Investigation of the mixture formation process with combined injection strategies in high-performance SI-engines

An SI-race engine’s performance depends largely on how the combustible mixture is formed. In light of severely restrictive technical regulations of the various racing series, the optimization of the mixture formation process is one of the few remaining ways to increase engine performance. Being the predominant injection strategies in SI engines, both direct injection (DI) at high fuel pressures and port fuel injection (PFI) with much lower fuel pressures show intrinsic advantages. Hence, the potential of a combination of said injection strategies in the context of a motorsports application was investigated in a joint effort by means of both an experimental and a numerical approach. The former was carried out at the Institute of Internal Combustion Engines of the Technische Universität München (TUM). The latter, a 3d-CFD-simulation of the gas exchange and mixture formation process, was conducted by the Forschungsinstitut für Kraftfahrwesen und Fahrzeugmotoren Stuttgart (FKFS). As the preliminary investigations revealed, the combination of said injection strategies seems to have increased engine performance by a marginal yet measurable amount, thus supporting the initial assumption that in a motorsports application the otherwise superior DI injection strategy has its limitations. Subsequently, the focus of this paper is to conduct a more thorough analysis to deepen the understanding of a combined injection system’s impact on the mixture formation process.