| 摘要 |
<P>PROBLEM TO BE SOLVED: To minimize the influence of sulfur poisoning in a selective reduction catalytic reaction. <P>SOLUTION: A diesel exhaust emission control system reduces NO<SB>X</SB>in a lean exhaust environment by use of an upstream oxidizing catalyst and a downstream SCR catalyst. An engine 10 and the upstream oxidizing catalyst 95 are constituted so that the ratio of NO to NO<SB>2</SB>carried to the downstream catalyst 97 is 1:1. According to this, the downstream catalyst is hardly influenced by sulfur poisoning, and the NOx conversion efficiency of the whole catalyst is improved. When the ratio of NO to NO<SB>2</SB>is not close to the desired ratio of 1:1, the deterioration of the system is determined. Such a state is detected by use of the measurement value of the engine operation state, for example, as the signal output from an NO<SB>X</SB>sensor 140 arranged on the catalyst downstream. Finally, the control operation of adjusting the reducing agent injection quantity in exhaust gas is performed in the SCR catalyst up stream based on the ratio of NO to NO<SB>2</SB>in the oxidizing catalyst downstream. <P>COPYRIGHT: (C)2004,JPO |
