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Modeling of a Diesel Engine with VGT and EGR capturing Sign Reversal and Non-minimum Phase Behaviors
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 mean value model of a diesel engine with VGT and EGR is developed and validated. The intended model applications are system analysis, simulation, and development of model-based control systems. The goal is to construct a model that describes the dynamics in the manifold pressures, turbocharger, EGR, and actuators with few states in order to have short simulation times. Therefore the model has only eight states: intake and exhaust manifold pressures, oxygen mass fraction in the intake and exhaust manifold, turbocharger speed, and three states describing the actuator dynamics. The model is more complex than e.g. the third order model in [12] that only describes the pressure and turbocharger dynamics, but it is considerably less complex than a GT-POWER model or a Ricardo WAVE model. Many models in the literature, that approximately have the same complexity as the model proposed here, use three states for each control volume in order to describe the temperature dynamics. However, the model proposed here uses only two states for each manifold. Model extensions are investigated showing that inclusion of temperature states and pressure drop over the intercooler only have minor effects on the dynamic behavior and does not improve the model quality. Therefore, these extensions are not included in the proposed model. Model equations and tuning methods are described for each subsystem in the model. In order to have a low number of tuning parameters, flows and efficiencies are modeled using physical relationships and parametric models instead of look-up tables. To tune and validate the model, stationary and dynamic measurements have been performed in an engine laboratory at Scania CV AB. Static and dynamic validations of the entire model using dynamic experimental data show that the mean relative errors are 12.7 % or lower for all measured variables. The validations also show that the proposed model captures the essential system properties, i.e. a non-minimum phase behavior in the channel EGR-valve to intake manifold pressure and a non-minimum phase behavior, an overshoot, and a sign reversal in the channel VGT to compressor mass flow.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2009. , 56 p.
Series
LiTH-ISY-R, ISSN 1400-3902 ; 2882
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-18333ISRN: LiTH-ISY-R-2882OAI: oai:DiVA.org:liu-18333DiVA: diva2:218314
Note

When citing this work, it is recommended that the citation is the improved and extended work, published in the peer-reviewed article Johan Wahlstr¨om and Lars Eriksson, Modeling diesel engines with a variable-geometry turbocharger and exhaust gas recirculation by optimization of model parameters for capturing non-linear system dynamics, Proceedings of the Institution of Mechanical Engineers, Part D, Journal of Automobile Engineering, Volume 225, Issue 7, July 2011, http://dx.doi.org/10.1177/0954407011398177.

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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Link to Ph.D. ThesisWhen citing please refer to this paperSee also the report LITH-ISY-R-2747

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Wahlström, JohanEriksson, Lars

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