Catalytic converter thermal model for hybrid electric vehicle engine on/off control strategy development

A 3-dimensional (3-D), thermochemical catalytic converter model was developed to investigate the effects of engine-off periods typical in hybrid electric vehicle (HEV) operation on overall emissions conversion effectiveness. The model includes a 3-reaction mechanism to account for the majority of heat generation due to exhaust species chemical conversion during engine operation. The modeled cross-sectional area of the catalytic converter was decreased to reduce computational complexity. This simplification resulted in an over prediction of shell heat loss to the surroundings due to the incorrect shell surface area to volume ratio. Therefore, an adiabatic assumption was used to analyze the substrate’s thermal behavior without the influence of external heat transfer. The analytical model was experimentally validated with an engine that provided feedgas to a catalytic converter. The catalytic converter was instrumented with thermocouples for internal and surface temperature measurement. The reduced-size, catalytic converter model with the adiabatic assumption produced mid-catalytic converter temperature predictions within 3%. However, thermal behavior during engine-off period could not be predicted since radial heat transfer was eliminated with the adiabatic assumption but is the dominating effect in real cool-down. Accurate temperature predictions during cool-down requires modeling a realistic surface area to volume ratio which is outside of the computational limitations of the modeling platform used in this work.