Full-Scale CFD Prediction of the Performance of Advanced After-Treatment Systems during Severe RDE Test Cycle 2024-01-2624

Air pollution is a significant environmental issue, and exhaust emissions from internal combustion engines are one of the primary sources of harmful pollutants. The transportation sector, which includes road vehicles, contributes to a large share of these emissions. In Europe, the latest emission legislation (Euro 7) proposes more stringent limits and testing conditions for vehicle emissions. To meet these limits, the automotive industry is actively developing innovative exhaust emission-control technologies.

With the growing prevalence of electrification, internal combustion engines are subject to continuous variations in load and engine speed, including phases where the engine is switched off. The result is an operating condition characterized by successive cold starts. In this context, the challenge in coping with the emission limits is to minimize the light-off time and prevent fast light-out conditions during idling or city driving. This goal can be achieved by reducing heat losses and thermal inertia, and suitably exploiting electrically heated solutions to maintain the catalyst inlet temperature at the desired level. In addition, issues related to mechanical durability must be considered, to allow the long-term life of the catalyst during continuous heat-up and cool-down cycles under severe flow conditions.

This paper aims to contribute to the development of an efficient after-treatment system, designed specifically for passenger cars, and to provide insights into the optimization of the catalyst design. This study employed advanced computational fluid dynamics (CFD) simulations to investigate the performance of a catalyst under a real driving emission cycle (RDE). A close-coupled configuration in a turbocharged gasoline engine was investigated. A detailed analysis of the external region of the substrate, which is critical because the temperatures are lower due to the heat transfer towards the environment, allows the identification of a suitable configuration. Flow conditions with post-turbo swirled flow along with the actuation of the wastegate valve were considered, and their impact on the pollutant abatement efficiency of the catalyst was evaluated.

A CFD framework has been implemented based on the open-source OpenFOAM code, modeling the complex phenomena of heat and mass transfer and catalytic reactions occurring in the substrate. Measured data of pollutant emissions and gas temperatures have allowed the validation of the CFD predictions and the optimization of the after-treatment system to limit the heat losses and reduce the pollutants emitted in the atmosphere during a real driving emission test cycle.