A small gadget that can be fitted to diesel engines boosts fuel efficiency by up to 19% and can make them run more cleanly, engineers report.

A weak electric field is used to make fuel less viscous before it is injected into the engine. That makes it possible to spray smaller drops that burn more completely.

The device was developed at Temple University in Philadelphia, Pennsylvania and costs less than $200 to produce.

In tests over six months on a 2002 Mercedes-Benz 300D sedan, a prototype device increased fuel efficiency by 12 to 15% under urban driving conditions, and 19% in highway driving – taking it from 32 to 38 miles per gallon.


“This is the biggest efficiency increase since the advent of fuel injection,” claims Rongjia Tao from Temple University. The device has been licensed to Californian firm Save the World Air, which is now testing it in road haulage vehicles.

Fluctuating flow

An electric field makes diesel thinner because some molecules in the fuel become charged and aggregate together, reducing their overall surface area. That means less friction between them, and a less viscous fuel.

Tao and colleagues believe fuel efficiency gains were lower under stop-start urban driving conditions because the rate at which fuel flows through their device constantly varies.

They are working on a version that varies its electric field to match fuel flow rate and keep viscosity constantly reduced.

Matt Thomas of CFD Research Corporation works on similar fuel electrification techniques. He says fitting the device to new cars will not produce such spectacular efficiency gains, but adds that it would still cut emissions.

“[If] you charge spray prior to fuel injection you could lower particulate emissions by as much as a factor of 10.”

Journal reference: Energy and Fuels (DOI: 10.1021/ef8004898)

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