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Hybrid Electric School Bus Technical Feasibility
ISSN: 0148-7191, e-ISSN: 2688-3627
Published November 01, 2005 by SAE International in United States
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The hybrid electric vehicle is currently changing the automotive market at an impressive rate. While not as highly publicized, the transit bus market is being transformed at an equal rate. As these markets move forward, the school bus market remains largely unchanged. As an unchanged market, there is still the opportunity to optimize a hybrid vehicle platform for school buses.
This study begins the modeling process of an existing class C school bus and investigates the potential that both series and parallel hybrids hold to reduce fuel consumption and emissions for a school bus. The primary focus of this study is to investigate the potential benefits of adding an electricity grid interconnection to hybrid electric school buses, allowing them to add to the hybrid potential with a pre-charged battery pack from the electric utility grid. These vehicles are known as plug-in hybrids.
The school bus models shown in this paper were generated in a Matlab/Simulink-based program developed by NREL called ADVISOR. ADVISOR is used by vehicle manufacturers as a tool to experiment with different vehicle configurations. In this study both a generic series hybrid and a generic parallel hybrid are generated and then each is used in both charge-sustaining and charge-depleting scenarios with varying sizes of battery packs to increase the “grid energy.” The results of each model are presented by both fuel economy and emissions reductions taking into account the power plant emissions and electricity costs.
The results of the study show that by adding a plug-in connection to existing hybrids, significant savings can be achieved, both in fuel costs and in overall emissions. By analyzing the emissions both at the power plant level and at the vehicle level we show that emission of NOx, Particulate Matter and Carbon Dioxide emissions can all be reduced while saving on fuel costs. This study also shows that some models of traditional hybrid can be operated as plug-in models with little or no change to the system to gain significant benefit from the initial charge.