Model Predictive Control of a Combined EGR/SCR HD Diesel Engine 2010-01-1175
Achieving upcoming HD emissions legislation, Euro VI/EPA 10, is
a challenge for all engine manufacturers. A likely solution to meet
the NOx 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.
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
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.
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
NOx 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.