Improvement of Post-Oxidation for Low-Emission Engines through 3D-CFD Virtual Development 2023-24-0107

There is a growing need for low-emissions concepts due to stricter emission regulations, more stringent homologation cycles, and the possibility of a ban on new engines by 2035. Of particular concern are the conditions during a cold start, when the Three-Way Catalyst is not yet heated to its light-off temperature. During this period, the catalyst remains inactive, thereby failing to convert pollutants. Reducing the time needed to reach this temperature is crucial to comply with the more stringent emissions standards. The post oxidation by means of secondary air injection, illustrated in this work, is a possible solution to reduce the time needed to reach the above-mentioned temperature. The strategy consists of injecting air into the exhaust manifold via secondary air injectors to oxidize unburned fuel that comes from a rich combustion within the cylinder. This strategy can be implemented without major modifications to the engine's hardware or control system, making it an attractive option for retrofitting older engines or incorporating into new designs. The investigation was conducted experimentally and numerically, with test bench measurements and 3D-CFD simulations. The test bench data were helpful for validating and calibrating the 3D-CFD simulations, which employ two interrelated approaches. The first approach utilizes a full-engine mesh, which includes a 0D turbocharger model, to extrapolate reliable boundary conditions. The second approach uses a detailed exhaust model that includes the mentioned accurate boundary conditions and a chemical reaction mechanism. This paper presents the effects of post oxidation in two different engine operating points. Various secondary air injection strategies, including different temperatures and mass flows, and an alternative exhaust manifold design, are evaluated to assess potential improvements in post oxidation by means of 3D-CFD virtual development.