(511a) Electrically Heated Catalysts for Hybrid Applications: Mathematical Modeling and Analysis

In view of the significant cold-start hydrocarbon emission reduction potential of the electrically heated converter (EHC) technology for conventional stoichiometric gasoline engines, there is considerable interest in better understanding the thermal/conversion characteristics and optimizing the design/operating aspects of an EHC system as applied to plug-in hybrid electric vehicles (PHEVs). The application of the EHC technology to PHEVs is unique in that catalyst cooling to below reaction temperatures can occur during extended electric vehicle driving periods (with engine-off) or during intermittent engine stops/starts and the EHC can be heated prior to engine re-start (pre-heating) for enhanced emission reduction. In this study, the design aspects and heating strategies of an EHC system have been analyzed using a transient monolith converter model which accounts for the electrical heating of an inert metal-substrate monolith placed ahead of a conventional three-way catalytic converter. The results of model calculations presented here quantify the effects of various heating strategies on the emission performance of PHEVs during the first 250 seconds of a Federal Test Procedure (FTP) drive cycle. It is also shown that there exists an optimum electric heater volume for cases with either pre-heating only or a combination of pre- and post-heating. Other heating strategies to understand and improve the effectiveness of the system will also be presented.