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One of the fundamental topics in the design of new injection systems for Dl Diesel engines is to decrease the soot emissions. A promising approach to minimize soot production are injection nozzles having clustered holes. The basic idea of Cluster Configuration (CC) nozzles is to prevent a fuel rich area in the center of the flame where most of the soot is produced. For this purpose each hole of a conventional nozzle is replaced by two smaller holes, which are sized to yield the same flow rate. The basic strategy of the cluster nozzles is to provide a better primary break up, and therefore a better mixture formation, caused by the smaller nozzle holes, but a comparable penetration length of the vapor phase due to merging of the spray plumes.

It is the objective of this work to characterize mixture formation in the sprays emanating from Multi-Layer (ML) nozzles under approximately engine-like conditions by quantitative, spatially, and temporally resolved fuel-air ratio and temperature measurements. ML nozzles are cluster nozzles which have more than one circle of orifices. They were introduced previously, in order to overcome the limitations of conventional nozzles. In particular, the ML design yields the potential of variable spray interaction, so that mixture formation could be controlled according to the operating condition. In general, it was also a primary aim of the cluster-nozzle concepts to combine the enhanced atomization and pre-mixing of small nozzle holes with the longer spray penetration lengths of large holes. The applied diagnostic, which is based on 1d spontaneous Raman scattering, yields the quantitative stoichiometric ratio and the temperature in the vapor phase.