Cold-Start Modeling and On-Line Optimal Control of the Three-Way Catalyst

TL;DR

This paper develops a physics-based model for the three-way catalyst during cold-start, calibrates it with experimental data, and designs a Pareto-optimal control strategy to reduce emissions and improve fuel efficiency.

Contribution

It extends existing TWC models to include variable discretization and hydrogen heat effects, and demonstrates a Pareto-optimal control approach for cold-start emissions.

Findings

Model predicts emissions with -20% to +80% error.

Pareto control reduces cold-start emissions.

Potential fuel efficiency improvements.

Abstract

We present a three-way catalyst (TWC) cold-start model, calibrate the model based on experimental data from multiple operating points, and use the model to generate a Pareto-optimal cold-start controller suitable for implementation in standard engine control unit hardware. The TWC model is an extension of a previously presented physics-based model that predicts carbon monoxide, hydrocarbon, and nitrogen oxides tailpipe emissions. The model axially and radially resolves the temperatures in the monolith using very few state variables, thus allowing for use with control-policy based optimal control methods. In this paper we extend the model to allow for variable axial discretization lengths, include the heat of reaction from hydrogen gas generated from the combustion engine, and reformulate the model parameters to be expressed in conventional units. We experimentally measured the temperature and emission evolution for cold-starts with ten different engine load points, which was subsequently used to tune the model parameters (e.g.~chemical reaction rates, specific heats, and thermal resistances). The simulated cumulative tailpipe emission modeling error was found to be typically -20% to +80% of the measured emissions. We have constructed and simulated the performance of a Pareto-optimal controller using this model that balances fuel efficiency and the cumulative emissions of each individual species. A benchmark of the optimal controller with a conventional cold-start strategy shows the potential for reducing the cold-start emissions.