Diesel air path control using pressure difference: Pumping loss and aging considerations

Abstract

Pressure difference across the exhaust and intake manifolds ( $\Delta$ P) is a crucial variable to control the pumping loss and cylinder charge dilution through the exhaust gas recirculation in a diesel engine. This paper presents a novel architecture for controlling $\Delta$ P and the engine-out NO _x emissions, which increases the controller tolerance to engine components aging. The architecture has an internal control loop, designed as a two-input two-output controller, to coordinate the exhaust gas recirculation and variable geometry turbine valves. Using feedback from $\Delta$ P and the estimated cylinder oxygen ratio $\chi$ _cyl , the two-input two-output controller regulates the pumping loss and the engine NO _x emissions. To reduce high turbo lag and its associated slow air–fuel ratio ( $\lambda$ ) response, which are inherent features of a $\Delta$ P-based control strategy, the two-input two-output linear quadratic controller is tuned such that $\lambda$ is also regulated, but only during fast transients. An external loop is supplementing the core two-input two-output controller correcting the internal loop set points to reduce the effects of $\chi$ _cyl estimation errors on NO _x control and ensure $\lambda$ stays above a minimum value, $\lambda$ _min , critical for smoke emissions. As a feature of the proposed control system, direct feedback from $\Delta$ P increases pumping loss robustness to common degradation in diesel engines, namely, turbine efficiency and diesel particulate filter blockage due to ash deposit, compared to a conventional boost pressure–based controller. Also, it is shown that the input–output coupling structure of the proposed two-input two-output controller and use of the NO _x feedback mitigate effects of exhaust gas recirculation fouling and associated exhaust gas recirculation valve saturation on increase in NO _x emission.