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A compressed air car is an alternative fuel car that uses a motor powered by compressed air. The car can be powered solely by air, or combined (as in a hybrid electric vehicle) with gasoline/diesel/ethanol or electric plant and regenerative braking.

History

Technology

Engines

Compressed air cars are powered by engines fueled by compressed air, which is stored in a tank at high pressure such as 30 MPa (4500 psi or 300 bar). Rather than driving engine pistons with an ignited fuel-air mixture, compressed air cars use the expansion of compressed air.

Storage tanks are often made of carbon-fiber for weight reduction while maintaining strength; if penetrated carbon fiber will crack but not produce shrapnel.

There have been prototype cars since the 1920s and compressed air has been used in torpedo propulsion as well.

Storage tanks

Compressed air is a relatively heavy way of storing energy when compared to conventional gasoline. 300 litres (11 cu ft) of air at 30 MPa (4,500 psi) contains about 16 kWh of energy (the equivalent of 1.7 liters of gasoline, assuming a 100% efficiency of the engine).

The 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 4500 psi, making them comparable to 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 over 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 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.
• Compressed air engines reduce the cost of vehicle production by about 20%, because there is no need to build a cooling system, spark plugs, starter motor, or mufflers.
• 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.
• Expansion of the compressed air lowers its temperature; this may be exploited for use as air conditioning.
• Compressed-air vehicles emit few pollutants, mostly dust from brake and tire wear.
• 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 produce less road wear.
• Reduction or elimination of hazardous chemicals such as gasoline or battery acids/metals
• Some mechanical configurations may allow energy recovery during braking by compressing and storing air.

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 heating 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 cool, moist 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.

• Tanks get warm when filled rapidly. It would be difficult to cool the tanks efficiently while charging 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.

• 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. MDI has recently claimed that an air car will be able to travel 140 km in urban driving , and have a range of 80 km with a top speed of 110 km/h (68 mph) on highways, when operating on compressed air alone.

Crash safety

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.

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. 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. Air cars may use low rolling resistance tires, which typically offer less grip than normal tires. In addition, the weight (and price) of safety systems such as airbags, ABS and ESC may discourage manufacturers from including them.

Developers and manufacturers

Various companies are investing in the research, development and deployment of Compressed air cars. Overoptimistic reports of impending production date back to at least May 1999. For instance, the MDI Air Car made its public debut in South Africa in 2002, and was predicted to be in production "within six months" in January 2004. As of January 2009, the air car never went into production in South Africa. Most of the cars under development also rely on using similar technology to Low-energy vehicles in order to increase the range and performance of their cars.

MDI and Tata Motors

MDI has proposed a range of vehicles made up of AirPod, OneFlowAir, CityFlowAir, MiniFlowAir and MultiFlowAir.. One of the main innovations of this company is its implementation of its "active chamber", which is a compartment which heats the air (through the use of a fuel) in order to double the energy output.

The AirPod is a small egg shaped urban transporter running only on compressed air, with a reported 120 miles (190 km) range and a top speed of 40 mph (64 km/h). It seats 3 and is said to be available by the end of 2009.

The OneFlowAir is a very basic dual energy car seating three to five, with a 500 miles (800 km) range and a top speed of 65 mph (105 km/h), expected to be launched early 2010, anticipated to be priced in a range ($5,100 to $7,800) within reach of consumers in a developing economy, such as India.

The CityFlowAir is a larger and fully equipped car of which the same chassis will serve for a pick-up, a family six seater, a van or a taxi, with a range of 930 miles (1,500 km) and a top speed of 80 mph (130 km/h), expected to be launched one year after the OneFlowAir.

The MiniFlowAir is a smaller urban car with the same range and top speed as the CityFlowAir, expected one year after the CityFlowAir.

The MultiFlowAir is a kind of modular bus, consisting of a front driver unit to which several additional units can be added as needed. The plan is to make them also available in a truck version for transport of goods.

The ultralight bodies of the vehicles would be made of glued-together fiberglass and injected foam, and the aluminum chassis would also be glued, not welded, to simplify manufacturing.

The engine will be available in two versions. The Mono Energy air engine is a true air engine. The Dual Energy engines are External combustion engines, which use hydrocarbon fuels to heat the compressed air when entering the engine.

They have licensed around 50 factories and have signed two contracts with Tata Motors for the use of the MDI compressed air technology in India.

Tata Motors

As of May 2007 Tata Motors of India planned to launch a car with an MDI compressed air engine in 2008. As of May 2009 this has not happened.

Air Car Factories

Air Car Factories SA is proposing to develop and build a compressed air engine. This Spanish based company was founded by Miguel Celades. Currently there is a bitter dispute between Motor Development International, another firm called luis which developed compressed-air vehicles, and Mr. Celades, who was once associated with that firm.

