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Modeling and Analytical Solutions for Optimal Heating of Aftertreatment Systems
Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0001-8646-8998
2019 (English)In: IFAC PAPERSONLINE, ELSEVIER , 2019, Vol. 52, no 5, p. 523-530Conference paper, Published paper (Refereed)
Abstract [en]

Cold start emissions are the most significant contributor to the accumulated emissions of a vehicle and poses a critical design limit for the design of clean and efficient vehicles. The core reasons for the emissions are the initial low temperature and the thermal inertia of the exhaust aftertreatment systems. Moreover, it also costs fuel to perform the heating of the catalyst. It is therefore of high interest to develop efficient control schemes that can reduce the time to light off. To facilitate this a model structure and a method, based on the explicit solution to the catalyst differential equations are developed, that can be used to analyze both time and fuel optimal heating control strategies. The method is developed to be applicable to both gasoline and diesel aftertreatment systems. A case study is performed on a Diesel engine and the results show that the solutions exhibit a structured and simple two-phase pattern. There is a first heating phase, where the catalyst is fed with a high temperature gas, building up a high inlet temperature. Then in a second phase the flow is kept high and the temperature is pushed through the catalyst. The strategy is easy to understand and realize in a real time control system. (C) 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
ELSEVIER , 2019. Vol. 52, no 5, p. 523-530
Series
IFAC papers online, E-ISSN 2405-8963
Keywords [en]
Exhaust aftertreatment systems; Thermal management; Automotive control & emissions; Diesel engines; Engine control
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:liu:diva-161222DOI: 10.1016/j.ifacol.2019.09.083ISI: 000486629500084OAI: oai:DiVA.org:liu-161222DiVA, id: diva2:1365645
Conference
9th IFAC International Symposium on Advances in Automotive Control (AAC)
Available from: 2019-10-25 Created: 2019-10-25 Last updated: 2022-01-13
In thesis
1. Modeling and Control for Emission Management in Hybrid Electric Commercial Vehicles
Open this publication in new window or tab >>Modeling and Control for Emission Management in Hybrid Electric Commercial Vehicles
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electrification of powertrains is a major trend in the vehicle industry. The reason behind this is mainly that electrification of a powertrain generally results in better fuel economy, by eliminating inefficient, low load, operation of the engine. This can be done in two ways: load shifting to shift the operation point of the engine to a more efficient one, or by turning off the engine completely. When it comes to emissions, load shifting generally have positive effect since it usually result in higher exhaust temperatures which are beneficial for the aftertreatment system. The effect from turning off the engine completely is more complicated. When the engine is turned off the aftertreatment system will start to cool down and will eventually lose its effectiveness, resulting in higher emissions when the engine is restarted. So-called green zones, zones established by legislation or demand of costumers, where the use of combustion engines is prohibited, are a good example of where this can be expected and is therefore a focus of this thesis. The applications are not limited to hybrids but also useful for all vehicles that make stops, e.g., commercial vehicles that make regulated 45 minutes breaks and loading/off-loading cargo. 

A model of a complete hybrid electric heavy-duty vehicle is developed and validated. The model is a compilation of several submodels of the different components in the vehicle. To correctly estimate the pollutive emissions, the components in the aftertreatment system are the most important components and emphasis is put on how the concentrations in them are calculated. It is shown that a quasi-static model for the concentrations gives the best balance in terms of accuracy and simulation time for the application. The aftertreatment system submodels are validated against data from a high-fidelity model and the complete powertrain is validated against experimental data from a powertrain in a test stand, all with satisfactory results. The model is used to create a virtual environment where the effect different control strategies have on the emissions around green zones can be studied and optimized. 

A control strategy based on pre-heating of the aftertreatment system is developed. The strategy heats the aftertreatment before turning off the engine in an optimal way to reduce NOx. This strategy is shown to be effective for engine-off times up to a few hours. However, for longer engine-off times, pre-heating of the aftertreatment system induces a limitation on the amount of stored ammonia, making the strategy ineffective or even bad. The strategy is extended to handle scenarios with multiple engine-off events using an algorithm that finds the engine-off events and handle them separately, but with a common equivalence factor between fuel and NOx to link them. The strategy is shown to handle scenarios with multiple engine-off events well, and the resulting distribution of fuel between the events is close to optimal. 

Using a quasi-static engine model and by assuming instantaneous equilibrium between the gas and substrate temperatures in the aftertreatment system a simplified model with analytical solutions is developed. Using this model, numerical optimal control is used to calculate the optimal way of heating the aftertreatment system above a specific minimum temperature. The results show a two-phase behavior starting with a heating phase, where the front of the aftertreatment system is heated, followed by a blowing phase where the heat is distributed in the aftertreatment system. This stresses the importance of considering both temperature and mass flow and for this a concept called heating enthalpy is introduced. 

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2022. p. 14
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2204
National Category
Control Engineering
Identifiers
urn:nbn:se:liu:diva-182298 (URN)10.3384/9789179291921 (DOI)9789179291914 (ISBN)9789179291921 (ISBN)
Public defence
2022-02-04, Ada Lovelace, B-building, Camous Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2022-01-13 Created: 2022-01-13 Last updated: 2022-01-13Bibliographically approved

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