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The KIVA-II code is probably the most advanced CFD code for simulating diesel engine fuel spray, but the atomization sub model remains imperfect. For this reason, several break-up models exist in published literature. The poor physical understanding of liquid break-up prevents it from being modeled faithfully. In our 1997 SAE Paper, a new approach was proposed, based on a jet fully atomized when leaving the nozzle. It avoids the break-up description by fixing some fictional initial conditions for droplet velocity, average diameter and size distribution. The originality lies in the choice of droplet injection velocity. The proposed initial velocity is roughly twice that normally used, i.e. the value found using the Bernoulli equation with a discharge coefficient of around 0.75.

The non-reactive diesel spray is studied in a constant volume combustion chamber. Droplet sizes and velocities are measured using Particle Doppler Analyzer instrumentation. The effects of aerodynamic drag and vaporization on the droplets size are emphasized. An increase of the mean diameters is observed downstream of the break-up region. The well known KIVA-II code is used to achieve spray computations. The break-up model is disabled and the spray is assumed to be already atomized at the nozzle exit. Size distribution and velocities of the injected droplets are deduced from downstream experimental data. A good agreement is obtained between numerical and experimental results. Size distributions at various locations and temperature conditions are correctly predicted. A diesel spray can be thus modeled in a satisfactory way, when we alleviate the complex processes of break-up, but with appropriate initial droplets conditions.