Pötsch, C., Baumgartner, L., Koch, D., Bernhard, F. et al., "Optimization of the Mixture Formation for Combined Injection Strategies in High-Performance SI-Engines," SAE Technical Paper 2015-24-2476, 2015, doi:10.4271/2015-24-2476.
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.With regard to the mixture formation processes and thus engine performance, both SI-engines with direct and port fuel injection show intrinsic advantages and drawbacks. The combination of the above systems may give rise to new possibilities in combining the particular benefits of both systems. Therefore, the potential of combined injection strategies, with reference to high performance and race engine applications, is presently investigated at the Institute of Internal Combustion Engines of the Technische Universität München by means of experimental approaches. Both a single cylinder research engine and optical spray diagnostics are used. Thus, the question of whether combined injection strategies can potentially enhance power output is examined.Furthermore, numerical 3d-CFD-simulations of gas exchange, mixture formation as well as combustion are carried out at the Forschungsinstitut für Kraftfahrwesen und Fahrzeugmotoren Stuttgart with regard to the above injection strategies. The numerical data can then be validated by the experimental investigations from the single cylinder research engine.