
A compressed-air car is a
compressed-air vehicle fueled by
pressure vessels filled with
compressed air
Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, and o ...
. It is propelled by the release and expansion of the air within a
motor adapted to compressed air. The car might be powered solely by air, or combined (as in a hybrid electric vehicle) with other fuels such as
gasoline,
diesel, or an electric plant with
regenerative braking.
Compressed-air cars utilize a
thermodynamic process
Classical thermodynamics considers three main kinds of thermodynamic process: (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 change ...
. Air cools when expanding and heats when compressed. Thermal energy losses in the compresser and tankage reduce the
capacity factor of
compressed air
Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, and o ...
systems.
Isothermal compressed air energy storage ICAES plants can
store energy
Energy storage is the capture of energy produced at one time for use at a later time to reduce imbalances between energy demand and energy production.
A device that stores energy is generally called an accumulator or battery.
Energy comes in ...
with up to four times the energy per volume (capacity factor) of
lithium-ion batteries. The capacity factor can reach up to 3.6 MJ/m
3
In 2020, Dr. Reza Alizade Evrin of
Ontario Tech University developed an
isothermal 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 ...
.
This prototype used
low pressure air tanks and exhaust air recovery to power a paraffin
heat exchanger system. Its
energy efficiency reached 74%. This is as much as 90% of the efficiency of
lithium-ion electric car
An electric car, battery electric car, or all-electric car is an automobile that is propelled by one or more electric motors, using only energy stored in batteries. Compared to internal combustion engine (ICE) vehicles, electric cars are quie ...
s. It had a driving range of 140 km. Efficiency and range might be increased by a number of practical improvements. For example, combining the storage tank into the car chassis, higher pressure tanks, new rotary engines, and a more efficient heat exchanger. Also, the weight and cost of tanks and pneumatic parts might be reduced by using
recycled
Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...
and
bio-based thermoplastics.
This technology might develop into an inexpensive green transportation technology. The energy, vehicles and compressors might be easily produced by decentralized methods, even
circular industry. Using the plastics might permit open source fabrication using
numerical control
Numerical control (also computer numerical control, and commonly called CNC) is the automated control of machining tools (such as drills, lathes, mills, grinders, routers and 3D printers) by means of a computer. A CNC machine processes a pi ...
, including
additive manufacturing. The compressed air for such vehicles might be easily produced by common forms of
renewable energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
. For example, multistage
air compressors and intercoolers or
hydraulic pump
Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or hydrodynamic. A hydraulic pump is a mechanical source of power that converts mechanical power into hydraulic energy ( hydrostatic energy i.e. flow, pressure). It generat ...
s might be attached directly to
trompes,
hydropower,
VAWT wind turbines or
stirling engines using a
solar concentrator. Direct mechanical compression avoids the Carnot inefficiencies of heat engines. Insulated storage of compressed air avoids
energy conversion and battery storage. Heat-based systems might utilize tankage of solar-heated
molten salts driving a
heat exchanger rather than an onboard
heat recovery
Heat recovery ventilation (HRV), also known as mechanical ventilation heat recovery (MVHR), is an energy recovery ventilation system which works between two air sources at different temperatures. Heat recovery is a method which is used to reduce ...
system.
Electric energy,
electric grids and their issues might be avoided.
Tech
Engines for compressed air

There have been several dubious claims with undisclosed information. The "di pietro" engine has been partially tested with
CAD and
finite element analysis
The finite element method (FEM) is a popular method for numerically solving differential equations arising in engineering and mathematical modeling. Typical problem areas of interest include the traditional fields of structural analysis, heat ...
programs. The results were published by
Jarosław Zwierzchowski
Jarosław (; uk, Ярослав, Yaroslav, ; yi, יאַרעסלאָוו, Yareslov; german: Jaroslau) is a town in south-eastern Poland, with 38,970 inhabitants, as of 30 June 2014. Situated in the Subcarpathian Voivodeship (since 1999), pre ...
from
Lodz University of Technology in 2017,. This motor is an eccentric shaft vane motor that uses low air pressure.
Compressed air tanks and collision safety

The tanks must be designed to safety standards 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 ...
