A Physically-Based, Lumped-Parameter Model of an Electrically-Heated Three-Way Catalytic Converter 2012-01-1240
The impact of cold-start emissions is well known on conventional and hybrid electric vehicles. Plug-in electric vehicles offer a unique challenge in that there are opportunities for prolonged engine-off conditions which can lead to catalyst cooling and elevated emissions on engine re-start. This research investigates the development and validation of a system for controlling emissions under these conditions, with an emphasis on a catalytic converter model used for design and analysis. The model is a one-dimensional, lumped-parameter model of a three-way catalytic converter developed in Matlab/Simulink. The catalyst is divided into discrete, axial elements and each discrete element contains states for the temperatures of the gas, substrate, and can wall. Heat transfer mechanisms are modeled from physics-based equations. For each discrete element, these equations modeled the enthalpy of the gas flow axially through the catalyst, convective heat transfer between the gas and substrate, conduction between discrete elements axially along the catalyst for the substrate and for the can, conduction between the substrate and can wall, and convection from the can wall to ambient. Model predictions were validated against experimental results for thermal transients. The application of this model is for analysis of a plug-in hybrid electric vehicle (PHEV) application with electrically-heated catalyst (EHC). The model is used to compare the catalyst thermal response with and without the EHC, to facilitate the development of a control strategy for the EHC, and to improve the overall vehicle control strategy. For further development, this model can also be extended to a two- or three-dimensional application.