Using novel drivetrain technologies in city buses has the potential to decrease harmful exhaust emissions, noise emissions and energy consumption in urban areas. Even if the technology is still on the threshold of full marketability, the question about quantifiable test data concerning those emissions arises. In two subsequent research programmes, those research topics are covered with an extensive measurement and testing campaign. Within the first research project the exhaust gas emissions of two conventional diesel buses were analyzed on 16 bus lines operated by the Transport Organisation Rhine-Ruhr. Based on route characteristics eight lines were chosen on which the hybrid buses of each manufacturer were tested in two test series. Comparing the emissions of the articulated buses with conventional and hybrid drivetrain architectures, the reduction of direct NO2-emissions by 74.9% stands out from the conventional diesel buses, while the total NOx-emissions of the hybrid buses were lower as well. Furthermore an average reduction of the CO2-emissions by 10.3% was achieved. A comparison between the solo buses was only possible using older measurements which were made in the city of Hagen. The average reduction of NO2-emissions was 53.9% while CO2-emissions were reduced by 21% in average. On the other hand the NOx-emissions of the hybrid buses were higher by 6.2%. In general the obtained results of the work package noise emissions and acceptance validate the potentials of hybrid buses for a reduction of noise emissions (interior and exterior noise) as well as an enhanced passenger comfort. Nevertheless, the specific noise behavior is strongly dependant on the vehicle type, the hybrid system architecture and furthermore the operating conditions. Some hybrid buses were able to achieve a reduction up to 10 dB (A) sound pressure level (peak values) inside the passenger compartment compared to the standard diesel buses. For the external noise emissions a reduction up to 12 dB (A) could be measured. In contrast, some of the investigated hybrid bus concepts showed no real advantages compared to standard diesel buses when referring to maneuvers with practical relevance like leaving a bus stop. However, the mean interior noise level of all investigated hybrid buses is lower than the mean interior noise level of the measured diesel buses. Thus a lower noise exposure to the passengers is achieved. Referring to the passenger survey, a positive acceptance of the hybrid buses could be verified. The evaluation of long term data supports the general trends that surfaced during the measurement test runs. While the early hybrid vehicles show a high potential of saving fuel under real world driving conditions, it is crucial to optimize the operating conditions first. Otherwise, is also possible to achieve higher fuel consumption figures under adverse lane characteristics. The results generated during the first programme show a high distribution range that needs to be countered by a larger control sample and a longer duration in the subsequent study. In summary it can be stated, that buses with hybrid propulsion systems show promising potentials for the reduction of exhaust and noise emissions. Generally speaking, the acceptance in public is positive. None the less, additional technical development and optimization measures are mandatory for all investigated hybrid buses in order to exploit these potentials as benefits in daily practice.
City buses with alternative power trains under realistic driving conditions. Results of the accompanying research
2013
30 Seiten, 29 Bilder, 7 Quellen
Conference paper
English
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