Facelifted Mercedes-Benz B-Class with diesel, gasoline, natural gas and electric drives debuting at Paris show
Wrightbus Flybrid flywheel KERS bus entering service with Arriva

Peugeot showcasing 208 Hybrid Air 2L Demonstrator at Paris show

PEUGEOT is showcasing its 208 HYbrid Air 2L Demonstrator at next month’s Paris Motor Show. The 2L stands for two liters per 100 km, equivalent to 118 mpg US, and is based on a production version of the Peugeot 208 1.2-liter PureTech 82 hp 5-seater Hatchback.

Peugeot’s Hybrid Air (earlier post) is a full-hybrid solution combining compressed air and hydraulic power, with no battery required for energy storage. Hybrid Air combines the PureTech gasoline engine; a compressed air energy storage unit located beneath the trunk; a hydraulic pump/motor unit in the engine bay; and and an automatic transmission with an epicyclic gear train.

Peugeot 208 HYbrid Air 2L Demonstrator. Click to enlarge.

The compressed air is used to assist and even replace the gasoline engine to enable maximum efficiency during transition phases, such as acceleration and starts.

  • In Air (ZEV) mode, the car runs on compressed air alone. This method of driving does not consume fuel and gives off no CO2 emissions, making it ideal for urban environments.

  • In Gasoline mode, the car is powered only by the 1.2-liter gasoline engine. This is more suitable for travelling at a steady speed on main roads and highways.

  • The Combined mode is designed for transition phases in urban environments, such as standing starts and acceleration. It draws on the two energy sources in proportions adjusted to achieve optimal fuel consumption.

The compressed-air tank is recharged when slowing down (while braking or taking the foot off the pedal) or by part use of the energy developed by the three-cylinder engine to compress the air. Both methods can achieve maximum pressure in just 10 seconds.

At the 2013 Geneva Motor Show, Peugeot showed an application of the Hybrid Air powertrain in a 2008 crossover.

Weighing just 860kg—100kg less than the production car—the 208 Hybrid Air 2L demonstrator is a mix of steel, aluminium and composites. Engineers selected only those materials compatible with existing production facilities and a high manufacturing output. In addition, the process involves reducing consumption without altering the car’s characteristics, retaining a style synonymous with high-end products and services.

Carbon composites are used for the body panels, sides, doors and roof, along with the coil springs providing suspension. In the latter case, the use of composites has a positive impact on dynamic handling by reducing unsprung weight. The car has also been fine-tuned aerodynamically, with a number of improvements to reduce drag, including a lower stance on the road.

The campaign to reduce weight has not focused solely on the use of new materials; it has also sought to redesign existing parts. This has led to changes in the thickness of the stainless steel exhaust system, enabling a 20% improvement on this part alone.



Could this technology be used or adapted for larger 7-seat VUS for the American market?

No batteries and no FCs is interesting?


It is the sort of thing which sounds as though it really should not work.

It will be amazing if Peugeot pull this off.


How about just an 860kg car with carbon composites used for the body panels, sides, doors and roof and the coil springs.

That would give low fuel consumption, but would it be affordable? Probably not.

Adding the compressed air hydraulic system will add cost and weight along with the better MPG. Also not likely to be affordable.

And they imply that the engine somehow supplies compressed air directly. Does the system actually just pump the oil into the tank and compress the air?

I also think it "sounds as though it really should not work"


I don't want to pay more to save fuel later and often it's so costly that you end up paying more on total than doing economies.

The best trick will be to offer a nat gas tank with the gasoline tank and you run on cheaper less polluting natural gas most of the time but you keep the security of gasoline if there is no nat gas for sale.


This appears to be a hydraulic hybrid, using standard hydraulic accumulators.  The language of the article suggests that the storage medium is ambient air; the previous articles don't support that.

The fuel economy does not appear to be unrealistic.  The study of London diesel cabs a while ago (I'd have to dig, no time) found that a hydraulic drivetrain could double fuel economy by allowing the engine to operate in a highly efficient low-RPM, high torque region that conventional transmissions rarely if ever reached.  Combined with downsizing the engine, 2 liters appears to be quite doable.

The wonderful part of the hydraulic hybrid is that it needs nothing of the supply chain of batteries and high-power electronics needed for electric hybrids.  By going to a supply chain already established for other things, years can be cut off the time needed to ramp up production.  Frankly, I'm shocked that these things haven't hit the market already.


The Peugeot Hybrid Air 2L consumes only 2 L per 100 Km (118 mpg) but uses a standard 3-cyls 1.3L ICE + compressed air and a very light weight body.

