Supervisory controller for a LNT-SCR Diesel Exhaust After-Treatment System

Abstract

Statistical analysis of route history and online traffic information system can provide real-time look-ahead information regarding the route ahead which could be used for powertrain optimisation. A diesel engine $NO_{x}$ Exhaust After-Treatment System (EATS) for a passenger car application comprised of an engine close-coupled Lean $NO_{x}$ Trap (LNT) and an underfloor Selective Catalytic Reduction (SCR) is studied. Conventionally, the LNT-SCR operation is coordinated using a rule based controller that primarily utilises the SCR catalyst bed temperature. This paper presents a supervisory control structure that uses look ahead information to improve the performance of the EATS coordinator. Therefore, the supervisory control based EATS coordinator is parameterised with respect to the look ahead data. The parameterised controller calculates setpoints for the $NO_{x}$ EATS based on Emission Equivalent Fuel Consumption (EEFC). A simulation environment that has been validated with data from the production system was used to carry out the evaluation and compare against the baseline controller. The Supervisory control performance using the EEFC strategy is analysed for the Worldwide harmonized Light vehicles Test Cycle (WLTC). The paper explores a method to utilise a supervisory control structure for the EATS coordinator in an Engine Control Unit. Subsystem synergies that could be harnessed using the supervisory control approach are demonstrated for the EATS. The future work will focus on extending the approach to more subsystems and characterising the look ahead information.