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Engine Optimized Turbine Design
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The focus on our environment has never been as great as it is today. The impact of global warming and emissions from combustion processes become increasingly more evident with growing concerns among the world’s inhabitants. The consequences of extreme weather events, rising sea levels, urban air quality, etc. create a desperate need for immediate action. A major contributor to the cause of these effects is the transportation sector, a sector that relies heavily on the internal combustion engine and fossil fuels. The heavy-duty segment of the transportation sector is a major consumer of oil and is responsible for a large proportion of emissions.

The global community has agreed on multiple levels to reduce the effect of man-made emissions into the atmosphere. Legislation for future reductions and, ultimately, a totally fossil-free society is on the agenda for many industrialized countries and an increasing number of emerging economies.

Improvements of the internal combustion engine will be of importance in order to effectively reduce emissions from the transportation sector both presently and in the future. The primary focus of these improvements is undoubtedly in the field of engine efficiency. The gas exchange system is of major importance in this respect. The inlet and exhaust flows as the cylinder is emptied and filled will significantly influence the pumping work of the engine. At the center of the gas exchange system is the turbocharger. The turbine stage of the turbocharger can utilize the energy in the exhaust flow by expanding the exhaust gases in order to power the compressor stage of the turbocharger.

If turbocharger components can operate at high efficiency, it is possible to achieve high engine efficiency and low fuel consumption. Low exhaust pressure during the exhaust stroke combined with high pressure at the induction stroke results in favorable pumping work. For the process to work, a systems-based approach is required as the turbocharger is only one component of the engine and gas exchange system.

In this thesis, the implications of turbocharger turbine stage design with regards to exhaust energy utilization have been extensively studied. Emphasis has been placed on the turbine stage in a systems context with regards to engine performance and the influence of exhaust system components.

The most commonly used turbine stage in turbochargers, the radial turbine, is associated with inherent limitations in the context of exhaust energy utilization. Primarily, turbine stage design constraints result in low efficiency in the pulsating exhaust flow, which impairs the gas exchange process. Gas stand and numerical evaluation of the common twin scroll radial turbine stage highlighted low efficiency levels at high loadings. For a pulse-turbocharged engine with low exhaust manifold volume, the majority of extracted work by the turbine will occur at high loadings, far from the optimum efficiency point for radial turbines. In order for the relevant conditions to be assessed with regards to turbine operation, the entire exhaust pulse must be considered in detail. Averaged conditions will not capture the variability in energy content of the exhaust pulse important for exhaust energy utilization.

Modification of the radial turbine stage design in order to improve performance is very difficult to achieve. Typical re-sizing with modifying tip diameter and trim are not adequate for altering turbine operation into high efficiency regions at the energetic exhaust pulse peak.

The axial turbine type is an alternative as a turbocharger turbine stage for a pulse-turbocharged engine. The axial turbine stage design can allow for high utilization of exhaust energy with minimal pressure interference in the gas exchange process; a combination which has been shown to result in engine efficiency improvements compared to state-of-the-art radial turbine stages.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. , p. 137
Series
TRITA-ITM-AVL ; 2019:14
Keywords [en]
Turbocharger, Heavy-duty, Turbine, Axial, Radial
National Category
Mechanical Engineering
Research subject
Machine Design
Identifiers
URN: urn:nbn:se:kth:diva-248390ISBN: 978-91-7873-166-4 (electronic)OAI: oai:DiVA.org:kth-248390DiVA, id: diva2:1302822
Public defence
2019-05-16, Sal F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20190423

Available from: 2019-04-18 Created: 2019-04-05 Last updated: 2019-04-23Bibliographically approved
List of papers
1. Twin-scroll turbine performance evaluation from gas stand data
Open this publication in new window or tab >>Twin-scroll turbine performance evaluation from gas stand data
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2016 (English)Conference paper, Published paper (Refereed)
National Category
Energy Engineering
Research subject
Machine Design
Identifiers
urn:nbn:se:kth:diva-244861 (URN)
Conference
21th Supercharging Conference Dresden
Note

QC 20190406

Available from: 2019-03-01 Created: 2019-03-01 Last updated: 2019-04-08Bibliographically approved
2. Exhaust volume dependency of turbocharger turbine design for a heavy duty otto cycle engine
Open this publication in new window or tab >>Exhaust volume dependency of turbocharger turbine design for a heavy duty otto cycle engine
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2017 (English)In: Proceedings of the ASME Turbo Expo: Turbomachinery Technical Conference and Exposition, GT 2017, ASME Press, 2017, Vol. 2C, article id V02CT44A015Conference paper, Published paper (Refereed)
Abstract [en]