.
ISO 11439 is a similar standard, for compressed natural gas tanks.
The air storage tanks usable in compressed air cars can be low pressure (9 atm) or high pressure (240+ atm). Thus, they can be made of
composite materials like
thermoplastics and fiber reinforced thermoplastics,
This might permit low priced tankage. It might be made by
rotational molding. Such tanks can be much lighter than
lithium-iron batteries and 70% lighter than steel tanks. They resist rust from air, water and condensation. They last longer with less maintenance.
To reduce car weight further the
pressure vessels can be used as structural parts of the
chassis
A chassis (, ; plural ''chassis'' from French châssis ) is the load-bearing framework of an artificial object, which structurally supports the object in its construction and function. An example of a chassis is a vehicle frame, the underpart ...
. Advanced 700-atmosphere pressure vessels have been developed for
hydrogen cars
A hydrogen vehicle is a vehicle that uses hydrogen fuel for motive power. Hydrogen vehicles include hydrogen-fueled space rockets, as well as ships and aircraft. Power is generated by converting the chemical energy of hydrogen to mechanical energ ...
.
Crash tests
A crash test is a form of destructive testing usually performed in order to ensure safe design standards in crashworthiness and crash compatibility for various modes of transportation (see automobile safety) or related systems and componen ...
showed good safety. Fiber reinforced
thermoplastic tanks only rupture in collisions. They do not shatter or explode.
Hydrogen tanks require ‘high strength’ to prevent rupture and ‘high stiffness’ for durability. Strength resists an external force. Stiffness maintains a shape. Carbon fiber hydrogen fuel tanks are as light as plastic but six times the strength of steel and four times the stiffness. “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 is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, and o ...
has a low
energy density
In physics, energy density is the amount of energy stored in a given system or region of space per unit volume. It is sometimes confused with energy per unit mass which is properly called specific energy or .
Often only the ''useful'' or extract ...
, however nearby isothermal compressed air storage (ICAES) has almost 4 times
lithium-ion batteries capacity: 2.7 MJ/kg or 3.6 MJ/m
3.
Compressed air can also be produced by attaching an
air compressor or
hydraulic pump
Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or hydrodynamic. A hydraulic pump is a mechanical source of power that converts mechanical power into hydraulic energy ( hydrostatic energy i.e. flow, pressure). It generat ...
to a wind turbine
or by using a river, tidal or wave
hydropower turbine. These all convert directly from mechanical to pneumatic energy. Eliminating electricity from the loop gives higher efficiency overall. It is also possible to use thermal solar energy with a parabolic or
Fresnel lens solar concentrator to power a thermal
Stirling engine. This can move the compressor or pump. Solar Stirling is more efficient than solar steam or photovoltaic.
Emissions
Compressed air cars are emission free. They also do not require a connection to the electric grid. A
wind turbine or other
renewable energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
source can directly drive an
air compressor or
hydraulic pump
Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or hydrodynamic. A hydraulic pump is a mechanical source of power that converts mechanical power into hydraulic energy ( hydrostatic energy i.e. flow, pressure). It generat ...
. Compressed air cars do not rely on
petrol stations or an
electric grid. While centralized infrastructure might not be needed, it is an option. Tankage can be directly shipped, or a pipeline can be utilized.Compressed air is normally filtered to protect the compressor machinery. Therefore discharge air has very little suspended dust. There may be some lubricants emitted by some systems, but further development might reduce this with oil free compressors and intercoolers
Resource consumption
Composite
pressure vessels and pneumatic components could permit compressed air cars to be a
circular industry. The materials would have to be
biobased or
recycled
Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...
. Electric energy is not used, so there is no need for metals like copper, iron in magnets, etc.
Advantages
There can be a single conversion of mechanical energy to pneumatic or hydraulic energy.
Therefore compressed air can have high
energy efficiency when using mechanical
renewable energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
such as wind turbines or hydropower.
Thermal energy to
mechanical energy conversion is possible, but less efficient due to Carnot conversion inefficiencies. Thermal storage of heat from a renewable solar source is also possible using a phase change material such as a
molten salt.
