A compressed-air vehicle (CAV) is a transport mechanism fueled by tanks of pressurized

atmospheric An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosphere ...

gas and propelled by the release and expansion of the gas within a

pneumatic motor A pneumatic motor (air motor), or compressed-air engine, is a type of motor which does mechanical work by expanding compressed air. Pneumatic motors generally convert the compressed-air energy to mechanical work through either linear or rotary ...

. CAV's have found application in

torpedoes A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, such ...

, locomotives used in situations where standard locomotives are a hazard, and early prototype

submarines A submarine (often shortened to sub) is a watercraft capable of independent operation underwater. (It differs from a submersible, which has more limited underwater capability.) The term "submarine" is also sometimes used historically or info ...

. Compressed-air vehicles operate according to a

thermodynamic process Classical thermodynamics considers three main kinds of thermodynamic processes: (1) changes in a system, (2) cycles in a system, and (3) flow processes. (1) A Thermodynamic process is a process in which the thermodynamic state of a system is c ...

in which air cools down when expanding and heats up when being compressed, resulting in unwanted energy losses. However, with recent developments in

isothermal An isothermal process is a type of thermodynamic process in which the temperature ''T'' of a system remains constant: Δ''T'' = 0. This typically occurs when a system is in contact with an outside thermal reservoir, and a change in the sys ...

compressed air energy storage Compressed-air-energy storage (CAES) is a way to store energy for later use using compressed air. At a utility scale, energy generated during periods of low demand can be released during peak load periods. The first utility-scale CAES project ...

(ICAES) plants, compressed air storage has reached 3.6 MJ/m³ and four times the

capacity factor The net capacity factor is the unitless ratio of actual electrical energy output over a given period of time to the theoretical maximum electrical energy output over that period. The theoretical maximum energy output of a given installation is def ...

lithium-ion A lithium-ion or Li-ion battery is a type of rechargeable battery that uses the reversible Intercalation (chemistry), intercalation of Li+ ions into electronically Electrical conductor, conducting solids to store energy. Li-ion batteries are c ...

batteries with 2.7 MJ/kg. In 2020 there were developments published by Dr. Reza Alizade Evrin from

Ontario Tech University The University of Ontario Institute of Technology, branded as Ontario Tech University or Ontario Tech, is a public university, public research university located in Oshawa, Ontario, Canada. The university's main campus is located on approximately ...

with an isothermal compressed-air vehicle prototype that uses low-pressure air tanks and exhaust air recovery to power a paraffin

heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...

system with a global energy efficiency of 74% and a driving range of . This efficiency and range can be increased by using storage tanks as vehicle structure, high-pressure tanks, new rotary engines, and a more efficient heat exchanger. Compressed-air propulsion may also be incorporated in hybrid systems, such as with battery electric propulsion. This kind of system is ''hybrid pneumatic–electric'' propulsion.

Regenerative braking Regenerative braking is an energy recovery mechanism that slows down a moving vehicle or object by converting its kinetic energy or potential energy into a form that can be either used immediately or stored until needed. Typically, regenerativ ...

can also be used in such systems.

Compressed-air engines

In principle, any

can be used for a compressed-air vehicle, but some engines were specifically developed for this application and/or have specific advantages.

Di Pietro engine

There have been several dubious claims with undisclosed information. However, the "Di Pietro" engine has been partially tested with CAD and

finite element analysis Finite element method (FEM) is a popular method for numerically solving differential equations arising in engineering and mathematical models, mathematical modeling. Typical problem areas of interest include the traditional fields of structural ...

program and published in scientific papers by Jarosław Zwierzchowski from Lodz University of Technology in 2017, which is an eccentric shaft vane motor that uses low air pressure.

Liquidpiston

Another recent engine that could be adapted to compressed air is the

Liquidpiston The red line is a three lobe epitrochoid, which is the shape of the LiquidPiston's swept volume The X-engine is a type of pistonless rotary engine manufactured by LiquidPiston of Bloomfield, Connecticut. The X engine is a hybrid cycle rotar ...

rotary engine.

