Compressed-air vehicle

The Victor Tatin airplane of 1879 used a compressed-air engine for propulsion. Original craft, at Musée de l'Air et de l'Espace.
The first mechanically powered submarine, the 1863 Plongeur, used a compressed-air engine. Musée de la Marine (Rochefort).

A compressed-air vehicle (CAV) is powered by an air engine, using compressed air, which is stored in a tank. Instead of mixing fuel with air and burning it in the engine to drive pistons with hot expanding gases, compressed-air vehicles use the expansion of compressed air to drive their pistons. One manufacturer claims to have designed an engine that is 90 percent efficient.[1]

Compressed-air propulsion may also be incorporated in hybrid systems, such as with battery electric propulsion. This kind of system is called a hybrid-pneumatic electric propulsion. Additionally, regenerative braking can also be used in conjunction with this system.

Technology

Engine

Main article: Compressed air engine

Typical compressed air engines use one or more expander pistons or rotary expanders. It is necessary to heat the air or the engine during expansion. For example, the Mekarski system heated compressed air with steam.

Tanks

Main article: Compressed air tank

The tanks must be designed to safety standards appropriate for a pressure vessel, such as ISO 11439.[2]

The storage tank may be made of metal or composite materials. The fiber materials are considerably lighter than metals but generally more expensive. Metal tanks can withstand a large number of pressure cycles, but must be checked for corrosion periodically.

One company stores air in tanks at 4,500 pounds per square inch (about 30 MPa) and hold nearly 3,200 cubic feet (around 90 cubic metres) of air.[3]

The tanks may be refilled at a service station equipped with heat exchangers, or in a few hours at home or in parking lots, plugging the car into the electrical grid via an on-board compressor. The cost of driving such a car is typically projected to be around €0.75 per 100 km, with a complete refill at the "tank-station" at about US$3.

Compressed air

Compressed air has a low energy density. In 300 bar containers, about 0.1 MJ/L and 0.1 MJ/kg is achievable, comparable to the values of electrochemical lead-acid batteries. While batteries can somewhat maintain their voltage throughout their discharge and chemical fuel tanks provide the same power densities from the first to the last litre, the pressure of compressed air tanks falls as air is drawn off. A consumer-automobile of conventional size and shape typically consumes 0.3–0.5 kWh (1.1–1.8 MJ) at the drive shaft[4] per mile of use, though unconventional sizes may perform with significantly less.

Emission output

Like other non-combustion energy storage technologies, an air vehicle displaces the emission source from the vehicle's tail pipe to the central electrical generating plant. Where low emissions sources are available, net production of pollutants can be reduced. Emission control measures at a central generating plant may be more effective and less costly than treating the emissions of widely dispersed vehicles.

Since the compressed air is filtered to protect the compressor machinery, the air discharged has less suspended dust in it, though there may be carry-over of lubricants used in the engine. The car works when gas expands.

History

Gotthardbahn: Pneumatic Locomotive with attached pressure container.[5]

Compressed air has been used since the 19th century to power mine locomotives and trams in cities such as Paris (via a central, city-level, compressed air energy distribution system), and was previously the basis of naval torpedo propulsion.

During the construction of the Gotthardbahn from 1872 to 1882, pneumatic locomotives were used in the construction of the Gotthard Rail Tunnel and other tunnels of the Gotthardbahn.

In 1903, the Liquid Air Company located in London England manufactured a number of compressed-air and liquified-air cars. The major problem with these cars and all compressed-air cars is the lack of torque produced by the "engines" and the cost of compressing the air.[6]

Recently several companies have started to develop compressed air cars, although none has been released to the public, or been tested by third parties.

Advantages

Compressed-air vehicles are comparable in many ways to electric vehicles, but use compressed air to store the energy instead of batteries. Their potential advantages over other vehicles include:

Disadvantages

PSA Peugeot Citroën Hybrid Air concept exhibited at the 2013 Geneva Motor Show.

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, and when fuel, either coal, natural gas or nuclear, is burned to drive the electrical generators. Energy collectors such as dams, wind turbines and solar collectors, are expensive and have their own problems in manufacture, pollution, transport and maintenance.

Possible improvements

Compressed-air vehicles operate according to a thermodynamic process because air cools down when expanding and heats up when being compressed. Since it is not practical to use a theoretically ideal process, losses occur and improvements may involve reducing these, e.g., by using large heat exchangers in order to use heat from the ambient air and at the same time provide air cooling in the passenger compartment. At the other end, the heat produced during compression can be stored in water systems, physical or chemical systems and reused later.

It may be possible to store compressed air at lower pressure using an absorption material within the tank. Absorption materials like Activated carbon,[12] or a metal organic framework[13] is used for storing compressed natural gas at 500 psi instead of 4500 psi, which amounts to a large energy saving.

