Bangalore: It is possible, at least theoretically, to produce electric current using exhaust gases emitted by automobiles, if Ajay Sood and his student Shankar Ghosh are to be believed.

The duo - physicists at the Indian Institute of Science (IISc) Bangalore, have produced electricity by passing a jet of gas over a variety of materials.

The current generated was miniscule, but still the experiment is a break-through, for in this process no fuel is burnt.

A report of the discovery, made using nothing more than a bottle of compressed gas and low-cost equipment, is to appear in the coming issue of Physical Review Letters, a prestigious journal of the American Physical Society.

Sood and Ghosh have also applied for a patent.

"We have reported here a method for direct generation of measurable voltages and currents when a gas flows over a variety of solids - even at the modest speed of a few meters per second," Sood told reporters.

"We searched the literature and found no report of a similar phenomenon," he said.

Sood and Ghosh said that a sensor to measure the "flow-velocity" of the gases can be made based on the generated electrical signal.

They claim that their results also suggest, "that gas flow energy can be converted directly into the electrical signal without any moving part, thus having a potential for applications in generating electricity."

The discovery gives rise to many interesting possibilities. For example, since current is produced by flow of air, one potential application would be using powerful winds to directly generate electricity without windmills or turbines.

Another possibility is generation of electricity from the flow of gases through automobile exhausts.

Of course, practical use of the invention hinges upon many other things. "Our finding is just a proof of concept. It is for technologists to take it up from here," Sood said.

In their experiment, the duo succeeded in generating voltage and current by passing common gases like argon, nitrogen and oxygen over samples of doped semiconductors, carbon nano-tubes, graphite and metals like copper kept in an inclined position.

Gas velocities ranging from a few kilometres per hour to those approaching cyclonic speed (350 kilometres per hour) were used.

The voltages and current generated in their experiments are still in the region of few millionths of volts. For instance, argon gas at a flow velocity of 11 metres per second generated 16.4 millionths of a volt. The voltage, however, increases with speed of gas flow, the scientists said.

Last year, the duo along with Prof N Kumar of IISc demonstrated that the flow of liquids over carbon nanotubes generates a voltage in the tubes along the flow direction.

"Having done that we asked ourselves if a similar effect will be produced by passing gases instead of liquids and found that an equally striking effect exists for gas flow as well but for entirely different reason," Sood said.

What exactly happens in this phenomenon?

Scientists said there is an interesting interplay of two well-known physical principles. Pressure differences in the gas flow along streamlines gives rise to temperature differences across the sample (Bernoulli's principle), which in turn produces the measured voltage (called Seebeck effect).

Sood and Ghosh emphasise that the effect they observed is not restricted to the few materials they studied. Any material with high Seebeck coefficient, like selenium, tellurium, gallium arsenide, and electrically conducting polymers are good candidates.

According to the scientists the magnitude of voltage and current can be easily scaled up by connecting millions of these nano-generators in the same way numerous photovoltaic cells are connected to generate power from Sunlight.