In the future, synthetic fuels could replace fossil fuels to minimize the CO2 emissions of combustion engines. Dimethyl carbonate (DMC) and methyl formate (MeFo) represent not only possible synthetic fuels but, due to their oxygen content, also have properties to reduce the pollutant emissions. For a good combustion process, the spray targeting and evaporation properties are important. Due to the less known injection behavior of DMC and MeFo, the spray characteristics were examined in a pressure chamber. The penetration depth, projected spray area, and spray angle were investigated at injection pressures of 100 and 200 bar, chamber pressures of 1 and 2.5 bar, and a temperature variation of up to 90°C for two different injector spray angles and flow rates in comparison with gasoline E5. The spray was recorded with a high-speed camera in a constant-volume chamber with a N2 environment. Both fuels showed a faster evaporation than E5 even with a higher injection mass due to their lower LHV. MeFo showed extreme spray collapse and flash boiling effects, which lead to even faster evaporation rates and higher penetration velocities.

Direct injection in internal combustion engines is often realized with a multi hole injector which forms a spray pattern consisting of multiple jets with a small distance between their origin. This leads to an interaction of adjacent spray jets. The spray characteristic is significantly influenced by this interaction, and can considerably change the fuel evaporation and with it the emission behavior with varying number of holes or hole nozzle geometry [8]. Experimental investigations, especially if a good optical access to a single jet is necessary, often needs to use a comparable injector with a reduced number of holes. In addition to that, 3D-CFD simulation models can also use a reduction of spray jet number for a partial consideration of fuel mixture to reduce the computing time. For these cases a determination of the correlation between spray formation and reduced nozzle holes is important. In this work the spray patterns of an original 6-hole gasoline DI-injector and, after closing of 5 holes, the resulting 1-hole injector were compared. The fuel mass flow through one hole can change due to a change of hydrodynamic effects inside the nozzle and leads to a correcting factor for the injecting time, to get comparable fuel mass flows. The penetration depth, droplet speed, size and spatial distribution were measured. Additional investigations of the influence of the fuel pressure and fuel temperature were carried out.

Since the technology of direct injected engines has become more and more prevalent, combustion anomalies such as pre-ignition events have been occurring with increasing frequency. The interaction between the fuel-spray and the oil wetted cylinder liner is considered to be a partial cause for these phenomena. The incoming fuel jet can lead to a detachment of secondary droplets, which may affect pre-ignition events due to their changed flammability properties. To characterize these secondary droplets, spatially and temporally highly resolved optical investigations on the fuel-oil-film-interaction are carried out in this work. Using laser induced fluorescence and two high-speed cameras both fluids are optically separated. Thereby the secondary droplets can be detected and characterized in size, velocity vector, and composition.

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