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-optimalcold-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.
Highlights
The Three-Way Catalyst (TWC) is used in most conventional vehicles with spark-ignited (SI) engines to reduce the level of harmful emissions generated by the combustionEmiss
Green-colored cells indicate cases where Λn penalizes only one emission species, while other are ignored, and can be compared with the penalized case the sum of penalized emissions decrease, while the mean BSFC increases. This data indicates that the potential for reducing nitrogen oxides (NOx) emissions is significantly larger than carbon monoxide (CO) and THC emissions, as shown in the last 3 rows where NOx emissions are reduced by 94% compared to the unpenalized case, while CO and THC emissions are reduced by 35% and 41% respectively
In this paper we extended the model to support varying axial discretization lengths, use tuning parameters expressed in well-known SI units, model heat generation by the oxidation of hydrogen, consider a TWC consisting of two separate monoliths of different construction, and use a more rigorous evaluation method with separate tuning and validation datasets
Summary
The Three-Way Catalyst (TWC) is used in most conventional vehicles with spark-ignited (SI) engines to reduce the level of harmful emissions generated by the combustionEmiss. The Three-Way Catalyst (TWC) is used in most conventional vehicles with spark-ignited (SI) engines to reduce the level of harmful emissions generated by the combustion. Several methods for reducing cold-start emissions have been studied from a multiple perspectives. Our goal is to develop a model-based optimal TWC cold-start controller that can be feasibly be implemented in a standard engine control unit (ECU). We will consider a conventional SI engine and TWC, where the engine’s load point can be freely controlled during the coldstart, making the controller suitable for e.g. hybrid vehicles. We view the TWC cold-start problem as determining the optimal engine speed, load, and spark timing to apply over time while balancing the conflicting goals of maximizing fuel efficiency and minimizing the cumulative emissions. This paper can naturally be divided into two parts, one where we develop a TWC cold-start model, and one where we evaluate the performance of an optimal controller generated using said model
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