Glowing aerodynamic add-ons could boost big-rig fuel economy by 7-10%

“Headlight white” and “stoplight red,” the characteristic colors of the highway at night, could soon get a companion: “plasma purple”-that is, if a new fuel-saving, aerodynamic technology catches on big with big-rig trucks. The electric plasmas emitted by the devices, which glow purple-violet in the dark, can smooth the turbulent wakes that sweep off the rear edges of truck trailers travelling at highway speeds. Simulations and wind tunnel tests indicate that these novel active-flow control systems could reduce the aerodynamic drag generated by semi-trailers by almost one-fifth, thus lowering fuel consumption by up to 10%.

Plasmas, the lesser-known “fourth state of matter,” are clouds of charged atomic ions created in the air by high-voltage electric fields. The glowing electric-flame phenomena are commonly seen in household air purifiers and more rarely in natural phenomena such as St. Elmo's Fire, the ghostly purple haze sometimes seen hanging off airplane wings. For application to trucks, strong electric fields emitted by surface electrodes push the plasmas around, producing breezes that can redirect critical airflows at the trailing edges of “bluff-bodied” vehicles such as Class 8 cargo trucks, helping to smooth out the turbulent, high-drag wakes.