| 摘要 |
A method of controlling the concentration of nitrogen oxides, hydrocarbons, and carbon monoxide in waste gases. A first lambda value (lambda1) of the air-fuel mixture is set to less than 1. The gases pass through a first catalyst and then through a second catalyst. The CO-concentration of the gases in the first catalyst is sufficiently high to reduce NO<SUB>x </SUB>to N<SUB>2</SUB>so that the NOx concentration is reduced to a predetermined value. Oxygen (O<SUB>2</SUB>) is introduced between the first catalyst and the second catalyst to oxidize both CO and HC to CO<SUB>2 </SUB>and H<SUB>2</SUB>O, to reduce the CO-concentration to a predetermined value. A second lambda value (lambda2) is measured in the gases downstream of the second catalyst, and a valve for regulating the air-fuel ratio is controlled so that the second lambda value (lambda2) lies within a predetermined range whose lower limit is higher than 1. |
