Diesel Exhaust Fluid (DEF), also known as "AdBlue" or "Aqueous Urea Solution" or simply "Aqueous Urea Solution," is a liquid that is injected into the post-combustion exhaust steam of diesel engines in order to minimise emissions. Inadvertent jet fuel mixing can result in engine flameout, fuel filter clogging, fuel injector fouling, loss of engine power, and RPM rollback. In the worst case situation, these circumstances can ultimately result in the aircraft's loss.
Pure urea and deionized water are combined to make diesel exhaust fluid in a mixture that is around one third to two thirds each. It is a consumable part of a Selective Catalytic Reduction (SCR) exhaust system, which has been required in several countries since roughly 2010—including those in Europe, the US, and Canada. The Diesel Exhaust Fluid is added to the post-combustion exhaust stream, where it reacts with the nitrogen oxides in the exhaust to produce water and carbon dioxide through a long series of complicated chemical processes. Almost all of the toxic nitrogen emissions to the environment are eliminated by the method.
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