This study is considering turbocharger turbine performance at "on-engine" conditions with respect to turbine design variables and exhaust manifold volume. The highly unsteady nature of the internal combustion engine will result in a very wide range of turbine operation, far from steady flow conditions. As most turbomachinery design work is conducted at steady state, the influence of the chosen turbine design variables on the crank-angle-resolved turbine performance will be of prime interest. In order to achieve high turbocharger efficiency with the greatest benefits for the engine, the turbine will need high efficiency at the energetic exhaust pressure pulse peak. The starting point for this paper is a target full load power curve for a heavy duty Otto-cycle engine, which will dictate an initial compressor and turbine match. Three radial turbine designs are investigated, differing with respect to efficiency characteristics, using a common compressor stage. The influence of the chosen turbine design variables considering a main contributor to unsteadiness, exhaust manifold volume, is evaluated using 1D engine simulation software. A discussion is held in conjunction with this regarding the efficiency potential of each turbine design and limitations of turbine types.

Place, publisher, year, edition, pages
ASME Press, 2017
Keywords
Design, Radial, Steady, Turbocharger, Unsteady
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-216731 (URN)10.1115/GT2017-63641 (DOI)000412715300028 ()2-s2.0-85028987491 (Scopus ID)9780791850800 (ISBN)
Conference
ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition, GT 2017, 26 June 2017 through 30 June 2017
Note

QC 20171027

Available from: 2017-10-27 Created: 2017-10-27 Last updated: 2019-04-08Bibliographically approved
3. ON THE CHOICE OF TURBINE TYPE FOR A TWIN-TURBINE HEAVY-DUTY TURBOCHARGER CONCEPT
Open this publication in new window or tab >>ON THE CHOICE OF TURBINE TYPE FOR A TWIN-TURBINE HEAVY-DUTY TURBOCHARGER CONCEPT
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2018 (English)In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBOMACHINERY TECHNICAL CONFERENCE AND EXPOSITION, 2018, VOL 8, AMER SOC MECHANICAL ENGINEERS , 2018Conference paper, Published paper (Refereed)
Abstract [en]

In this study, a fundamental approach to the choice of turbocharger turbine for a pulse-charged heavy-duty diesel engine is presented. A standard six-cylinder engine build with a production exhaust manifold and a Twin-scroll turbocharger is used as a baseline case. The engine exhaust configuration is redesigned and evaluated in engine simulations for a pulse-charged concept consisting of a parallel twin-turbine layout. This concept will allow for pulse separation with minimized exhaust pulse interference and low exhaust manifold volume. This turbocharger concept is uncommon, as most previous studies have considered two stage systems, various multiple entry turbine stages etc. Even more rare is the fundamental aspect regarding the choice of turbine type as most manufacturers tend to focus on radial turbines, which by far dominate the turbochargers of automotive and heavy-duty applications. By characterizing the turbine operation with regards to turbine parameters for optimum performance found in literature a better understanding of the limitations of turbine types can be achieved. A compact and low volume exhaust manifold design is constructed for the turbocharger concept and the reference radial turbine map is scaled in engine simulations to a pre-set AFR-target at a low engine RPM. By obtaining crank-angle-resolved data from engine simulations, key turbine parameters are studied with regard to the engine exhaust pulse-train. At the energetic exhaust pressure pulse peak, the reference radial turbine is seen to operate with suboptimum values of Blade-Speed-Ratio, Stage Loading and Flow Coefficient. The study concludes that in order to achieve high turbine efficiency for this pulse-charged turbocharger concept, a turbine with efficiency optimum towards low Blade-Speed Ratios, high Stage Loading and high Flow Coefficient is required. An axial turbine of low degree of reaction-design could be viable in this respect.

Place, publisher, year, edition, pages
AMER SOC MECHANICAL ENGINEERS, 2018
Keywords
Turbocharging, Turbine, Radial, Axial
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-244162 (URN)10.1115/GT201875452 (DOI)000457071200005 ()2-s2.0-85053929818 (Scopus ID)
Conference
TURBOMACHINERY TECHNICAL CONFERENCE AND EXPOSITION, 2018
Note

QC 20190218

Available from: 2019-02-18 Created: 2019-02-18 Last updated: 2019-06-19Bibliographically approved
4. AXIAL TURBINE DESIGN FOR A TWIN-TURBINE HEAVY-DUTY TURBOCHARGER CONCEPT
Open this publication in new window or tab >>AXIAL TURBINE DESIGN FOR A TWIN-TURBINE HEAVY-DUTY TURBOCHARGER CONCEPT
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2018 (English)In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBOMACHINERY TECHNICAL CONFERENCE AND EXPOSITION, 2018, VOL 2B, ASME Press, 2018, article id UNSP V02BT44A008Conference paper, Published paper (Refereed)
Abstract [en]

