Patent ID: 9394820
Filing Date: 2016-07-19
CPC Classification: B01D,F01N,F02B,F02D,Y02T

Claim Text:
1. An exhaust gas purification system for removing nitrogen oxides in an exhaust gas of an internal combustion engine, comprising: an ammonia-based solution feeder, a previous-stage NOx selective reduction catalyst device, and a subsequent-stage NOx selective reduction catalyst device disposed in an exhaust system of the internal combustion engine in this order from an exhaust port side, a NOx selective reduction catalyst of the previous-stage NOx selective reduction catalyst device made of a catalyst containing a rare earth composite oxide, and a NOx selective reduction catalyst of the subsequent-stage NOx selective reduction catalyst device made of a zeolite catalyst; and a controller for the ammonia-based solution feeder, which controller is configured to— find, from an equivalence ratio of a chemical equation, an amount which enables reduction of an amount of NOx discharged from the internal combustion engine, calculate a first ammonia-based solution amount larger than the amount enabling the reduction, calculate a second ammonia-based solution amount from a difference between a NOx target discharge amount from the internal combustion engine, and an amount of NOx measured downstream of the subsequent-stage NOx selective reduction catalyst device, when an amount of NOx measured downstream of the previous-stage NOx selective reduction catalyst device is larger than the NOx target discharge amount of the internal combustion engine, set an amount of an ammonia-based solution to be fed to the exhaust system based on the sum of the first ammonia-based solution amount and the second ammonia-based solution amount, and feed the set amount of the ammonia-based solution from the ammonia-based solution feeder.