Peugeot Citroën PSA has unveiled a new hybrid drivetrain that uses compressed air instead of electricity to provide a secondary source of propulsion. Called Hybrid Air, the new technology could allow a car the size of a Citroën C3 or a Peugeot 208 to emit as little as 69g/km of CO2.

Hybrid Air consists of a conventional petrol-powered internal combustion engine, mated to a bespoke epicyclic transmission, assisted by a hydraulic motor that’s powered by compressed air. The motor and a pump are positioned in the engine bay, fed by a compressed air tank underneath the car, running parallel to the exhaust. Using regenerative braking to generate energy, the motor and pump can refill the tank with air.

It can run on the petrol engine or air power alone, or a combination of the two. Air power would be employed solely for urban use, automatically activated below 43mph, and available for “60 to 80 per cent of the time in city driving,” claims PSA. Three drive modes are provided: full petrol engine, combined (ICE and hybrid) and zero-emission.

The system adds about 100kg to the weight of a traditional ICE powered small car, which is around half that of a conventional hybrid system. PSA claims it uses very simple, serviceable parts, with no rare metals like lithium-ion. The goal is to devlop a 'global' system that's cheaper than existing hybrids to appeal to China and Russia as much as European markets.

The firm also cites a 45 per cent improvement in fuel consumption over a conventionally powered car with an equivalent power output, and a 90 per cent increase in range. 

PSA is looking to develop the technology for B- and C-segment cars, with petrol engines between 82 and 110bhp, as part of its drive to develop a car with 2l/100km (117mpg) fuel consumption by 2020. It also wants to use Hybrid Air in small vans. The first production models are planned for 2016, but both Peugeot and Citroen could display cars fitted with the technology at the Geneva motor show.