Numerical and experimental analysis of the spray momentum flux measuring on a GDI injector

In direct injection combustion systems, the spray momentum flux measurement can provide significant insight in the fuel jet development and the in-cylinder fuel-air mixing potential. The spray momentum flux can be determined by means of the impact force method, which was proved to be completely consistent when the basic measuring hypotheses are fulfilled, i.e. during the steady phase of the injection process. Conversely, in the transients the measurement technique details can significantly affect the results. An appropriate analysis of the possible effects exerted by the experimental setup is thus mandatory. In order to deepen the knowledge about this measurement technique applied to GDI (Gasoline Direct Injection) systems and to support the design of the experiment, in this paper a CFD 3-D model of a single-hole, research injector was developed and assessed with experimental data in terms of spray penetration curve, overall shape and droplet sizing and velocity. The validated numerical tool was then used to simulate the spray momentum measuring procedure in order to investigate the possible effects of the experimental set-up details on the momentum flux results. To this end, numerical results were compared to experimental data for different values of the main measurement parameters: target size, nozzle/target distance, discharge ambient pressure. This analysis confirmed both the experimental procedure sensitivity to some setup details and the model ability to capture the spray-target interaction phenomenon, supporting the need of a combined use of numerical and experimental approaches to obtain an adequate insight in the spray evolution.