Electric fields can boost a car's gas mileage by up to 20 percent, thanks to a well-known effect in which electric fields reduce the viscosity of a liquid [see “Electrorheological Fluids”; Scientific American, October 1993]. Reduced fuel viscosity means that much smaller droplets can be injected into the engine, leading to more efficient combustion. Investigators at Temple University thinned fuel by attaching an electrically charged tube to a diesel engine's fuel line near the fuel injector. In road tests, the attachment, which consumed less than 0.1 watt, increased highway fuel economy from 32 to 38 miles per gallon. The researchers, who describe the boost in the November 19 Energy & Fuels, expect the device will find use in all kinds of internal-combustion engines.