'Air hybrid' cars would be cheaper than electric hybrids, claims researcher

Storing energy as compressed air rather than in batteries would reduce the cost of green hybrid cars, say researchers in Sweden

 

Electric cars and electric hybrid cars already make use of brake energy to power a generator that charges the batteries. However, according to Per Tunestål, a researcher in Combustion Engines at Lund University in Sweden, air hybrids, or pneumatic hybrids as they are also known, would be much cheaper to manufacture.
"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 attractive for jerky and slow driving, for example for buses in urban traffic.
"My simulations show that buses in cities could reduce their fuel consumption by 60%," says Sasa Trajkovic, a doctoral student in Combustion Engines at Lund University who recently defended a thesis on the subject.
Trajkovic also calculated that 48% of the brake energy, which is compressed and saved in a small air tank connected to the engine, could be reused later. This means that the degree of reuse for air hybrids could match that of today's electric hybrids. The engine does not require any expensive materials and is therefore cheap to manufacture. It also takes up much less space than an electric hybrid engine. The method works with petrol, natural gas and diesel.
The idea of air hybrids was initially hit upon by Ford in the 1990s, but the American car company quickly shelved the plans because it lacked the necessary technology to move forward with the project. Today, research on air hybrids is conducted at ETH in Switzerland, Orléans in France and Lund University in Sweden. One company that intends to invest in engines with air hybrid technology is the American Scuderi. However, their only results so far have been from simulations, not from experiments.
"This is the first time anyone has done experiments in an actual engine," says Trajkovic. "The research so far has only been theoretical. 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 researchers in Lund hope that the next step will be to convert their research results from a single cylinder to a complete, multi-cylinder engine. They would thus be able to move the concept one step closer to a real vehicle.