Hendrickson, C., Upadhyay, D., and Van Nieuwstadt, M., "Selective Catalytic Reduction Control with Multiple Injectors," SAE Technical Paper 2017-01-0943, 2017, doi:10.4271/2017-01-0943.
Over the past decade urea-based selective catalytic reduction (SCR) has become a leading aftertreatment solution to meet increasingly stringent Nitrogen oxide (NOx) emissions requirements in diesel powertrains. A common trend seen in modern SCR systems is the use of "split-brick" configurations where two SCR catalysts are placed in thermally distinct regions of the aftertreatment. One catalyst is close-coupled to the engine for fast light-off and another catalyst is positioned under-floor to improve performance at high space velocities. Typically, a single injector is located upstream of the first catalyst to provide the reductant necessary for efficient NOx reduction. This paper explores the potential benefit, in terms of improved NOx reduction, control of NH3 slip or reduced reductant consumption, of having independently actuated injectors in front of each catalyst. A dynamic programming approach is used to find optimal dosing strategies for both single and multiple injector installations over standard drive cycles. The resulting NOx and NH3 emissions for each case are compared in simulation to provide insight into the conditions where multiple injectors provide the greatest benefit. With these ideal settings, a second injector is found to be advantageous in situations where the control authority of a single injector is restricted but provide limited benefit elsewhere.