Robust Indicated Mean Effective Pressure and Combustion Lambda Feedback Control for Lean NO_x Trap Regeneration in a 2.2 L Common Rail Direct Injection Diesel Engine

To meet stringent Euro-6 emission regulations, a lean NO_x trap (LNT) catalyst should be considered to effectively abate NO_x emissions. This LNT catalyst should be periodically regenerated without deteriorating driving quality and also satisfy emission constraints, such as CO, low particulate matter or smoke, and low O₂ during the regeneration phase. As a means of reductant delivery, in-cylinder post fuel injection with a feedforward (FF) control has been applied due to its simple implementation in an engine management system (EMS). However, with this method, it is difficult to satisfy the driving quality and emission constraints during the transition to or out of the regeneration phase. To solve this problem, we propose a novel LNT regeneration control method using an indicated mean effective pressure (IMEP) and a combustion lambda feedback (FB) control combined with the FF control. For the precise FB control of the post injection timing, among the location of the second rate of heat release (ROHR) peak, the magnitude of the second ROHR peak, and IMEP, the IMEP was selected as a control parameter because of its lowest cyclic variation. In addition, the exhaust lambda control was applied for the accurate FB control of the post injection quantity. The proposed method was implemented in an in-house EMS. The performance in several engine tests indicated that the torque fluctuation was minimized and all emission constraints were effectively satisfied. Furthermore, this method was also robust with regard to the thermal disturbance.