Exhaust gas purification system for lean burn engine

摘要

An exhaust gas purification system for a lean burn engine includes a thermal mass unit and a NOx conversion catalyst unit downstream of the thermal mass unit. The NOx conversion catalyst unit includes at least one catalyst section. Each catalyst section includes a catalytic layer for converting NOx coupled to a heat exchanger. The heat exchanger portion of the catalyst section acts to maintain the catalytic layer 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 upstream of the NOx conversion catalyst unit. The dual length exhaust pipe includes a second heat exchanger which functions to maintain the temperature of the exhaust gas flowing into the thermal mass downstream near a desired average temperature.