A diesel engine is possible solution for carbon dioxide (CO_2) reduction from automobiles. However, it is necessary for a diesel engine vehicle to reduce nitrogen oxide (NO_x) emission. Therefore, this research focused on a Urea-selective catalytic reduction (urea-SCR) system as an after-treatment system to convert NO_x and proposes the control method of the urea-SCR system based on the output of an ammonia (NH_3) sensor. By maximizing NH_3 storage rate of the SCR, conversion performance is maximized. To maximize the NH_3 storage rate, an NH_3 sensor is installed downstream of the SCR. The amount of urea-solution is controlled to keep NH_3 slip detected by the sensor. Thus, the NH_3 storage amount in the SCR or the SCRF (SCR on filter) can be maximized. The estimation and the control of NH_3 storage amount is also used to cause NH_3 slip immediately. NH_3 storage capacity changes with catalyst temperature. In a transient state, temperature distribution occurs in the SCR catalyst. For this reason, the catalyst is divided virtually. Then, by performing estimation of temperature discretely, the estimation of NH_3 storage amount can be accurately estimated. This system was installed in a passenger vehicle equipped with a diesel engine. Virtual segment temperature estimation could improve the estimation accuracy of NH_3 storage amount and contributed to reduce the tail-pipe NO_x to Euro-6 level.
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