Stocking Tractor-Trailers with MPGs
The semi-trucks you see on the highway were primarily designed for storage and transportation and not necessarily energy efficiency. Therefore, it may not be surprising that according to HPC for Energy, these trucks constitute 12 percent of the fuel consumption in the United States.
But work done by Navistar in concert with the Lawrence Livermore National Laboratory showed that a significant portion of that fuel consumption could be reduced by simple changes to the structure of the tractor-trailer.
They began by using a one-eight scale model of a semi-truck inside a wind tunnel to run various tests. With HPC modeling and simulation, HPC for Energy reports that they were able to extrapolate various windy conditions based on these small-model tests. From there, they could begin running optimization programs to target fuel economy.
Ultimately, the LLNL and Navistar proposed four alterations to be made to optimize aerodynamic conditions. A base at the end of the trailer would give the truck a more rounded feel, thus allowing the air flow more smoothly around it. A similar adjustment to the underbody of the trailer would introduce an element of lift (not enough, of course, to lift the trailer off the ground) that would reduce the mechanical weight of the truck as it went at higher speeds. This would also serve to reduce the drag on the back axle.
The third adjustment introduces a small barrier between the cabin and the trailer that prevents air from flowing between the two to further bring down the drag force.
The final suggestion is friction-related, as Navistar and LLNL recommend replacing the common two back tires with a single oversized tire to decrease rolling resistance.
According to the presentation, the proposed modifications could save up to 4.6 billion gallons of fuel per year in the United States alone, cutting semi fuel usage by 17%. As such, these trucks across the nation are beginning to be retro-fitted to these specifications.
These simulations are already having an effect on the tractor-trailer industry primarily because of the HPC capabilities shared between the two institutions. The years it would normally take to run these simulations were reduced to only a few months, allowing these changes to be implemented sooner, ultimately saving more fuel and delivering a greater impact.