The role of droplet fragmentation in high-pressure evaporating diesel sprays

The relative importance of the physical processes taking place during the development of Diesel sprays is evaluated through use of a dense-particle Eulerian-Lagrangian model. The physical processes considered include the influence of the injection conditions, as determined by a nozzle cavitating flow model, liquid-core atomisation, droplet break-up, turbulent dispersion, droplet-to-droplet interactions and vaporisation. For the latter, different physical mechanisms are included, considering high pressure and temperature as well as multi-component effects. Droplet aerodynamically-induced break-up is the dominant mechanism determining the contact area between the droplets and the surrounding air during their fragmentation period. Furthermore, a new model is considered for the droplet deformation induced during the fragmentation processes of the moving droplets. That is found to increase substantially the interface area available for heat transfer and vaporisation and to reproduce the observed trend of liquid penetration being independent of injection pressure. Model predictions are successfully compared against a wide range of experimental data for the liquid and vapour penetration, spray CCD (Charge Coupled Device) images and PDA (Phase Doppler Anemometry) measurements for various injector nozzle geometries. The results are found to predict trends as well as actual values of the penetrating fuel plumes, as function of nozzle geometry, injection pressure and air thermodynamic conditions covering the range of conditions of modern supercharged DI Diesel engines.