NREL study finds gasoline hybrid delivery trucks substantially reduce emissions and beat or maintain fuel economy compared to diesel vehicles
24 February 2011
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| 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.
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| 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 (NOx) 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.
Resources
R. Barnitt (2011) FedEx Express Gasoline Hybrid Electric Delivery Truck Evaluation: 12-Month Report (NREL/TP-5400-48896)
If you compare a gHEV to a modern diesel vehicle with particle filter, the 99% advantage in PM emissions attributed to gHEV is gone. Likewise, the NOx advantage will be more or less gone, if the diesel has modern NOx control. Furthermore, there is no law that forbids dHEV (although the relative impact on FC will be slightly less). More examples could be added but in cases like this, it is all about comparing apples to apples.
Posted by: Peter_XX | 24 February 2011 at 04:27 AM
Agree with Peter XX. This study seems superfluous since it states in the NREL report that a 2006 model year diesel vehicle was used. This predates USEPA regulations that significantly restricted emissions in 2007 and even further restricted emissions (mainly for NOx) in 2010.
A more useful study would be to compare a 2010+ model year diesel vehicle to a 2010+ gHEV.
Posted by: Carl | 24 February 2011 at 06:08 AM
Nothing new here. Everybody already know that hybrids consume a lot less fuel than pure gasoline ICE and even less than many diesel ICE units and therefore pollute less.
Posted by: HarveyD | 24 February 2011 at 07:40 AM
You have to wonder how this comparison would have come out if the trucks used the 3.5 liter Ecoboost.
Posted by: Engineer-Poet | 24 February 2011 at 07:56 AM
Why didn't they compare gHEV to dHEV?
Posted by: ai_vin | 24 February 2011 at 09:19 AM
With oil at $100+/barrel, hybrids and partially/fully electrified vehicles will become more and more interesting.
With food prices rising fast, the world can expect more and more uprisings and oil price could snowball.
Going to corn based ethanol will make it worse.
Posted by: HarveyD | 24 February 2011 at 09:49 AM
In the papers conclusion it says: "There was no statistically significant difference in total operating cost per mile between the gHEV ($0.63/mile) and diesel ($0.59/mile) groups." So there is no overall advantage other than emissions???
Posted by: Glien | 24 February 2011 at 11:42 AM
@ Neil Bob: diesel fuel is a distillate so its production produces way more GHG than gasoline which is produced by catatltic cracking. This is also why gasoline is typically cheaper at the pump.
Posted by: nordic | 24 February 2011 at 11:47 AM
I guess you would have lower maintenance costs with the hybrid and less wear on brakes. Also since you can seperate the weight of the engine and the battery it gives you a bit more freedom in the design of the vehicle
Posted by: 3PeaceSweet | 25 February 2011 at 12:44 PM