Simulation of catalytic oxidation and selective catalytic NOx reduction in lean-exhaust hybrid vehicles

We utilize physically-based models for diesel exhaust catalytic oxidation and urea-based selective catalytic NOx reduction to study their impact on drive cycle performance of hypothetical light-duty diesel-powered hybrid and plug-in hybrid vehicles (HEVs and PHEVs). The models have been implemented as highly flexible SIMULINK block modules that can be used to study multiple engine-aftertreatment system configurations. The parameters of the NOx reduction model have been adjusted to reflect the characteristics of commercially available Cu-zeolite catalysts, which are of widespread current interest. We demonstrate application of these models using the Powertrain System Analysis Toolkit (PSAT) software for vehicle simulations, along with a previously published methodology that accounts for emissions and temperature transients in the engine exhaust. Our results illustrate that the DOC-SCR combination can reduce CO, HC and NOx emissions without creating a significant direct fuel penalty, but there is also an increase in the possibility of ammonia slip. Also, the addition of an upstream DOC increases aftertreatment thermal inertia, delaying light-off of the SCR catalyst. We find that the emissions reduction efficiency of the DOC-SCR combination is better for our simulated HEV compared to our simulated PHEV.