Model Predictive Control of a Combined EGR/SCR HD Diesel Engine

Abstract

<div class="section abstract"><div class="htmlview paragraph">Achieving upcoming HD emissions legislation, Euro VI/EPA 10, is a challenge for all engine manufacturers. A likely solution to meet the NO<sub>x</sub> limit is to use a combination of EGR and SCR. Combining these two technologies poses new challenges and possibilities when it comes to optimization and calibration.</div><div class="htmlview paragraph">Using a complete system approach, i.e., considering the engine and the aftertreatment system as a single unit, is important in order to achieve good performance. Optimizing the complete system is a tedious task; first there are a large number of variables which affect both emissions and fuel consumption (injection timing, EGR rate, urea dosing, injection pressure, pilot/post injections, for example). Secondly, the chemical reactions in the SCR catalyst are substantially slower than the dynamics of the diesel engine and the rest of the system, making the optimization problem time dependent.</div><div class="htmlview paragraph">The engine studied is a 13-liter heavy-duty diesel engine equipped with a vanadia-based SCR system. The diesel engine uses common rail fuel injection, a variable geometry turbocharger (VGT) and cooled EGR.</div><div class="htmlview paragraph">In this paper, a Model Predictive Control (MPC) application is presented. The controller minimizes brake specific fuel consumption (including urea cost) by simultaneously optimizing engine out NO<sub>x</sub> and urea dosing, while maintaining emissions at Euro VI levels. The MPC is applied to the World Harmonized Test Cycles (WHSC/WHTC). Improvements in both fuel economy and emissions can be achieved by using the optimization/control method suggested.</div></div>