Abstract
In the present paper, two models of primary atomization, including conventional blob injection model with a measured rate of injection profile and a one-way coupling VOF (volume of fluid) and Eulerian-Lagrangian spray model, are assessed in ECN spray A. The RNG k-ε model is used for all the simulations. A VOF method is used to simulate the nozzle flow and near nozzle spray. The results near the nozzle exit are recorded and used as the input of primary atomization in the Eulerian-Lagrangian spray model. The blob injection model and one-way coupling VOF and Eulerian-Lagrangian spray model are applied to the same evaporating and combustion spray cases. A simplified reaction mechanism for dodecane is employed in the SAGE model for combustion modeling. For the evaporating spray, liquid penetration lengths from simulations and experiments are compared. Both models well capture the measurements. The one-way coupling VOF and Eulerian-Lagrangian spray model gives slightly better agreements with the measured liquid penetration length. Additionally, its profile is smoother that is due to its much higher number of droplet parcels. For the combusting case, the CFD results are compared with available lift-off length (LOL), images of chemiluminescence and Schlieren imaging. The predicted LOLs of both models match the experimental data very well during the steady state. Relatively, the one-way coupling VOF and Eulerian-Lagrangian spray model does a better job during the early transient stage. It implies that the primary atomization model is critical for this stage. The contour plots of predicted temperature are used to compare with the results of chemiluminescence and Schlieren imaging. Good agreements are achieved for both models. The one-way coupling VOF and Eulerian-Lagrangian spray model shows better agreement with the chemiluminescence images after the end of injection. A hot-spot that is observed in chemiluminescence images is reproduced by the blob injection model. Further analysis of OH and CH2O concentration distribution shows that it is an auto-ignition site. The one-way coupling VOF and Eulerian-Lagrangian spray model does not capture this hot-spot that may be due to its more homogeneous fuel/air mixture near the spray plume that is not favorable for auto-ignition events.
