Modeling Fuel Film Formation and Wall Interaction in Diesel Engines

Abstract

A fuel film model has been developed and implemented into the KIVA-II code to help account for fuel distribution during combustion in diesel engines. Spray-wall interaction and spray-film interaction are also incorporated into the model. The model simulates thin fuel film flow on solid surfaces of arbitrary configuration. This is achieved by solving the continuity and momentum equations for the two dimensional film that flows over a three dimensional surface. The major physical effects considered in the model include mass and momentum contributions to the film due to spray drop impingement, splashing effects, various shear forces, piston acceleration, and dynamic pressure effects. In order to adequately represent the drop interaction process, impingement regimes and post-impingement behavior have been modeled using experimental data and mass, momentum and energy conservation constraints. The regimes modeled for spray-film interaction are stick, rebound, spread, and splash. Numerical simulations are compared to experimental data for spray impingement normal to the wall. The film model compared extremely well with experimental data for secondary droplet velocities, spray radius, spray height, film thickness estimations, and percent of fuel adhering to the wall. In addition, diesel engine simulations are also presented. The film spreading characteristics, amount of fuel deposited on the wall, and fuel film thickness provide insight into cold starting spray-wall interactions. Finally, recommendations are given concerning the addition of thermal and evaporative processes to the model.