A project that started in top secret four years ago is now being shared with other car makers as Peugeot seeks a partner for its hybrid air technology which is helping it achieve CO2 emissions as low as 46g/km from a two-litre petrol engine.

To make hybrid air viable, annual production needs to be around 400,000 units a year, Eric Lalliard, powertrain senior chief engineer at Peugeot, told just-auto.

PSA Peugeot-Citroen will be able to account for 200,000-250,000 of those but the balance will need to come from another manufacturer.

"We’re looking worldwide with our strategic partner Bosch who are also very interested in the technology," said Lalliard.

"Bosch is knocking on doors for us," he added, saying many competitors have driven the hybrid air development vehicle and now understand the technology.

PSA is targeting 2016 for the start of series production and Lalliard is confident a partner will come forward to make that target a reality.

He said it was important to keep the project secret even inside Peugeot otherwise, for every person who supported it, there would have been 100 saying it couldn’t be done.

This is despite the fact that hybrid air uses existing hydraulic technology, familiar to those in the avionics industry, to pump oil to drive the wheels when conditions allow. 

Development costs included EUR100m for a CVT gearbox with ancillary pumps which have a dual role as motors used to drive the wheels when the internal combustion engine is not needed.

The challenge was to develop a hybrid at an acceptable price, said Lalliard. "What could we use instead of a battery?" The answer was air, or in this case nitrogen because it is safer than oxygen, he said.

The hybrid air works best in 300m bursts and takes 10 seconds to recharge so it's ideal for city centre driving between traffic lights.

"You shouldn’t use any hybrid on a long journey, it doesn’t make sense," said Lalliard.