Control of a Combined SCR on Filter and Under-Floor SCR System for Low Emission Passenger Cars

Jean Balland; Michael Parmentier; Julien Schmitt

doi:10.4271/2014-01-1522

Similar to single-brick SCR architectures, the multi-brick SCR systems described in this paper require urea injection control software that meets the NO_x conversion performance target while maintaining the tailpipe NH₃ slip below a given threshold, under all driving conditions.

The SCR architectures containing a close-coupled SCRoF and underfloor SCR are temperature-wise more favorable than the under-floor location and lead to significant improvement of the global NO_x conversion, compared to a single-brick system. But in order to maximize the benefit of close-coupling, the urea injection control must maximize the NH₃ stored in the SCRoF.

The under-floor SCR catalyst can be used as an NH₃ slip buffer, lowering the risk of NH₃ slip at the tailpipe with some benefit on the global NO_x conversion of the system. With this approach, the urea injection strategy has a limited control on the NH₃ coverage of the under-floor SCR catalyst.

To take more advantage of the under-floor SCR catalyst for improving the NO_x conversion, the NH₃ coverage of the under-floor SCR must be taken into account, and therefore a combined control of both catalysts is required. This paper presents a control strategy proposal for such multi-brick SCR systems: the NH₃ coverage of the SCRoF is optimized while taking into account the current states of front and rear SCR catalysts. The strategy focuses on achieving highest NO_x conversion efficiency while preventing excessive tailpipe NH₃ slip, even in the worst driving conditions, such as sudden full-load acceleration.

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Control of a Combined SCR on Filter and Under-Floor SCR System for Low Emission Passenger Cars 2014-01-1522

SAE MOBILUS