Combatting air pollution

摘要

NOx pollution from a lean-burn engine whose exhaust gas contains NOx and SOx is combatted by the engine's exhaust apparatus containing a NOx absorbent which absorbs NOx when the air-fuel ratio of the exhaust gas passing into it is lean and releases the absorbed NOx when the air-fuel ratio of the exhaust gas passing into it is rich, and a catalyst over which the released NOx is reduced to nitrogen, which apparatus also contains, upstream of the NOx absorbent, a SOx absorbent which absorbs SOx when the air-fuel ratio of the exhaust gas passing into it is lean and releases the absorbed SOx when the air-fuel ratio of the exhaust gas passing into it is rich, the engine being adapted so that the temperature of the exhaust gas of rich air-fuel ratio passing into the SOx absorbent containing the absorbed SOx is sufficiently high that the absorbed SOx is released into the exhaust gas and the exhaust gas then passes into the NOx absorbent without the released SOx being absorbed thereby and releases the absorbed NOx from the NOx absorbent.