Engineering Large Eddy Simulation of Diesel Sprays

Abstract

The main objective of this PhD thesis is the study of Diesel sprays under evaporative conditions by means of Large Eddy Simulations (LES) techniques. This study has been performed implementing a precise, low-demanding LES model in the free, full-purpose Computational Fluid Dynamics (CFD) code OpenFOAM.12 Under similar spatial discretization 13 The ensemble average of distinct simulations under the same BC is valid as well.

Application of a flamelet-based CFD combustion model to the LES simulation of a diesel-like reacting spray

“…The length of its base measures 1.688 mm and is composed of square cells with a constant size of 62.5 µm, following the recommendation given in the literature for the use of Lagrangian droplet models [38,39]. The A DS model has been adopted to solve the residual stresses in the diesel spray simulation in the formulation described in [19,40] and the implementation given in [20], which accounts for the sub-grid interactions between the gas phase and the fuel droplets. For these droplets a Lagrangian approach has been used with 165 the Reitz model [41] that accounts for the Kelvin-Helmholtz/Rayleigh-Taylor instabilities.…”

“…This model fulfils some important properties that are desirable for any turbulence model. Due to its capabilities to perform accurate simulations it has been adopted in the current work [19,20].…”

Macroscopic and microscopic characterization of non-reacting diesel sprays at low and very high injection pressures

“…Regarding the collision mechanisms, these are complex considering that several types of droplet-droplet interaction are possible and they may not end up in permanent coalescence (figure 2.23). In this regard, researchers agree on the difficulty to measure droplet-air relative velocity and coalescence rate inside the dense region, specially because the spatial resolution is limited and the flow is opaque to optic diagnostic [9,114]. However, collision has a direct influence on the average diameter, dispersion and velocity of the droplets.…”

“…Under evaporative conditions, spray angle suffers a contraction. Conversely, and increase in the spreading angle is caused by the increase of temperature, as a consequence of the heat release associated to the combustion process [27,114].…”