Combined CFD-Phenomenological Approach to the Analysis of Diesel Sprays under Non-Evaporative Conditions

In the present work a CFD analysis of formation and spray evolution emerging from a Multi-holes-Common Rail Diesel injector under non-evaporative conditions has been carried out. The aim of the work was to set up a tool for fuel spray simulation that could offer reasonable accuracy for the prediction of the spray tip penetration, droplet size and a reduction of CPU time. For this purpose the influence of different primary and secondary break-up models as well as drop interaction has been investigated. Phenomenological relationships have also been implemented in the code in order to enhance the prediction of the stable diameter inside the break-up models, allowing the mean drop size to be better predicted and a reduction of the time necessary to set-up the model. Different empirical relationships of the droplet drag coefficient have been tested to assess the predicted results, including modification of the standard drag correlation which leads to take into account the droplet deformation and the presence of other droplets.

The proposed model has been validated by comparing simulation results with experimental data obtained using laser sheet techniques for spray tip penetration, spray cone angle and spray shapes, and with experimental data obtained through PDPA technique for droplet sizes and velocities. Different pressure levels have been considered for the rail injection pressure (40, 80 and 180 MPa) and for the vessel backpressure (2 and 5 MPa).

Encouraging results have been obtained, in good agreement with the experimental data available.