Since January 2011, all new heavy vehicles using diesel in Australia, have been fitted with systems to limit the pollution coming from their exhaust. The most popular system uses DEF or diesel exhaust fluid. In practice this means new heavy diesel vehicles now have two tanks- one for the diesel, and one for the DEF (Diesel exhaust fluid). The DEF tank inlet is blue because the most popular brand of DEF is AdBlue®. AdBlue is NOT a diesel fuel additive. It is used to treat the exhaust, not the diesel fuel. Do not add it to your diesel tank!
The fluid used in the DEF tank is a 32.5% aqueous solution of urea. Hence the name AUS32 (aqueous urea solution), the most common brand name offered is AdBlue, but it is not the only AUS32 available. There is also CatBlue, NoNox® and Air1®. Any AUS32 that passes the ISO 22241 can be used in your DEF tank. The purity of the solution is very important to the long life of the SCR – selective catalytic reduction chamber. As you can see in the diagram, new vehicles have a separate storage tank where the AUS32 is stored. It is sprayed in the mixer directly onto the exhaust, which changes the NOx gases into ammonia. The SCR chamber converts the pollutants into safe atmospheric nitrogen (N2). The mix works out at about 5% of the diesel usage. That is, for every 100 litres of diesel you need 5 litres of DEF. But this varies depending on how the machinery is used. Urea and AUS32 are corrosive, so your external storage tank and delivery system must be purpose built for this use. Ours uses urea-grade polyethylene, stainless steel fittings, and a urea compatible pump.