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To simulate the air-fuel mixing in the intake ports and cylinders of internal combustion engines, a fuel liquid film model is developed for integration in 3D CFD codes. Phenomena taken into account include wall film formation by an impinging spray, film transport such as governed by mass and momentum equations with wall and air flow interactions and evaporation considering energy and convection mass transfer equations. A continuous-fluid method is used to describe the wall film over a three dimensional complex surface. The basic approximation is that of a laminar incompressible boundary layer; the liquid film equations are written in an integral form and solved by a first-order ALE finite volume scheme; the equation system is closed without coefficient fitting requirements. The model has been implemented in a Multi-Block version of KIVA 2 (KMB) and tested against problems having theoretical solutions.

Computation of high pressure Diesel injection requires improvement of present spray atomization and droplet breakup models. The surface wave instability atomization (Wave) model of Reitz [2] has been coupled to a new breakup model (FIPA) which is based on the experimental correlations of Pilch et al.[3]. It has been integrated in the 3D KMB code [1] derived from the Kiva 2 code [4] of Los Alamos already including a stochastic Lagrangian description of sprays. The droplet breakup FIPA model was first fitted and validated using the monodisperse drop breakup experiments of Liu and Reitz [5]. The response of the modified spray model including the global Wave-FIPA breakup model is compared to well characterized data obtained in a high pressure and temperature vessel. This vessel is fitted with a common-rail injection system with a single hole injector tip.

A lumping model has been formulated to calculate the thermodynamic properties required for internal combustion engine multidimensional computations, including saturation pressure, latent heat of vaporization, liquid density, surface tension, viscosity, etc. This model consists firstly in reducing the analytical data to a single (i.e. pure) pseudo-component characterized by its molecular weight, critical pressure and temperature, and acentric factor. For a gasoline fuel, the required analytical data are those provided by gas chromatography. For a Diesel fuel, the required data are a true boiling point (TBP) distillation curve and the fuel density at a single temperature. This model provides a valuable tool for studying the effects of fuel physical properties upon the behavior of a vaporizing spray in a chamber, as well as upon direct injection gasoline and Diesel engines using the multidimensional (3D) KMB code.

The Lagrangian-Eulerian approach is commonly used to simulate engine sprays. However typical spray computations are strongly mesh dependent. This is explained by an inadequate space resolution of the strong velocity and vapor concentration gradients. In Diesel sprays for instance, the Eulerian field is not properly computed close to the nozzle exit in the vicinity of the liquid phase. This causes an overestimated diffusion that leads to inaccuracies in the modeling of fuel-air mixing. By now it is not possible to enhance grid resolution since it would violate requested assumptions for the Lagrangian liquid phase description. Besides, a full Eulerian approach with an adapted mesh is not practical at the moment mainly because of prohibitive computer requirements. Keeping the Lagrangian-Eulerian approach, a new methodology is introduced: the full Lagrangian-Eulerian Coupling (CLE).

Progress in Diesel spray modelling highly depends on a better knowledge of the instantaneous injection velocity and of the hydraulic section at the exit of each injection hole. Additionally a better identification of the mechanisms which cause fragmentation is needed. This necessitates to begin with a precise computation of the two-phase flow which arises due to the presence of cavitation within the injectors. For that aim, a VOF type interface tracking method has been developed and improved (Segment Lagrangian VOF method) which allows to describe numerically the onset and development of cavitation within Diesel injectors. Furthermore, experiments have been performed for validation purpose, on transparent one-hole injectors for high pressure injection conditions. Two different entrance geometries (straight and rounded) and various upstream and downstream pressure levels have been considered.