A New 3D Model For Vaporizing Diesel Sprays Based on Mixing-Limited Vaporization

Results from numerical computations performed to represent the transient behavior of vaporizing sprays injected into a constant volume chamber and into a High Speed Direct Injection combustion chamber are presented. In order to describe the liquid phase, a new model has been developed from ideas brought forward by recent experimental results (Siebers, 1999) and numerical considerations (Abraham, 1999). The liquid penetration length is given by a 1D model which has been validated on a large number of experiments. In the 3D calculation, break-up, vaporization, drag, collision and coalescence are not modeled. The mass, momentum and energy transfers from the liquid to the gas phase are imposed from the nozzle exit surface to the liquid penetration length. This model enables us to reach time step and grid-independent results. The gas penetrations obtained with the model are checked against experimental results in a constant volume chamber (Verhoeven et al., 1998). The influence of the gas temperature, gas density and injection pressure on the gas phase penetration is well captured. The fuel vapor radial distribution is checked with recent measurement (Bruneaux, 2000) for different injection pressures and times. The model is also shown to provide combustion results coherent with the conceptual model of Dec (1997). Finally, engine simulations have been carried out for non-burning sprays to test the feasibility of the approach in a realistic configuration.

This model can only represent vaporizing sprays for which the mixing-limited vaporization concept is valid and for which the liquid phase does not impinge onto the bowl surface.