Rising Costs Renew Interest in Fuel-Saving Techniques

Tag : fuel products

The dramatic increase in diesel prices has led the truckingindustry to reconsider aerodynamic fuel efficiency improvementsthat might not have been cost effective only a few years ago, saidRobert Englar, a GTRI principal research engineer and principalinvestigator for the project. Though there are technicalchallenges ahead, we believe our techniques for improving fuelefficiency offer significant potential to reduce the impact ofthese fuel cost increases. Beyond the trucking industry, that wouldhelp consumers who see the effects of fuel costs in everything theybuy.

Since diesel prices began their rapid increase, Englar has seengrowing interest in the GTRI low-drag active flow controlaerodynamic technologies, which were developed with support fromthe U.S. Department of Energy starting in the late 1990s. He hasreceived numerous inquiries for information from both large andsmall trucking companies, and also from railroads  whosehigher-speed western track runs could also benefit from aerodynamicdrag reduction.

Aerodynamic drag is the major component of heavy vehicle resistanceat typical highway speeds, and overcoming that resistance requiresincreased energy use. Truck designers have reduced drag on thetractor portion of the vehicles by applying such aerodynamicstreamlining approaches as roof fairings, but those have donelittle to address drag on the aft portion of the trailers.

Because only limited streamlining can be done for trailers due totheir length, the GTRI researchers added the active flow controltechniques, which use patented pneumatic devices to blow air fromslots over small curved aerodynamic surfaces at the rear of thetrailers. These air jets smooth the flow of air over the boxytrailers to eliminate air-flow separation, vorticity and suction onthe aft doors, which reduces aerodynamic drag at highway speeds.

The researchers also evaluated aerodynamic improvements thatinvolved rounding aft trailer corners, installing fairings aroundwheels and making other changes designed to better streamline thetrailers.

These active flow control techniques are based on aerodynamicresearch done during the 1980s for applications on U.S. militaryaircraft. Beyond the fuel savings, they have also been shown toenhance braking and directional control for the heavy truckswithout using any moving external parts, potentially improvingsafety.

Aerodynamically, we have resolved unknowns raised in earliertesting, and the next step is to get this into a fleet of trucksfor more extensive testing, Englar said. At highway speeds, eachone percent improvement in fuel economy would result in savingabout 200 million gallons of fuel for the U.S. heavy truck fleet.We believe that is worth pursuing.

The fuel efficiency project began in the late 1990s with tests ofsimple scale model tractor-trailers in GTRIs low-speed windtunnel. The researchers then applied those principles to afull-sized test truck, working with Volvo Trucks of North Americaand Great Dane Trailers, manufacturers of the basic test tractorand trailer respectively.

A series of Interstate-speed test runs at the TransportationResearch Centers Ohio fuel-economy test track have demonstratedsubstantial fuel savings. The tests involved operating a testtractor-trailer for several different 45-mile runs around a7.5-mile oval track at highway speeds of 65 and 75 miles per hour.A control truck that did not have either the aerodynamicimprovements or pneumatic flow control system was operated underthe same conditions to provide a comparison. For additionalcomparisons, the test truck was also run without the experimentalblowing equipment.

The tests showed that the techniques could provide drag coefficientreductions of up to 31 percent, which translates to a fuelefficiency increase of 11 to 12 percent. When the energy requiredby the air compressor installed on the truck to provide thecompressed air for these prototype tests was subtracted from thosesavings, those tests showed that the low-drag techniques couldproduce an overall fuel efficiency increase of 8 to 9 percent.

Before the pneumatic control system can be widely used in trucks,however, researchers will have to choose the best source ofcompressed air for the blowing system, Englar notes. An aircompressor more efficient than the one used in the testing wouldprovide higher overall fuel efficiency. Options include a smalldiesel-powered compressor installed on or under the trailer likecurrent refrigeration units; bleeding pressurized air from thetrucks supercharger/turbocharger, or a simple chain drive from thetrailers wheels to turn air blowers.

Other practical issues  such as protecting the pneumatic surfacesfrom damage during docking  still must be resolved. A simplesolution, Englar noted, could be to use stiff rubber surfaces.

Beyond boosting fuel efficiency, the pneumatic system can alsoprovide a form of aerodynamic braking to assist the mechanicalbrakes. The pneumatic systems can turn a low-drag configurationinto a high-drag configuration very rapidly, providing a lot morebraking power, Englar said. By turning the trailer into anon-moving pneumatic rudder, blowing can also restore directionalstability should the truck be operating in destabilizing high sidewinds.

Further energy savings could come using a pulsed pneumatic system,which preliminary wind-tunnel studies show could produce the sameaerodynamic efficiency with 40 to 50 percent less energy consumedby the blowing system. Englar hopes to receive additional fundingto study how this might affect the truck aerodynamics  as well asfuel consumption.

The ultimate proof would be to apply this overall aerodynamicsystem to a small fleet of heavy trucks and run them on theirnormal cross-country routes for a month or so to measure theoperational increases in fuel efficiency and safety, Englar said.

Details of this project were presented at the SAE CommercialVehicle Engineering Congress in November 2005: [Englar, Robert J.Improved Pneumatic Aerodynamics for Drag Reduction, Fuel Economy,Safety, and Stability Increase for Heavy Vehicles, SAE paper2005-01-3627.]


Technical Contact: Robert Englar (404-407-6222); E-mail:(bob.englar@gtri.gatech.edu).
John Toon | Source: newswise
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