Exhaust purification system for internal combustion engine

摘要

An exhaust purification system for an internal combustion engine is provided that can steadily maintain a NOx purification rate of a selective reduction catalyst to be high without allowing the fuel economy or marketability to deteriorate. The exhaust purification system includes a NO2—NOx ratio adjustment mechanism that causes a NO2—NOx ratio to change; and a NO2—NOx ratio perturbation controller that executes NO2—NOx ratio perturbation control so that a NO2 balance of the selective reduction catalyst in a predetermined time period, with NO2 adsorption being positive and NO2 release being negative, is 0. Herein, NO2—NOx ratio perturbation control is defined as control that alternately executes NO2 increase control to cause the NO2—NOx ratio to be greater than a reference value near 0.5, and NO2 decrease control to cause the NO2—NOx ratio to be less than the reference value.

主权项

1. An exhaust purification system for an internal combustion engine, the system comprising:
a NOx selective reduction catalyst provided in an exhaust channel of the internal combustion engine, and having a function of selectively reducing NOx in exhaust under the presence of a reducing agent, and adsorbing NO2 in the exhaust; a reducing agent supply device provided on an upstream side of the NOx selective reduction catalyst, and supplying a reducing agent or a precursor thereof into the exhaust channel on the upstream side of the NOx selective reduction catalyst; a NO2—NOx ratio adjustment mechanism provided on the upstream side of the NOx selective reduction catalyst, and causing a NO2—NOx ratio corresponding to a ratio of NO2 to NOx in exhaust flowing into the NOx selective reduction catalyst to change; and a perturbation control unit configured to execute NO2—NOx ratio perturbation control, which is control that alternately executes NO2 increase control to cause the NO2—NOx ratio to be greater than a reference value in a range of at least 0.4 to less than 0.7 by way of the NO2—NOx ratio adjustment mechanism, and NO2 decrease control to cause the NO2—NOx ratio to be less than the reference value by way of the NO2—NOx ratio adjustment mechanism, wherein the NO2—NOx ratio perturbation control is executed so that a NO2 balance of the NOx selective reduction catalyst in a predetermined time period, with NO2 adsorption being positive and NO2 release being negative, is a target value.