Exhaust gas purification system for lean burn engine

摘要

An exhaust gas purification system for a lean burn engine comprising a thermal mass unit (32) and a NOx conversion catalyst unit (34) downstream of the thermal mass unit (32). The NOx conversion catalyst unit includes at least one catalyst section (36). Each catalyst section includes a catalytic layer (38) for converting NOx coupled to a heat exchanger (40). The heat exchanger portion of the catalyst section acts to maintain the catalytic layer (38) substantially at a desired temperature and cools the exhaust gas flowing from the catalytic layer into the next catalytic section in the series. In a further aspect of the invention, the exhaust gas purification system includes a dual length exhaust pipe (20) upstream of the NOx conversion catalyst unit (34). The dual length exhaust pipe (20) includes a second heat exchanger (24) which functions to maintain the temperature of the exhaust gas flowing into the thermal mass (32) downstream near a desired average temperature.