AdBlue is a trade name for AUS32, which is essentially a 32.5% urea solution mixed with dematerialized water. A required operating fluid stored in a separate reservoir, this diesel fluid is injected into the exhaust system. Therefore it is not a diesel fuel additive and is never to be added or mixed with the fuel. AdBlue is a relatively clear synthetically manufactured solution that contains ammonia, and is corrosive to some metals. It is used in conjunction with Selective Catalytic Reduction exhaust treatment to promote NOX conversion into nitrogen and water.