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ON THE CHOICE OF TURBINE TYPE FOR A TWIN-TURBINE HEAVY-DUTY TURBOCHARGER CONCEPT
Scania CV AB, SE-15138 Sodertalje, Sweden..
Lund Univ, Energy Sci, SE-22100 Lund, Sweden..
Scania CV AB, SE-15138 Sodertalje, Sweden..
Scania CV AB, SE-15138 Sodertalje, Sweden..
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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 [en]
Turbocharging, Turbine, Radial, Axial
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-244162DOI: 10.1115/GT201875452ISI: 000457071200005Scopus ID: 2-s2.0-85053929818OAI: oai:DiVA.org:kth-244162DiVA, id: diva2:1289354
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
In thesis
1. Engine Optimized Turbine Design
Open this publication in new window or tab >>Engine Optimized Turbine Design
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
Turbocharger, Heavy-duty, Turbine, Axial, Radial
National Category
Mechanical Engineering
Research subject
Machine Design
Identifiers
urn:nbn:se:kth:diva-248390 (URN)978-91-7873-166-4 (ISBN)
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

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