Most electric and electric hybrid cars make use of the energy generated when the car brakes 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 could achieve the same fuel saving at a much lower manufacturing cost.

The researchers calculate that 48% of the brake energy could be compressed and saved in a small air tank connected to the engine and could be reused later. This is about the same degree of reuse as in today’s electric hybrids.

The method could be used with petrol, natural gas or diesel engines without any expensive materials and is, therefore, cheap to manufacture. It would also take up much less space than an electric hybrid engine.

Engineers at Ford originally developed the idea of air hybrids in the 1990s but the company quickly shelved the plans.

The researchers in Lund say that the next step will be to convert their research results from a single cylinder to a complete, multi-cylinder engine.