Compressed air
Compressed air is a versatile energy source that can power engines and perform various types of work. It is stored in pressure vessels, similar to how batteries store electrical energy, allowing for long-term storage with minimal energy loss. Compressed air is generated by air-compressing machines and delivered through a distribution system of tanks and pipes. Historically, the use of compressed air dates back to ancient times with bellows for furnace combustion, leading to innovations in metalworking and later the development of air-powered tools, such as drills and hammers.
Modern applications of compressed air include powering air-operated valves in industrial settings and serving as a control mechanism in various machines, including aircraft. Compressed air can also assist in the operation of submarines and is used in specific missile systems. In transportation, air-powered vehicles have been explored since the 19th century, with advancements allowing for cars that run on compressed air, offering a potentially eco-friendly alternative to gasoline vehicles. These vehicles can reach speeds of up to 68 miles per hour, though their range remains limited compared to traditional fuel-powered cars. Overall, compressed air presents a unique approach to energy utilization across diverse fields.
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Compressed air
Summary: Compressed air is a potential energy source that can be used to power engines and perform work.
Compressed air can be stored in pressure vessels as potential energy. These vessels can store the energy in a way that is analogous to the way a battery stores electrical energy. The compressed gas does not degrade in a pressure vessel, and thus the potential energy can be stored for long periods of time with little or no energy loss. Compressed air can also be supplied by air-compressing machines to a distribution system of tanks, accumulators, and pipes that deliver the compressed air on demand. Compressed air can also be used to regulate processes, and air-controlled actuators, relays, and positioners are common. Air compressors that provide compressed air come in many forms and can be piston-based reciprocating compressors, centrifugal compressors, or turbine wheel compressors.
The use of compressed air power started in ancient times with the use of bellows to compress air to enhance furnace combustion. Both human- and animal-powered bellows allowed furnace temperatures to be raised, making possible the development of metalworking. The bellows was just the start; it was soon learned that compressed air’s potential energy could be converted to useful work in many devices.
The first air compressor was invented by German Otto von Guericke in 1650. This invention led to air-powered tools, including drills, hammers, saws, and rams, which are now common in industry. The light weight and compact size per unit of power make air-powered tools very desirable and inexpensive. Air compressors and air delivery piping are easily engineered and relatively safe. Air-powered vehicles and tools can be used in hazardous locations where tools and vehicles powered by fossil fuels would be dangerous and prohibited; some of these environments include underground mines and other confined spaces. Another use of compressed air is to transport parcels in pneumatic tubes. This type of transport uses compressed air to propel a capsule, containing the item to be delivered, through a transport tube. Pneumatic transfer tubes have been extensively used in the postal and banking industries to move small paper items, such as checks, cash, letters, and other documents. Diesel and jet engines can be started using relatively small air motor starters to get the larger main engine turning. The use of air-powered starters for aircraft and ship engines is common if compressed air is readily available.
Compressed air is used for control power to operate systems of machines and processes. Air-operated valves are common in industry and are also used for aircraft controls. Compressed air, when exposed to a movable diaphragm, can produce large forces if either the air pressure or the diaphragm surface area is large enough. Compressed air bladders and rams can be used to lift very heavy loads. Compressed air is used in the submarine service to raise the submarine to the surface of the ocean by pushing water out of ballast tanks to make the submarine more buoyant. The compressed air can also be used to level a submarine by shifting weight in ballast tanks and removing water as needed to level the submarine. There are also several weapons that use compressed air. Small-bore rifles as pistols that use compressed air are accurate and economical for target shooting and small-game hunting. Some missile systems use compressed air to help eject the missile out of a launch tube. Air assist launch in a tube launcher is a good way to limit the heat and exhaust of the rocket, as well as to get the rocket moving prior to main propulsion start.
Another use of compressed air engines is in transportation. Air-powered vehicles have been in service since the nineteenth century. Some of the first of these vehicles were made in France by Andraud and Tessie du Motay in 1838. In the late 1800s, the H. K. Porter company in Pittsburgh and Mekarsji in France built several air-powered trolleys and trains. In the 1990s in India, engineer Guy Negre developed several cars that can operate on compressed air. These cars can operate at speeds up to 68 miles (110 kilometers) per hour and have a range of up to 111 miles (180 kilometers) when operating on air alone. The cars have tanks that can be filled with compressed air, which acts as the car’s fuel. These cars weigh between 320 and 850 kilograms (705 to 1,873 pounds) and can carry up to five passengers.
The air tank can be pressurized to approximately 300 bars (4,531 pounds per square inch), and the cars have a fossil-fuel-powered air compressor to provide air while traveling to extend the operating range of the vehicle. The air tanks hold approximately 90 liters of compressed air. The stored potential energy of 90 liters of air is about 8 horsepower for 1 hour. If electricity cost 10 cents per kilowatt-hour, it would cost about $12 to compress the air for one tank load using a standard-efficiency air compressor. As a result, this type of air-powered car gets about 9 to 10 miles per dollar of fuel, using 10-cent-per-kilowatt electricity to compress the air for the car. The equivalent efficiency in a gasoline-powered vehicle would, at a cost of $4 per gallon, need to get 40 miles per gallon.
As the price of gasoline rises and the cost of a vehicle’s carbon footprint increases, air-powered cars using electricity from hydropower, wind power, or nuclear powered electric generators may be a viable option for transportation. It is important to note, however, that the mileage range of a compressed-air vehicle is much lower than that of a comparable gasoline-powered car.
Bibliography
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Fang, Yidong et al. "A Review of Compressed Air Systems in Vehicle Transport." Energy Strategy Reviews, vol. 33, Jan. 2021, doi.org/10.1016/j.esr.2020.100583. Accessed 30 July 2024.
Gizmag. “French Auto Runs on Compressed Air Technology.” www.gizmag.com/go/3523/. Accessed 30 July 2024.
"Under Pressure: Compressed Air Systems Can Make or Break Your Environmental Goals." The Engineer, 7 Nov. 2023, www.theengineer.co.uk/content/product/under-pressure-compressed-air-systems-can-make-or-break-your-environmental-goals/. Accessed 30 July 2024.