ABSTRACT The objective of the paper is the characterization of the macroscopic behavior of Diesel sprays by focusing in at the first instants of the injection process at which the spray is clearly affected by the injector needle dynamic. There are several works dealing with the characterization of Diesel sprays in stationary conditions. Most of them conclude with empirical correlations which predict spray tip penetration as a function of the most important parameters involved in the injection process, such as: injection pressure, gas ambient density, hole diameter and time elapsed from the start of injection. In all these experiments, authors find similar power law dependencies with more or less high level of confidence. Nevertheless, few works have tried to validate or to obtain new correlations for the first instants of the injection process where the spray develops in not stationary conditions because of the influence of injector needle lift. In this paper, a wide parametrical study based on a zoomed visualization in the nozzle near-field including the first 15 millimeters of the spray has been carried out. The research has permitted the quantification of effects of the main injection parameters on spray tip penetration and spray cone angle at the initial stages of the injection process. From this study, significant differences have been found when comparing results with previous analysis based on sprays in stationary conditions especially in time dependence of spray tip penetration and injection pressure. INTRODUCTION The efficiency of combustion and pollution formation of Diesel engine depends on the quality of the fuel-air mixture [1, 2]. In direct injection Diesel engines, where the fuel is injected directly into air, it is necessary to provide adequate conditions for a good macrostructure of the mixture in the combustion chamber. This implies that the injected fuel must be properly distributed in the combustion chamber in an extremely short interval available for the mixture formation. It is known that the fuel-air mixture process is strongly influenced by the spray behavior, which depends on several parameters. These parameters can be classified into two groups: parameters related to the diesel injection system and parameters related to the environment where the spray is injected. Although there are several works dealing with the characterization of diesel sprays in stationary conditions [2-6], only in few works in the current literature the authors have tried to obtain new correlations focused in the first millimeters of spray [7-9]. Considering the fact that, in this type of engines, the characteristic length for spray development is around 25 mm. So, it would be interesting to know how the spray behaves in such particular conditions. In this work, a parametrical study based on a zoomed visualization in the nozzle near-field including the first 15 millimeters of the spray has been carried out. In the study, the macroscopic spray characteristics of a six- hole nozzle assembled in a solenoid injector holder have been characterized in a nitrogen pressurized test rig in non evaporative conditions (room temperature) and thus avoiding fuel evaporation. An extensive test matrix has been used using different values of injection pressure and density in the chamber. From experimental data, spray tip penetration and spray cone angle have been characterized. The analysis of the results have permitted to quantify the dependencies of the involved parameters on the spray characteristics in order to determine to what extend can the dependencies of the involved parameters on spray tip penetration in stationary conditions be extrapolated to a non-stationary spray. The paper is structured in five sections. First of all, a review of previous works available in the literature about Diesel spray behavior is presented. After that, the experimental facilities are described in the second section, basically the nitrogen test rig where the visualization study has been done. Image acquisition system and post-processing software are also described in this section. The third section includes a description of experimental procedure, introducing the test matrix used for this study. In section four, the results obtained are 2008-01-0929 Macroscopic Behavior of Diesel Sprays in the Near-Nozzle Field R. Payri, F. J. Salvador, J. Gimeno and J. de la Morena Copyright © 2008 SAE International Universidad Politécnica de Valencia SAE Int. J. Engines | Volume 1 | Issue 1 528