vehicles together with Selective Catalytic Reduction (SCR) technology to reduce emissions which cause atmospheric pollution.

The combination of an SCR system with the injection of the DEF additive targets harmful NOx (nitrous oxides) which are a major cause of smog in many cities. NOx emissions can be a major problem for anyone who suffers from lung conditions and is known to aggravate asthma. 
 
This SCR system is now the standard technology being utilised to meet the requirements for diesel engines in passenger cars and LGV’s, as specified in European legislation and European Standards Euro 6 (HGVs have already been using the SCR system since Euro V).

Downstream from the engine, DEF is introduced into the SCR system, being injected into a specialist catalyst where a chemical reaction, known as 'reduction' is set off.  When heated over the precious metal bed of the catalyst, the DEF acts as the reducing agent, converting NOx into harmless vapour which leaves the catalyst and is safely passed through the exhaust.

How should it be stored

DEF is not hard or complicated to store (it is non hazardous) but there are certain conditions surrounding its storage that petrol stations and truck stops should be aware of. This is to ensure that the DEF remains pure from the point of delivery, right up until the moment it is put into the vehicle.

1. DEF should always be stored in at least double skinned tanks (bunded) to protect against unsightly spills and environmental issues
2. Use Tanks Compliant with Manufacturing Standards. DEF should always be stored in a tank which has been specially designed for the task; one which is compliant with manufacturing and material compliance standards (e.g ISO 22241, DIBT, BS EN ISO 9001:2008).  This will give you both peace of mind, keep fleets on the road, and future-proof your business as legislation around environmental pollution and emissions continue to tighten
3. Avoid Contamination.  Even the smallest amount of dust, metal or contaminant can seriously damage an SCR system, which can lead to the vehicle becoming inoperative and incur potentially expensive repair costs. The damage may take place over time but any incorrect storage of DEF may affect any insurance cover.  Kingspan’s engineers have developed a closed fluid path system to help ensure the integrity of its tanks’ contents
4. Keep at its Ideal Temperature.  Ideally, your DEF should be stored between 0-30°C.  It freezes at minus 11°C so it is important your tank is built to buffer extremes of temperature in cold climates, for example, the addition of cold weather pack options.  You can, however, use your DEF again once it has completely thawed
5. It should always be shielded from direct sunlight and high temperatures as this can cause evaporation
6. Protect Against Accidental Tank Damage.  The latest generation of  with a “TriComp” construction ensures that your stocks of DEF are protected and will not leak out should there be any damage to the outside skin, thus avoiding disruption to the retailer and of course its customers
7. Manage Stocks Through Remote Access.  Other useful additional management tools that retailers or transport operators might want to consider include the latest generation of in-tank monitoring systems.  These provide remote access to round-the-clock, real-time information on tank levels to ensure stock levels are monitored closely, as well as digital flowmeters, submersible pumps, automatic nozzles, leak detection alarms, and overfill alarms

 
Note: DEF’s technical name is AUS 32 (Ref ISO 2224) and it has a number of different product names across the world.  In the Unired Kingdom, it’s known as AdBlue®; in Brazil, ARLA32.