Optimization of the gas exchange of a naturally aspirated engine for EU7 emission regulations

The increasingly rigorous regulations on pollutant emissions emitted by internal combustion engines have affected and will continue to affect the automotive industry strongly in the future. Moreover, although these regulations are leading to an ever-increasing thrust towards vehicle electrification, internal combustion engines will continue to play a leading role in the propulsion of passenger cars in the near future, especially in the world of high-performance engines. Therefore, it is important to understand how these requirements can be fulfilled. With regard to engines fueled by direct injection of gasoline into the combustion chamber, the so-called GDI (Gasoline Direct Injection) engines, from several years regulations have imposed limits on particulate emissions. In order to cope with these restrictions, it is necessary to adopt mechanical filters that allow these carbon particles to be retained inside. The addition of this component, the GPF (Gasoline Particulate Filter), to the exhaust line of the engine produces a significant increase in exhaust back pressure. Consequently, a worsening in engine performance is expected due to increasing pumping work and residual gases and to efficiency reduction. In this scenario, it is indubitable that emission regulations and engine performance show two opposite trends. Since performance represents a customer relevant marketing factor, it is needed to find a way to comply latest emission regulations without jeopardizing engine performance. In turbocharged engines, the reduction of volumetric efficiency can be compensated by an increment of the boost pressure. However, the engine under examination is a naturally aspirated high-performance engine thus its performance is strongly connected to the ability to intake the larger amount of air from environment without any external devices, such as turbochargers. This can be obtained with a proper design of intake and exhaust manifolds, which allows the dynamic effects exploitation of the air within these systems. The goal of this work is to develop a coupled simulation methodology by combining 1D-CFD and 3D-CFD tools in order to predict in the most accurate way dynamic effects occurring in the manifolds of a naturally aspirated engine to improve its performance. The 1D-CFD tool allows the simulation of the whole gas-exchange process whereas the 3D-CFD tool yields to a more accurate solution of the flow field in complex geometries, such as those of intake and exhaust manifolds. For this aim, GT-Power software has been used as 1D-CFD tool whereas Converge Lite has been chosen as 3D-CFD tool. Before approaching the optimization process, the developed methodology has been validated by means of a comparison of simulation results against experimental data for the reference engine. Afterwards, the optimization process focused on intake manifold as packaging constraints precluded any changes to exhaust manifold geometry. During the optimization process, different intake manifold geometries have been simulated to reach an optimal configuration. Finally, the best configuration was built using rapid prototyping techniques and tested on the dyno. The comparison between simulation results and experimental measurements allows to confirm the robustness of the developed methodology and get tangible proof of performance improvement. In light of the results achieved, this 1D/3D-CFD methodology is an effective means for the development of naturally aspirated engines.