3D-CFD Full Engine Simulation Application for Post-Oxidation Description

The introduction of real driving emissions cycles and increasingly restrictive emissions regulations force the automotive industry to develop new and more efficient solutions for emission reductions. In particular, the cold start and catalyst heating conditions are crucial for modern cars because is when most of the emissions are produced. One interesting strategy to reduce the time required for catalyst heating is post-oxidation. It consists in operating the engine with a rich in-cylinder mixture and completing the oxidation of fuel inside the exhaust manifold. The result is an increase in temperature and enthalpy of the gases in the exhaust, therefore heating the three-way-catalyst. The following investigation focuses on the implementation of post-oxidation by means of scavenging in a four-cylinder, turbocharged, direct injection spark ignition engine. The investigation is based on detailed measurements that are carried out at the test-bench. Due to the complexity of the investigated phenomenon, the analysis at the test-bench has been sustained by 3D-CFD simulations. At first a 3D-CFD full-engine model has been implemented to reproduce the complete engine from the air-box up to the turbine inlet. This model is able to simulate all the relevant full-engine effects like scavenging, cylinder-to-cylinder interaction and local inhomogeneity inside the cylinder. The second implemented model focuses on the exhaust manifold, from the exhaust valve up to the turbine volute, and it is characterized by a fine computational grid and by the implementation of a chemical reaction mechanism. Both models have been validated using the detailed measurements of the test-bench. The simulation matched precisely the measurements and enabled a better interpretation of experimental data. The simulation methodology has been applied also to other engine operating points enabling a mapping of post-oxidation, the development of a post-oxidation model for 1D engine simulation and the implementation of a simplified model for the full-engine simulation.