Diesel Exhaust Fluid (DEF)

Diesel exhaust fluid (DEF; also known as AUS 32 and marketed as AdBlue) is a liquid used to reduce the amount of air pollution created by a diesel engine. Specifically, DEF is an aqueous urea solution made with 32.5% urea and 67.5% deionized water.DEF is consumed in selective catalytic reduction (SCR) that lowers nitrogen oxides (NO)concentration in the diesel exhaust emissions from a diesel engine. Diesel engines can be run with a lean burn air-to-fuel ratio (overstoichiometric ratio), to ensure the full combustion of soot and to prevent their exhausting unburnt fuel. The excess air necessarily leads to generation of NO x, which are harmful pollutants, from the nitrogen in the air. SCR is used to reduce the amount of NO released into the atmosphere. DEF from a separate tank is injected into the exhaust pipeline. Within the SCR catalyst, the NO are reduced by the ammonia into water and nitrogen, which are both less polluting. The water and nitrogen are then released into the atmosphere through the exhaust.