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In typical passenger car diesel engines,multi-hole nozzles with small spray hole diameters are advantageous under low and part load conditions due to improved atomization and faster evaporation of the injected fuel.In contrast,nozzles with larger diameters are needed at full load in order to rapidly inject larger quantities of fuel and to mix them with air.To combine these two divergent goals,it has been suggested to replace individual,larger spray holes with pairs of closely spaced,nearly parallel but smaller "grouped holes".The interaction and eventual merging of the two individual spray plumes is then thought to better control overall spray penetration and mixing behavior.The main object of the present study is to investigate the interaction of sprays generated by a group-hole nozzle under evaporating conditions.To achieve unobstructed optical access and highlight the relevant phenomena without sacrificing realistic flow conditions,a nozzle with three spray hole pairs was used.The experiments were conducted in a high-pressure chamber heated by a hydrogen-oxygen pre-combustion.The sprays were visualized with high-speed schlieren,shadowgraphy and scattered light techniques,with particular emphasis being placed on the near-nozzle region.For comparisons,additional data from conventional and group-hole nozzles with seven sprays or spray pairs was available.For the configuration investigated in this paper,the lower hole is positioned less than 1 mm below the upper one.The corresponding spray is found to be wider and much less stable than the spray from the upper hole.A gap between the two jets can be recognized up to about 5 mm from the nozzle outlet.The liquid length of the merged sprays is similar to single holes with the same overall hydraulic flow rate.High-frequency fluctuations of the liquid length are observed and studied,and the details of the spray boundary show evidence of supercritical behavior.