The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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LES of Certain Droplet Size Effects in Fuel Sprays

Ville Vuorinen

Doctoral dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Engineering and Architecture for public examination and debate in Auditorium K3/118 at the Aalto University School of Science and Technology (Espoo, Finland) on the 29th of May 2010 at 12 noon.

Overview in PDF format (ISBN 978-952-60-3166-8)   [11354 KB]
Dissertation is also available in print (ISBN 978-952-60-3165-1)

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.

This thesis consists of an overview and of the following 7 publications:

  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).
  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).
  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).
  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).
  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).
  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).
  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).

Keywords: droplet size, mixing, sprays, OpenFOAM, Large-Eddy Simulation

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Last update 2011-05-26