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.
Within this study, six cluster nozzles with cluster angles from 0° up to 15° are investigated and compared to two nozzles of a conventional design, one with the same flow number as the cluster nozzles and the other one with 50%of this value, according to a single hole of the cluster nozzles. The common rail diesel injector is installed in a combustion vessel, in order to provide nearly quiescent high-pressure and high-temperature conditions. Each injection is investigated using three different measurement techniques quasi-simultaneously. The liquid and the vapor phase are visualized using the scattered light of a Nd:YAG laser and back-lit schlieren imaging, respectively. Furthermore, the hot reaction zone is visualized using OH* chemiluminescence imaging. OH* occurs during the second stage of the ignition process. The penetration lengths of the liquid and the vapor phase, as well as the lift-off length and the ignition delay, are determined. The influence of the cluster configuration and the cluster angle on the penetration and the subsequent combustion are analyzed and discussed.