No costly batteries or FCs are used.

If the retail price is competitive with battery equipped PHEVs such as the Chevy and others it could become an alternative Hybrid technology.



The idea is that it should be cheaper and more efficient than a PHEV, compressed air based energy recovery can swallow better burst of energy from breaking than a 1.5KW battery like the one use on a Prius. An Hybrid air-hydraulic can return 70% of the initial breaking energy where the Prius only return 30%. And for only half of the cost of a PHEV transmission. In city driving this car would out-beat the Prius by a long shot in term of not only efficiency but also driving fun, the hydraulic-air system provides a lot of torque at low speed. And I think this system would work better on a heavy pick up truck or SUV than a PHEV system, PHEV don't work well for heavy vehicle because you need a too big battery which would be too costly



Efficiency is certainly higher for reasons you explained so well. At 118 mpg versus 50 mpg for the Prius, Toyota will have to do much better or join the new train.

The ultra light weight body may/will cost more than equivalent heavier steel body? However, the new much lighter (2015) F-150 will be competitively priced.

Will the major reduction in liquid fuel consumption and associated emission reduction be enough to convince buyers to buy this technology.

Could be an excellent interim technology for taxis and city buses to reduce local pollution?


The pneumatic/hydraulic combination is brilliant,
I wish them all the best.

Roger Pham

You're comparing apples with oranges. The Prius Gen II weighs nearly 1400 kg vs this Peugeot weighing 860 kg. The Prius has mostly steel construction with some aluminum parts, and much larger engine of 1.8 liter vs 1.2 liter in the Peugeot. The Prius has less efficient and far heavier NiMh battery that is about to be changed over to much lighter and more compact solid-state Li-ion batteries.

Round-trip efficiency for Li-ion battery with SiC inverter will be even better than the 70% round-trip efficiency that you're claiming for this hydraulic hybrid.

The Toyota Concept Car Ft-Bh with similar curb weight of 1,800 lbs is capable of 112 mpg, using electric hybrid.

This hydraulic hybrid will more likely be more expensive than electric HSD hybrid because it also requires a dedicated planetary automatic transmission that the electric hybrid does not have, while the hydraulic pump and motor are analogous to the Motor/Gen I amd II of the HSD hybrid system. High-pressure tanks are expensive, perhaps more so that Li-ion batteries that are rapidly going down in costs. Electric motors have much lower friction and much more durable than hydraulic pump and motor.

Train locomotives were tried using hydraulic drive and mechanical drive in the past, but due to durability issues, electric drive were used instead and continued to be used today and proven to be the most reliable...sticking to what is proven to work the best!

Roger Pham

I must hasten to add that at 40 C discharge capability, solid-state Lithium battery will be very powerful and will be able to beat anything a hydraulic hybrid system can do. For example, a 1.3 kWh solid-stare future Prius battery at 40C is capable of 50 kW, which is twice that of current Prius. However, due to the light weight and compactness of this battery, a 2-kWh pack can be used to boost power to 80 kW, which will give very spirited acceleration boost as well as very efficient braking energy recuperation. Adding to this a 70-kW engine and you will have 150 kW, or over 200 hp of power...in a car under 3,000 lbs, this will give very spirited sport-car performance at very high efficiency, while the reliability will be unbeatable!


This new kid on the block may force Toyota to redesign their HEVs and battery to increse efficiency from 50 mpg to 118 mpg.

It is a very tall order?


Let’s not get ahead of ourselves here.

1. This Peugeot 208 Hybrid Air 2L will be just a Demonstrator.

2. Its claimed capabilities, at this point, are vapor.

3. It uses compressed air which loses much energy to heat during compression - but maybe not an issue if all it provides is IMMEDIATE and very SHORT bursts of power - see #4 below.

4. The hybrid capacity is apparently closer to “just 10 seconds” than to 10 minutes.

5. The future improvements of the Prius might come at to high a cost but the existing Prius is much more car (and more for the money) than this 850kG future car is likely to be.


1. This 2 l is probably NEDC estimate, Yaris HSD does 3.5 l (67 vs 118 MPG)
2. It does not use ambient air but nitrogen that is pumped from low pressure tank to high pressure tank
3. for 2 l there must be some kind of a break thru in gasoline engine efficiency (D-EGR maybe?), anything lower than 45% will not get us there.

We will have to wait and see.

Roger Pham

Toyota already has an HEV capable of 112 mpg, it is known as the Ft-Bh, and it doesn't even have solid state Lithium battery nor SiC inverter, but simply depends on lightness and downsized engine.

