Modeling of Close-Coupled SCR Concepts to Meet Future Cold Start Requirements for Heavy-Duty Engines 2019-01-0984
The low-NOx standard for heavy-duty trucks proposed by the California Air Resources Board will require rapid warm-up of the aftertreatment system (ATS). Several different aftertreatment architectures/technologies are being considered to meet this need. One of these, the close-coupled SCR catalyst (cc-SCR), was evaluated in this study using two different physics-based, 1D models; the simulations focused on the first 300 seconds of the cold-start FTP. The first model, describing a real, EuroVI-compliant engine equipped with series turbochargers, was used to evaluate a cc-SCR located either i) immediately downstream of the low-pressure turbine, ii) in between the two turbines, or iii) in a by-pass around the high pressure turbine. These simulations indicate that the location downstream of the low-pressure turbine offers nearly the best NOx conversion, and that the optimal volume of the cc-SCR in this location is 25% of a conventional SCR catalyst. The second model describes a conventional heavy-duty aftertreatment system, to which a cc-SCR was added. This model was used to examine the performance of the cc-SCR in the context of the full ATS. Optimization of the DOC and SCR catalyst designs in this system was considered, as well as the use of an NH3 storage-based control strategy for DEF dosing to the SCR catalysts.
Thomas Miller Harris, Kristoffer Mc Pherson, Reza Rezaei, David Kovacs, Hendrik Rauch, Yinyan Huang