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Flow Simulation in a Diesel Engine during the Intake Stroke
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Helsinki University of Technology |
Master's thesis
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Kul-34
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en
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viii + 57 s. + liitt.
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Abstract
In the Diesel engine industry, increasing developments are conducted based on computational fluid dynamics (CFD) studies.
The main goal of this newly available tool is to develop engines with improved efficiency and lower emissions through a better understanding of the flow and combustion processes.
This study aims at providing the required information about initial flow conditions for combustion simulations.
So far, engine models have relied on empirical estimates for defining the initial state of the flow.
However, depending on the engine, these quantities are strongly varying.
Some attempts have been made to produce general correlations, but their accuracy is questionable.
Here, the attempt is to produce these initial conditions and re-tuning the correlations for the WÄRTSILÄ 20 engine.
The major achievement here consists of developing a CFD model that will accurately represent the turbulent flow in the cylinder of the case engine.
Initial and boundary conditions for the flow were provided from a one-dimensional model used in this study.
A three-dimensional structured model of about 1.5 million cells was specifically built to represent the geometry of the engine, and two turbulence models were compared.
The study provided detailed evaluation of the state of turbulence in the cylinder in the form of flow velocity, turbulent kinetic energy and dissipation distributions.
Volume-averaged information on the flow was produced in the form used by the usual combustion models and a correlation was refined for the actual case.
The proposed results and correlations are specific to the WÄRTSILÄ 20 engine and cannot be readily generalized.
The computation time remained reasonable at 5 days on a 2 CPU machine.
More generally, this available computation power shows that future computations will aim at uniting the flow model with the combustion model until the whole cycle can be modelled.