NREL study finds gasoline hybrid delivery trucks substantially reduce emissions and beat or maintain fuel economy compared to diesel vehicles

Criteria emissions by drive cycle. Source: Barnitt 2011. Click to enlarge.

NREL’s Fleet Test and Evaluation Team recently completed a year-long technology evaluation of gasoline hybrid electric (gHEV) FedEx Express delivery trucks compared with conventional diesel vehicles. The team found that the gasoline hybrid electric (gHEV) trucks produced substantially reduced tailpipe emissions during all drive cycles tested in the laboratory when compared to conventional diesel vehicles.

On a drive cycle representing routes with frequent stops and accelerations, the gHEV trucks exhibited a 20% improvement in fuel economy. On drive cycles representing routes with fewer stops and accelerations, the gHEV trucks demonstrated similar fuel economy to the diesels. A report on the work was written by Robb Barnitt of the Center for Transportation Technologies and Systems.

FedEx Express has deployed 20 gasoline hybrid electric vehicles (gHEVs) on parcel delivery routes in the Sacramento and Los Angeles areas. These gHEVs are built upon a Ford E-450 strip chassis, and each vehicle is powered by a Ford 5.4L gasoline engine and Azure Dynamics, Inc. (AZD) Balance Hybrid System.

Influence of route kinetic intensity on fuel economy. Source: Barnitt 2011. Click to enlarge.

The AZD parallel hybrid system consists of a 100 kW AC induction motor with regenerative braking; a 120 kW inverter; electric 5-speed Torqshaft automatic O/D transmission; and Cobasys 288 V, 60 kW, 8.5 Ah NiMH battery pack. The system operates at 288 VDC nominal, and uses a separate low-temperature cooling loop.

The report presents the results of parcel delivery drive cycle data collection and analysis activities; 12-month in-use fuel economy and maintenance costs; and emissions and fuel economy results of chassis dynamometer testing of a gHEV and a comparative diesel truck at the National Renewable Energy Laboratory’s (NREL’s) Renewable Fuels and Lubricants (ReFUEL) laboratory.

The drive cycle data collection and analysis effort framed the selection of study vehicles and routes and structured the measurement of vehicle emissions and fuel economy on the chassis dynamometer at NREL’s ReFUEL laboratory. Tailpipe emissions from the gHEV were substantially lower across all three tested drive cycles than emissions from the diesel baseline vehicle. Notably, the gHEV exhibited 75–89% lower oxides of nitrogen (NO_x) and over 99% lower particulate matter.

Laboratory-measured diesel-equivalent fuel economy was similar between the gHEV (7.3 – 11.4 mpg) and diesel vehicle (6.1 – 11.7 mpg). On the most kinetically intensive drive cycle tested in the laboratory, the hybrid exhibited 21% higher fuel economy than the diesel. There was no statistical difference in calculated on-road diesel equivalent fuel economy for the gHEV (7.5 mpg) and diesel (7.9 mpg) study groups. The fuel economy findings are encouraging considering that gasoline engines in general have lower fuel economy than diesel engines. These gHEV’s were able to provide similar or improved fuel economy while also providing significantly reducing emissions.

—Barnitt 2011

The team also found no statistically significant difference in fuel cost per mile or maintenance cost per mile between the gHEV and diesel groups. As a result, there was no statistically significant difference in total operating cost per mile between the gHEV ($0.63/mile) and diesel ($0.59/mile) groups.

The evaluation was part of a collaborative effort co-funded by the US Department of Energy’s (DOE’s) Vehicle Technologies Program and the South Coast Air Quality Management District (SCAQMD) via CALSTART. The in-use technology evaluation was conducted by NREL and primarily sponsored by DOE. The chassis dynamometer testing was conducted by NREL and primarily funded by SCAQMD via CALSTART.

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