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In the last two decades, piston engine specifications have deeply evolved. Indeed, new challenges nowadays concern the reduction of pollutant emissions (EURO regulations) and CO2 emissions. To satisfy these new requirements, powertrains have become very complex systems including a large number of high technology components (high pressure injectors, turbocharger, Exhaust Gas Recirculation (EGR) loop, after-treatment devices...). In this context, the engine control plays a major role in the development and the optimization of powertrains. Few years ago, engine control strategies were mainly defined by experiments on engine test benches. This approach is not adapted to the complexity of future engines: on the one hand, tests are too expensive and on the other hand, they do not give much information to understand interactions between components. Today, a promising alternative to tests may be the use of 0D/1D simulation tools.

In this study, a 3D model for atomization based on an Eulerian single-phase approach has been implemented in a professional CFD code for simulations in engines: AVL Fire 8.3. The method improves the description of the primary break-up by representing the strong interactions between the liquid and the gas phase that take place in the atomization process. In the region where the spray is considered to be diluted enough, the classical representation of the spray by the way of a set of stochastic particles representing the droplets with a Lagrangian approach (DDM Method, see [1]) is then initiated to precisely describe the dispersed spray finally formed. Coming back to this standard approach also permits to benefit of an important background, in particular concerning vaporization models and eventually combustion models. Up to now, the model permits to simulate continuously the spray from inside the injector to the completely vaporized spray.

Atomizing systems must be able to form sprays with predetermined characteristics. There are affected by the shape of the injector as well as external conditions. Thus, in order to avoid numerous experiments, this is necessary to develop predictive atomization models able to deal with the complete atomization process. This can be done using a Eulerian model for primary break-up. This approach describes the flow continuously from inside the injector to the dispersed spray region. In this paper the Eulerian multiphase approach and the Eulerian single-phase approach are compared and the results lead to an intermediate quasi-multiphase approach for describing the spray core. Finally a transition zone permits to represent the diluted spray region by using the classical Lagrangian approach to benefit of the experience accumulated on this method, in particular for the vaporization and the combustion.