If you would apply fundamental understanding of physics, there is nothing that would permit a comparable hydraulic hybrid vehicle to be more efficient than an electric hybrid. Future high-powered, light-weight, and compact solid-state battery and SiC inverter will make electric hybrid even more efficient.


Would this work? Yes, but. I tried make some reasonable (maybe even generous) estimates and then do some calculations. If you do like my estimates put your own in but no fair ignoring physics. I assume that is a hydraulic accumulator type hybrid but it does not really matter.

Anyway, energy is change in Press * Volume. I assumed that change in pressure is about 2000 PSI or 14,000,000 Pa (Newtons/m**2) and the tank volume is 50 liter or 0.050 m**3. Multiplying the two, yields 700,000 Nm or 700,000 Joules. Remembering that a watt sec is a Joule, so a watt hour is 3600 J and a kilowatt hour is 3,600,000 Joules. Anyway, with my assumptions (which may even be generous), you end up with about 0.2 kilowatt hour equivalent. OK, so this would work if you were doing most stop and go but you are not going to get far on just the stored energy.

One other fly in the ointment and that is efficiency. With electric power, you can chop the current or use pulse width modulation to control the power. Full on for a few micro seconds and then full off for a few micro seconds. You can not do this with hydraulics. You have to throttle the flow. Even if the system was 90% efficient at full power (which I doubt), it would only be 45% efficient at half power. And we have not even worried about the heat that is lost if we do not immediately use the power.

Anyway, this might work OK for mail delivery or trash collection where you start and stop every 50 meters but, even then, my money would be on electric power with ultra caps. This is also how John Deere and Caterpillar bet with their hybrid excavators.

Bottom line -- I do not think that this is break-thru technology.


sd, there are variable displacement hydraulic pump/motors.  Throttling is not necessary.

The virtue of the hydraulic hybrid is that it has a completely independent supply chain from the electric hybrids.  This allows rapid expansion without running into shortages of components or manufacturing capacity.


So the consensus is that this compressed air system will be theoretically slightly less efficient than a hugely more expensive (and also unproven) next-gen electric hybrid?
Also, this system will mostly work in cities where the majority of automobile trips take place?

I'm not sure that I see the downside as clearly as others do. It seems like a technological path that is well-worth pursuing.


The air part can capture a lot of braking energy, not so much with less than 1 kWh of batteries. Those batteries degrade in performance over time and use, not so with air/hydraulics. As long as the seals last, the device works the same as the first day.


Roger Pham

I don't know if your prediction are true, but I own a Camry Hybrid and the battery is absolutely unable to accelerate the car from a stop unless you have an extreme and unlimited patience, even doubling the power of the battery wouldn't make it a very convincing energy boost...



Let's hope that Toyota will soon produce their 'better than' 118 mpg HEV soon.

Reduced 'dead weight' may indeed be one of the best way to reduce the energy required to move a vehicle from A to Z.

When Toyota comes out with this super HEV, We would change our Prius and Camry Hybrids fast enough.


1% of the energy in gasoline is used to move the driver down the road, the rest is the vehicle and waste heat.



Your are right in that power is pressure * flow rate and with a variable displacement motor, it is possible to reduce power without throttling losses by changing the flow rate. You do need a variable speed transmission as the pressure gives you torque and the displacement gives you rotational speed.

No matter what you do, you will have a less efficient system with hydraulics than you would with electric. However, the hydraulics may have a lower initial cost but would probably require more maintenance.

Roger Pham

Bent-axis axial piston hydraulic pump and motor can function as automatic transmission, as commonly used in Honda's 4-wheel offroader vehicles and in riding lawnmowers. The input torque and output torque can be varied by varying the displacement of the pistons depending on how much the bent is in the axis.
The lower efficiency and lower durability in comparison to a "Hydramatic-type" of planetary automatic transmission is perhaps why it is not used in automobiles in which people expect much greater durability and efficiency.


Roger Pham

I work as an engineer and am also a principal of a small company that builds a relatively high tech agricultural harvester. We use a hydrostatic transmission which is what you are describing for the wheel drives. Electric would be more efficient but a relatively small amount of the total power is used for traction. We also use some hydraulic motors and cylinders for other functions such as conveyor drives and lifts but where we are different is that all of the high speed positioning is done with 375 V electric servo motors. The use of the electric drives gives us a substantial efficiency and maintenance advantage over our competitors. As we go forward, we will be electrifying more of the functions and may add ultracaps to recover some of the available power from deceleration.

The comments to this entry are closed.