| 摘要 |
PROBLEM TO BE SOLVED: To improve purifying efficiency of NOX in exhaust gas from a lean-burn engine driven at a lean air-fuel ratio. SOLUTION: The subject facility is so composed that a ternary catalyst 5, a NOX occulusion-reduction catalyst 7 and a NH3 adsorption-denitrification catalyst 9 are located from the upstream side in an exhaust passage 4 of an engine 1 having fuel injection valves, 71 to 74, in a cylinder. Fuel injections from the fuel injection valves in the cylinder are controlled by a control circuit 30, and burning with a lean air-fuel ratio is started in the cylinder. Most of NOX in the exhaust gas of a lean air-fuel ratio from each cylinder is absorbed by the NOX occulusion-reduction catalyst 7, and a small quantity of NOX reaches the NH3 adsorption-denitrification catalyst 9 and is purified by NH3 absorbed in the catalyst. Additionally, fuel injection is performed periodically during a designated period into the cylinder in its expansion stroke or exhaust stroke of each cylinder by the control unit, and the air-fuel ratio of the exhaust gas is adjusted richly. Thereby, the rich exhaust gas, containing a large quantity of NOX as an ingredient of NH3 , flows into the ternary catalyst, and a large quantity of NH3 is produced, and therefore NOX is released from the NOX occulusion-reduction catalyst 7 and NH3 is supplied to the NH3 adsorption- denitrification catalyst 9. |
