EXHAUST GAS PURIFICATION APPARATUS FOR INTERNAL COMBUSTION ENGINE

摘要

An object is to provide technology that enables an NOx catalyst to exercise its NOx reduction capability satisfactorily at any flow speed of the exhaust gas flowing into the NOx catalyst. An exhaust gas purification apparatus for an internal combustion engine includes a selective catalytic reduction NOx catalyst including at least a first catalyst layer having capability of reducing NOx and a second catalyst layer having oxidation capability and arranged closer to a catalyst substrate than the first catalyst layer. The apparatus has a supply valve for adding a specific addition quantity of reducing agent for reducing NOx to inflowing exhaust gas flowing into the selective catalytic reduction NOx catalyst. The apparatus further has a controller that is configured to control addition of the reducing agent by the supply valve based on the flow speed of the inflowing exhaust gas in such a way that the concentration of the reducing agent in a reducing agent atmosphere formed in the inflowing exhaust gas in a reducing agent addition period becomes equal to a specific concentration that is determined based on the flow speed of the inflowing exhaust gas and at which the reducing agent is assumed not to reach the second catalyst layer, when the temperature of the selective catalytic reduction NOx catalyst exceeds a specific temperature at which reduction of NOx by the first catalyst layer is carried out.

主权项

1. An exhaust gas purification apparatus for an internal combustion engine comprising:
a selective catalytic reduction NOx catalyst having a catalyst substrate and catalyst layers made up of catalyst particles having the property of selectively reducing NOx with a reducing agent derived from ammonia arranged on the catalyst substrate, the catalyst layers including at least a first catalyst layer having capability of reducing NOx and a second catalyst layer having oxidation capability arranged closer to said catalyst substrate than said first catalyst layer; a supply valve for adding a specific addition quantity of reducing agent for reducing NOx to inflowing exhaust gas flowing into said selective catalytic reduction NOx catalyst; and a controller that is configured to control addition of the reducing agent by said supply valve based on the flow speed of said inflowing exhaust gas in such a way that the concentration of the reducing agent in a reducing agent atmosphere formed in said inflowing exhaust gas in a reducing agent addition period becomes equal to a specific concentration that is determined based on the flow speed of said inflowing exhaust gas and at which the reducing agent is assumed not to reach said second catalyst layer, when the temperature of the selective catalytic reduction NOx catalyst exceeds a specific temperature at which reduction of NOx by said first catalyst layer is carried out.