Current model-based design research on automotive catalytic converters mainly fall into three basic categories: either modeling the catalyst as a continuous system based on physics, discretizing the system to reduce modeling complexity, or developing a highly-simplified, mean-value model for control. Continuous models are computationally intensive and therefore not well-suited for implementation into a vehicle model for Hardware in the Loop or control design. Highly-simplified models are calibrated for a particular system without incorporating the governing physical laws into the model, and mean-value models are only able to predict the response for a single lumped element. Although a simplified, mean-value model can be developed to accurately predict system response, it does not lend itself to being extended to broader applications without significant re-calibration efforts. Therefore, a model is needed that can account for the physics of the system so it can be extended to further applications while decreasing computation time to allow the model to be implemented for Hardware in the Loop and vehicle control design.
This research investigates the development of such a model to predict automotive catalytic converter thermal response during warm-up. A one-dimensional, lumped-parameter model of a three-way catalyst was developed in Matlab/Simulink. The catalyst length was divided into discrete elements. Each discrete element contained states for the temperatures of the gas, substrate, and can wall. Heat transfer mechanisms were 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 was analysis for a plug-in electric vehicle application with electrically-heated catalyst (EHC). The model was used to compare the catalyst thermal response with and without the EHC. These results facilitated the development of a control strategy for the EHC, as well as recommendations for improving the overall vehicle control strategy. For further development, this model can also be extended to a two- or three-dimensional application. A two-dimensional catalyst model would be of interest to account for temperature gradients in the radial direction through the catalyst.