3D-CFD Full Engine Simulation of Post-Oxidation by Means of Secondary Air Injection

The current and future development of internal combustion engines must face several challenges related to the upcoming new emissions regulations. For the design of new low-emission concepts, cold start conditions are of crucial importance. Reducing the time needed to reach the light-off temperature by the TWC is crucial to meet the increasingly stringent emission standards. There are many possible strategies to heat up the catalyst. Among them, post-oxidation is particularly promising because it is simple, reliable and cost-effective. The following investigation focuses on the implementation of post-oxidation by means of secondary air injection in a four-cylinder, turbocharged, direct injection spark ignition engine. Secondary air injection is implemented by adopting an air pump to inject fresh air in the proximity of the exhaust valves. The investigation is based on detailed measurements that are carried out at the test-bench, which have been confirmed by 3D-CFD simulations. The test bench role is relevant to understand which conditions are more crucial for the post-oxidation, so these operating points can be deeply investigated by means of 3D-CFD. The 3D-CFD analysis relies on two approaches: a full engine model from upstream the air filter to downstream the catalyst, including a 0D model of the turbocharger; a detailed model of the exhaust manifold from the exhaust valves up to the turbine inlet for the implementation of chemical reaction mechanism.