Tuesday, June 14, 2011

Gasoline Hybrid Electric Delivery Vehicles Reduce Tailpipe Emissions While Maintaining Fuel Economy

The U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) recently completed a yearlong technology evaluation of gasoline hybrid electric (gHEV) trucks compared with conventional diesel vehicles. A report detailing NREL’s efforts to determine the impact of hybridization on performance, emissions, and fuel economy is available at http://www.nrel.gov/vehiclesandfuels/fleettest/pdfs/48896.pdf.

The 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 percent improvement in fuel economy while drive cycles representing routes with fewer stops and accelerations demonstrated similar fuel economy to the diesels.

“We conducted this study to show how a gasoline hybrid might perform compared to a conventional diesel truck given that gasoline engines are less efficient than diesel engines and generally not used in heavier vehicles,” said Lee Slezak, program manager for DOE’s Advanced Vehicle Testing Activity.

NREL’s Fleet Test and Evaluation Team collected and analyzed fuel economy, maintenance, and other vehicle performance data on three gHEV trucks and three conventional diesel trucks used for FedEx parcel delivery service in the Los Angeles area. The team also tested a hybrid and conventional truck at NREL’s Renewable Fuels and Lubricants Research Laboratory in Denver, Colo.

“Southern California continues to experience the worst air quality in the nation, and transitioning heavy-duty vehicle fleets to cleaner-burning vehicle technology is an important element of our overall clean air goals,” said Barry R. Wallerstein, executive officer of the South Coast Air Quality Management District.

Manufactured by Ford, the gHEV trucks feature 5.4L gasoline engines and hybrid propulsion systems produced by Azure Dynamics with 100kW electric motors, regenerative braking, and nickel-metal-hydride batteries.

FedEx Express operates more than 32,000 motorized vehicles in the United States, including 20 gHEVs on parcel delivery routes in Los Angeles and Sacramento, Calif. The FedEx Express hybrid fleet, which has driven more than 8 million miles in revenue service, includes an all-hybrid station in Bronx, N.Y., where nearly half of the vehicles are gHEVs.
Six similar trucks were selected for this in-use evaluation project. Three of the trucks are gHEVs, and three are conventional diesel trucks that serve as a control group. Comparison data were collected and analyzed for in-use fuel economy and fuel costs, maintenance costs, total operating costs, and vehicle uptime. Based upon the data collected during this study, there was 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.
In-use maintenance data were supplied by FedEx Express and transmitted to NREL for analysis. NREL removed warranty items and associated costs from this comparison. During the study period, the gHEVs had labor and parts warranted, while the diesel vehicles did not. Had warranty costs been included, the total gHEV maintenance costs for the study period would have been $6,815, or $0.229/mile. Maintenance data for the study period are presented below (Figure 8 and Table 11). There is no statistically significant difference (two-tailed P value of 0.637) in maintenance cost per mile between the gHEV and diesel groups.
During the study period, no brake repairs were performed on the hybrid vehicles; this was an expected result due to their low mileage and regenerative braking capability. Diesel trucks D670 and D830 had two-wheel brake replacements during the study period, for a total cost of $220.04. FedEx Express examines brakes every time preventive maintenance is performed and replaces them as necessary. Quantifying any differences in brake maintenance costs between the gHEV and diesel vehicle groups may require a study period in excess of 12 months. At the time of this study, FedEx Express did not provide a brake life metric for their W700 fleet.
The full report is available free of charge at http://www.nrel.gov/vehiclesandfuels/fleettest/pdfs/48896.pdf
This evaluation was funded by DOE’s Vehicle Technologies Program with additional funding from CALSTART and the South Coast Air Quality Management District.

National Renewable Energies Laboratory (NREL) www.NREL.gov, The Department of Energy’s primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for DOE by The Alliance for Sustainable Energy, LLC.
February 23, 2011

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