Optimization of a Urea SCR System for On-Highway Truck Applications

In order to satisfy tightening global emissions regulations, diesel truck manufacturers are striving to meet increasingly stringent Oxides of Nitrogen (NOx) reduction standards. The majority of heavy duty diesel trucks have integrated urea SCR NOx abatement strategies. To this end, aftertreatment systems need to be properly engineered to achieve high conversion efficiencies. A EuroV intent urea SCR system is evaluated and failed to meet NOx conversion targets with severe urea deposit formation. Systematic enhancements of the design have been performed to enable it to meet targets, including emission reduction efficiency via improved reagent mixing, evaporation, distribution, back pressure, and removing of urea deposits. Multiple urea mixers, injector mounting positions and various system layouts are developed and evaluated, including both CFD analysis and full scale laboratory tests. The optimized system improved NOx reduction uniformity by 4%, eliminated urea deposits, improved NOx conversion efficiency by up to 30% while reducing the overall mixing length by 30%. This study demonstrates that good system performance can be achieved despite the challenges of meeting strict and often-conflicting performance targets. System perspectives combined with proper assessment and an understanding of unique components are critical to achieving aggressive performance targets while reducing development time for urea SCR systems.