Compressed-air tanks and collision safety

The tanks must be designed to safety standards appropriate for a

pressure vessel A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. Construction methods and materials may be chosen to suit the pressure application, and will depend on the size o ...

, such as

ISO 11439 Compressed natural gas (CNG) is a fuel gas mainly composed of methane (CH4), compressed to less than 1% of the volume it occupies at standard atmospheric pressure. It is stored and distributed in hard containers at a pressure of , usually in ...

. The pressure vessels or air storage tanks that can be used in compressed-air vehicles can be made for low pressure () or high (more than ), and can be made of composite materials like thermoplastic and fiber-reinforced thermoplastics, that means that the price can drop by using recycled or biobased thermoplastics using

rotational molding Rotational molding (BrE: moulding) involves a heated mold which is filled with a charge or shot weight of the material. It is then slowly rotated (usually around two perpendicular axes), causing the softened material to disperse and stick to t ...

and they are much lighter than lithium-ion batteries and 70% lighter compared to steel tanks, also they have more lifespan and don't need much maintenance. To reduce vehicle weight further the air tanks can be used as structural storage so the tank is the main part of the vehicle chassis while using appropriate impact isolation, however fiber reinforced thermoplastic tanks only have ruptures in case of collision and don't explode. Some advances in pressure vessels for vehicles have been developed for hydrogen vehicles with high compression pressure vessels. Automobile designer Hyundai states:

Hydrogen tanks require ‘High Strength’ to prevent rupture and ‘High Stiffness’ for durability. Strength is defined as the level of resistance to an influence of an external force. Stiffness is the level of resistance maintaining its original shape. The carbon fiber materials used in making hydrogen fuel tanks is as light as a plastic but has six and four times the strength and stiffness of steel, respectively. “When a bullet penetrates a hydrogen tank, it does not explode. Instead, hydrogen leaks out through the bullet hole. In a standard collision test, not even a tiny amount of hydrogen was detected because none had leaked out.

Compressed-air production, storage and energy efficiency and density

Compressed air Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air in vehicle tires and shock absorbers are commonly used for improved traction and reduced vibration. Compressed air is an important medium for t ...

has a low

energy density In physics, energy density is the quotient between the amount of energy stored in a given system or contained in a given region of space and the volume of the system or region considered. Often only the ''useful'' or extractable energy is measure ...

, however near-isothermal compressed air storage ICAES can reach 3.6 MJ/m³ and has almost four times the energy density of

batteries with 2.7 MJ/kg. Compressed air can be produced by attaching an

air compressor An air compressor is a machine that takes ambient air from the surroundings and discharges it at a higher pressure. It is an application of a gas compressor and a Pneumatics, pneumatic device that energy conversion, converts mechanical power (from ...

hydraulic pump A hydraulic pump is a mechanical source of power that converts mechanical power into hydraulic energy ( hydrostatic energy i.e. flow, pressure). Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or hydrodynamic. They gen ...

to a wind turbine or using river, tidal, wave

hydropower Hydropower (from Ancient Greek -, "water"), also known as water power or water energy, is the use of falling or fast-running water to Electricity generation, produce electricity or to power machines. This is achieved by energy transformation, ...

turbine with only a conversion from mechanical to pneumatic energy, eliminating electricity from the loop which gives higher efficiency overall. Additionally, there is the possibility of using thermal energy with a parabolic or

Fresnel lens A Fresnel lens ( ; ; or ) is a type of composite compact lens (optics), lens which reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections. The simpler Dioptrics, d ...

solar concentrator to power a thermal

Stirling engine A Stirling engine is a heat engine that is operated by the cyclic expansion and contraction of air or other gas (the ''working fluid'') by exposing it to different temperatures, resulting in a net conversion of heat energy to mechanical Work (ph ...

to move the compressor or pump, as solar-powered Stirling engines are more efficient than solar steam and photovoltaic.

