Low Temperature Urea Decomposition and SCR Performance 2005-01-1858

Urea-SCR systems are potentially a highly-effective means of NO_X reduction for light-duty diesel vehicles. However, use of urea-SCR technologies at low temperatures presents unique technical challenges. This study was undertaken to provide more knowledge about low temperature urea decomposition and the resulting effects on SCR performance. Data are presented for experiments using two SCR catalysts of differing size with a light-duty diesel engine. Analyses of the NO_X reduction efficiency, NH₃ storage phenomena, and unregulated emissions are shown. Over production of NO₂ by the oxidation catalyst is demonstrated to be problematic at 25,000 hr-1 space velocity for a range of temperatures. This leads to production of N₂O by both SCR catalysts that is higher when urea is injected than when NH₃ is injected.