| 摘要 |
PROBLEM TO BE SOLVED: To protect an EGR pipe from corrosion, while reducing NOx in exhaust gas by using aqueous gas shift reaction.SOLUTION: An engine 10 includes an EGR passage 36 and an EGR valve 38 or the like. When predetermined execution conditions (A)-(C) meet, an ECU 70 executes an air-fuel ratio slightly rich control. In the air-fuel ratio slightly rich control, while a target air-fuel ratio is set in a predetermined range on a slightly rich side, an air-fuel ratio feedback control is executed, and NOx is reduced by aqueous gas shift reaction. However, in reduction reaction of the NOx, ammonia is generated and ammonia compound may cause corrosion of a pipe of the EGR passage 36. During execution of the air-fuel ratio slightly rich control, the ECU 70 closes the EGR valve 38 to prohibit an EGR control. Therefore, corrosion of the pipe of the EGR passage 36 can be suppressed, while cleaning NOx in exhaust gas. |
