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Atomization and Sprays
Facteur d'impact: 1.262 Facteur d'impact sur 5 ans: 1.518 SJR: 0.814 SNIP: 1.18 CiteScore™: 1.6

ISSN Imprimer: 1044-5110
ISSN En ligne: 1936-2684

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Atomization and Sprays

DOI: 10.1615/AtomizSpr.v20.i5.50
pages 435-451

LARGE EDDY SIMULATION OF DROPLET STOKES NUMBER EFFECTS ON MIXTURE QUALITY IN FUEL SPRAYS

Ville Vuorinen
Aalto University, School of Engineering, TKK, Internal Combustion Engine Research Group, Department of Energy Technology, Helsinki University of Technology, Finland
Harri Hillamo
School of Science and Technology, Aalto University; and Internal Combustion Engine Research Group, Department of Energy Technology, Helsinki University of Technology, Finland
Ossi Kaario
Aalto University, Department of Energy Technology, Aalto University, FI-00076 Aalto, Finland
M. Nuutinen
Aalto University School of Engineering, P.O. Box 14300, FIN-00076, Aalto, Finland
Martti Larmi
Aalto University, Department of Energy Technology, Aalto University, FI-00076 Aalto, Finland
Laszlo Fuchs
Department of Mechanics, KTH, CICERO, SE-10044 Stockholm; Division of Fluid Mechanics Lund University Lund, 22363, Sweden

RÉSUMÉ

This paper provides a continuing study to the recent study by the authors and the results presented herein are based on the same numerical experiments enriching the previously obtained picture (Vuorinen, V., Hillamo, H., Kaario, O., Larmi, M., and Fuchs, L., Atomization Sprays, vol. 20, pp. 93−114, 2010). Large eddy simulations (LES) and Lagrangian particle tracking (LPT) techniques are applied to simulate turbulent fuel spray evolution using high spatial and temporal resolution (Δx < 10−4 m and Δt < 10−7 s), hence providing detailed information on the anisotropy of the spray problem. The aim of this paper is to apply LES/LPT to identify possible causes to observed fuel spray heterogeneities in nonevaporating fuel sprays (Cao, Z., Nishino, K., Mizuno, S., and Torii, K., Exp. Fluids, vol. 29, pp. S211−S229, 2000; Hillamo, H., Kaario, O., and LarmiM., SAE Paper No. 2008-08PFL-552, 2008). In this context, the numerical setup is new since it avoids the dense spray region by emulating the dilute spray part as a droplet laden jet. The apparent role of droplet diameter (d) to spray dispersion, spray structure, and the mixture quality can then be investigated in detail. This paper is motivated by previous investigations in which smaller nozzle hole diameters and higher injection pressures together are known to yield smaller droplets, improved mixing, and higher levels of entrainment. The main emphasis is on monodisperse sprays, but for comparison, also some polydisperse sprays and a single-phase jet (which is slightly loaded with tracer particles) are considered. The droplets are assumed to be spherical; they are of constant size and do not interact with each other (i.e., assuming only two-way momentum coupling). The droplets have a Stokes number within the range of 0.07 ≤ Stp ≤ 2.56, corresponding to diameters between 2 ≤ d ≤ 12 μm. The results include (i) visualization of spray structures, combined with (ii) quantitative and statistical analysis of the results. The spray cloud shape and its internal structure are shown to depend on Stp and the apparent differences in spray dispersion are quantified using two mixing indicators that both depend strongly on Stp and imply that the smaller droplets yield better mixing than the larger droplets: (i) a diffusion coefficient, and (ii) a mixing index.


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