Modeling Heat Transfer to Impinging Fuel Sprays in Direct-Injection Engines

A physically based spray wall heat transfer model has been developed and implemented in the KIVA II computer code to simulate heat transfer to impinging liquid fuel sprays with application to direct-injection engines. The wall heat transfer model accounts for various wall impingement regimes including rebounding drops or drops sliding along the surface with enhanced breakup after impingement. The model identifies flooded and nonflooded regimes depending on whether or not a liquid film is determined to be present on the surface, respectively. In the flooded case, heat transfer is modeled based on boundary-layer correlations. In the nonflooded regime, heat transfer is modeled by considering correlations for individual drops. The heat transfer predictions were compared to three studies in which the wall heat flux was measured experimentally. These studies include evaporating sprays directed onto cool surfaces and heat transfer from a hot surface to a cooler impinging spray. The predictions of the model and the experimental results were generally in good agreement. In validating the heat transfer models, the spray atomization and hydrodynamic drop impingement models were also tested and validated against the experimental spray penetration data for a spray impinging in a pressurized bomb. It is concluded that the improved KIVA code is now capable of predicting heat transfer to impinging transient fuel sprays under engine conditions.