The CEISMC Gazette

Relieving Gas-Guzzlers of Their Thirst
by Andrew Kerr
June 2008
The CEISMC Gazette

If $4 for a gallon of gas sounds like a lot (and if you are not yet old enough to drive a car, I assure you that it is), consider the fate of those who drive big rigs requiring diesel fuel. They're paying more than half-again that price, and they're filling up enormous fuel tanks. Consider the fact that truckers transport goods and materials across our country, and somebody has to pay for the rising cost of fuel, and you will see a legitimate economic worry. The oil rig in particular has even become a somewhat poetic symbol of oil consumption.

The Georgia Tech Research Institute (GTRI), a sort of think-tank/laboratory (and possibly the most fun place to work at Tech), has a history of thinking outside the cliche. There, GTRI researcher Bob Englar has spent years on a project that might drastically reduce the amount of fuel trucks consume on their journeys. His work has caught the eye of major media, including the New York Times, Washington Post, CNN, the Associated Press, and numerous local news channels in Georgia.

Mr. Englar describes how local television news pieces usually go: "Almost invariably the first thing TV news crews do on their way out to GTRI is stop at a diesel truck stop and film a bunch of truckers filling up their rigs. They'll show the gas pump going around, and before long you see numbers of a thousand to 12 hundred dollars. Then, of course, you see unhappy truckers and then they lead into what we're doing to help out."

When a big rig travels down at road it must overcome a number of forces. "Rolling resistance" (basically, the resistance of rubber to the road, affected by the weight bearing down on those tires) and aerodynamic drag (which, as the name suggests, holds an object back) are the two biggest forces a truck must overcome. When a truck is moving slowly, rolling resistance exerts a greater influence on it; but once it's really flying down the highway the aerodynamic drag becomes a bigger influence.

To address both forces, Mr. Englar has come up with is a way to transform the aerodynamic force that acts against a truck into something beneficial. Thanks to the installation of a "Circulation Control" system, which is one utilizing carefully-controlled bursts of compressed air, aerodynamic drag is turned into pressure applied to the back of the vehicle, pushing the truck along the highway. Mr. Englar has found ways to redirect these forces to push a truck downward--very useful when driving in slippery conditions, not to mention with breaking--as well as counteract side-wind forces (which could conceivably blow a truck over otherwise). One can also do the opposite: apply lift to the truck in order to reduce the amount of pressure on the tires and allow it to glide along a bit more, in this way triumphing over rolling resistance. In all these cases, the compressed air acts as a sort of invisible rudder, serving much the same function as the flaps on an airplane's wings and tail do.

The airplane connection is no coincidence; Mr. Engar's research is an extension of that which he had conducted while in the Navy. As anyone who has caught "Top Gun" on TBS knows, jet planes landing on aircraft carriers hook arresting wires on the deck which rein them in (this prevents them from rolling, rolling, rolling right off the other end of the carrier). As for take-off, they are mechanically catapulted off the carrier like "60,000 pound rocks," in Mr. Englar's words. But the rules of physics can replace the more Neanderthal concepts of arresting wires and catapults. The result of going from these to a Circulation Control system is as significant as going from a Medieval catapult to a V2 rocket. It may mean that big jets could one day use smaller airports (since they could break more effectively on shorter tracks).

Others have tried approaching the same problem (for example, here and here), apparently focusing on increasing the aerodynamicness of the carriage. But Mr. Engar's less-pretty solution, which adds a mere six inches to a truck's trailer, has set the bar extraordinarily high. His system reduced tractor trailer drag by 84% in a wind tunnel test and produced a drag coefficient that is less than a Corvette's. He readily concedes that the system "is not free"; after all, pressure must somehow be produced to move the air around to do all these things. But the concept works, and there are clear benefits.

An interesting aside: if you are considering coming to Georgia Tech as a student, Mr. Engar regularly employs co-op students (those who work part time and study part time) to help out in his lab. Forgive the shameless plug, but that's another pretty good reason to come to Tech. :-)