Air Cars: A New Wind for America's Roads?

[Anonymous]

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[dogman dan]

I'll belive that much air can be compressed by a small motor with little gas when I see it. These things don't run on 100 psi. And once they can pass the crash test, they will weigh quite a bit more. Nevertheless, it's a great idea for the big city, where gas stations can be set up to dispense air using electricity to compress it, at least keeping emissions out of the city center. Even if fossil fuel is used to compress the air, a stationary motor can be set up to emit a lot less with exhaust stack scrubbers. It's an extremely cool idea for some applications. Might be great for inner city taxi's and such. But I am now in the habit of cutting everybodies range claims in half or more.

 

[TylerDurden]

Without doubt,
More pressure has to go in
Than goes out.

"One test is worth... uh... eliminates the need for manufacturers' claims entirely." ( a good test, that is)

 

[fechter]

There is a good mathematical analysis here:
http://en.wikipedia.org/wiki/Compressed-air_car

Storage tanks
Main article: Compressed air tank
Compressed air is a heavy way of storing fuel, 300 litres (11 cu ft) air at 30 MPa (4,500 psi) contains about 16 kWh of energy (the equivalent of 1.7 liters [0.44 US gal, 0.37 imp gal] of gasoline, assuming a 100% efficiency of the engine). During rupture testing, the tank cracks, but does not break up, producing no splinters or fragments.[citation needed]

All four major manufacturers that are developing air cars have designed safety features into their containers. In contrast to hydrogen's issues of damage and danger involved in high-impact crashes, air, on its own, is non-flammable. It was reported on Discovery's Beyond Tomorrow that on its own, carbon-fiber is brittle and can split under sufficient stress, but creates no shrapnel when it does so. Carbon-fiber tanks safely hold air at a pressure somewhere around 4500psi, which is good when compared with steel tanks.


Emission output
Compressed air cars are emission-free at the 'tailpipe'. Since a compressed air car's source of energy is usually electricity, its total environmental impact depends on how clean the source of this electricity is.

Due to this reason, a compressed air car's emission output can vary both with location and time. Different regions can have very different sources of power, ranging from high-emission power sources such as coal to zero-emission power sources such as wind. A given region can also update its electrical power sources with time, thereby improving or worsening emissions output.


Advantages
The principal advantages of an air powered vehicle are:

Refueling can be done at home using an air compressor [2] or at service stations. The energy required for compressing air is produced at large centralized plants, making it less costly and more effective to manage carbon emissions than from individual vehicles.
Reduced vehicle weight is the principal efficiency factor of compressed-air cars. Furthermore, they are mechanically more rudimentary than traditional vehicles as many conventional parts of the engine may be omitted. Some plans include motors built into the hubs of each wheel, thereby removing the necessity of a transmission, drive axles and differentials. A four passenger vehicle weighing less than 800 pounds (360 kg) is a reasonable design goal[citation needed].
One manufacturer promises a range of 200 kilometres (120 mi) by the end of the year at a cost of € 1.50 per fill-up.[3]
Compressed air engines reduce the cost of vehicle production by about 20%, because there is no need to build a cooling system, spark plugs, transmission, axles, starter motor, or mufflers.[4]
Most compressed air engines do not need a transmission, only a flow control.[citation needed]
The rate of self-discharge is very low opposed to batteries that deplete their charge slowly over time. Therefore, the vehicle may be left unused for longer periods of time than electric cars.
Lower initial cost than battery electric vehicles when mass produced. One estimate is €3,000 less.[citation needed]
Expansion of the compressed air lowers in temperature; this may be exploited for use as air conditioning.
Compressed-air vehicles emit no pollutants.
Air turbines, closely related to steam turbines, are a technology over 50 years old. It is simple to achieve with low tech materials. This would mean that developing countries, and rapidly growing countries like China and India, could easily implement a less polluting means of personal transportation than an internal combustion engine automobile.
Lighter vehicles would result in less wear on roads.
The price of fueling air powered vehicles may be significantly cheaper than current fuels. Some estimates project $3.00 for the cost of electricity for filling a tank.[1]
Reduction or elimination of hazardous chemicals such as gasoline or battery acids/metals

Disadvantages
Like the modern car and most household appliances, the principal disadvantage is the indirect use of energy. Energy is used to compress air, which - in turn - provides the energy to run the motor. Any conversion of energy between forms results in loss. For conventional combustion motor cars, the energy is lost when oil is converted to usable fuel - including drilling, refinement, labor, storage, eventually transportation to the end-user. For compressed-air cars, energy is lost when electrical energy is converted to compressed air.

When air expands, as it would in the engine, it cools dramatically (Charles law) and must be heated to ambient temperature using a heat exchanger similar to the Intercooler used for internal combustion engines. The cooling is necessary in order to obtain a significant fraction of the theoretical energy output. The heat exchanger can be problematic. While it performs a similar task to the Intercooler, the temperature difference between the incoming air and the working gas is smaller. In heating the stored air, the device gets very cold and may ice up in colder climates.
Refueling the compressed air container using a home or low-end conventional air compressor may take as long as 4 hours though the specialized equipment at service stations may fill the tanks in only 3 minutes.[2]
Tanks get very hot when filled rapidly. SCUBA tanks are sometimes immersed in water to cool them down when they are being filled. That would not be possible with tanks in a car and thus it would either take a long time to fill the tanks, or they would have to take less than a full charge, since heat drives up the pressure.
Early tests have demonstrated the limited storage capacity of the tanks; the only published test of a vehicle running on compressed air alone was limited to a range of 7.22 km.[5]
A 2005 study demonstrated that cars running on lithium-ion batteries out-perform both compressed air and fuel cell vehicles more than three-fold at same speeds.[6] MDI has recently claimed that an air car will be able to travel 140km in urban driving , and have a range of 80 km with a top speed of 110km/h on highways,[7] when operating on compressed air alone.

Crash Safety Unproven
North American crash testing has not yet been conducted, and skeptics question the ability of an ultralight vehicle assembled with adhesives to produce acceptable crash safety results. Shiva Vencat, vice president of MDI and CEO of Zero Pollution Motors, claims the vehicle would pass crash testing and meet U.S. safety standards. He insists that the millions of dollars invested in the AirCar would not be in vain. To date, there has never been a lightweight, 100-plus mpg car which passed North American crash testing. Technological advances may soon make this possible, but the AirCar has yet to prove itself, and collision safety questions remain.[8]


The key to achieving an acceptable range with an air car is reducing the power required to drive the car, so far as is practical. This pushes the design towards minimizing weight. In a collision the occupants of a heavy vehicle will, on average, suffer fewer and less serious injuries than the occupants of a lighter vehicle.[9] An accident in a 2000 lb (900 kg) vehicle will on average cause about 50% more injuries to its occupants than a 3000 lb (1350 kg) vehicle.[10] Air cars may use low rolling resistance tires, which typically offer less grip than normal tires.[11][12] In addition, the weight (and price) of safety systems such as airbags, ABS and ESC may encourage manufacturers not to include them.

 

[Toshi]

Like fechter I'll believe it when I see it. 800 lbs for a 4 passenger vehicle does _not_ sound like a reasonable design goal for a crash-worthy vehicle.

 

[PaulM]

Great!! So the carbon fiber tank does not produce shrapnel, but what about the rest of the car? I don't think I want 4500 psi "venting" under my ass. I'll stick with electric.

 

[dogman dan]

If you think about it, 60 miles, presumably pretty flat ground range at 35 mph is pretty common for converted ICE cars that run on golf cart batteries. Not that impressive really. Nevertheless, a technology worth persuing since they can be quick charged. As for highway use with an on board compressor, have you priced a 4,500 psi compressor lateley? But it is great technology for certain niches, shuttles, taxi, anything that starts and stops constantly and needs to run all day by recharging in a few minuites.

 

[rguy56]

I followed the air car forum on yahoo for at least 7 years. It got great hype, and I believe it raised a lot of investor/govenment money, to no known end. Early on, the aircar was going to be tested in Mexico in a major way to replace part of their huge taxi fleet.

Be it battery, or compressed air, or even gas, alcohol, etc., all these technologies are storing a form of energy, and releasing it to provide motion. Theoretically, compressed air energy storage will work, but I really doubt that eventual efficiency will make it any kind of a leading technology for vehicles.

The addition of an efficient engine running a compressor allows the motor to run within it's best range, but the inefficiencies of compression/decompression likely eat that up faster than a good transmission would.

Bob

 

[svt/r&d]

People are worried about the wrong things, sure safety is an issue but any car can be unsafe everyone should always drive like some is out to kill you? i know i do and one of my cars is a 1970 honda 600 the most unsafe car honda made and it has survived 30+ years i think air could solve allot of in city hybrid problems and greatly reduce to cost. plus this stuff is already running around in other countries

 

[dogman dan]

Yeah that is all true, but your 1970 car would not be allowed on the road today if they started making them again, meeting modern emissions. But it seems to me what we need out of washington is a category of car in between the NEV, which is suicide in a crash and can't go over 25 mph, and a full highway crashworthy car. Your old honda would fit in this category, and if limited to about 40 mph, would be not safe, but safer than any NEV. This category would allow importing a lot of the higher economy cars from other countries as long as they stayed off highways. There is nothing inherently wrong with any of these new , or old technologys, just the lies of the marketing people. A good example is the recent Yesa battery thread. Sheesh, they must think we're morons.

 

[paultrafalgar]

I have posted this before:
http://www.youtube.com/watch?v=Dq8aZVLpf-c
It's the Italian/Australian version of the air engine. A sort of Wankel development by Angelo Di Pietro. His website is here:
http://www.engineair.com.au/