Diesel Spray CFD Simulations Based on the Σ-Υ Eulerian Atomization Model

Abstract

This work presents an implementation and evaluation of the Σ-Y atomization model for Diesel spray CFD simulations. The Σ-Y model is based on an Eulerian representation of the spray atomization and dispersion by means of a single-fluid variable density turbulent flow within a RANS framework. The locally homogeneous flow approach has been applied in order to develop a spray vaporization model based on state relationships. A finite-volume solver for model equations has been created using theOpenFOAM CFD open-source C++ library. Model predictions have been compared to experimental data from free Diesel sprays under nonvaporizing and vaporizing conditions. High-speed imaging, PDPA, and Rayleigh-scattering measurements have been used in order to assess the CFD model. Accurate predictions of liquid and vapor spray penetration, as well as axial velocity and mixture fraction profiles, can be simultaneously achieved for a wide range of injection pressure and ambient conditions, despite only having qualitatively correct predictions of droplet size. The success of these predictions supports the mixing-limited vaporization hypothesis. Model accuracy is better for high ambient density and injection pressure conditions. It is proposed that under low ambient density and injection pressure conditions, interfacial dynamics become more important and the single velocity field assumption is less appropriate.

Modelling and validation of near-field Diesel spray CFD simulations based on the Σ -Y model

“…The previously described model equations have been implemented into a solver [20] constructed by using the OpenFOAM [28] CFD libraries.…”

“…In this paper, a LES approach is also applied and its impact on spray dispersion is evaluated. The interfacial density predictions have rarely been validated, and these validations have been in the context of downstream drop size [20][21], which is not ideal since we wish to avoid the assumption that the liquid is in the form of droplets. A few prior examples used DNS simulations [7] for validation, and in this paper the validation is performed via USAXS measurements, which directly measures the interfacial surface density.…”

Effect of turbulence model and inlet boundary condition on the Diesel spray behavior simulated by an Eulerian Spray Atomization (ESA) model

“…Although the model is described in detail by Vallet et al (2001); Demoulin et al (2007); García-Oliver et al (2013) and Beheshti et al (2007), the basics are summarized in this paper. The key point of the original model is the striking analogy between atomization and turbulent mixing of a jet with a very large density difference with the ambient medium.…”

“…Other authors, Blokkeel et al (2003) and Lebas et al (2005), modified that model by adding a switch to Lagrangian framework when liquid droplets are dispersed enough; this model was called Eulerian-Lagrangian Spray Atomization (ELSA). These models and their further improvements have proved its reliability in simulating diesel fuel injection processes under different conditions in works presented by Ning et al (2009); Lebas et al (2009); Hoyas et al (2013) and García-Oliver et al (2013).…”

“…on the spray behavior is simple: using the Σ − Y model of Vallet et al (2001) to simulate internal and external flows in one unique domain. Notwithstanding, this methodology also has some limitations or drawbacks: computational time steps and mesh resolutions characteristic of nozzle flows are small, so the computational cost increases quite a lot; ambient conditions are limited to the range where hypothesis of Σ − Y model are true; and no cavitation nor evaporation (process studied by García-Oliver et al (2013) for the Σ − Y model) models are included so far because a third phase, fuel vapor, would be necessary.…”