Modeling Drop Drag Effects on Fuel Spray Impingement in Direct Injection Diesel Engines

A modified drop drag (MOD) model based on the droplet deformation and breakup (DDB) model has been developed and implemented in the KIVA II code for describing fuel spray impingement against the walls of the combustion chamber in D.I. diesel engines. The model accounts for the effects of both the drop's frontal area and its drag coefficient as a function of its distortion. In the MDD model, the stochastic rotation of drops that have impacted and bounced off the wall is considered. This makes it possible to model the highly distorted drop's frontal area variation and its effect on the drag coefficient in sprays. At the same time, the distribution of sizes of drops formed from parent drops after their breakups is modeled by using a stochastic model. A modified RNG κ - ε model is also included in the present computations. The details of fuel spray impingement against a wall were investigated by using the present models. The model predictions and the experimental results were in good agreement for fuel spray impingement. The effect of the modified drop drag model was seen to be very important on both the spray penetration and the wall spray height after impingement. In contrast to earlier models, it was found that the calculated data were insensitive to the choice of the breakup time constant, B1 after impingement. This indicates that the physics of drop destabilization processes following wall impingement are accounted for more reasonably with the present models.