US boffins have outlined a system to provide "pollution free cars" by capturing, storing and eventually recycling carbon from vehicles.

Researchers at the Georgia Institute of Technology said that the work could lead to zero emission cars, and a transportation system completely free of fossil fuels.

The goal is to create a sustainable transportation system that uses a liquid fuel and traps the carbon emission in the vehicle for later processing at a fuelling station.

The carbon would then be shuttled back to a processing plant where it could be transformed into liquid fuel.

Georgia Tech researchers are developing a fuel processing device to separate the carbon and store it in the vehicle in liquid form.

"We have an unsustainable carbon-based economy with several severe limitations, including a limited supply of fossil fuels, high cost and carbon dioxide pollution," said Andrei Fedorov, associate professor in the Woodruff School of Mechanical Engineering at Georgia Tech and lead researcher on the project.

"We wanted to create a practical and sustainable energy strategy for automobiles that could solve each of those limitations, eventually using renewable energy sources and in an environmentally conscious way."

The research has been funded by Nasa, the US Department of Defense and Georgia Tech's Creating Energy Options program.

Georgia Tech settled on a hydrogen-fuelled vehicle for its carbon capture plan because pure hydrogen produces no carbon emissions when used as a fuel to power the vehicle.

The fuel processor produces the hydrogen onboard from the hydrocarbon fuel without introducing air into the process, resulting in an enriched carbon by-product that can be captured with "minimal energetic penalty".

"We had to look for a system that never dilutes fuel with air because once the CO2 is diluted, it is not practical to capture it on vehicles or other small systems," said David Damm, PhD candidate in the School of Mechanical Engineering, the lead author on the paper and Fedorov's collaborator on the project.

The team has created a fuel processor, called CO2/H2 Active Membrane Piston reactor capable of efficiently producing hydrogen and separating and liquefying CO2 from a liquid hydrocarbon or synthetic fuel used by an internal combustion engine or fuel cell.

After the carbon dioxide is separated from the hydrogen, it can then be stored in liquefied state onboard the vehicle. The liquid state provides a much more stable and dense form of carbon, which is easy to store and transport.