Energy efficiency of the 2020 isothermal prototype vehicle was 59.4% of a
lithium-ion vehicle.
Isothermal compressed air
energy storage
Energy storage is the capture of energy produced at one time for use at a later time to reduce imbalances between energy demand and energy production.
A device that stores energy is generally called an accumulator or battery.
Energy comes in ...
(ICAES)
energy density
In physics, energy density is the amount of energy stored in a given system or region of space per unit volume. It is sometimes confused with energy per unit mass which is properly called specific energy or .
Often only the ''useful'' or extract ...
is good, whether measured by weight or volume: It can be as much as 2.7 MJ/kg or 3.6 MJ/m
3, which is four times
that of a
lithium-ion battery. This might be improved with higher pressure vessels, better motors and better
heat exchangers.
Compressed air technology adapts to
renewable energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
and possibly a
circular economy
A circular economy (also referred to as circularity and CE) is a model of production and consumption, which involves sharing, leasing, reusing, repairing, refurbishing and recycling existing materials and products as long as possible. CE aims ...
, if
biobased or recycled composites can be used. Thus it is more sustainable than
electric car
An electric car, battery electric car, or all-electric car is an automobile that is propelled by one or more electric motors, using only energy stored in batteries. Compared to internal combustion engine (ICE) vehicles, electric cars are quie ...
s. For example, there is much less use of metals, or toxic
battery chemistries. A centralized manufacturing and electric grid might be less necessary.
Efficiency is also helped by the
low weight of composite
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 ...
s relative to steel tanks or
lithium-ion batteries
Battery most often refers to:
* Electric battery, a device that provides electrical power
* Battery (crime), a crime involving unlawful physical contact
Battery may also refer to:
Energy source
*Automotive battery, a device to provide power t ...
.
Weight might be further reduced if the tanks support the car chassis. Pneumatic engines also have lower weights than electric engines.
Refueling is possible in many places using only wind,
solar power or
hydropower to move an
air compressor,
hydraulic pump
Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or hydrodynamic. A hydraulic pump is a mechanical source of power that converts mechanical power into hydraulic energy ( hydrostatic energy i.e. flow, pressure). It generat ...
or
Stirling engine.
Pneumatic power has energy synergy, because it is well suited to automotive
mechatronics. Many car systems can be powered by small air motors. For example,
active pneumatic suspension
Active may refer to:
Music
* ''Active'' (album), a 1992 album by Casiopea
* Active Records, a record label
Ships
* ''Active'' (ship), several commercial ships by that name
* HMS ''Active'', the name of various ships of the British Royal ...
, pneumatic steering, or pneumatic shock absorbers. Expansion of the compressed air creates cold temperatures, and can directly provide
air conditioning or climate control.
Energy recovery systems with
regenerative suspension A regenerative shock absorber is a type of shock absorber that converts parasitic intermittent linear motion and vibration into useful energy, such as electricity. Conventional shock absorbers simply dissipate this energy as heat.
When used in an ...
and
regenerative braking produce low pressure compressed air. This can be stored in 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 ...
.
Pistonless engines using compressed air are very quiet.
There is no
fire hazard after accidents, unlike systems that utilize combustion fuels or high power batteries.
Compressed air engines reduce the cost of car production, because there is no need to build a cooling system, spark plugs, starter motor, or mufflers.
The rate of
self-discharge is very low compared to batteries. A fueled, compressed-air vehicle may be left unused for a longer time than an electric car.
They reduce or eliminate hazardous chemicals such as gasoline, battery acids and related metals such as lead.
Compressed air cars are safer in more situations:
* potentially explosive work atmospheres
* brush-fire areas
* the vicinity of strong magnetic electric fields
*
radio quiet zones
Disadvantages
Compressed air
Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, and o ...
has a lower
Energy density
In physics, energy density is the amount of energy stored in a given system or region of space per unit volume. It is sometimes confused with energy per unit mass which is properly called specific energy or .
Often only the ''useful'' or extract ...
than
liquid nitrogen
Liquid nitrogen—LN2—is nitrogen in a liquid state at low temperature. Liquid nitrogen has a boiling point of about . It is produced industrially by fractional distillation of liquid air. It is a colorless, low viscosity liquid that is wide ...
or
hydrogen.
