Peugeot, Citroen Research Compressed Air Energy Storage For Hybrids

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Air-powered cars are a familiar source of amusement within the green car fraternity, an ideal example of a concept that would be wonderful if it worked, but simply isn't viable in the real-world.

Up until now, the compressed air car has been... well, a load of hot air.

Undeterred, French automaker PSA--owner of both Peugeot and Citroen--is approaching air from a different angle--as a replacement for battery power in hybrid vehicles.

PSA currently makes a small range of through-the-road hybrid vehicles, from the beautiful Citroen DS5 Hybrid to practical Peugeots like the 3008 HYbrid4 and 508 RXH.

These use a diesel engine to power the front wheels, and a battery-fed electric motor to assist via the rear wheels--varying the input of each drivetrain depending on driving conditions.

The new "Hybrid Air" concept is a little different.

The car's main source of power remains an internal combustion engine, albeit powered by gasoline rather than diesel.

But instead of using batteries to supply additional power, or zero-emissions driving when needed, the concept instead uses a compressed air tank mounted in the central transmission tunnel to turn a hydraulic motor.

In regular highway driving, the car uses the internal combustion engine alone. Ask for more power for acceleration or hills, and high-pressure air can be called upon for extra shove--the power of both engine and motor being fed through an epicyclic transmission, not dissimilar to that on a Prius.

In city driving and at speeds of up to 43 mph, where less power is required and emissions-free driving is a priority, the air can work on its own. The air tanks are filled under braking or deceleration, where the motor draws in air and compresses it for future use.

The concept is based around a small, light weight city car. In this format, combined economy of up to 117 mpg is suggested.

The system also makes some sense on smaller cars, where the weight of heavy batteries would normally offset some of the advantage of a regular hybrid drivetrain. It's also cheaper--equally important on small cars.

PSA expects to have the first running prototypes by 2016.


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Comments (7)
  1. Another french company working on air-power, oh boy.

    When I have looked at this in the past, it seems clear that compressing air and then expanding it is very inefficient. They will be lucky to get 25% of the energy back out of it.

  2. I agree. A lot of that energy will be lost. But I think they are looking at all the weight and cost savings comparing to an electric motor and battery pack. Also, those "air tanks" can last potentially longer than batteries...

  3. How is this all that different from using compressed liquid? It is just air vs. liquid. In this case, the air temperature will rise and you end up losing a lot of energy that way.

    I think it will be cheaper and lighter. It is probably the sole reason for this research...

  4. Liquid is incompressible. Hydraulic systems use a working fluid to transfer force but that fluid is never actually compressed.

  5. Acutally, liquid (depending on the liquid) is "compressible". The difference is just very small. Of course, due to that property, that is why we use hydraulic system b/c it has a very small compression.

  6. What will they think of next. Maybe a coil spring system for energy storage? Seems only fitting for these small cars. Maybe add a crank for "home charging".

  7. I visited MDI, the other compressed air company back in 2007 and test drove their prototypes. It was interesting, but the real strength was in the distribution business model. Compressed air cars make sense in airports where there already are plenty of compressors and air tanks for other systems. The short routes make these vehicles efficient. The A chile's Heel is still the compression systems we use. Pistons are not efficient, although Michelin has been working on volumetric disc compressors.

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