Modelling the influence of the nozzle geometry on the primary breakup of diesel jets

In this work, the performance of an enhancement of a well-known, energy based CFD model for the primary breakup of high pressure diesel jets is presented. This new formulation of the model has been developed in order to take into account the different turbulent and cavitating flow conditions experimentally found inside the injection hole (geometric cavitation and "string" cavitation). A detailed spatial and temporal resolution of the cavitating flow in the hole is used by the model to deliver three-dimensional sprays, providing all the starting conditions for the calculation of the secondary breakup of the diesel spray by means of a Lagrangian approach. The characteristic feature of the model is the variable size and velocity distribution of the primary droplets as a function of the available breakup energy. Another main advantage of the model is the direct calculation of the droplet size distribution and spray angle based on the flow properties, so that empirical correlations or measurement data are not needed as input for the calculations. Measurements carried out on real engine nozzles were conducted to validate the simulations of both nozzle flow and spray development.