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Compressor Modeling for Control of Automotive Two Stage Turbochargers
Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, The Institute of Technology.
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

There is a demand for increasing efficiency of automotive engines, and one way to achieve this is through downsizing and turbocharging. In the design compromises are made, for example the maximum power of the engine determines the size of the compressor, but since the compressor mass flow range is limited, this affects the torque for low engine speeds. A two stage system, with two different sized turbochargers, reduces this compromise, but the system complexity increases. To handle the complexity, models have come to play a central role where they aid engineers in the design. Models are used in simulation, for design optimization and also in the control synthesis. In all applications it is vital that the models have good descriptive capabilities for the entire operating range studied.

A novel control oriented compressor model is developed, with good performance in the operating regions relevant for compressors in a two stage system. In addition to the nominal operating regime, also surge, choke and operation at pressure ratios less than unity, are modeled. The model structure can be automatically parametrized using a compressor map, and is based on static functions for low computational cost. A sensitivity analysis, isolating the important characteristics that influence surge transients in an engine is performed, and the gains of a novel surge controller are quantified.

A compressor map is usually measured in a gas stand, that has different surrounding systems, compared to the application where the compressor is used. A method to automatically determine a turbo map, when the turbo is installed on an engine in an engine test stand is developed. The map can then be used to parametrize the developed compressor model, and effectively create a model parametrized for its intended application.

An experimental analysis of the applicability of the commonly used correction factors, used for estimating compressor performance when the inlet conditions deviate from nominal, is presented. Correction factors are vital, to e.g. estimate turbocharger performance for driving at high altitude or to analyze second stage compressor performance, where the variations in inlet conditions are large. The experimental campaign uses measurements from an engine test cell and from a gas stand, and shows a small, but clearly measurable trend, with decreasing compressor pressure ratio for decreasing compressor inlet pressure, for points with equal corrected shaft speed and corrected mass flow. A method is developed, enabling measurements to be analyzed with modified corrections. An adjusted shaft speed correction quantity is proposed, incorporating also the inlet pressure in the shaft speed correction. A high altitude example is used to quantify the influence of the modified correction.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2010. , 28 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1463
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-64342Local ID: LIU-TEK-LIC-2010:32ISBN: 978-91-7393-254-7 (print)OAI: oai:DiVA.org:liu-64342DiVA: diva2:389592
Supervisors
Available from: 2011-01-19 Created: 2011-01-19 Last updated: 2013-04-30Bibliographically approved
List of papers
1. Time to Surge Concept and Surge Control for Acceleration Performance
Open this publication in new window or tab >>Time to Surge Concept and Surge Control for Acceleration Performance
2008 (English)In: Proceedings of the 17th IFAC World Congress, 2008 / [ed] Chung, Myung Jin; Misra, Pradeep, International Federation of Automatic Control (IFAC) , 2008, 2063-2068 p.Conference paper, Published paper (Refereed)
Abstract [en]

Surge is a dangerous instability that can occur in compressors. It is avoided using a valve that reduces the compressor pressure. The control of this valve is important for the compressor safety but it also has a direct influence on the acceleration performance. Compressor surge control is investigated by first studying the surge phenomenon in detail. Experimental data from a dynamic compressor flow test bench and surge cycles measured on an engine is used to tune and validate a model capable of describing surge. A concept time to surge is introduced and a sensitivity analysis is performed to isolate the important characteristics that influence surge transients in an engine. It is pointed out that the controller clearly benefits from a feed-forward term due to the small time frames associated with the transition to surge. In the next step this knowledge is used in the design of a novel surge controller. This surge controller is then compared to two other controllers and it is shown that it avoids surge and improves the acceleration performance by delivering both higher engine torque and turbo shaft speed after a gear change.

Place, publisher, year, edition, pages
International Federation of Automatic Control (IFAC), 2008
Keyword
automobile powertrains, engine control, compressor, turbo, system modeling
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-50768 (URN)10.3182/20080706-5-KR-1001.00350 (DOI)978-3-902661-00-5 (ISBN)
Conference
IFAC World Congress, July 6-11, Seuol, Korea
Available from: 2013-04-09 Created: 2009-10-14 Last updated: 2013-05-07Bibliographically approved
2. Engine Test Bench Turbo Mapping
Open this publication in new window or tab >>Engine Test Bench Turbo Mapping
2010 (English)Conference paper, Published paper (Refereed)
Abstract [en]

A method for determining turbocharger performance on installations in an engine test bench is developed and investigated. The focus is on the mapping of compressor performance but some attention is also given to the turbine mapping. An analysis of the limits that an engine installation imposes on the reachable points in the compressor map is performed, in particular it shows what corrected flows and pressure ratios can be reached and what these limitations depend on. To be able to span over a larger  region of the corrected flow a throttle before the compressor is suggested and this is also verified in the test bench.

