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System analysis of a Diesel Engine with VGT and EGR
Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, The Institute of Technology.
2009 (English)Report (Other academic)
Abstract [en]

A system analysis of a diesel engine with VGT and EGR is performed in order to obtain insight into a VGT and EGR control problem where the goal is to control the performance variables oxygen fuel ratio and EGR-fraction using the VGT actuator and the EGR actuator. Step responses over the entire operating region show that the channels VGT to oxygen fuel ratio, EGR-valve to oxygen fuel ratio, and VGT to EGR-fraction have non-minimum phase behaviors and sign reversals. The fundamental physical explanation of these system properties is that the system consists of two dynamic effects that interact: a fast pressure dynamics in the manifolds and a slow turbocharger dynamics. It is shown that the engine frequently operates in operating points where the non-minimum phase behaviors and sign reversals occur for the channels VGT to oxygen fuel ratio and VGT to EGR-fraction, and consequently, it is important to consider these properties in a control design. Further, an analysis of zeros for linearized multiple input multiple output models of the engine shows that they are non-minimum phase over the complete operating region. A mapping of the performance variables oxygen fuel ratio and EGR-fraction and the relative gain array show that the system from EGR-valve and VGT to oxygen fuel ratio and EGR-fraction is strongly coupled in a large operating region. It is also illustrated that the pumping losses decrease with increasing EGR-valve and VGT opening for almost the complete operating region.

Place, publisher, year, edition, pages
2009. , 39 p.
Series
LiTH-ISY-R, ISSN 1400-3902 ; 2881
Keyword [en]
diesel engine, VGT, EGR
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-18334ISRN: LiTH-ISY-R-2881OAI: oai:DiVA.org:liu-18334DiVA: diva2:218321
Available from: 2009-05-28 Created: 2009-05-19 Last updated: 2014-10-08Bibliographically approved
In thesis
1. Control of EGR and VGT for Emission Control and Pumping Work Minimization in Diesel Engines
Open this publication in new window or tab >>Control of EGR and VGT for Emission Control and Pumping Work Minimization in Diesel Engines
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Legislators steadily increase the demands on lowered emissions from heavy duty vehicles. To meet these demands it is necessary to integrate technologies like Exhaust Gas Recirculation (EGR) and Variable Geometry Turbochargers (VGT) together with advanced control systems. Control structures are proposed and investigated for coordinated control of EGR valve and VGT position in heavy duty diesel engines. Main control goals are to fulfill the legislated emission levels, to reduce the fuel consumption, and to fulfill safe operation of the turbocharger. These goals are achieved through regulation of normalized oxygen/fuel ratio and intake manifold EGR-fraction. These are chosen as main performance variables since they are strongly coupled to the emissions. To design successful control structures, a mean value model of a diesel engine is developed and validated. The intended applications of the model are system analysis, simulation, and development of model-based control systems. Dynamic validations show that the proposed model captures the essential system properties, i.e. non-minimum phase behaviors and sign reversals. A first control structure consisting of PID controllers and min/max-selectors is developed based on a system analysis of the model. A key characteristic behind this structure is that oxygen/fuel ratio is controlled by the EGR-valve and EGR-fraction by the VGT-position, in order to handle a sign reversal in the system from VGT to oxygen/fuel ratio. This structure also minimizes the pumping work by opening the EGR-valve and the VGT as much as possible while achieving the control objectives for oxygen/fuel ratio and EGR-fraction. For efficient calibration an automatic controller tuning method is developed. The controller objectives are captured by a cost function, that is evaluated utilizing a method choosing representative transients. Experiments in an engine test cell show that the controller achieves all the control objectives and that the current production controller has at least 26% higher pumping losses compared to the proposed controller. In a second control structure, a non-linear compensator is used in an inner loop for handling non-linear effects. This compensator is a non-linear state dependent input transformation. PID controllers and selectors are used in an outer loop similar to the first control structure. Experimental validations of the second control structure show that it handles nonlinear effects, and that it reduces EGR-errors but increases the pumping losses compared to the first control structure. Substantial experimental evaluations in engine test cells show that both these structures are good controller candidates. In conclusion, validated modeling, system analysis, tuning methodology, experimental evaluation of transient response, and complete ETC-cycles give a firm foundation for deployment of these controllers in the important area of coordinated EGR and VGT control.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2009. 230 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1256
National Category
Control Engineering
Identifiers
urn:nbn:se:liu:diva-18484 (URN)978-91-7393-611-8 (ISBN)
Public defence
2009-06-12, Visionen, B-huset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2009-05-29 Created: 2009-05-28 Last updated: 2009-05-29Bibliographically approved

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System analysis of a Diesel Engine with VGT and EGR(3957 kB)1654 downloads
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Wahlström, JohanEriksson, LarsNielsen, Lars

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