Emissions

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 compressor or engine. This can be mitigated by using oil-free air compressors.

Resource consumption

The recent developments of composite

pressure vessels A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. Construction methods and materials may be chosen to suit the pressure application, and will depend on the size o ...

and pneumatic components mean that compressed-air vehicles can be part of the circular industry with biobased or

recycled Recycling is the process of converting waste materials into new materials and objects. This concept often includes the recovery of energy from waste materials. The recyclability of a material depends on its ability to reacquire the propert ...

components. Also, by cutting electric energy from the loop there is no need for an electric grid and the metals used like copper, iron in magnets, etc.

History

CompressedAirLocomotive Section1 AdolpheBraun1811to1877

Compressed air has been used since the 19th century to power mine

locomotives A locomotive is a rail vehicle that provides the motive power for a train. Traditionally, locomotives pulled trains from the front. However, push–pull operation has become common, and in the pursuit for longer and heavier freight train ...

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 A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, such ...

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, United Kingdom, manufactured several 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. 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

With the

efficiency Efficiency is the often measurable ability to avoid making mistakes or wasting materials, energy, efforts, money, and time while performing a task. In a more general sense, it is the ability to do things well, successfully, and without waste. ...

of using wind turbines to power compressors or pumps, there is a single conversion of mechanical to pneumatic or hydraulic energy. Also, by powering the compressor with a

using a parabolic or

solar concentrator, there is thermal to

mechanical energy In physical sciences, mechanical energy is the sum of macroscopic potential and kinetic energies. The principle of conservation of mechanical energy states that if an isolated system is subject only to conservative forces, then the mechanical ...

conversion. Lastly, by using a phase change material in the

heated with

concentrated solar power Concentrated solar power (CSP, also known as concentrating solar power, concentrated solar thermal) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight into a receiver. Electricity is generated whe ...

there is only solar thermal energy involved. The most efficient compressed-air vehicle as of 2020 is an isothermal prototype at 74%, which is similar to the 73-90% of

electric vehicles An electric vehicle (EV) is a motor vehicle whose propulsion is powered fully or mostly by electricity. EVs encompass a wide range of transportation modes, including road vehicle, road and rail vehicles, electric boats and Submersible, submer ...

using

batteries. Compared to lithium-ion, isothermal

(ICAES) can be at least 2.7 MJ/kg or 3.6 MJ/m³, 4 times of lithium-ion batteries, which can be improved with high-pressure vessels and heat exchanger systems. Resources, compressed air technology can be adapted to

renewable energy Renewable energy (also called green energy) is energy made from renewable resource, renewable natural resources that are replenished on a human lifetime, human timescale. The most widely used renewable energy types are solar energy, wind pow ...

and circular industry with biobased or recycled composites and so compared to

electric vehicle An electric vehicle (EV) is a motor vehicle whose propulsion is powered fully or mostly by electricity. EVs encompass a wide range of transportation modes, including road vehicle, road and rail vehicles, electric boats and Submersible, submer ...

s they can be exempt from finite mineral resources or toxic processes used in battery and

electric motor An electric motor is a machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a electromagnetic coil, wire winding to gene ...

manufacturing and also from the electric grid use. Refilling is possible in almost any place or with onboard equipment. It may take advantage of other renewable sources such as wind,

solar power Solar power, also known as solar electricity, is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Solar panels use the photovoltaic effect to c ...

or river, tidal, wave

to move an

. The structural weight of composite

s is low relative to

batteries and also to steel tanks (70% lighter), which can be reduced by using the tanks as vehicle chassis structures with appropriate impact isolation. The wheel hub motor rotary engines are also light weight. They have energy synergy with the available pneumatic energy, so all vehicle

mechatronics Mechatronics engineering, also called mechatronics, is the synergistic integration of mechanical, electrical, and computer systems employing mechanical engineering, electrical engineering, electronic engineering and computer engineering, and also ...

systems can be powered by small air motors, and the vehicle can also use active pneumatic suspension, pneumatic steering or pneumatic shock absorption bumpers, and provide

air conditioning Air conditioning, often abbreviated as A/C (US) or air con (UK), is the process of removing heat from an enclosed space to achieve a more comfortable interior temperature, and in some cases, also controlling the humidity of internal air. Air c ...

or climate control using the low temperature created during air expansion.