Turbocharger mapping is a time consuming process and there is a need for a systematic process that can be executed automatically. An engine and test cell control structure that can be used to automate and monitor the measurements by controlling the system to the desired operating points is also proposed.

In experiments, used for constructing the compressor speed lines, it is virtually impossible to control the turbocharger to the exact corrected speed that is postulated by the speed line. To overcome this two methods that compensate for the deviation between measured speed and the desired speed are proposed and investigated. Detailed data from a gas stand is used to evaluate the measurements compared to those that are generated in the engine test cell installation. The agreements are generally good but there is more noise in the engine data and there are also some small systematic deviations.

Place, publisher, year, edition, pages
SAE International, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-64337 (URN)10.4271/2010-01-1232 (DOI)
Conference
SAE 2010 World Congress, April 13-15, Detroit, Michigan, USA
Available from: 2011-01-19 Created: 2011-01-19 Last updated: 2013-05-07
3. Parametrization and Validation of a Novel Surge Capable Compressor Model for MVEM using Experimental Data
Open this publication in new window or tab >>Parametrization and Validation of a Novel Surge Capable Compressor Model for MVEM using Experimental Data
(English)Manuscript (preprint) (Other academic)
Abstract [en]

A compressor model is developed. It is capable of representing mass flow and pressure characteristic for three different regions: surge, normal operation as well as for when the compressor acts as a restriction, i.e. having a pressure ratio of less than unity. Different submodels are discussed and methods to parametrize the given model structure are given. Both the parameterization and validation are supported extensively by measured data. Transient data sets include measurements from engine test stands and a surge test stand. The compressor model is further validated against a data base of stationary compressor maps. The proposed model is shown to have good agreement with measured data for all regions, without the need for extensive geometric information or data.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-64339 (URN)
Available from: 2011-01-19 Created: 2011-01-19 Last updated: 2011-01-19Bibliographically approved
4. Investigation of compressor correction quantities for automotive applications
Open this publication in new window or tab >>Investigation of compressor correction quantities for automotive applications
2012 (English)In: International Journal of Engine Research, ISSN 1468-0874, E-ISSN 2041-3149, Vol. 13, no 6, 588-606 p.Article in journal (Other academic) Published
Abstract [en]

Turbo performance is represented using maps, measured for one set of inlet conditions. Corrections are then applied to scale the performance to other inlet conditions. A turbo compressor for automotive applications experiences large variations in inlet conditions, and the use of two stage charging increases these variations. The variations are the motivation for analyzing the correction quantities and their validity. The corrections reveals a novel surge avoidance strategy, where the result is that a reduction in inlet pressure increases the surge margin for eight maps studied. The method to investigate the applicability of the strategy is general.

An experimental analysis of the applicability of the commonly used correction factors, used when estimating compressor performance for varying inlet conditions, is presented. The experimental campaign uses measurements from an engine test cell and from a gas stand, and shows a small, but clearly measurable trend, with decreasing compressor  pressure ratio for decreasing compressor inlet pressure. A method is  developed, enabling measurements to be analyzed with modified corrections.

An adjusted shaft speed correction quantity is proposed, incorporating also the inlet pressure in the shaft speed correction. The resulting decrease in high altitude engine performance, due to compressor limitations, are quantified and shows a reduction in altitude of 200 – 600 m, for when engine torque has to be reduced to due limited compressor operation.

Place, publisher, year, edition, pages
SAGE Publications (UK and US) / Professional Engineering Publishing (Institution of Mechanical Engineers), 2012
Keyword
Experimental analysis; map; inlet conditions; speed line; measurements
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-64340 (URN)10.1177/1468087412439018 (DOI)000311831200004 ()
Available from: 2011-01-19 Created: 2011-01-19 Last updated: 2017-12-11Bibliographically approved

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Leufvén, Oskar

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