PSA PeugeotPeugeotFrance, 1882 > present120 models
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-CitroënCitroënFrance, 1919 > present94 models
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and Bosch have developed a brand new hybrid system that eschews batteries in favor of a compressed air tank. It calls the hybrid system Hybrid Air and claims that the system will be on sale in its B-segment cars by 2016. 

PSA says that the system can power the car by itself for short intervals or work with the internal combustion engine. It can improve fuel economy by about 35%. In a vehicle like the Citroën C3Citroën C3 Gen.2France, 2009 > 2016111 versions
166 photos
and Peugeot 208Peugeot 208 Gen.1France, 2012 > present103 versions
198 photos
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it will produce at 69g/km of CO2 and use 2.9l/100km. In city driving, the system can run on the compressed air for 60% to 80% of the time. They say that it will be cheaper than a traditional hybrid and have a lower cost to own. 

The system works with an internal combustion engine with a hydraulic pump attached to it. Down the center of the vehicle is a tank for the compressed air. Under braking, energy is regenerated, and it is used to compress more air into the tank. The system automatically functions in hybrid mode below 70km/h. According to PSA, the system adds about 100kg to the weight of the car. 

According to Bosch, the cost of the system for each gram of CO2 reduced is on par with a battery hybrid system. 

PSA did not say what range a full charge of compressed air will have for the vehicle. It also did not address any extra sound the system might add to the car. Charging a battery is relatively quiet, while an air compressor can be quite noisy. 

This technology appears to offer a real advantage over the hybrid systems offered in small cars at the moment. The issue is that the amount of energy that can be held in a compressed air tank is relatively finite. Once you know the volume of air it will hold, you can calculate the energy. Battery development is happening at a rapid pace because they are needed for cars, laptops, tablets, phones and other gadgets. Billions are being spent to make batteries have a better power density. While PSA and Bosch's compressed air technology is attractive now; it is hard to see it as more than a stop gap. 

Source: Automotive News Europe