Just as the aerodynamics of a race car play a role in reaching the finish line, the way a tractor trailer cuts through the air at 65 miles per hour impacts the bottom line. A University of Notre Dame researcher says the aerodynamic drag of a tractor trailer is one of the largest sources of its fuel consumption. He’s putting the brakes on that gas-guzzling factor by improving the aerodynamics of trucks with special attachments called plasma actuators.
“At highway speeds, 65 percent of [the engine’s] horsepower is used to overcome the truck’s aerodynamic drag,” says Director of Notre Dame’s Institute for Flow Physics and Control Dr. Thomas Corke. “That horsepower, obviously, translates into fuel usage.”
Corke’s team has created a method that, in computer models, reduces drag by nearly 23 percent, yielding 11 percent fuel savings at normal highway speeds. The strategy centers on attachments called plasma actuators; the team’s research shows attaching these devices on certain parts of the truck streamlines airflow, which reduces drag.
“[A plasma actuator] locally ionizes the air, then applies an electric field to the ionized air to push the air—or make it, effectively, like a jet of air on a surface,” says Corke. “It’s really very simple; that’s one of the advantages of this. The plasma actuator is, literally, like a decal that you apply to a surface, then just connect electric leads to it and it produces the effect.”
Corke says plasma actuators are an improvement upon the standard solution: flat plate wings, which are four-and-a-half foot flaps that deflect air from the rear of the trailer, are a common sight on highways. They work, says Corke, reducing aerodynamic drag by about 20 percent and fuel consumption by about 10 percent—very similar to the results Corke’s computer models show for plasma actuators.
However, Corke says the four-and-a-half foot plates are “right at the limit” of complying with federal rules for truck extensions, and countries like Australia and Canada limit extensions to just six inches.
“The motivation for using plasma is it’s an active—not passive—flow control approach that can produce an effect like the four-and-a-half foot plates, but do it in a length of about four inches,” says Corke. “Now you have a device that can comply with all of the standards for trucks around the world in a much more compact design.”
The private industry soon caught wind of Notre Dame’s research, and Iowa-based Plasma Stream Technologies has licensed the technology. The startup is working on the first commercial application for the plasma actuators, called eTail. A computer model-based study that Notre Dame completed for Plasma Stream revealed that plasma actuators reduce drag most significantly when placed on the tail of the truck.
To the average person, the strips are hardly noticeable; the four-inch extensions attach along three sides of the trailer’s rear. The actuators connect to a proprietary power supply mounted on the trailer. Plasma Stream is designing the eTail system to automatically activate at 45 miles per hour and believes it will reduce fuel consumption by about 10 percent.
The startup is building prototypes now and will evaluate the design and fuel consumption results in the coming months when it tests the eTail on trucks. It will be the first full-scale test of Corke’s discoveries for the trucking application. Plasma Stream expects to launch limited production of the eTail in early 2018.
In addition to the eTail, Plasma Stream is developing plasma actuators for other “hot spots” on trailers and researching the technology’s use for cars; Plasma Stream cofounder Pranay Bajjuri says General Motors is “very keen” to implementing plasma actuators on its vehicles.
“There’s a huge demand for this,” says Bajjuri. “What we’re creating is very unique. From a commercial viability aspect, I see it being a success if the testing goes well.”
Plasma Stream believes the results could be staggering; American Trucking Associations says diesel fuel cost for motor carriers is second only to labor and can account for as much as 20 percent of total operating costs.
“If you’re talking about a 12 percent fuel economy improvement, and factor in how many hours per day the truck is at highway speeds, how many trucks you have in your fleet and the cost of fuel,” says Corke, “that comes up with significant savings.”
Corke says the plasma actuators produce better results and are more compact than the four-and-a-half foot wings currently used.
Corke says the technology produces 22 percent drag reduction and 11 percent fuel savings in “perfect” conditions.