High diesel fuel prices are putting the pinch on the trucking industry, especially independent owner-operators, many of whom already operate on small profit margins. The current spike in fuel costs has led some to park their rigs for good.

There are a number of ways to increase fuel economy in a heavy-duty truck. Many have to do with engines and drivetrain systems. Another revolves the reduction of efficiency-killing aerodynamic drag.

This can be achieved using aerodynamic improvements and airflow control techniques based on technology developed for jet aircraft wings. Using this technology, the research currently underway at Georgia Institute of Technology's Georgia Tech Research Institute (GTRI) could turn a trucker's bottom line from red to black. It could also save the U.S. trucking industry, and the nation, hundreds of millions of gallons of fuel per year, much of which is imported.

As an example of the potential, recent SAE Type-II Furl Economy tests using a full-size tractor-trailer truck equipped with this technology show that these techniques increase furl economy by as much as 11 to 12%. According to Robert Englar, principal research engineer in the GTRI's Aerospace, Transportation and Advanced Systems Laboratory, "at highway speeds, each 1% improvement in furl economy results in savings of about 200 million gallons of furl per year for the U.S. heavy truck fleet."

GTRI's research indicates that geometry changes, like rounding the rear corners of trailers, installing fairings over rear wheels and other efforts to smooth the airflow over boxy trailers can produce furl savings of up to 6 to 7%. Another 5% improvement can be achieved by installing pneumatic devices that blow air from slots at the rear of the trailer to prevent airflow separation that normally increases drag.

Improving the aerodynamics of big rigs is not a new concept as research on smoothing heavy-duty trucks dates back several decades. The fairings now seen above many tractor cabs made their initial appearance during the energy crisis of the early 1970s.

This particular project, sponsored by the U.S. Dept. of Energy, actually began in the 1990s with tests of simple scale model tractor-trailers in GTRI's low-speed wind tunnel. While these early experiments with simple models promised dramatic fuel savings, the results from testing on full-scale test vehicles fell short of expectations. The GTRI researchers went back to the wind tunnel with more realistic truck models to study lessons learned from the first tests and made appropriate changes.

Englar's research team worked with truck manufacturer Volvo Trucks of North America and trailer builder Great Dane Trailers in this latest research. With the help of Novatek Inc., a prototype shop in Smyrna, Ga., GTRI installed a new set of aerodynamic devices and revised the blower system fitted on the test trailer. When tested at the Transportation Research Center fuel economy test track in Ohio last fall, these modified devices now showed the real fuel savings that had been expected earlier.

The test truck equipped with the aerodynamic improvements and the blower device made different 45-mile runs around a 7.5-mile oval at speeds of 65 and 75 mph. To quantify the fuel savings, a control truck without the aerodynamic improvements or blower device was operated under the same conditions. For additional comparisons, the test truck was also run without the experimental blower equipment.

"We have shown that this technology now works quite successfully," Englar concluded, "and we expect that the industry will find a potential 12% fuel economy improvement worth pursuing."

Besides reducing aerodynamic drag, wind tunnel tests have confirmed that the techniques could also enhance braking and directional control to improve the safety of big rigs. For instance, the pneumatic system can provide aerodynamic braking to assist the normal air brakes by quickly turning the trailer from a low-drag configuration into a high-drag configuration to provide much more braking power. Differential blowing--that is different amounts of airflow control around the trailer--could improve control in crosswinds by helping compensate for aerodynamic side loads resulting from the wind direction. Both the improved braking and directional control would most likely be automatic so it would not require any action from the driver.

While test results show great promise, there is much to be done before systems would be ready for widespread use in the trucking industry. For example, the best source of compressed air for the blower system has to be selected. Choices include a diesel-powered engine installed on the trailer, similar to current refrigeration units. Other options include bleeding pressurized air from the engine turbocharger or a simple chain drive attached to the trailer's wheels to turn air blowers. Since aerodynamic drag becomes an issue only at higher speeds, the blower system would be turned off when the trucks were idling or operating at low speeds.

Further energy savings, about half to three-quarters of the fuel needed by the pneumatic system, could be achieved using a pulsed rather than a continuous blower system, a phenomenon also confirmed at GTRI by recent wind-tunnel tests on blown wings for NASA.

Other practical considerations include reducing costs of the technology to the point where the investment to install the equipment has a realistic payback time. Also the devices cannot interfere with loading and unloading, be easily damaged during docking or compromise safe truck operation.


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