Controlling the exhaust gases from an internal combustion engine, alters the exhaust air-fuel ratio to ensure regeneration of the nitrogen-oxide catalyst without accelerating its degradation

摘要

If detected exhaust air-fuel ratio (47) is poor relative to a first preset value, the controller (30) raises the ratio to the first value and then brings the ratio intermittently to a second richer value which allows the catalyst to regenerate after sulfur-oxides poisoning. The temperature of the catalyst (50b) is held within a range which allows regeneration but does not accelerate degradation. The apparatus comprises a NOx catalyst (50b) in the exhaust pipe (18, 19), means of detecting the catalyst temperature (48a, 48b), means of detecting the exhaust air-fuel ratio (47) in the exhaust pipe, and means of controlling the exhaust air-fuel ratio (30) on the basis of the NOx catalyst temperature and the detected exhaust air-fuel ratio. A valve (13) controls the air inlet into the combustion chamber (2) and a control valve (26) controls the amount of exhaust gases recirculated in the combustion chamber.