EXHAUST GAS CONTROL APPARATUS AND CONTROL METHOD FOR THE SAME

摘要

PROBLEM TO BE SOLVED: To restrain the occurrence of an ammonia slip, while enhancing the NOx reduction ratio, in an NOx reduction catalyst for reducing and removing NOx in exhaust gas by adsorbing ammonia.

SOLUTION: An exhaust gas control apparatus includes a control means for controlling a urea addition valve for adding urea from the upstream side of the NOx reduction catalyst. The control means obtains the ammonia adsorption amount distribution in the NOx reduction catalyst, and controls the urea addition valve to stop or reduce a supply amount of the urea when an ammonia adsorption amount in a predetermined part on the exhaust gas flow direction downstream side equals or exceeds a predetermined threshold in the obtained adsorption amount distribution. The urea addition valve is controlled based on the adsorption amount distribution obtained by a model of dividing the inside of the NOx reduction catalyst into a plurality of cells so that the ammonia adsorption amount in a first cell positioned furthest upstream equals or exceeds a predetermined threshold close to a saturation adsorption amount and the ammonia adsorption amount in a second cell positioned downstream of the first cell reaches a predetermined target value smaller than the threshold.

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