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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The Influence of Certain Submodels on Diesel Engine Modeling Results

Ossi Kaario

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Mechanical Engineering for public examination and debate in Auditorium K216 at Helsinki University of Technology (Espoo, Finland) on the 16th of March, 2007, at 12 noon.

Overview in PDF format (ISBN 978-951-22-8664-5)   [5168 KB]
Dissertation is also available in print (ISBN 978-951-22-8663-8)

Abstract

This thesis considers several aspects of the application of CFD to the study of diesel engines. In this work, certain submodels used in diesel engine modeling have been compared and analyzed. The submodels studied are related to the modeling of turbulence, drop breakup, ignition, chemistry, combustion, and emissions. Most of the submodels have been used extensively in different engines and with different engine loads. Many of the models have been implemented by the author and some of the models have been modified for better predictive capabilities.

The results from the comparison of turbulence models showed that the best pressure trend predictive capabilities were with a modified version of the RNG k-ε turbulence model. The tests using a LES model for turbulence showed, however, that more research is needed before it can be applied completely. Considering droplet breakup modeling, good results were obtained in terms of spray penetration and drop sizes with different models. It was also observed that even more important than the chosen drop breakup model is the proper tuning of the chosen model according to the experimental conditions. Comparison of two different ignition treatments revealed that, especially under low-load conditions, accurate modeling of the ignition process becomes important. The results from different descriptions of the main chemistry, as well as from the comparison of two very different mixing models of combustion, suggest that the mixing-limited assumption in the modeling of the heat release rate in diesel engines is a good approximation. Soot emissions have been predicted with the Hiroyasu-Magnussen soot model, as well as with a proposed soot model that is based on available soot Phi-T maps. The developed soot model was compared with the Hiroyasu-Magnussen model with different engine loads and to the measured soot emissions, and it was observed to yield promising results.

This thesis consists of an overview and of the following 6 publications:

  1. Kaario, O. T., Larmi, M., and Tanner, F. X., Relating Integral Length Scale to Turbulent Time Scale and Comparing k-ε and RNG k-ε Turbulence Models in Diesel Combustion Simulation. SAE 2002 Transactions Journal of Engines, pp. 1886-1900, SAE 2002-01-1117, 2002.
  2. Kaario, O. T., Pokela, H., Kjäldman, L., Tiainen, J., and Larmi, M., LES and RNG Turbulence Modeling in DI Diesel Engines. SAE Paper 2003-01-1069, Detroit, 3.3.-6.3.2003.
  3. Kaario, O. T., Larmi, M., and Tanner, F. X., Non-Evaporating Liquid Spray Simulations with the ETAB and WAVE Droplet Breakup Models. Ilass-Europe 2002, Zaragoza, 9.9.-11.9.2002.
  4. Kaario, O. T., Larmi, M., and Tanner, F. X., Comparing Single-Step and Multi-Step Chemistry Using the Laminar and Turbulent Characteristic Time Combustion Model in Two Diesel Engines. SAE Paper 2002-01-1749, Reno, 6.5.-9.5.2002.
  5. Kaario, O. T., Comparison Between Single-Step and Two-Step Chemistry in a Compression Ignition Free Piston Engine. SAE Paper 2000-01-2937, Baltimore, 16.10.-19.10.2000.
  6. Kaario, O. T., Antila, E., and Larmi, M., Applying Soot Phi-T Maps for Engineering CFD Applications in Diesel Engines. SAE Paper 2005-01-3856, San Antonio, USA, 24.10.-27.10.2005.

Keywords: diesel combustion modeling, computational fluid dynamics, turbulence, fuel spray, emissions

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© 2007 Helsinki University of Technology

Last update 2011-05-26