Abstract
The fuel economy and emissions of conventional and hybrid buses
equipped with emissions aftertreatment were evaluated via computational
simulation for six representative city bus drive cycles. Both series
and parallel configurations for the hybrid case were studied. The simulation
results indicated that series hybrid buses have the greatest overall
advantage in fuel economy. The series and parallel hybrid buses were
predicted to produce similar carbon monoxide and hydrocarbon tailpipe
emissions but were also predicted to have reduced tailpipe emissions
of nitrogen oxides compared with the conventional bus in higher
speed cycles. For the New York bus cycle, which has the lowest average
speed among the cycles evaluated, the series bus tailpipe emissions
were somewhat higher than they were for the conventional bus; the parallel
hybrid bus had significantly lower tailpipe emissions. All three bus
power trains were found to require periodic active diesel particulate filter
regeneration to maintain control of particulate matter. Plug-in operation
of series hybrid buses appears to offer significant fuel economy
benefits and is easily employed because of the relatively large battery
capacity that is typical of the series hybrid configuration.