They have less
energy efficiency and range than
gas turbines,
internal combustion engines or battery vehicles. However the production of
compressed air
Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, and o ...
is more
energy efficient and so requires less
wind power and infrastructure per unit of energy.
While batteries 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. There are mechanical methods (e.g.
continuously variable transmission
A continuously variable transmission (CVT) is an automatic transmission that can change seamlessly through a continuous range of gear ratios. This contrasts with other transmissions that provide a limited number of gear ratios in fixed steps. T ...
s or auxiliary motors) to reduce this effect, but they add expense.
Developers and manufacturers
Various companies are investing in the
research, development and deployment of compressed air cars. The MDI Air Car made its public
South African debut in 2002.
It was predicted to be in production "within six months" in January 2004.
As of 2022, it was not in production.
MDI
MDI has proposed a range of vehicles made up of
AIRPod, OneFlowAir, CityFlowAir, MiniFlowAir and MultiFlowAir.
[Learn everything about the compressed air cars!](_blank)
. 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. This 'innovation' was first used in
torpedoes in 1904.
Tata Motors
,
Tata Motors of
India had planned to launch a car with an MDI compressed air engine in 2011.
In December 2009 Tata's vice president of engineering systems confirmed that the limited range and low engine temperatures were causing problems.
Tata Motors announced in May 2012 that they have assessed the design past phase 1, the "proof of the technical concept", and were proceeding to full production for the Indian market. Tata moved to phase 2, "completing detailed development of the compressed air engine into specific vehicle and stationary applications".
In February 2017, Dr. Tim Leverton, president and head at Advanced and Product Engineering at Tata revealed that the project was "starting industrialisation" with the first vehicles to be available by 2020. Other reports indicate Tata is also reviving plans for a compressed air version of the
Tata Nano, This had previously been under consideration as part of their collaboration with MDI.
Engineair Pty Ltd
Engineair is an Australian company. It produced prototypes of small vehicles using a rotary air engine designed by
Angelo Di Pietro
Angelo Di Pietro (22 May 1828 – 5 December 1914) was a cardinal of the Catholic Church and prefect of the Congregation of the Council.
Biography
Angelo Di Pietro was born in Vivaro Romano, Tivoli. He was educated at the Seminary of Tivoli ...
. The company is seeking commercial partners to utilise its engine.
Peugeot/Citroën
Peugeot and Citroën announced that they intended to build a car using compressed air as an energy source. However, it utilizes a hybrid system. A gasoline engine propels the car over 70 km/h or when the compressed air tank has been depleted.
In January 2015, there was disappointing news from France: PSA Peugeot Citroën has put an indefinite hold on the development of its promising-sounding Hybrid Air powertrain, apparently because the company has been unable to find a development partner willing to split the huge costs of engineering the system. Development costs are estimated to 500 million Euros. Production volumes would have to be more than 500,000 cars a year to repay these costs. The head of the project left Peugeot in 2014.
APUQ
APUQ (Association de Promotion des Usages de la Quasiturbine) has made the APUQ Air Car, a car powered by a
Quasiturbine.
See also
*
Air engine
*
Charging station
A charging station, also known as a charge point or electric vehicle supply equipment (EVSE), is a piece of equipment that supplies electrical power for charging plug-in electric vehicles (including electric cars, electric trucks, electric ...
*
Compressed air energy storage
*
Compressed air battery
*
Compressed air vehicles
*
Engine swap
*
Plug-in hybrid
A plug-in hybrid electric vehicle (PHEV) is a hybrid electric vehicle whose battery pack can be recharged by plugging a charging cable into an external electric power source, in addition to internally by its on-board internal combustion engin ...
*
Pneumatics
Pneumatics (from Greek ‘wind, breath’) is a branch of engineering that makes use of gas or pressurized air.
Pneumatic systems used in industry are commonly powered by compressed air or compressed inert gases. A centrally located and elec ...
References
External links
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{{DEFAULTSORT:Compressed Air Car
Automotive technologies
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