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The LNT(Lean NOx Trap) system has been developed for NOx reduction to meet Tier2Bin5 by using 2.2ℓ-diesel engine which was recently introduced by Hyundai Kia Motor company. The compression ratio was adjusted to 15.5 and the trim size of the turbine was reduced to increase EGR rates. During the FTP75 mode test, the engine out NOx was reduced by about 30% compared to the standard engine. The rich mode combustion was developed for the wide operating range despite of the low compression ratio. It was accomplished by adjusting air and FIE system, mainly by increasing post2 injection quantity. The A/F (Air-to-Fuel) ratio was controlled by additional post2 injection quantity. The neutral transition between lean mode and rich mode combustion was completed. The noise and torque change could not be recognized by the drivers during the transition of combustion mode (lean-to-rich or rich-to-lean). The transition procedure was finished within about 1sec for the whole operating range.