| 摘要 |
PROBLEM TO BE SOLVED: To control HC and SOF in a low temperature range of exhaust gas, and also suppress formation of sulfate in a high temperature range thereof, by increasing a linear velocity of exhaust gas on an exhaust gas outlet side higher than a linear velocity of exhaust gas on an exhaust gas inlet side. SOLUTION: An exhaust emission control catalyst is formed into a circular cone shape and many honeycomb passages 1 are arranged in the catalyst, so that a linear velocity of exhaust gas on the exhaust gas outlet side of the exhaust emission control catalyst is increased higher than a linear velocity of exhaust gas on the exhaust gas inlet side thereof. Hereby, the linear velocity of exhaust gas on the exhaust gas inlet side is decreased, contact time between exhaust gas and the catalyst is secured, and HC and SOF can be controlled from the low temperature range of exhaust gas to the high temperature range thereof. As the kind of the catalyst, a honeycomb catalyst in which a carrying layer such as aluminum is formed in a honeycomb carrying case material formed of heat-proof ceramics such as cordierite or metallic foil, and so on, and catalytic noble metals such as rhodium and palladium is carried in the carrying layer, or a pellet catalyst in which the catalytic noble metals are carried in pellet such as amunina, can be exemplified. |
