EXHAUST GAS PURIFYING METHOD

摘要

PROBLEM TO BE SOLVED: To well purify exhaust gas by using a small capacity of NOx absorbent. SOLUTION: NOx absorbents NA1, NA2 are arranged in a pair of branch exhaust passages, respectively. The exhaust gas from an internal combustion engine is introduced into both NOx absorbents to cause NOx contained in the exhaust gas at this time to be absorbed by both NOx absorbents. When the NOx absorbing amount of one NOx absorbent exceeds an upper limit amount, exhaust gas from a combustion heater 30 is temporarily supplied to one NOx absorbent while temporarily shutting off the flow of the exhaust gas to one NOx absorbent, and the exhaust gas from the internal combustion engine is introduced into the other NOx absorbent to cause NOx contained in the exhaust gas at this time to be absorbed by the other NOx absorbent. When the NOx absorbing amount of both NOx absorbents exceeds an upper limit amount, the exhaust gas from the internal combustion engine is introduced into both NOx absorbents and the air/fuel ratio of the exhaust gas from the internal combustion engine is temporarily changed from lean state to rich state.