NREL study finds 2nd-generation diesel hybrid delivery vans show significant gains in fuel economy over conventional vans
29 September 2012
|Laboratory and in-use fuel economy results Source: NREL. Click to enlarge.|
The US Department of Energy’s (DOE)’s National Renewable Energy Laboratory (NREL) has published a report on an 18-month evaluation of in-service second-generation diesel-electric hybrid delivery vans and found significant fuel economy benefits of the hybrids compared to similar conventional vans.
The NREL team collected and analyzed in-service fuel economy, maintenance, and other vehicle performance data on 11 hybrid (P100H) and 11 conventional diesel (P100D) step vans operated by the United Parcel Service (UPS) in Minneapolis. The two study groups were on different duty cycles and required a route switch to provide a valid comparison, which UPS accommodated. The hybrid group accumulated 33% fewer miles than the conventional group during the complete 18-month study. The team also performed dynamometer testing at the Renewable Fuels and Lubricants (ReFUEL) Research Laboratory in Denver.
The NREL team evaluated fuel economy during equal 5-month periods from different years. During the second period, the route assignments originally assigned to the conventional and hybrid van groups were swapped so that the conventional vehicles were assigned to the original hybrid van routes and vice versa.
During the on-road portion of our study, the hybrid vans demonstrated a 13 to 20 percent higher fuel economy than the conventional vans. During dynamometer testing, three standard drive cycles were chosen to represent the range of delivery routes. The hybrids showed a 13 to 36 percent improvement in fuel economy and up to a 45 percent improvement in ton-miles-per-gallon. This wide range in fuel economy is largely dependent on drive cycle.—NREL Project Engineer Michael Lammert
The team found that the fuel economy of the hybrid group on the original conventional route assignments over 5 months was 10.4 mpg, 13% greater than the 9.2 mpg of the conventional group on those routes a year earlier.
They also found that the fuel economy of the hybrid group on the original hybrid route assignments over 5 months was 9.4 mpg, 20% greater than the 7.9 mpg of the conventional group on those routes a year later.
The difference in hybrid advantage in fuel economy is as expected. The hybrids demonstrated a greater advantage on the initial hybrid route assignments, which were more “urban” (low speed, high stops-per-mile routes) and lower advantage on initial conventional route assignments with a longer highway leg and less dense delivery zones.—“Eighteen-Month Final Evaluation of UPS Second Generation Diesel Hybrid-Electric Delivery Vans”
The reliability of the hybrids was slightly lower, 92.5% compared to 99.7%, in part due to troubleshooting and recalibration issues related to prototype components, Lammert said. The differences in per-mile maintenance and operating costs were not statistically significant.
|Primary hybrid components arranged in the undercarriage of a UPS delivery van. Source: NREL. Click to enlarge.|
The hybrids studied represented a second-generation,an evolution from UPS’ original 50 Eaton hybrids that NREL documented in earlier studies. The new hybrids have more advanced control algorithms and an integrated “engine off at idle” feature that automatically stops and restarts the engine at stoplights and other short stops when certain conditions are met.
The revised Eaton hybrid system consists of a Fuller medium-duty automated manual 6-speed transmission; a synchronous brushless, permanent magnet motor delivering continuous power of 26 kW and peak power of 44 kW; a 340 VDC Li-ion battery pack with 1.8 kWh capacity; and power electronics.
NREL has been working in partnership with UPS for five years to track and evaluate the performance of its hybrid vehicles. The first study, performed in 2008, focused on first-generation hybrid vans operated by UPS in Phoenix. (Earlier post.) In 2010, UPS deployed 200 second-generation hybrid vans to eight US cities, including the 11 under study in Minneapolis.
M. Lammert and K. Walkowicz (2012) Eighteen-Month Final Evaluation of UPS Second Generation Diesel Hybrid-Electric Delivery Vans. NREL/TP-5400-55658
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