NO<SB>X</SB>PURIFICATION SYSTEM, AND METHOD FOR CONTROL OF NO<SB>X</SB>PURIFICATION SYSTEM

摘要

In an NOx purification system and a method for control of the NOx purification system, two oxidation catalysts 4, 5 are provided upstream of an ammonia solution supply unit 6, and the in-cylinder fuel injection is so controlled that hydrocarbon in exhaust gas is mainly oxidized by the upstream oxidation catalyst 4 and nitric oxide in the exhaust gas is mainly oxidized by the downstream oxidation catalyst 5. In the purification of NOx in the exhaust gas by feeding an ammonia solution for NOx reduction to a selective reduction NOx catalyst 6, this technique enables the system to adjust the concentrations of HC, NO and NO 2 in the exhaust gas flowing into the selective reduction NOx catalyst 6 to proper values so as to purify the NOx efficiently by the selective reduction NOx catalyst 6. The NOx purification performance in a lower temperature range can be thus improved.