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In the present work the benefit of a 50 MPa gasoline direct injection system (GDI) in terms of particle number (PN) emissions as well as fuel consumption is shown on a 0.5 l single cylinder research engine in different engine operating conditions. The investigations show a strong effect of injection timing on combustion duration. As fast combustion can be helpful to reduce fuel consumption, this effect should be investigated more in detail. Subsequent analysis with the method of particle image velocimetry (PIV) at the optical configuration of this engine and three dimensional (3D) computational fluid dynamics (CFD) calculations reveal the influence of injection timing on large scale charge motion (tumble) and the level of turbulent kinetic energy. Especially with delayed injection timing, high combustion velocities can be achieved. At current series injection pressures, the particle number emissions increase at late injection timing.

This study provides an overview of injector design adaptations and fuel pressure variations for oxygenated synthetic fuels, benchmarked against gasoline. The promising oxygenated fuels exhibited reduced emissions, especially with respect to particles. In gasoline engines, high fuel pressures are needed to keep the particle emissions below the permitted level. In oxygenated fuels, high fuel pressures are required to compensate for the lower volumetric energy density when used with non-adapted injectors. This study demonstrates that an adapted injector design enables engine operation with a fuel pressure reduction from 35 MPa to 10 MPa, without emission drawbacks. The fuel investigated contained dimethyl carbonate (DMC) and methyl formate (MeFo). The fuel mass contained around 50% oxygen. A relatively high percentage of 35 vol.% MeFo was chosen because of its high vapor pressure, thus providing fast mixture formation and enabling very late compression stroke injections.

On the way to a climate-neutral mobility, synthetic fuels with their potential of CO2-neutral production are currently in the focus of internal combustion research. In this study, the C1-fuels methanol (MeOH), dimethyl carbonate (DMC), and methyl formate (MeFo) are tested as pure fuel mixtures and as blend components for gasoline. The study was performed on a single-cylinder engine in two configurations, thermodynamic and optical. As pure C1-fuels, the previously investigated DMC/MeFo mixture is compared with a mixture of MeOH/MeFo. DMC is replaced by MeOH because of its benefits regarding laminar flame speed, ignition limits and production costs. MeOH/MeFo offers favorable particle number (PN) emissions at a cooling water temperature of 40 °C and in high load operating points. However, a slight increase of NOx emissions related to DMC/MeFo was observed. Both mixtures show no sensitivity in PN emissions for rich combustions. This was also verified with help of the optical engine.