1998-02-23

Multi-Dimensional Modeling of Heat and Mass Transfer of Fuel Films Resulting from Impinging Sprays 980132

To help account for fuel distribution during combustion in diesel engines, a fuel film model has been developed and implemented into the KIVA-II code [1]. Spray-wall interaction and spray-film interaction are also incorporated into the model. Modified wall functions for evaporating, wavy films are developed and tested.
The model simulates thin fuel film flow on solid surfaces of arbitrary configuration. This is achieved by solving the continuity, momentum and energy 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, dynamic pressure effects, and convective heat and mass transfer. 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. Further details of the model are found in [2, 3].
The spray-wall interaction and fuel film models are used to simulate evaporating sprays impinging on a flat surface. The vapor and liquid phase distributions are compared to exciplex fluorescence data. Additionally, the models are used to investigate the performance of a two-stroke, direct injection diesel engine with loop-scavenging. Numerical simulations compared well with experimental data for fuel film thickness, percentage of fuel that adheres to the wall and the spreading area of the film, as well as global engine parameters such as cylinder pressure. The film model provides a predictive tool for examination of wall wetting and secondary atomization characteristics at varying engine loads.

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