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Comparative analyses of a high-performance 4-cylinder DISI-engine and its equivalent single-cylinder research engine were performed by means of fast response 3D-CFD simulations. Both engines have identical geometries of intake and exhaust channels, cylinder head and piston. The used 3D-CFD tool QuickSim was developed at the Forschungsinstitut für Kraftfahrwesen und Fahrzeugmotoren Stuttgart (FKFS), particularly for the numerical simulation of internal combustion engines (ICE). A calibration of the air consumption enabled a comparison of in-cylinder processes, including charge motion, mixture formation and combustion. All calculated operating points showed a similar trend. Deviations during the gas exchange phase led to a higher turbulence level and hence combustion velocity for the single-cylinder research engine. This resulted in a slightly higher maximum cylinder pressure and indicated mean effective pressure.

Alongside with the severe restrictions according to technical regulations of the corresponding racing series (air and/or fuel mass flow), the optimization of the mixture formation in SI-race engines is one of the most demanding challenges with respect to engine performance. Bearing in mind its impact on the ignition behavior and the following combustion, the physical processes during mixture formation play a vital role not only in respect of the engine's efficiency, fuel consumption, and exhaust gas emissions but also on engine performance. Furthermore, abnormal combustion phenomena such as engine knock may be enhanced by insufficient mixture formation. This can presumably be explained by the strong influence of the spatial distribution of the air/fuel-ratio on the inflammability of the mixture as well as the local velocity of the turbulent flame front.