Modeling of Wall Film Formed by Impinging Spray Using a Fully Explicit Integration Method

A wall film model has been implemented in a customized version of KIVA-3 code developed at University of Bologna. The model simulates the dynamics of a liquid wall film generated by impinging sprays by solving the mass, momentum and energy equations of a two-dimensional liquid flow over a three-dimensional surface under the basic hypothesis of a ‘thin laminar flow’. The major phenomena taken into account in the present model are: wall film formation by impinging spray; body forces, such as gravity or acceleration of the wall; shear stress at the interface with the gas and no slip condition on the wall; momentum contribution and dynamic pressure generated by the tangential and normal component of the impinging drops; film evaporation by heat exchange with wall and surrounding gas. The governing equation have been integrated in space by using a finite volume approach with a first order upwind differencing scheme and they have been integrated in time with a fully explicit method. Particular care has been taken in numerical implementation of the model. Two different test cases reproducing PFI gasoline and DI Diesel engine wall film conditions have been simulated. The comparisons with experimental data show that the present wall film model well reproduces the evolution in time and the spatial distribution of the liquid film thickness in both cases.