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Numerical Investigation of Internal Combustion Engine Related Flows
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. (Laszlo Fuchs)ORCID iD: 0000-0003-1511-2235
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Internal combustion engines has been used for more than 100 years. The use of the abundant energy supply stored as hydrocarbon fueled unprecedented economic growth. The use of hydrocarbons increased the work output of human labor significantly, thus increasing the economy and prosperity. However, during the latter part of the twentieth century negative consequences of the internal combustion engine has been noticed. Initially the being emissions of local pollutants such as carbon monoxide, nitrogen oxides and unburnt hydrocarbons. These pollutants have to this day in the western world been reduced significantly and further reductions are under way. Thereafter, has the focus been shifted somewhat to global emissions such as carbon dioxide due to the effect on the climate. However, as the most accessible oil resources have been exhausted the price of oil has five folded since the turn of the century, straining the exponential economic growth enjoyed for two centuries.

Heavy duty diesel engine efficiency is still below 50\%, there is thus a need and a possibility to further increase engine efficiency. In this thesis, work has been done to increase the understanding of the flow prior to combustion. A better knowledge of pre-combustion in-cylinder flow would increase the possibility to reduce engine emissions and fuel consumption, through better mixing and lower heat transfer.

The work presented is ordered in such a way that the flow structures created during the intake is presented first. Thereafter, the effect of compression is investigated. Intake flow structures are studied using Large-Eddy Simulations (LES) and experiments on a steady swirl test rig. The effects of compression are studied using simulations of predefined flow structures undergoing compression.

It is found that the flow structures created during intake is qualitatively different depending of intake valve lift. And that a single Swirl Number (SN) is an insufficient quantity to characterize the flow created at low valve lifts, due to high fluctuations. During compression it is found that a high swirl number suppress small scale turbulence while the compression has an increasing effect of axial fluctuations due to vorticity-dilation interaction. Additionally, it is shown that turbulent kinetic energy is introduced in the flow field by the piston in the absence of tumble breakdown.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , viii, 68 p.
Series
Trita-MEK, ISSN 0348-467X ; 2013:15
Keyword [en]
CFD, LES, Engine, Intake, Compression
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-124237ISBN: 978-91-7501-824-9 (print)OAI: oai:DiVA.org:kth-124237DiVA: diva2:633845
Presentation
2013-08-20, E2, Lindstedsvagen 3, Kungliga Tekniska Högskolan, Stockholm, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency
Note

QC 20130704

Available from: 2013-07-04 Created: 2013-06-27 Last updated: 2013-07-04Bibliographically approved
List of papers
1. A Coupled PIV-LES Approach to Understand PortGenerated Structures
Open this publication in new window or tab >>A Coupled PIV-LES Approach to Understand PortGenerated Structures
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Inside an engine cylinder the flow field is very complex due to high gas velocities, flowseparation and pressure pulses at the ports. Historically, simple characteristic numbers such as swirland tumble have been used in order to quantify the flow in the cylinder. These integral quantities are likely to be insucient for optimization of the mixing process and combustion in IC engines. Instead,there is a need for detailed data with adequate temporal and spatial resolution. We simulate the flowpast the valves and validate these simulations using PIV measurements. By using LES data upstreamof the measurement plane an explanation to the structures seen in the PIV measurement plane can begiven.Here we show that at low valve lifts, the flow was blocked in such a way that the inertia created at theports were counteracted leading to the formation of two unstable counter rotating vortices. We alsodetected that the fluctuations in swirl number was one order of magnitude larger at the lower valvelifts. Furthermore, the small scale turbulence created at lower lifts was more anisotropic than for thehigher valve lifts. This work has thus increased the confidence in the CFD simulations in addition toproviding an explanation to the structures identified in PIV data.

Keyword
CFD, Engine
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-124233 (URN)
Funder
Swedish Energy Agency
Note

QS 2013

Available from: 2013-06-27 Created: 2013-06-27 Last updated: 2015-04-20Bibliographically approved
2. Study of in-cylinder ow structures using PIV and LES
Open this publication in new window or tab >>Study of in-cylinder ow structures using PIV and LES
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In-cylinder ow structures have a large eect on combustion eciency and emissions. Thus, understanding these structures is of great importance in the work of reducing fuel consumption and emissions. In this paper, the in-cylinder flow is studied using stereoscopic Particle Image Velocimetry (PIV) measurements and Large Eddy Simulations (LES). The measurements and simulations have been carried out on a steady swirl test rig, commonly used to measureengine characteristics such as the swirl number. In this study, the cause of the fluctuation in swirl is explained, showing that the fluctuation can be of greater importance as compared to the mean value of the swirl number. Moreover, we show how the flow from the inlet ports are distributed.

Keyword
CFD, Engine, LES, PIV
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-124234 (URN)
Funder
Swedish Energy Agency
Note

QS 2013

Available from: 2013-06-27 Created: 2013-06-27 Last updated: 2013-07-04Bibliographically approved
3. Compression of a swirling and tumbling flow
Open this publication in new window or tab >>Compression of a swirling and tumbling flow
2013 (English)In: ASME 2013 Internal Combustion Engine Division Fall Technical Conference, ICEF 2013: Fuels; Numerical Simulation; Engine Design, Lubrication, and Applications, 2013Conference paper, Published paper (Refereed)
Abstract [en]

The effect of compression on a swirling/tumbling flow is studied using Large-Eddy Simulations (LES). In this study the geometry investigated is a cylinder with an artificially created swirling/tumbling motion. During compression the evolution of turbulence and vorticity are investigated. An increase of turbulence and vorticity is observed and linked to vorticity-dilatation interaction. It is shown that for swirling/tumbling flows turbulent kinetic energy available at Top Dead Center (TDC) is introduced by the piston through the vorticity-dilatation interaction and that turbulence increases independently of the presence of instability of the large scale flow structures.

Keyword
LES, Engine
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-124236 (URN)10.1115/ICEF2013-19128 (DOI)000359026600034 ()2-s2.0-84902359148 (Scopus ID)978-079185610-9 (ISBN)
Conference
ASME 2013 Internal Combustion Engine Division Fall Technical Conference, ICEF 2013; Dearborn, MI; United States; 13 October 2013 through 16 October 2013
Funder
Swedish Energy Agency
Note

QC 20140912. Updated from manuscript to conference paper.

Available from: 2013-06-27 Created: 2013-06-27 Last updated: 2015-09-10Bibliographically approved
4. Effects of compression on coherent structures in an enclosure
Open this publication in new window or tab >>Effects of compression on coherent structures in an enclosure
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The effects of compression on turbulent swirling flows are studied using Large-Eddy Simulations (LES). In this study, the geometry investigated is a cylinder with swirling motions of dierent strengths with superimposed isotropic turbulence. During compression the evolution of turbulence and vorticity is investigated. During early compression, rapid diusion of turbulence is found. In the later part of the compression an increase of turbulence and vorticity is observed and linked to vorticity-dilatation interaction. It is shown that the swirling motion suppresses turbulence and turbulent anisotropy. The longitudinal integral length scale of the tangential fluctuations is found to be approximately twice the transverse length scale. The longitudinal length scale is largely unaffected by compression whereas an effect on the transverse length scale is observed.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-124235 (URN)
Funder
Swedish Energy Agency
Note

QS 2013

Available from: 2013-06-27 Created: 2013-06-27 Last updated: 2015-04-20Bibliographically approved

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