A Swedish team has developed a technology that it says could halve fuel consumption by using the energy generated as a vehicle brakes.
While electric cars and electric hybrid cars already make use of brake energy, powering a generator that charges the batteries, Per Tunestål, a Lund University researcher, says that his 'air hybrids' would be much cheaper to manufacture.
His system saves the energy in the form of compressed air, which can then provide extra power to the engine when the car is started.
"The technology is fully realistic. I was recently contacted by a vehicle manufacturer in India which wanted to start making air hybrids," he says.
The technology is particularly suitable, he says, for jerky and slow driving, such as buses in urban traffic. Simulations have shown it can cut buses' fuel consumption in urban areas by up to 60 percent.
The team says the engine would take up much less space than an electric hybrid engine, and would work with gasoline, natural gas and diesel.
The researchers have worked with the Swedish company Cargine, which supplies valve control systems.
"This is the first time anyone has done experiments in an actual engine. The research so far has only been theoretical," says doctoral student Sasa Trajkovic. "In addition, we have used data that means we get credible driving cycle results, for example data from the driving patterns of buses in New York."
The next step is to progress from a single cylinder to a complete, multi-cylinder engine, moving the design closer to a real vehicle.