LES of certain droplet size effects in fuel sprays

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Aalto-yliopiston teknillinen korkeakoulu | Doctoral thesis (article-based)
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Date
2010
Major/Subject
Mcode
Degree programme
Language
en
Pages
Verkkokirja (11354 KB, 116 s.)
Series
TKK dissertations, 225
Abstract
This thesis belongs to the field of mechanical engineering, more precisely to computational fluid dynamics and fuel injection modelling. This type of problems have been extensively studied because of their practical importance, for example, in combustion processes of automotive industry. Novel challenges are reduction of exhaust gas emissions in the present diesel fuel-based and also in bio diesel-based concepts. The problem studied in this work is of generic nature and it can be related to many real world problems. A model problem of droplet-laden jet is studied to emulate a fuel spray. The most essential parameter that is studied is fuel droplet size. More precisely, the ratio of droplet timescale and fluid timescale i.e. the Stokes number. Mathematically, the studied system can be formulated in terms of the Navier-Stokes equation with a spray momentum source term at low Mach number regime. A feature characteristic to this study is to use large scale computer simulation to simulate the system. For adequate modelling, this work makes use of a method called Large-Eddy Simulation (LES) to simulate the motion of the turbulent gas and Lagrangian Particle Tracking (LPT) to simulate the motion of the droplets. The main computational tool used in this work is the OpenFOAM software. In fact, the present work is one of the first computational studies on LES/LPT diesel spray modeling in which droplet-level phenomena are discussed in light of the global behavior of the spray jet in an extensive manner. In view of the literature on this topic the results of the work seem to be realistic. The dependence of spray shape on droplet size (Stokes number) is studied and differences between the shapes are consistently explained. It is noted that mixing inside the spray depends significantly on the fuel droplet size. Quantitative and statistical analysis methods are developed in order to explain the connection between spray shape and mixing. The presented analysis explains the results and, on its behalf, the analysis explains the practical observation on the decrease of soot emissions together with decreasing nozzle diameter and increasing injection pressure.
Description
Supervising professor
Larmi, Martti, Prof.
Thesis advisor
Fuchs, Laszlo, Prof., KTH
Kaario, Ossi, Dr.
Keywords
droplet size, mixing, sprays, OpenFOAM, Large-Eddy Simulation
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Parts
  • [Publication 1]: Vuorinen V., Larmi M., Antila E., Kaario O., El-Hannouny E. and Gupta S., Near Nozzle Diesel Spray Modeling and X-Ray Measurements, SAE Technical Paper Series 2006-01-1390, (2006).
  • [Publication 2]: Vuorinen V., Larmi M. and Fuchs L., Large-Eddy Simulation of Spray-Originated Turbulence Production and Dissipation, S4_Tue_A_14, Proceedings of the 6th International Conference on Multiphase Flow, ICMF-2007, Leipzig, Germany, ISBN 978-3-86010-913-7, (2007).
  • [Publication 3]: Vuorinen V., Larmi M. and Fuchs L., Large-Eddy Simulation on the Effect of Droplet Size Distribution on Mixing of Passive Scalar in a Spray, SAE Technical Paper Series 2008-01-0933, (2008).
  • [Publication 4]: Vuorinen V., Larmi M. and Fuchs L., Large-Eddy Simulation of Particle Size Distribution Effects on Turbulence in Sprays, AIAA-2008-0514, Proceedings of the 46th AIAA Aerospace Sciences Meeting and Exhibit, Grand Sierra Resort, Reno, ISBN 978-1-60560-201-1, (2008).
  • [Publication 5]: Vuorinen V., Hillamo H., Nuutinen M., Kaario O., Larmi M. and Fuchs L., Effect of Droplet Size and Atomization on Spray Shape: A Priori Study Using Large-Eddy Simulation, accepted for publication from the best papers of the 6th International Symposium on Turbulence, Heat and Mass Transfer, Rome (2009), into a special edition of Flow, Turbulence and Combustion (09.05.2010).
  • [Publication 6]: Vuorinen V., Hillamo H., Nuutinen M., Kaario O., Larmi M. and Fuchs L., Large-Eddy Simulation of Droplet Stokes Number Effects on Turbulent Spray Shape, Atomization and Sprays, 20, 2, 93-114, (2010).
  • [Publication 7]: Vuorinen V., Hillamo H., Nuutinen M., Kaario O., Larmi M. and Fuchs L., Large-Eddy Simulation of Droplet Stokes Number Effects on Mixture Quality in Fuel Sprays, accepted for publication in Atomization and Sprays (05.05.2010).
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