In the process of evaluating a parallel twin-turbine pulse-turbocharged concept, the results considering the turbine operation clearly pointed towards an axial type of turbine. The radial turbine design first analyzed was seen to suffer from sub-optimum values of flow coefficient, stage loading and blade speed-ratio. Modifying the radial turbine by both assessing the influence of "trim" and inlet tip diameter all concluded that this type of turbine is limited for the concept. Mainly, the turbine stage was experiencing high values of flow coefficient, requiring a more high flowing type of turbine. Therefore, an axial turbine stage could be feasible as this type of turbine can handle significantly higher flow rates very efficiently. Also, the design spectrum is broader as the shape of the turbine blades is not restricted by a radially fibred geometry as in the radial turbine case. In this paper, a single stage axial turbine design is presented. As most turbocharger concepts for automotive and heavy-duty applications are dominated by radial turbines, the axial turbine is an interesting option to be evaluated for pulse charged concepts. Values of crank-angle-resolved turbine and flow parameters from engine simulations are used as input to the design and subsequent analysis. The data provides a valuable insight into the fluctuating turbine operating conditions and is a necessity for matching a pulse-turbocharged system. Starting on a 1D-basis, the design process is followed through, resulting in a fully defined 3D-geometry. The 3D-design is evaluated both with respect to FEA and CFD as to confirm high performance and durability. Turbine maps were used as input to the engine simulation in order to assess this design with respect to "on-engine" conditions and to engine performance. The axial design shows clear advantages with regards to turbine parameters, efficiency and tip speed levels compared to a reference radial design. Improvement in turbine efficiency enhanced the engine performance significantly. The study concludes that the proposed single stage axial turbine stage design is viable for a pulse-turbocharged six cylinder heavy-duty engine. Taking into account both turbine performance and durability aspects, validation in engine simulations, a highly efficient engine with a practical and realizable turbocharger concept resulted.

Place, publisher, year, edition, pages
ASME Press, 2018
Keywords
Turbocharging, Axial, Turbine, Design
National Category
Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-243978 (URN)10.1115/GT2018-75453 (DOI)000456493700053 ()2-s2.0-85054062680 (Scopus ID)978-0-7918-5100-5 (ISBN)
Conference
ASME Turbo Expo: Turbomachinery Technical Conference and Exposition
Note

QC 20190221

Available from: 2019-02-21 Created: 2019-02-21 Last updated: 2019-04-08Bibliographically approved
5. Twin-Scroll turbocharger turbine stage evaluation of experimental data and simulations
Open this publication in new window or tab >>Twin-Scroll turbocharger turbine stage evaluation of experimental data and simulations
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2018 (English)Conference paper, Published paper (Refereed)
National Category
Energy Engineering
Research subject
Machine Design
Identifiers
urn:nbn:se:kth:diva-244860 (URN)
Conference
The 13th International Conference on Turbochargers and Turbocharging, IMECHE
Note

QC 20190312

Available from: 2019-03-01 Created: 2019-03-01 Last updated: 2019-04-08Bibliographically approved
6. The Sector Divided Single Stage Axial Turbine Concept: A Feasibility Study For Pulse-Turbocharging
Open this publication in new window or tab >>The Sector Divided Single Stage Axial Turbine Concept: A Feasibility Study For Pulse-Turbocharging
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2018 (English)Conference paper, Published paper (Refereed)
National Category
Energy Engineering
Research subject
Machine Design
Identifiers
urn:nbn:se:kth:diva-244862 (URN)
Conference
23rd Supercharging Conference Dresden
Note

QC 20190408

Available from: 2019-03-01 Created: 2019-03-01 Last updated: 2019-04-08Bibliographically approved
7. The 6-Inlet Single Stage Axial Turbine Concept for Pulse-Turbocharging: A Numerical Investigation
Open this publication in new window or tab >>The 6-Inlet Single Stage Axial Turbine Concept for Pulse-Turbocharging: A Numerical Investigation
2019 (English)Conference paper, Published paper (Refereed)
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-248388 (URN)
Conference
SAE International 2019
Note

QC 20190408

Available from: 2019-04-05 Created: 2019-04-05 Last updated: 2019-04-08Bibliographically approved

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CiteExportLink to record
Permanent link

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Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
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Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf