Normal air could halve fuel consumption

Feb 07, 2011

Every time a car brakes, energy is generated. At present this energy is not used, but new research shows that it is perfectly possible to save it for later use in the form of compressed air. It can then provide extra power to the engine when the car is started and save fuel by avoiding idle operation when the car is at a standstill.

Air hybrids, or pneumatic hybrids as they are also known, are not yet in production. Nonetheless, and electric hybrid cars already make use of the brake energy, to power a generator that charges the batteries. However, according to Per Tunestal, a researcher in Combustion Engines at Lund University in Sweden, air hybrids would be much cheaper to manufacture. The step to commercialisation does not have to be a large one.

"The technology is fully realistic. I was recently contacted by a vehicle manufacturer in India which wanted to start making air hybrids", he says.

The technology is particularly attractive for jerky and slow driving, for example for buses in urban traffic.

"My simulations show that buses in cities could reduce their by 60 per cent", says Sasa Trajkovic, a doctoral student in Combustion Engines at Lund University who recently defended a thesis on the subject.

Sasa Trajkovic also calculated that 48 per cent of the brake energy, which is compressed and saved in a small air tank connected to the , could be reused later. This means that the degree of reuse for air hybrids could match that of today's electric hybrids. The engine does not require any expensive materials and is therefore cheap to manufacture. What is more, it takes up much less space than an electric hybrid engine. The method works with petrol, and diesel.

For this research the Lund researchers have worked with the Swedish company Cargine, which supplies valve control systems.

The idea of air hybrids was initially hit upon by Ford in the 1990s, but the American car company quickly shelved the plans because it lacked the necessary technology to move forward with the project. Today, research on air hybrids is conducted at ETH in Switzerland, Orléans in France and Lund University in Sweden. One company that intends to invest in engines with air hybrid technology is the American Scuderi. However, their only results so far have been from simulations, not from experiments.

"This is the first time anyone has done experiments in an actual engine. The research so far has only been theoretical. In addition, we have used data that means we get credible driving cycle results, for example data from the driving patterns of buses in New York", says Sasa Trajkovic.

The researchers in Lund hope that the next step will be to convert their research results from a single cylinder to a complete, multi-cylinder engine. They would thus be able to move the concept one step closer to a real vehicle.

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User comments : 15

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Burnerjack
not rated yet Feb 07, 2011
Energy is NOT created via braking. The kinetic energy expended by the power plant of the vehicle is converted into heat by the braking system. Common knowledge of those who have a middle school level of understanding of physics. Regenerative braking used in electric vehicles is not new. I am rather disappointed by this post.
Herd Management is better left to the advertisers of main stream media. You should be a cut above this.
d_robison
not rated yet Feb 07, 2011
Energy is NOT created via braking. The kinetic energy expended by the power plant of the vehicle is converted into heat by the braking system. Common knowledge of those who have a middle school level of understanding of physics. Regenerative braking used in electric vehicles is not new. I am rather disappointed by this post.
Herd Management is better left to the advertisers of main stream media. You should be a cut above this.


If you want to be technical about it, some of kinetic energy from the car is transfered to heat energy when you apply your brakes. No, energy isn't really created just converted from one form to another. You can in theory take that energy and transfer it back into the system (albeit this would be fairly complex and there would be a good amount of energy loss), you aren't creating energy, but you are making your automobile slightly more efficient. This could be analogous to how hydroelectric power works (see USGS website for more info).
Burnerjack
not rated yet Feb 07, 2011
Yes, you do speak the truth. One would require a clutch driven compressor, a pneumatic motor(s) and most importantly, the volumetric storage vessel.
Considering that the modern automobile is a "packaging marvel", that last point is not insignificant.
I suggest that this idea is largely a red herring.
My cynical side tells me this post is related to funding.
With so many other ways to lessen the voracious appetite of our domestic transportation scheme, that funding is better spent in another direction.
BTW, all things practical have their basis in theory. If this were not true we'd all be driving around in/on perpetual energy machines.
Skepticus
not rated yet Feb 07, 2011
The compressed air concept is simple in theory but hard to realize full potential efficiency in real hardware. Adiabatic heating and cooling will necessitate insulation and extra heat exchange circuits between storage tank and compressor for minimum energy losses from heat waste.
At first glance, compressors will provide more braking force to lower speeds than electric motors in regenerating braking mode, but both can be made to brake the vehicle effectively. By having a CVT between the wheels and the electric motor the [brake-pedal controlled] continuosly changing gear ratios will force the motor to run at the required speed for required level of braking. If this is implemented, then there is really no advantage of having a complicated compressed air system. The only bottle neck is a batteries and electronics system that can handle extremly fast charging when the motor is forced to spin to insane speeds when maximum braking is required.
pauljpease
5 / 5 (2) Feb 07, 2011
Speaking of efficiency, has anyone yet falsified the hypothesis that allowing everyone to participate equally in an intelligent complex system reduces the efficiency of that intelligent system to approximately zero?
Burnerjack
not rated yet Feb 07, 2011
Is this the law of intellectual entropy perhaps? If it hasn't been falsified, maybe reiterated in say, the political arena?
RHaston
not rated yet Feb 07, 2011
This combined with a split cycle engine (one cylinder works as a compressor, the other a combustor) makes sense.

Pop Sci has an article about some advances in this type of engine.

This could still be used as part of an electric hybrid.
david_42
not rated yet Feb 07, 2011
HLA (hydraulic launch assistance) has been in use in Australia for almost a decade. It adds a variable-pitch hydraulic motor (and reservoir) to the drive train to provide regenerative braking and acceleration assistance. This is a very simple, inexpensive and compact technology. Naturally, it is most useful when the vehicle starts and stops a lot, like a bus or delivery truck. It scales easily.
dirk_bruere
5 / 5 (1) Feb 08, 2011
As soon as you take your foot off the gas the engine turns into a compressor - that's what "engine braking" is all about.
Quantum_Conundrum
2.5 / 5 (2) Feb 08, 2011
The problem with regenerative breaking are many:

1) The systems add more mass to the car, lowering initial efficiency. So the system must recover more of the energy just to pay for the energy wasted by the mass of the system.

2) Compressed air is bad because it has mass, which also further increases the energy losses because you have to accelerate the mass of the compressed air.

3) They add maintenance and repair expenses which are geometrically more than their value in energy savings.
d_robison
not rated yet Feb 08, 2011
Yes, you do speak the truth. One would require a clutch driven compressor, a pneumatic motor(s) and most importantly, the volumetric storage vessel.
Considering that the modern automobile is a "packaging marvel", that last point is not insignificant.
I suggest that this idea is largely a red herring.
My cynical side tells me this post is related to funding.
With so many other ways to lessen the voracious appetite of our domestic transportation scheme, that funding is better spent in another direction.
BTW, all things practical have their basis in theory. If this were not true we'd all be driving around in/on perpetual energy machines.


Yeah I agree completely with what you are saying, the Physicist side of me just had to point out the it is possible...however, as you pointed out something possible isn't necessarily practical. I agree when mentioned there are many different and more reasonable ways to improve our efficiency. Though the more the merrier!
d_robison
not rated yet Feb 08, 2011
The problem with regenerative breaking are many:

1) The systems add more mass to the car, lowering initial efficiency. So the system must recover more of the energy just to pay for the energy wasted by the mass of the system.

2) Compressed air is bad because it has mass, which also further increases the energy losses because you have to accelerate the mass of the compressed air.

3) They add maintenance and repair expenses which are geometrically more than their value in energy savings.


I agree with the last two statements, however I'm not so convinced with the mass added being significant compared to the kinetic energy being harnessed (I honestly don't know how much more mass one would need to add to get the regenerative braking). Remember that velocity has a larger effect on kinetic energy than mass.
Moebius
not rated yet Feb 08, 2011
The idea is totally feasible. As long as the regenerator is also the motive source this adds very little extra weight and returns a lot of power back to the system. The brake pads can be the clutch. Since some electric vehicles use an electric motor at each wheel they are perfect for this, they just become a generator to help stop. There is no reason that an air powered vehicle can't do it too, the motor is already connected to the drive wheels and just needs to be turned into compressor mode. Almost every air motor design is basically a compressor. People with manual transmissions already do this, it's called downshifting, it doesn't capture any energy but it saves on brake wear. Pretty sure an air car is already manufactured in Europe.
salve
not rated yet Feb 08, 2011
"This is the first time anyone has done experiments in an actual engine"
___________________________________________________

That's not quite correct. In 1972 Russian professor Nurbey Gulia achieved 50% fuel reduction on a Kursk city bus using compressed air. Professor Gulia is the inventor of Flywheel energy storage and has more than 250 patents.
Burnerjack
5 / 5 (1) Feb 08, 2011
As fluids are not compressible, a hydraulic system would have a compressed gas reservoir to accept and release the charge ( known as a air over hydraulic system ), again, back to that "packaging marvel" point. A transport bus is not a passenger car.
A flywheel system is one of those systems that can be small in mass and volume given sufficient RPM. Its only real drawback is it must (or should) be mounted in a spherical mount as to isolate the gyroscopic effect from the vehicle. One other concern is a possible explosion hazard but that has largely been dealt with via a containment vessel as well as cutting edge high strength alloys. The idea is to couple the flywheel to a motor/generator ( dynamo). Basically a mechanical battery.
I suspect modern materials such as graphene will bring this old technology back around.
"That which is old shall be new again"

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