Mapping of Urea Deposits in Engine Aftertreatment Systems of Heavy Duty Trucks

Randal  Goffe, PACCAR

Urea deposit formation in engine aftertreatment systems is a common occurrence, with sometimes devastating consequences on heavy duty truck performance.  A systematic study of such deposits using TGA and IR spectroscopic analysis has been undertaken to characterize deposits at various location, from the tip of the DEF doser to the tailpipe of the engine aftertreatment system.  An important goal of this work was to develop an empirical model for use in the control of DEF dosing to avoid over dosing and potential derating of the truck.  The study included engine dynamometer, as well as both summer and winter test trucks.  The results of this study is discussed in terms of the role of urea deposits as a form of ammonia storage and its potential impact on over dosing of DEF; the potential negative impact on SCR performance and catalyst aging; as well as the contribution of urea deposits to particulate matter emissions from the tailpipe.