Let’s be clear: there’s no such thing as a truly air-powered car. But PSA Peugeot Citroën has a new take on how to use compressed air to store energy that a car can use for propulsion. Showcased in two concepts, a Citroën C3 and a Peugeot 208, the Hybrid Air system powertrain combines air, hydraulics and petrol. Peugeot claims its system improves fuel economy by 35 per cent and is capable of under 3 litres/100 km in the New European Drive Cycle test. A projected price of about R250 000 means the Hybrid Air would be roughly R8 000 less than what a Toyota Prius costs in Europe. If Peugeot brings out the Air Hybrid in 2016 as promised, it could challenge electrical batteries as a hybrid power reservoir. – Andrew English
How it works
A 62-kW 1,2-litre petrol engine provides most of the power, driven through an epicyclic automatic transmission. During deceleration, the wheels’ energy drives a hydraulic pump that pushes hydraulic fluid into an accumulator and compresses the nitrogen gas within. When the car needs to accelerate, the system works in the opposite way: the pressurised nitrogen gas pushes the hydraulic fluid, which drives a hydraulic motor connected to the transmission.
Petrol only: Intended for highway driving Air only: For speeds below 70 km/h, where the engine stops and hydraulics power the wheels 80 per cent of the time Combined: Powered by the petrol engine and hydraulic motor.
Hydraulic systems are an established technology. The motors and pumps are simple, relatively low-cost and easy to package – as are epicyclic gears – so the Hybrid Air could be lighter and cheaper than a petrol–electric hybrid. And unlike chemical batteries, hydraulics have fewer recycling issues.
With no big battery to run the air conditioning at standstill, the engine would have to run, using petrol; a crash-safe accumulator large enough to hold the requisite amount of pressure (up to 300 bar) might be heavy enough to negate any benefit. With unproven reliability, hydraulic systems could find it difficult to gain consumer acceptance.