| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a method for enhancing an effect for purifying carbon monoxide, carbohydrate and the like of an oxidation type catalyst and an effect for purifying nitric oxide of a reduction type catalyst inside an exhaust passage. <P>SOLUTION: Inside the exhaust passage connected with an exhaust end of an engine, the front stage reduction type catalyst and the rear stage oxidation type catalyst are provided. Secondary air is introduced to inside of the exhaust passage, and front stage exhaust gas exhausted from the exhaust end of the engine to inside of the exhaust passage is purified by using the front stage reduction type catalyst. Nitric oxide in the front stage exhaust gas with an air fuel ratio (A/F)≤ 14.7 is reduced to harmless nitrogen and oxygen. Secondary air is introduced from outside into inside of the exhaust passage at the rear of the reduction type catalyst, with an air fuel ratio (A/F) of the rear stage exhaust gas > 14.7. By purifying the rear stage exhaust gas by using the rear stage oxidation type catalyst, residual carbon monoxide and carbohydrate in the rear stage exhaust gas are oxidized to become harmless carbon dioxide and water and emitted to outside. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
