Investigation of HDDE exhaust flow mixing devices to enhance SCR performance.

摘要

The 2010 regulations implemented by the U.S. Environmental Protection Agency (EPA) require significant reduction in Oxides of Nitrogen (NO x) and Particulate Matter (PM). These regulations have driven a significant amount of research and development into more advanced engine combustion strategies and after-treatment systems. This study focuses on NOx reduction in Heavy Duty Diesel Engines (HDDE) equipped with Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) catalyst by optimizing the mixing of DPF out exhaust gas with urea injected upstream of the SCR. Proprietary wired mesh substrates were installed between the DPF and SCR system at three locations and showed further NOx reduction from the previous emissions results. Different wired mesh catalytic substrates of varying lengths were used in this study. Experiments were conducted on four of the 13 modes of the European Stationary Cycle (ESC), modes in which the engine yielded high NOx emissions. Results from these experiments show that the wired mesh substrates enhanced the mixing of the exhaust stream and urea, which improved the performance of the SCR catalyst. When the wired mesh was tested on ESC and Federal Transient Procedure (FTP), NOx emissions were reduced 20-25% by introducing the wired mesh substrates in the exhaust flow for the ESC cycles. This study demonstrated that the wired mesh substrates enhanced the mixing of the exhaust gas and the injected urea. The mixing effect caused by the wired mesh improved the thermolysys of urea into ammonia (NH 3). This study draws a conclusion that using a wired mesh catalytic substrate in the exhaust upstream of the SCR catalyst improves the mixing of the exhaust with urea and gives additional NOx reduction for certain steady state modes, but showed no change for the NO x emissions for the FTP cycle.