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First experiences of ethanol hybrid buses operating in public transport
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.ORCID iD: 0000-0002-1691-091X
(Scania CV AB)
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.ORCID iD: 0000-0002-0635-7372
2011 (English)Conference paper, Presentation (Refereed)
Abstract [en]

With the ambitions to further increase its share of renewable fuels and to reduce the amount of local carbon dioxide emissions and noise, Stockholm Public Transport (SL), together with bus manufacturer Scania and bus operator Nobina, hosted a one year project to evaluate the performance of ethanol hybrid buses. Six ethanol hybrid buses were operating in regular public transport between June 2009 and June 2010. During this period the buses were operating at three different suburban routes. The purpose was to accumulate experimental data and to validate the robustness of the ethanol hybrid system and its components. In addition, in order to obtain comparable data, standardized duty cycle tests were performed. Furthermore, with the objective to assemble experimental data during heavy traffic and low mean velocity conditions, two urban routes were selected for staged tests with one ethanol hybrid bus.

The purpose of this paper is to evaluate the energy efficiency of the electrified driveline and hybrid components of the Scania ethanol hybrid bus based on experimental data.

The bus is a series hybrid vehicle with regenerative braking. A start/stop software to avoid idling was optional. The key components of a series hybrid are internal combustion engine, generator, energy storage, electric engine and resistor. The energy storage was commercially available super capacitors. The components of the electric powertrain were developed and delivered by Voith Turbo. A bus with identical exterior properties, an ethanol internal combustion engine coupled to a conventional automatic gearbox but without a hybrid system was used as a reference throughout the project. The measurement equipment was installed in the hybrid system to capture energy flows in and out of key components. Parallel logging of GPS coordinates generated a velocity profile which coupled with energy flow data constitute to the foundation of the analysis.

The main results are presented as Sankey diagrams visualizing the energy flow through the electrified powertrain and determines the energy efficiency for each of the different traffic situations. The initial experimental results indicate that the reduction of fuel consumption benefits from routes with low mean velocity and a high number of stop. At such favorable conditions the fuel reduction are in the order of 30 %. The potential additional fuel savings of the start/stop software has been simulated and adds another 5-10 % fuel reduction. Not all of the hybrid system’s components are not yet robust enough and need further development. The super capacitors work consistent and are suitable as energy storage for this application. 

Place, publisher, year, edition, pages
Keyword [en]
Ethanol hybrid bus, Series hybrid, Duty cycle, Urban public transportation
National Category
Energy Systems
URN: urn:nbn:se:kth:diva-107424OAI: diva2:575874
World Renewable Energy Congress, May 8-13 2011, Linköping, Sweden

QC 20130527

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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