Internal combustion engine having lean NOx catalyst

Claim 1

An internal combustion engine having in an exhaust system a lean NOx catalyst for purifying nitrogen oxide in an exhaust gas in an oxygen excessive state by using a reducing agent, comprising: CO 2 concentration increasing means for increasing a concentration of carbon dioxide in an intake air flowing through an air intake system of said internal combustion engine; and intake air quantity decreasing means for decreasing a quantity of the intake air flowing through the intake system when the nitrogen oxide is required to be purified by said lean NO x catalyst, wherein said CO 2 concentration increasing means is a combustion device provided separately from a body of said internal combustion engine, and said combustion device functions as a CO 2 adding device for adding the carbon dioxide to the intake system by introducing a combustion gas into the intake system of said internal combustion engine, and wherein said CO 2 concentration increasing means functioning as the CO 2 adding device adds the carbon dioxide to the intake air in the intake system when the flowing rate of the intake air in the intake system is decreased by the operation of said intake air quantity decreasing means.