Energine

The Energine Corporation was a South Korean company that claimed to deliver fully-assembled cars running on a hybrid compressed air and electric engine. These cars are more precisely named pneumatic-hybrid electric vehicles. Engineers from this company made, starting from a Daewoo Matiz, a prototype of a hybrid electric/compressed-air engine (Pne-PHEV, pneumatic plug-in hybrid electric vehicle). The compressed-air engine is used to activate an alternator, which extends the autonomous operating capacity of the car.

The CEO is the first compressed air car promoter to be arrested for fraud.

A similar (but only for braking energy recovery) concept using a pneumatic accumulator in a largely hydraulic system has been developed by U.S. government research laboratories and industry, and is now being introduced for certain heavy vehicle applications such as refuse trucks.

K'Airmobiles

K'Airmobiles has presented two running prototypes of VPA (Vehicles with Pneumatic Assistance). Their leaders now seek to gain the means of developing several projects of urban or leisure VPP (Vehicles with Pneumatic Propulsion). K'Airmobiles propose a different technology with their VPP , which may allow a reasonable range, generally with compressed air tanks of about 50L-100L/3000 psi capacity only.

These ecological vehicles use the technology of the compressed-air engine K'Air, developed in France by a small group of researchers, which thus proposes a range of projects around an idea: that of the urban or leisure compressed-air vehicles.

K'Airmobiles is the name given to a set of projects relating to "VPA" (Vehicles with Pneumatic Assistance) and "VPP" (Vehicles with Pneumatic Propulsion), These models are conceived like ultra light vehicles (limited to 250 kg (551 lb) max.), and their consumption of compressed air was calculated to remain lower than 120 L/min., although developing a dynamic push able to reach 4kN.

Two VPA prototypes are operational today, the "K'AirBike" and the K'AirKart. Two new VPP prototypes, the one-seater "K'AirTrike" and the three-seater "K'AirMobile Max" were intended for public presentation in October and November 2007 respectively.

Electro-Tech Enterprises

Electro-Tech Enterprises is a small company that specializes in electric air vehicles using a new technology discovered by themselves that is currently in the proto-type phase.

Engineair

Engineair is an Australian company which manufactures small industrial vehicles using an air engine of its own design. http://www.engineair.com.au

See also

• Air engine
• Charging station
• Compressed air energy storage
• Compressed air vehicles
• Engine swap
• Eolo Car
• Plug-in hybrid
• Pneumatics
• Virginia Polytechnic Institute

References

1. ^ "Car runs on compressed air, but will it sell?". Associated Press. Retrieved 2008-09-12.
2. "Advantages of compressed air as an energy vector". theaircar.com. Retrieved 2008-09-16.
3. MDI refilling stations
4. Patrick Mazza. "Wind-to-Wheel Energy Assessment" (PDF). Institute for Lifecycle Environmental Assessment. Retrieved 2008-09-12. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
5. MDI Enterprises S.A
6. By  A. Pawlowski CNN (2008-08-08). "106 mpg 'air car' creates buzz, questions". CNN.com. Retrieved 2009-04-25. {{cite news}}: |author= has generic name (help); no-break space character in |author= at position 3 (help)
7. Charles J. Kahane. "NHTSA Technical Report" (PDF). United States Department of Transportation. Retrieved 2008-09-12.
8. The safest cars of 2003
9. "Low-rolling-resistance tires". Consumer Reports. Retrieved 2008-09-12.
10. "Planned EU Requirements for Tires Would Reduce Road Traffic Safety". Continental AG. Retrieved 2008-09-12.
11. Kevin Bonsor (2005-10-25). "How Air-Powered Cars Will Work". HowStuffWorks. Retrieved 2006-05-25.
12. Robyn Curnow (2004-01-11). "Gone with the wind". The Sunday Times (UK). Retrieved 2006-05-25.
13. ^ www.aircars.tk information, pictures and videos Cite error: The named reference "autogenerated3" was defined multiple times with different content (see the help page).
14. MDI's active chamber
15. MDI Enterprises S.A
16. Matt Sullivan. "World's First Air-Powered Car: Zero Emissions by Next Summer". Popular Mechanics. Retrieved 2007-05-28.
17. "The Air Car". theaircar.com. Retrieved 2008-09-12.
18. "WARNING". Motor Development International. Retrieved 2008-09-12.
19. "CLARIFICATION". theaircar.com. Retrieved 2008-09-12.
20. http://www.patentstorm.us/patents/7028482.html
21. Digital Chosunilbo (English Edition) : Daily News in English About Korea
22. Bosch Rexroth Named Subcontractor for Hydraulic Hybrid Refuse Truck Field Test, Bos

• Articles with disputed statements from August 2008
• Car classifications
• Compressed air vehicles
• Green vehicles
• Alternative propulsion