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 Citroen hybrid air car infographic
Graphic shows principle of hybrid air energy storage. Prototype Citroen C3 has achieved fuel economy of 2.9 litres per 100km (81mpg), and CO2 emissions of 69g/km.


Citroen hybrid air car

By Duncan Mil

June 5, 2013 - Peugeot’s award-winning Hybrid Air system combines a petrol engine with a high-pressure air tank rather than heavy batteries to store recaptured energy. Air power can boost both fuel economy and cut CO2 emissions by as much as 45 percent.

Car manufacturers are investing billions to build an alternative to the internal combustion engine. The trouble is, they don't know yet which new technology will win.

There is no shortage of pretenders racing to replace 100-year-old petrol and diesel-powered motors. Purists who want to quickly replace carbon-dioxide spewing traditional engines are pushing battery-only electric cars and fuel-cells. Others who believe it makes more sense to replace traditional technology gradually by helping make it more fuel efficient are cheering on hybrids, which use batteries to raise efficiency, or making internal combustion engines more efficient with fly-wheels, cylinder de-activation and turbo-charging. New global supplies of gas using fracking techniques suggest this may also be a plentiful and cleaner fuel to power cars into the future.

None of these new ideas have achieved more than stop-gap or niche status yet, but Peugeot of France has come up with a contender called HybridAir, which experts say could be a game-changer. This uses compressed air to replace the battery. Peugeot showed a 2008 small car with the new technology at the Geneva Car Show earlier this year.

Compressed air power is not a new idea and has been used to power torpedoes. It works like steam in an old locomotive because after being compressed, it expands on release and this generates power. Peugeot's system for the 2008 car has three modes -- petrol-only operation, a mixture of the two, or compressed air only. The Peugeot 2008 concept car has a tank just behind the front wheels full of compressed air. This is generated by the compressor using power saved as the car free-wheels -- so-called regenerative braking. The computer meters the flow of compressed air to augment the 3-cylinder petrol engine during combined operation, cuts out the supply entirely during high speed driving, and takes over completely when the vehicle needs to be CO2-free in city centres, using only the hydraulic pump and motor.

Peugeot, which with its sister company Citroen is currently in a financial crisis with annual losses of around €2 billion, says HybridAir is cheaper than current petrol-electric hybrids and can achieve 2.9 litres per 100km, (97.4mpg imperial, 81.1mpg U.S.) the equivalent of 69g per kilometre of CO2. Air power only can be used for 60-80 percent of the time in city driving, depending on traffic density and its ability to recapture energy while free-wheeling. The lack of batteries slashes costs and CO2 use in production, and makes recycling easier.

Peugeot admits that all the technological problems have yet to be solved, but hopes to bring the HybridAir to market by 2016. Frost & Sullivan analyst Anjan Kumar said the system, a brilliant idea in theory, could have a big impact by 2018 to 2020. But questions about durability and safety have to be sorted, and there is challenging research and development still to be done.

And you have to wish a company luck which concludes its video presentation with this great quote from Mark Twain: "They didn't know it was impossible, so they did it."

PUBLISHED: 05/06/2013; STORY: Neil Winton