Lean NOx trap regeneration control strategy on a 1.9L turbocharged diesel

Various diesel NOx control technologies are being explored today as solutions for minimizing NOx emissions. The Lean NOx Trap is one of two products that offer high NOx conversion efficiency, but the LNT requires a regeneration strategy. The Lean NOx Trap control strategy offers a systematic approach in which engine control parameters are fully utilized to create an exhaust “rich” environment necessary for LNT catalyst regeneration. In the present study EGR throttling, inlet air-throttling and late-injections were the three control parameters tuned for LNT regeneration. The strategy was tested in-house and by GM engineers on a 1.9 L diesel engine coupled to a Diesel Oxidation Catalyst, Diesel Particulate Filter and a Lean NOx Trap. Siemens NOx sensors were used to evaluate the NOx conversion efficiency. It was found that the catalyst did reduce NOx output but was neither efficient at low-loads nor fully-effective throughout the drive-cycle as the DPF did clog as a result of too low a CO/HC ratio. The regeneration mode is open loop and should be closed loop to minimize the additional fueling necessary for creating a rich environment for LNT regeneration. There was no evidence that late injections contributed to regeneration. Instead of late-injections, a more robust, closed-loop control strategy should be explored that uses the air/fuel ratio from the exhaust manifold as the control parameter for maximizing NOx conversion efficiency while minimizing the fuel penalty.