Modelling of spray characteristics from multi-hole injectors for direct-injection gasoline engines

Gasoline sprays from high-pressure multi-hole nozzles for direct injection spark-ignition engines have been simulated using a CFD spray model. Model validation takes place against experimental data available for injection into a constant volume chamber. These include CCD spray images and droplet velocity and diameter measurements obtained with a two-component phase Doppler anemometry (PDA) system at injection pressures up to 200bar and chamber pressures varying from atmospheric to 12bar. An 1-D FIE (Fuel Injection Equipment) hydraulic flow simulation provides the injection rate, while a 3-D and two-phase CFD nozzle flow model predicts the injection velocity increase due to cavitation. Finally, a cavitation-induced atomisation model predicts the droplet size distribution very near the nozzle exit. The subsequent spray development is predicted using the Eulerian-Lagrangian methodology, including for liquid droplet aerodynamic break-up, turbulent dispersion, droplet vaporisation and droplet-to-droplet interaction. Overall, both model predictions and measurements confirmed the advantages of high-pressure multi-hole injectors for gasoline direct-injection engines relative to swirl pressure atomisers, in terms of spray structure independency from chamber thermodynamic and injection operating conditions.