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Diesel exhaust fluid (DEF) is an aqueous urea solution made with 32.5% urea and 67.5% deionized water. It is standardised as AUS 32 (aqueous urea solution) in ISO 22241.〔(【引用サイトリンク】url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=42941 )〕 DEF is used as a consumable in selective catalytic reduction (SCR) in order to lower NOx concentration in the diesel exhaust emissions from diesel engines.〔(【引用サイトリンク】work=Cummins Filtration )〕 The German Association of the Automotive Industry (VDA) registered the trademark "AdBlue" for AUS 32. == Chemistry == 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 the exhaust of unburnt fuel. The excess of air necessarily leads to generation of nitrogen oxides (), which are harmful pollutants, from the nitrogen in the air. Selective catalytic reduction is used to reduce the amount of released into the atmosphere. Diesel exhaust fluid (DEF) from a separate tank is injected into the exhaust pipeline, where the aqueous urea vaporizes and decomposes to form ammonia and carbon dioxide. Within the SCR catalyst, the are catalytically reduced by the ammonia () into water () and nitrogen (), which are both harmless; and these are then released through the exhaust.〔(【引用サイトリンク】work=H2Blu )〕 DEF is a 32.5% solution of urea, . When it is injected into the hot exhaust gas stream, the water evaporates and the urea thermally decomposes to form ammonia and isocyanic acid: : → + HNCO The isocyanic acid hydrolyses to carbon dioxide and ammonia: : HNCO + → + From this point, ammonia, in the presence of oxygen and a catalyst, will reduce nitrogen oxides: 2NO + 2NH3 + ½O2 -> 2N2 + 3H2O and 3NO2 + 4NH3 + 3O2 -> 7/2N2 + 6H20 The overall reduction of by urea is: : 2 + 4NO + → 4 + 4 + 2 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Diesel exhaust fluid」の詳細全文を読む スポンサード リンク
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