Energy recovery Energy recovery includes any technique or method of minimizing the input of energy to an overall system by the energy transfer, exchange of energy from one sub-system of the overall system with another. The energy can be in any form in either sub ...

systems with regenerative suspension and

regenerative braking Regenerative braking is an energy recovery mechanism that slows down a moving vehicle or object by converting its kinetic energy or potential energy into a form that can be either used immediately or stored until needed. Typically, regenerativ ...

produce low pressure compressed air to be stored in an additional

. There is little noise from pistonless rotary engines while using compressed air, which can also being soundproofed because the low temperature in which it works. There is no fire hazard, which makes it one of the few

transportation Transport (in British English) or transportation (in American English) is the intentional Motion, movement of humans, animals, and cargo, goods from one location to another. Mode of transport, Modes of transport include aviation, air, land tr ...

systems that cannot produce spontaneous or after-collision fire or explosions as with petrol, ethanol, hydrogen and also battery vehicles.

Disadvantages

The

compressed air Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air in vehicle tires and shock absorbers are commonly used for improved traction and reduced vibration. Compressed air is an important medium for t ...

is low compared to

liquid nitrogen Liquid nitrogen (LN2) is nitrogen in a liquid state at cryogenics, low temperature. Liquid nitrogen has a boiling point of about . It is produced industrially by fractional distillation of liquid air. It is a colorless, mobile liquid whose vis ...

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

, and the energy efficiency of compressed air engine compared to micro

gas turbine A gas turbine or gas turbine engine is a type of Internal combustion engine#Continuous combustion, continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas gene ...

with adequate

soundproofing Soundproofing is any means of impeding sound propagation. There are several methods employed including increasing the distance between the source and receiver, decoupling, using noise barriers to reflect or absorb the energy of the sound waves, ...

that can be used in hybrid gas turbine-electric motor vehicles with a mixture of compressed air, liquid nitrogen or hydrogen (previous gas turbine vehicles have used a setup for speed, rather than efficiency consisting in a large noise gas turbines connected to the transmission) since the gas turbine (which are used in

thermal power plants A thermal power station, also known as a thermal power plant, is a type of power station in which the heat energy generated from various fuel sources (e.g., coal, natural gas, nuclear fuel, etc.) is converted to electrical energy. The heat ...

due to its

) outperforms pistonless rotary engines, however the production of

is more energy efficient and so requires less

wind power Wind power is the use of wind energy to generate useful work. Historically, wind power was used by sails, windmills and windpumps, but today it is mostly used to generate electricity. This article deals only with wind power for electricity ge ...

and infrastructure and also there is a loss of efficiency from

to generator and to

. 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, reducing available power.

Possible improvements

It may be possible to store compressed air at lower pressure using an absorption material within the tank. Absorption materials like

Activated carbon Activated carbon, also called activated charcoal, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed (activated) to have small, low-volume pores that greatly increase the surface ar ...

, or a metal organic framework is used for storing

compressed natural gas Compressed natural gas (CNG) is a fuel gas mainly composed of methane (CH4), compressed to less than 1% of the volume it occupies at standard atmospheric pressure. It is stored and distributed in hard containers at a pressure of , usually in ...

at instead of , which amounts to a large energy saving.

Vehicles

American compressed air locomotive used in boring the Rove Tunnel Scientific American 1916-11-25

Production cars

Several companies are investigating and producing

prototype A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and Software prototyping, software programming. A prototype ...

s 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 and MDI's US distributor Zero Pollution Motors says production of the AIRPod will commence in Europe in 2018.