Vehicles

Compressed-air locomotive used in boring the Rove canal tunnel in France
Main article: Compressed air car
Main article: Atmospheric railway

Several companies are investigating and producing prototypes, and one plans to offer cars late 2009, early 2010.[14]

Three mechanical engineering students from San Jose State University; Daniel Mekis, Dennis Schaaf and Andrew Merovich, designed and built a bike that runs on compressed air. The total cost of the prototype was under $1000 and was sponsored by Sunshops (on the Boardwalk in Santa Cruz, California) and NO DIG NO RIDE (from Aptos, California.). The top speed of the maiden voyage in May 2009 was 23 mph http://www.youtube.com/watch?v=NBeky4EuyBc. While their design was simple (http://www.youtube.com/watch?v=NBeky4EuyBc), these three pioneers of compressed air powered vehicles helped pave the way for French automaker Peugeot Citreon to invent a brand new air-powered hybrid. The 'Hybrid Air' system uses compressed air to move the car's wheels when driving under 43 mph. Peugeot says the new hybrid system should get up to 141 miles per gallon of gas. Models should roll out as early as 2016. http://screen.yahoo.com/hybrid-car-runs-air-001013615.html

"Ku:Rin" named air-compressed three-wheeler vehicle is created by TOYOTA in 2011. The speciality about this vehicle is it has registered a record-breaking highest speed 129.2 km/h (80mph) even if it has engine which uses only compressed air. This car was developed by the toyota companies "Dream car workshop". This car is nicknamed as "sleek rocket", or "pencil shaped rocket".[15]

A compressed-air powered motorcycle, called the Green Speed Air Powered Motorcycle was made by Edwin Yi Yuan, based on the Suzuki GP100 and using the Angelo Di Pietro compressed-air engine.[16]

As part of the TV-show Planet Mechanics, Jem Stansfield and Dick Strawbridge have converted a regular scooter to a compressed air moped.[17] This has been done by equipping the scooter with a compressed-air engine and air tank.[18]

MDI makes MultiCATs vehicle that can be used as buses or trucks. RATP has also already expressed an interest in the compressed-air pollution-free bus.

Compressed-air locomotives are a kind of fireless locomotive and have been used in mining[19] and tunnel boring.[20]

Compressed air railway vehicles also have existed for quite a long time.

Various compressed-air-powered trams were trialled, starting in 1876.[21]

Currently, no water or air vehicles exist that make use of the compressed air engine. Historically certain torpedoes were propelled by compressed-air engines.

See also

References

  1. Technology Review: The Air Car Preps for Market
  2. "Gas cylinders – High pressure cylinders for the on-board storage of natural gas as a fuel for automotive vehicles". Iso.org. 2006-07-18. Retrieved 2010-10-13.
  3. 1 2 "The Air Car Preps for Market". Technology Review. Retrieved 2010-10-13.
  4. http://www.speedace.info/electric_cars.htm
  5. Braun, Adolphe: Luftlokomotive in "Photographische Ansichten der Gotthardbahn", Dornach im Elsass, ca. 1875
  6. "History and Directory of Electric Cars from 1834 to 1987". Didik.com. Retrieved 2009-09-19.
  7. "What About Compressed Air Cars?". TreeHugger. Retrieved 2010-10-13.
  8. "Engineair". Engineair. Retrieved 2010-10-13.
  9. MDI refilling stations
  10. Patrick Mazza; Roel Hammerschlag. "Wind-to-Wheel Energy Assessment" (PDF). Institute for Lifecycle Environmental Assessment. Retrieved 2008-09-12.
  11. "MDI Enterprises S.A". Mdi.lu. Retrieved 2010-10-13.
  12. "National Science Foundation (NSF) News – From Farm Waste to Fuel Tanks – US National Science Foundation (NSF)". nsf.gov. Retrieved 2010-10-13.
  13. http://pubs.acs.org/doi/full/10.1021/ja0771639
  14. http://www.popularmechanics.com/automotive/new_cars/4217016.html; http://www.ecogeek.org/content/view/659/
  15. "Toyota three-wheeler does 80.3 mph on compressed air". Physorg.com. Retrieved 2012-08-11.
  16. Green Speed Air Powered Motorcycle
  17. Compressed air moped conversion Archived April 1, 2008 at the Wayback Machine
  18. "Compressed air moped being built by Jem Stansfield". Ecogeek.org. Retrieved 2010-10-13.
  19. Compressed-Air Propulsion
  20. Scientific American cover 1916-11-25
  21. "Tramway Information". Tramwayinfo.com. Retrieved 2010-10-13.

External links

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