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Analysis of the fuel economy improvement potential of ethanol hybrid buses
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.ORCID iD: 0000-0002-1691-091X
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.ORCID iD: 0000-0002-0635-7372
2011 (English)In: Proceedings of the 24th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, ECOS 2011, Nis University , 2011, 2220-2229 p.Conference paper (Refereed)
Abstract [en]

With the ambitions to further increase its share of renewable fuels and to reduce the amount of carbon dioxide emissions, local emissions and noise, Stockholm Public Transport (SL) hosted a one-year project to evaluate the performance of ethanol hybrid buses. An important part of the project was the duty cycle tests according to SORT - Standardised On-Road Tests cycles (developed by the International Association of Public Transport, UITP). The duty cycle tests generated experimental data, on which this paper’s discussion is based upon. The purpose of this article is to evaluate the potential of energy-efficiency improving measures on the powertrain. The ethanol hybrid bus is a series hybrid vehicle with regenerative braking. A start/stop software to avoid idling was optional. A bus with similar exterior properties, but with the ethanol internal combustion engine coupled to a conventional automatic gearbox instead of a hybrid powertrain was used as a reference throughout the project. Based on both experimental data and simulations, several measures to increase the overall energy-efficiency may be proposed. Assessed measures to increase the energy-efficiency include size optimization of powertrain components, such as energy storage and electric motor, and internal combustion engine (identified by using Sankey diagrams), adjustment of the super capacitors energy management system and utilisation of engine start/stop functionality. Analysis shows that the size of the energy storage is well attuned if applied as urban transport. It would be possible to downsize the ICE, from approximately 200 kW to approximately 150 kW, without losing substantial performance. Using the start/stop software reduces the fuel consumption with 15 % in the standardized city duty cycle but has the potential for even further fuel economy improvements in real traffic with more idling.

Place, publisher, year, edition, pages
Nis University , 2011. 2220-2229 p.
Keyword [en]
Ethanol hybrid bus, Series hybrid, Energy efficiency, Energy flow analysis, Sankey diagrams
National Category
Energy Systems
URN: urn:nbn:se:kth:diva-107440ScopusID: 2-s2.0-84903642241ISBN: 978-866055016-5OAI: diva2:575926
The 24th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, July 4-7 2011, Novi Sad, Serbia

QC 20130604

Available from: 2012-12-11 Created: 2012-12-11 Last updated: 2015-09-16Bibliographically approved
In thesis
1. Electric vehicles in action
Open this publication in new window or tab >>Electric vehicles in action
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis analyses the political and practical conditions for introducing electric vehicles in Swedish public authorites and discusses the potential for using electric vehicles in public transport and public fleets. The work has been carried out using an interdisciplinary research approach. Such an approach brings new insights to energy studies; the combination of technical methods and methods from social science allows the technology to be studied in its societal context.

Local self-government enables Swedish public authorities to implement local solutions in order to achieve national policy goals. However, the results show that for energy and transport policy a clear allocation of responsibilities between local and regional levels is lacking – and this clarity is also lacking between the different policy areas. The lack of policy integration implies a risk that local policy development can miss the mark when it comes to the overall policy goal. Furthermore, findings show that so-called policy entrepreneurs can succeed in putting electric vehicles on the political agenda, and they can enforce decisions and deploy the vehicles within the public bodies.

The usage of plug-in electric vehicles in public fleets has been studied using (among other sources) logbooks, interviews, questionnaires and focus groups. Findings demonstrate a great potential to introduce plug-in electric vehicles through fleets. Although the usage varied slightly during the year, and winter conditions implied a general reduction in use, the results show that the deployment strategy is a central factor for the extent of the vehicle usage. Vehicles that are assigned a certain user or a specific task show a high degree of utilisation. Even though plug-in electric vehicles available through car-pools have a large potential group of users, the options also implies that users can instead choose a conventional vehicle. However, interventions to increase usage have proven to be successful. Policy entrepreneurial actions attract new users and revising organisational regulations, i.e. vehicle or environmental policies, shapes new behaviours. In this study, fleet vehicle users have proven to be relative indifferent to which fuel or technology they use, but acceptance for operation failure is very low.

Based on a demonstration project of series hybrid buses in regular service, the possibility of increased electrification of public transport is discussed. The contribution of hybridisation is analysed through assessment of different types of driving conditions. Results show that significant improvements in energy efficiency can be achieved but, because actual and optimal driving conditions differ, there is a risk of overestimating the contribution.

Sweden has set very ambitious national targets for its road transport system, i.e. to be fossil-fuel independent by 2030, and electrification is an important measure in reaching this goal. Given the magnitude of the challenge, it is not only the responsible thing to do; findings also show several advantages of introducing electric vehicles in the public sector first. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. x, 71 p.
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:50
electric vehicles, interdisciplinary approach, public fleets, public transport
National Category
Chemical Engineering
urn:nbn:se:kth:diva-173647 (URN)978-91-7595-689-3 (ISBN)
Public defence
2015-10-09, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 13:30 (English)
Swedish Energy Agency

QC 20150916

Available from: 2015-09-16 Created: 2015-09-16 Last updated: 2015-09-16Bibliographically approved

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