Simulation of Catalytic Oxidation and Selective Catalytic NOx Reduction in Lean-Exhaust Hybrid Vehicles

Physically-based models for diesel exhaust catalytic oxidation and urea-based selective catalytic nitrogen oxide (NOx) reduction are used 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. 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. The models are applied 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. Results illustrate that the diesel oxidation catalyst-selective catalytic reduction (DOC-SCR) combination can reduce carbon monoxide, hydrocarbons 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. The emissions reduction efficiency of the DOC-SCR combination was found to be better for the simulated HEV compared to the simulated PHEV.