Experimental Demonstration of Ammonia Storage and Slip Modeling With Control for an SCR Aftertreatment System

Emission control is currently one of the biggest challenges and concerns in the automotive industry for cleaner diesel engines. Due to the low level of NO_x emission enforced by the Environmental Protection Agency (EPA), selective catalytic reduction (SCR) technology is currently one of the most feasible solutions. SCR technology uses diesel exhaust fluid (DEF), which is a urea solution of 32.7% urea with 67.3% water to reduce NO_x emission. The urea solution is converted to ammonia (NH₃), which reacts with NO_x over a catalyst to form N₂ and water. In this paper, a practical and dynamic model for modeling and controlling ammonia surface coverage or storage on an SCR system with a vanadia-based catalyst is implemented. It also included modeling of NH₃ slip. This work was implemented on an electronic control module and tested on a medium-duty diesel engine. The improved NO_x efficiencies observed with the corresponding reduction in urea usage illustrate a successful solution, indicating that this new dynamic modeling of ammonia surface coverage and its effective usage to manage urea dosing is a valuable tool for SCR after-treatment systems.