A lean NO
x
trap (LNT) followed by selective
catalytic reduction (SCR) without the urea injection system (LNT-urealess
SCR, LNT-pSCR) has been developed to meet the stringent regulations
on NO
x
emission. For the LNT-pSCR system
to be commercialized, optimal design and control of the system are
required. It is important to minimize the capital cost while satisfying
the NO
x
regulation standards and minimizing
fuel consumption. In this study, we propose a strategy to optimally
design the lengths of the LNT and pSCR and tune control parameters
by solving the multiobjective optimization problem and considering
control logic simultaneously. For decision makers, NO
x
emission and capital cost are critical factors to
consider. In addition, NH3 slip and fuel loss caused by
post injection must be considered. The Pareto optimal points are obtained
by solving the biobjective optimization problem with respect to NO
x
emission and capital cost while the other
factors are constrained. Among the Pareto optimal points, we suggest
a set of design and control tuning parameters. To reduce NO
x
only by 0.41% more than the suggested system, the
capital cost increases significantly by 21.82%. Meanwhile, the results
of multiobjective optimization without considering the control logic
(fixed timings and durations of the rich modes) are trivial, in that
the amount of NO
x
reduction increases
as the volume of the LNT-pSCR system increases.
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