A Simulation Study on Fuel Economy and Emissions of Parallel Hybrid Transit City Buses

Zhiming  Gao, ORNL

A Simulation Study on Fuel Economy and Emissions of Parallel Hybrid Transit City Buses

Zhiming Gao, Tim J. LaClair, C. Stuart Daw, David E. Smith
Oak Ridge National Laboratory

Abstract

Transient city bus is one of important transportation tools. Most city transit buses travel for more than ten hours and cover a hundred miles daily along local stop-and-go routes. The high frequency of stop-and-go and idling operation would appear to make transit buses good candidates for electric hybridization. However, despite the expected potential benefits, MD bus hybridization is still at a relatively early stage of development. In this poster, we present our simulated results for fuel economy and emissions of city transit buses powered by conventional diesel engines and diesel-hybrid electric powertrains of varying size. Six representative city drive cycles were included in this study. In addition, we included full aftertreatment device models for control of CO, HC, NOx, and particulate matter (PM) emissions. Our results reveal that bus hybridization significantly enhance fuel economy by reducing engine idling time, reducing demands for accessory loads, exploiting regenerative braking, and shifting engine operation to speeds and loads with higher fuel efficiency. Increased hybridization also tends to monotonically reduce engine-out emissions, but tailpipe (post-aftertreatment) emissions are affected by complex interactions between engine load and the transient catalyst temperatures, and the emissions results were found to depend significantly on motor size and details of each drive cycle.

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