Experimental cars and bikes

In 2008, a compressed air and

natural gas Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...

powered vehicle designed by engineering students at

Deakin University Deakin University is a public university in Victoria, Australia. Founded in 1974 with antecedent history since 1887, the university was named after Alfred Deakin, the second Prime Minister of Australia and a founding father of Australian Fede ...

in Australia was the joint winner of the

Ford Motor Company Ford Motor Company (commonly known as Ford) is an American multinational corporation, multinational automobile manufacturer headquartered in Dearborn, Michigan, United States. It was founded by Henry Ford and incorporated on June 16, 1903. T ...

T2 competition to produce a car with a range and an estimated cost of less than $7,000. Australian company Engineair has produced several 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. Three mechanical engineering students from

San Jose State University San José State University (San Jose State or SJSU) is a Public university, public research university in San Jose, California. Established in 1857, SJSU is the List of oldest schools in California, oldest public university on the West Coast of ...

; 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 Santa Cruz (Spanish language, Spanish for "Holy Cross") is the largest city and the county seat of Santa Cruz County, California, Santa Cruz County, in Northern California. As of the 2020 United States census, 2020 census, the city population ...

) and NO DIG NO RIDE (from

Aptos, California Aptos (Ohlone for "The People") is an unincorporated town in Santa Cruz County, California, United States. The town is made up of several small villages, which together form Aptos: Aptos Hills-Larkin Valley, Aptos Village, Cabrillo, Seacliff, ...

.). The top speed of the maiden voyage in May 2009 was . 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 . Peugeot said the new hybrid system should get up to 141 miles per gallon of gas. Models were claimed to start rolling out as early as 201

. However, 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. "Ku:Rin" named air-compressed three-wheeler vehicle was created by

Toyota is a Japanese Multinational corporation, multinational Automotive industry, automotive manufacturer headquartered in Toyota City, Aichi, Japan. It was founded by Kiichiro Toyoda and incorporated on August 28, 1937. Toyota is the List of manuf ...

in 2011. The specialty of this vehicle is it has registered a record-breaking highest speed of even if it has an engine that 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". As part of the TV-show Planet Mechanics, Jem Stansfield and Dick Strawbridge converted a regular scooter to a compressed air moped. This has been done by equipping the scooter with a compressed-air engine and air tank. In 2010, Honda presented the Honda Air concept car at the LA Auto Show. 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. PowAir

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

Trains, Trams, Boats and Planes

Compressed-air locomotives are a kind of fireless locomotive and have been used in mining and tunnel boring. Various compressed-air-powered trams were trialled, starting in 1876. In

Nantes Nantes (, ; ; or ; ) is a city in the Loire-Atlantique department of France on the Loire, from the Atlantic Ocean, Atlantic coast. The city is the List of communes in France with over 20,000 inhabitants, sixth largest in France, with a pop ...

and

Paris Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, largest city of France. With an estimated population of 2,048,472 residents in January 2025 in an area of more than , Paris is the List of ci ...

Mekarski system trams ran in regular service for over 30 years. See also Nantes tramway#Compressed-air trams (1879–1917). Currently, no water or air vehicles exist that make use of the compressed-air engine. Historically certain

es were propelled by compressed-air engines.

References

External links

Experimental investigation of a compressed air vehicle prototype with phase change materials for heat recoveryCompressed air cars for urban transportation Sep 7, 2020

Thermal analysis of near-isothermal compressed gas energy storage system
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(

Society of Automotive Engineers SAE International is a global professional association and standards organization based in Warrendale, Pennsylvania, United States. Formerly the Society of Automotive Engineers, the organization adopted its current name in 2006 to reflect bot ...

)
Hydraulic Hybrid Research
(

United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent agency of the United States government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it began operation on De ...

)
OSEN page about Compressed Air Technology

Environmentally Friendly, Engine, Invention , MelbourneAir Powered Vehicle designed and built by students at San Jose State University
{{DEFAULTSORT:Compressed-Air Vehicle *