Effect of Droplet Size and Atomization on Spray Formation: A Priori Study Using Large-Eddy Simulation

Abstract

The paper is mainly focused to the vast number of researchers who work within direct injection (DI) engine fuel spray simulations. The most common simulation framework today within the community is the Reynolds Averaged Navier Stokes (RANS) approach together with the Lagrangian Particle Tracking (LPT) method. In fact, this study is one of the first studies where high resolution LES/LPT diesel spray modeling is considered. The potential of LES to deepen the present day multidimensional LPT fuel spray simulations is discussed. Spray evolution is studied far from an injector by modeling a spray as a particle laden jet (PLJ). The effect of d on mixing in non-atomizing and atomizing sprays is thoroughly investigated at jet inlet Reynolds number Re = 10 4 and Mach number Ma = 0.3. Based on and justified by rather recent and also quite old ideas, novel and compact views on droplet breakup in turb ulent f lows are pointed out from the literature. We use LES/LPT to illustrate that even in a low Weber number flow (We < 13) the droplet breakup modeling may need considerable attention in contrast to what is typically assumed in the present-day breakup models. LES and LPT techniques are first applied to essentially confirm certain expected droplet size effects on spray shape in nonatomizing monodisperse sprays. In the simulations LES e.g. produces an expected turbulent dispersion pattern that depends on droplet diameter (d) without a droplet dispersion model in contrast to RANS. A new compact droplet breakup model is formulated and tested for droplets that break with a natural resonance time rate according to the Poisson process. As a result of the study: 1) the analysis gives a rigorous and enriching proof of currently existing views on droplet size effects on Flow Turbulence Combust (2011) 86:533-561 mixing, and 2) the presented a priori analysis points out the importance of modeling the resonance breakup even at a low We.

Engine LES with Fuel-Spray Modeling

“…Vuorinen et al (2011) argue that even for small Weber number (relation between the aero-dynamical forces acting on a fluid particle and its surface tension) flows (We < 13), the use of LES is able to show certain weaknesses in the current models. Hence, a new model based on LES/LPT was proposed and tested to consider the particle breakup with a natural resonance time rate.…”

“…The spray sub-models simulated the processes of penetration, vaporization and mixing adequately and it was pointed out that the CFD calculations combined with high-speed imaging experiments provided better scientific understanding for the optimization of such engines. Vuorinen et al (2011) performed a study on the effect of the droplet size and atomization on spray formation using LES and OpenFOAM. They claim that the major framework at the time of their work within the community in this field is the Reynolds Averaged Navier-Stokes (RANS) approach together with the Lagrangian Particle Tracking (LPT) method.…”

“…In fact, their work is one of the first studies where high resolution LES/LPT diesel spray is considered. (VUORINEN et al, 2011).…”

“…This resulting exchange of momentum between the liquid and gas phase takes place due to the relative velocity between them. The equation (45), as shown by Vuorinen et al (2011), denotes this exchange of momentum by evaluating the resulting drag force over a liquid parcel moving with relative velocity u res with respect to the gas phase. …”

Eulerian – Eulerian Large Eddy Simulations Applied to Non-Reactive Transient Diesel Sprays

“…However, most of preceding works on LES of Diesel sprays [6][7][8][9][10][11] were oriented towards quasi-steady behaviours in very long injection cases, also neglecting injection to injection variability effects. Therefore, dedicated studies have to be performed to assess the ability of LES models to correctly predict spray evolutions and cyclic variations in more realistic Diesel conditions.…”