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Modelling of diesel injection process using eulerian multiphase method

Numerical simulations of spray formed by high pressure fuel injectors are usually modelled by Eulerian-Lagrangian method, where motion and transport of the droplet parcels are tracked through the flow field using Lagrangian formulation. The computational effort for this method increases drastically with increasing parcels number, leaving its main use for sufficiently diluted spray where the volume fraction of the dispersed phase is low enough to allow numerical simulation. In the dense spray region where the volume fraction of dispersed phase is high this method is not applicable and another method, Eulerian multiphase, has been used. The Eulerian multiphase method provides stronger physical coupling of the gas and the liquid phase in the near nozzle dense spray region. This modelling approach treats all phases, gas and liquids, as interpenetrating multi-fluids represented by their volume fractions. The gas phase is treated as the primary phase, while the spray droplets are treated as the secondary phases. The droplets are classified into different size classes by volume fractions and diameters. A separate set of complete conservation equations with some additional source terms accounting for droplet dynamics is solved for each phase with the same discretization and similar numerical techniques. The interactions between the phases are calculated using empirical closure relations by interfacial exchange terms. The interfacial mass exchange between the gaseous phase and the liquid phase includes droplet evaporation, primary break-up and secondary break-up, while the interfacial momentum exchange includes drag forces and turbulent dispersion force. Several numerical simulations of high pressures diesel injections combined with different chamber pressure were calculated and compared with the results of measurement data. The results show good agreement compared with the measurements and yield the correct trends for both the liquid and the vapor penetration for different operating condition.

CFD; Diesel spray; Eulerian multiphase method

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