Development of Urea SCR Systems for Large Diesel Engines 2011-01-2204
EPA 2015 Tier IV emission requirements pose significant challenges to large diesel engine after treatment system development with respect to reducing exhaust emissions including HC, CO, NOx and Particulate Matter (PM). For a typical locomotive, marine or stationary generator engine with 8 to 20 cylinders and 2500 to 4500 BHP, the PM reduction target could be over 90% and NOx reduction target over 75% for a wide range of running conditions. Generally, HC, CO and PM reductions can be achieved by combining DOC, cDPF and active regeneration systems. NOx reduction can be achieved by injecting urea as an active reagent into the exhaust stream to allow NOx to react with ammonia per SCR catalysts, as the mainstream approach for on-highway truck applications. However, urea SCR applications for large diesel engines such as marine, locomotive and stationary generators are more challenging than smaller-size engines due to large system size, constrained packaging space, ultra low back pressure targets, and lower gas velocities / temperature. These factors result in greater mixing demands and more attention to the heat transfer required to facilitate evaporation of urea. To address these challenges, a systematic approach is essential to assess the system requirements and derive unique hardware design solutions to large system geometries.