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Citroen C3 Hybrid Air Concept: 2013 Geneva Motor Show

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French automaker Citroen has long been a pioneer of automotive technology, from headlights that turn as you steer on the Citroen DS, to hydropneumatic suspension so smooth it was licensed by Rolls-Royce.

Its latest development, "Hybrid Air" technology, is possibly the most intriguing innovation yet, and its first Hybrid Air prototype will be on display at the Geneva Motor Show in March.

User benefits

The benefits of hybrid-air are easy to understand.

Rather than relying on batteries to supplement the gasoline engine's power, the Citroen C3 Hybrid Air prototype uses compressed air. This minimizes the environmental impact associated with batteries, is lighter, less expensive, and doesn't impact on cabin space.

That's particularly important in the Citroen C3 on which the prototype is based, a subcompact car similar in size to the Toyota Yaris.

The efficiency benefits are also clear. The compressed air hybrid system is matched with an 82-horsepower, 1.2-liter four-cylinder gasoline engine.

Normally, this achieves a combined fuel economy figure of 52 mpg on the European cycle. As part of the Hybrid Air system, that rises to 80 mpg, with corresponding low CO2 and other emissions.

How it works

The main components of the Hybrid Air system are the 1.2-liter gasoline engine, a compressed air storage unit, a hydraulic pump/motor unit and an epicyclic automatic transmission.

It works almost identically to a typical full hybrid system--just with air replacing the job of batteries. Air Mode works like a regular hybrid's EV mode, and can power the vehicle up to 43 mph for short distances around town. Braking or decelerating compresses air back into the system, just as doing so on a normal hybrid would top up the battery.

Gasoline Mode uses only the engine, and the same regenerative benefits are available when braking or lifting off the gas, while Combined Mode uses both energy sources for quicker acceleration.

Further benefits

Citroen lists various technological benefits of Hybrid Air.

Low pricing has already been mentioned. There's no degredation of efficiency unlike you'll experience with batteries in cold or very hot conditions. It's easily adaptable between vehicles, put particularly appropriate for small, light cars and commercial vehicles, and as an essentially mechanical system it's simple and inexpensive to service--with few issues at the end of life recycling stage.

We're eager to see how it works in practice, but it could make a real difference to small vehicles, making fuel-saving hybrid technology much more accessible even at the bargain-basement end of the market.

The Hybrid Air C3 will debut at the Geneva Motor Show on March 5.

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Comments (6)
  1. Really great if it proves out however I don't agree its more compact than the typical hybrid components.If you notice there are two rather large air tanks consuming more space than a battery pack. Wonder if they thought of using the ICE as a compressor on overrun and as an air motor for low speed co2 free running.The ICE is essentially a compressor or air motor and this would eliminate a separate unit.
     
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  2. 1. Agree with Don; if power is good enough on air motor along, the ICE could be used as a compressor rather than requiring the extra transmission to connect to the wheels direct.
    2. Does anyone know what the range in 'air only' mode would be? - if it is 30-40km or so it would be good to be able to compress the air at home by plugging in rather than needing the inboard ICE to replenish the pressures (allowing around town fuel free driving).
     
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  3. In the end compressed air technology has very low energy efficiency - turning a large component of the energy captures by solar or the engine into heat which is lost to the surroundings.
    Mass energy storage of renewables in the form of compressed air is considering using rarefied water to capture this extra heat in heat tanks and add it back to the gas when it is expanded, but I doubt this would all be able to fit into a little car- especially if it is used intermittently.
    So we could keep dreaming on this front but I think batteries/super capacitors are the best bet for now in terms of efficiency and life-time cost.
     
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  4. I have thought about compressed air for improved fuel efficiency for years, ever since I saw a driver of a tipper truck vent compressed air from his air brakes reservoir. I still don't know why you would do this but he used to do it every morning at the Construction company I used to work for. Anyway - I think the benefit may be to increase the overall efficiency of the drive train, augmentation of the engine under load? I wondered about channeling the expelled compressed air into the manifold to further improve combustion?
     
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  5. He was venting the reservoir to dispel any water build up which is harmful to the system. This regularly done as a preventive maintenance measure.
     
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  6. The European cycle is like the Japanese cycle. The cars that get amazingly good mileage in testing come to the US and don't do so well.
    Compressing air is a waste of electricity, but it makes for a good, lightweight hybrid system apparently. I wonder how it stacks up against a a car with KERS regen.
     
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