Urea Solution (AUS 40)

AUS 40 is an aqueous urea solution at 40% urea by mass used as the reductant in selective catalytic reduction (SCR) systems on large marine engines, certified to ISO 18611 and ISO 22241. The higher concentration suits the larger dosing rates of marine SCR and the elevated freezing point matters less aboard a ship than on a road vehicle. Road AdBlue is AUS 32, at 32.5% urea; the two are not interchangeable, since dosing the wrong concentration upsets the NOx conversion and risks catalyst fouling. SCR with urea injection meets MARPOL Annex VI NOx Tier III in Emission Control Areas.