Compressed-air vehicle

A compressed-air vehicle (CAV) is a transport mechanism fueled by tanks of pressurized atmospheric gas and propelled by the release and expansion of the gas within a Pneumatic motor. CAV's have found application in torpedoes, locomotives used in digging tunnels, and early prototype submarines. Potential environmental advantages have generated public interest in CAV's as passenger cars,[1] but they have not been competitive due to the low energy density of compressed air and inefficiency of the compression / expansion process.[2]

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).

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.

Tanks

The tanks must be designed to safety standards appropriate for a pressure vessel, such as ISO 11439.[3]

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.[4]

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) [5] 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.[6]

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.[7]

Since 2010, several companies have started to develop compressed air cars including hybrid types that also include a petrol driven engine; none has been released to the public, or have 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.

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, whether coal, natural gas or nuclear, is burned to drive the electrical generators.

  • When air expands, as it would in the engine, it cools dramatically (adiabatic cooling; Joule–Thomson effect) 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, while the specialized equipment at service stations may fill the tanks in only 3 minutes.[8]
  • Tanks get very hot when filled rapidly. SCUBA tanks can be immersed in water to cool them 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. However, if well insulated, such as Dewar (vacuum) flask design, the heat would not have to be lost but put to use when the car was running.
  • 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 (4 mi).[9]
  • A 2005 study demonstrated that cars running on lithium-ion batteries out-perform both compressed-air and fuel cell vehicles more than threefold at same speeds.[10] MDI has recently claimed that an air car will be able to travel 140 km (87 mi) in urban driving, and have a range of 80 km (50 mi) with a top speed of 110 km/h (68 mph) on highways,[11] when operating on compressed air alone.

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

Production cars
Main article: Compressed air car

Several companies are investigating and producing prototypes including hybrid compressed-air/gasoline-combustion vehicles. As of August 2017, none of the developers have yet gone into production, although Tata has indicated they will begin selling vehicles from 2020[14] and MDI's US distributor Zero Pollution Motors says production of the AIRPod will commence in Europe in 2018.[15]

Experimental cars and bikes

In 2008, a compressed air and natural gas powered vehicle designed by engineering students at Deakin University in Australia was joint winner of the Ford Motor Company T2 competition to produce a car with a 200 km range and a cost of less than $7,000.[16][17]

Australian company Engineair has produced a number of vehicle types - moped, small car, small carrier, go-cart - around the rotary compressed air engine created by Angelo Di Pietro.

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.[18]

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. While their design was simple, these three pioneers of compressed air powered vehicles helped pave the way for French automaker Peugeot Citroën 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. . The head of the project left Peugeot in 2014 and in 2015 the company said it had been unable to find a partner to share the development costs, effectively ending the project.[19]

"Ku:Rin" named air-compressed three-wheeler vehicle was created by Toyota in 2011. The speciality about this vehicle is it has registered a record-breaking highest speed 129.2 km/h (80 mph) even if it has engine which uses only compressed air. This car was developed by the company's "Dream car workshop". This car is nicknamed as "sleek rocket", or "pencil shaped rocket".[20]

As part of the TV-show Planet Mechanics, Jem Stansfield and Dick Strawbridge converted a regular scooter to a compressed air moped.[21] This has been done by equipping the scooter with a compressed-air engine and air tank.[22]

In 2010, Honda presented the Honda Air concept car at the LA Auto Show.[23]

Since 2008 the former Bosch Rexroth, now Emerson is organizing the Emerson’s International AVENTICS Pneumobile Competition in Eger, Hungary. It is a competition for students in the higher education to build racing vehicles propelled by compressed air. [24]

Óbuda University PowAir Pneumobil Team

There is an international conference related to the event organized by Óbuda University, Department of Bánki Donát Mechanical and Safety Engineering. [25]

Trains, Trams, Boats and Planes

Compressed-air locomotives are a kind of fireless locomotive and have been used in mining[26] and tunnel boring.[27]

Various compressed-air-powered trams were trialled, starting in 1876. In Nantes and Paris such trams ran in regular service for 30 years.[28]

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. "What About Compressed Air Cars?". TreeHugger. Retrieved 2010-10-13.
  2. Ulf Bossel (2004). "Thermodynamic Analysis of Compressed Air Vehicle Propulsion" (PDF). Retrieved 2018-04-13.
  3. "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.
  4. "The Air Car Preps for Market". Technology Review. Retrieved 2010-10-13.
  5. "ELECTRIC CARS". www.speedace.info. Retrieved May 29, 2020.
  6. Braun, Adolphe: Luftlokomotive in "Photographische Ansichten der Gotthardbahn", Dornach im Elsass, ca. 1875
  7. "History and Directory of Electric Cars from 1834 to 1987". Didik.com. Retrieved 2009-09-19.
  8. "FAQ for the Airpod | Zero Pollution Motors". zeropollutionmotors.us. Retrieved 2017-04-03.
  9. "MDI refilling stations". web.archive.org. Mar 21, 2007. Retrieved May 29, 2020.
  10. Patrick Mazza; Roel Hammerschlag. "Wind-to-Wheel Energy Assessment" (PDF). Institute for Lifecycle Environmental Assessment. Archived from the original (PDF) on 2008-09-11. 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. Ma Shengqian (2008). "Metal-Organic Framework from an Anthracene Derivative Containing Nanoscopic Cages Exhibiting High Methane Uptake". Journal of the American Chemical Society. 130 (3): 1012–1016. doi:10.1021/ja0771639. PMID 18163628.
  14. "Tata Motors' air-powered car project still on, to be launch ready in 3 years". Auto Car Professional. Retrieved 24 August 2017.
  15. Zero Pollution Motors http://zeropollutionmotors.us/. Retrieved 25 August 2017. Missing or empty |title= (help)
  16. "Deakin Green Car Showcased in Ford Global Challenge". Deakin University. Retrieved 25 August 2017.
  17. "Ford Model T Design Challenge: the winners". Car Body Design. Retrieved 25 August 2017.
  18. "Green Speed Air Powered Motorcycle". Archived from the original on Feb 18, 2011. Retrieved May 29, 2020.
  19. "PSA : la révolution de l'Hybrid Air n'aura pas lieu". Les Echos. Jan 11, 2015. Retrieved May 29, 2020.
  20. "Toyota three-wheeler does 80.3 mph on compressed air". Physorg.com. Retrieved 2012-08-11.
  21. "Compressed air moped conversion". Archived from the original on Apr 1, 2008. Retrieved May 29, 2020.
  22. "Compressed air moped being built by Jem Stansfield". Ecogeek.org. Archived from the original on 2010-08-11. Retrieved 2010-10-13.
  23. "Honda Air concept car". Greenoptimistic.com. 2010-10-22. Retrieved 2012-01-26.
  24. "Pneumobile2020". pneumobil.hu. 2020-03-09. Retrieved 2020-03-09.
  25. "ACIPV2020". pneumobil.hu. 2020-03-09. Retrieved 2020-03-09.
  26. "Compressed-Air Propulsion". web.archive.org. Mar 3, 2016. Retrieved May 29, 2020.
  27. "Scientific American 1916-11-25". web.archive.org. Jun 25, 2016. Retrieved May 29, 2020.
  28. "Tramway Information". Tramwayinfo.com. Retrieved 2010-10-13.
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