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Citroën to showcase Hybrid Air technology at Geneva

Citroën will showcase its Hybrid Air system (earlier post) at the upcoming Geneva International Motor Show. The system, developed in partnership with Bosch, combines compressed air and hydraulic power to deliver fuel consumption of less than 3 l/100 km (78 mpg US).

This technology is well-suited to models in the B and C segments as well as LCVs. On the Marque’s stand at the Geneva Motor Show, it will be seen on a Citroën C3 prototype that offers fuel consumption of 2.9 l/100 km (81 mpg US) (69 g of CO2/km). It also cuts fuel consumption and CO2 emissions by 45% in urban driving, compared with an ICE vehicle fitted with the same engine.

The Hybrid Air powertrain combines a PureTech gasoline engine, a compressed air energy storage unit, a hydraulic pump/motor unit and an automatic transmission with an epicyclic gear train. Eighty patents were filed by the PSA Peugeot Citroën Group during the development process.

Three operating modes are available:

  • Air power, with zero emissions;
  • Gasoline power, using only the combustion engine;
  • Combined power, with the combustion engine and hydraulic motor working together.

Because Hybrid Air technology uses no additional batteries, it could be sold at an attractive price on both European and international markets, the company suggests.



Finally, a '3L' car which is a normal (C3) car and not some tiny prototype.
Note that it uses a petrol ICE engine, not a diesel.
(You could obviously get better motorway mileage if they used a diesel, but at higher cost).

Let's hope that they can bring it to market in a timely manner and there are no gotcha's in the technology.

Just because it is a hybrid, doesn't mean it has to be an electric hybrid.

I wonder could* you build a "PHAV" version where you have an extra large accumulator and pressurise it from mains power (or a compressor) every night to increase the 'air' range.

*or rather, would it be worth it.


Yes mahonj...I thought that the initial idea to be able to start from home with a fully loaded air tank? Depending on the tank size and pressure, one could go a few Km till the ICE had to start? Driving a few Km to work may not use much fuel, if one could refill the air tank at each end, much the same way as one could recharge the batteries on an electric-battery PHEV?

On longer drives, one could get a very quick 'air' recharge during normal rest stops to further reduce fuel consumption?

Will it be nosier than an electric verison?

Henry Gibson

If you want to see what how hydraulic hybrids compare to electric, look for the Artemis hybrid demonstrations. This vehicle uses high pressure air that is compressed by hydraulic fluids being pumped from one container into another closed container filled with air. Bosch-Rexroth bought the rights to use the Artemis digital hydraulic valve technology for highway use, but does not mention if they are using that very efficient technology. That technology has the ability to double efficiency with no other changes and eliminate any advantage of using biofuels on the roadways. Smaller engines with this technology will give equal city performance but not the highest motorway speeds which are the biggest wasteful use of fuels and energy. Hydraulic hybrid technology is far more simple and lightweight than electric hybrid technology and far cheaper too, but current versions do not but also need not store much energy. The Parry People Mover flywheel hydraulic machine uses less than a third the fuel to transport people on rails and could store energy for several miles of travel. The high pressure tanks developed for hydrogen storage can also be used in this vehicle for air or other gases. Ruptures of air filled bottles demonstrate the high power available but total energy is low and are the equivalent of super capacitors in this regard. The rest of Artemis has been bought out for a quixotic tilt at windmills. ..HG..


They gave no data on how much energy is stored but I would hazard a guess that the distance that could traveled on compressed air alone is measured in hundreds of meters not km. Compressed air is very poor for energy storage. Also, the total energy in, energy out efficiency is very poor unless the heat of compression can be preserved. Typically, air tools are about 10% efficient. Where this technology might make sense in for trash trucks or mail delivery vehicles where they constantly start and stop. Maybe, it would make sense for taxis large cities. The initial cost might be less than for electric hybrids but I doubt that the maintenance cost is less.


There is not much to gain from a PHEV over a HEV for systems with a small energy store like this one. You would also have to add an electric motor to make it a PHEV, an incremental cost that the electric PHEV does not incur.

I like that it is perhaps complementary to electric hybrids. The electric hybrids are perhaps quieter, less maintenance but more upfront cost - so market penetration via premium products like Lexus? The air hybrids noisier and less upfront cost so better suited to most popular models?

I fear that we are seeing this product because it's development was partly funded by French government rather than because it is effective. That it will be several years before being incorporated in Citroen's models (though reported as being easy to incorporate) and they are willing to sell to other car manufacturers seems odd to me. I hope to be proved wrong!

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