Pneumatic motor
A pneumatic motor or compressed air engine is a type of motor
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...

 which does mechanical work
Mechanical work
In physics, work is a scalar quantity that can be described as the product of a force times the distance through which it acts, and it is called the work of the force. Only the component of a force in the direction of the movement of its point of application does work...

 by expanding compressed air
Compressed air
Compressed air is air which is kept under a certain pressure, usually greater than that of the atmosphere. In Europe, 10 percent of all electricity used by industry is used to produce compressed air, amounting to 80 terawatt hours consumption per year....

. Pneumatic motors generally convert the compressed air to mechanical work through either linear or rotary motion. Linear motion can come from either a diaphragm or piston actuator, while rotary motion is supplied by either a vane type air motor or piston air motor.

Pneumatic motors have existed in many forms over the past two centuries, ranging in size from hand held turbines to engines of up to several hundred horsepower. Some types rely on pistons and cylinders, others use turbines. Many compressed air engines improve their performance by heating the incoming air, or the engine itself. Pneumatic motors have found widespread success in the hand-held tool industry and continual attempts are being made to expand their use to the transportation industry. However, pneumatic motors must overcome inefficiencies before being seen as a viable option in the transportation industry.


In order to achieve linear motion from compressed air, a system of pistons is most commonly used.  The compressed air is fed into an air-tight chamber that houses the shaft of the piston.  Also inside this chamber a spring is coiled around the shaft of the piston in order to hold the chamber completely open when air is not being pumped into the chamber.  As air is fed into the chamber the force on the piston shaft begins to overcome the force being exerted on the spring. As more air is fed into the chamber, the pressure increases and the piston begins to move down the chamber. When it reaches its maximum length the air pressure is released from the chamber and the spring completes the cycle by closing off the chamber to return to its original position. 

Piston motors are the most commonly used in hydraulic systems. Essentially, piston motors are the same as hydraulic pump
Hydraulic pump
Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or hydrodynamic.Hydrostatic pumps are positive displacement pumps while hydrodynamic pumps can be fixed displacement pumps, in which the displacement cannot be adjusted, or variable displacement pumps, which have a more...

s except they are used to convert hydraulic energy into mechanical energy.
Piston motors are often used in series of two, three, four, five, or six cylinders that are enclosed in a housing.  This allows for more power to be delivered by the pistons because several motors are in sync with each other at certain times of their cycle.


Another type of pneumatic motor, known as a rotary vane motor, uses air to produce rotational motion to a shaft.  The rotating element is a slotted rotor which is mounted on a drive shaft. Each slot of the rotor is fitted with a freely sliding rectangular vane. The vanes are extended to the housing walls using springs, cam action, or air pressure, depending on the motor design. Air is pumped through the motor input which pushes on the vanes creating the rotational motion of the central shaft. Rotation speeds can vary between 100 and 25,000 rpm depending on several factors which including the amount of air pressure at the motor inlet and the diameter of the housing.

Rotary motion vane-type air motors are used to start large industrial diesel or natural gas engines.  Stored energy in the form of compressed air, nitrogen or natural gas enters the sealed motor chamber and exerts pressure against the vanes of a rotor.  Much like a windmill, this causes the rotor to turn at high speed.  Because the engine flywheel requires a great deal of torque to start the engine, reduction gears are used. Reduction gears create high torque levels with the lower amounts of energy input. These reduction gears allow for sufficient torque to be generated by the engine flywheel while it is engaged by the pinion gear of the air motor or air starter.


A widespread application of small pneumatic motors is in hand-held tools, power ratchet wrenches, drills, sanders, grinders, cutters, and so on. Though overall energy efficiency of pneumatics tools is low and they require access to a compressed-air source, there are several advantages over electric tools. They offer greater power density (a smaller pneumatic motor can provide the same amount of power as a larger electric motor), do not require an axillary speed controller (adding to its compactness), generate less heat, and can be used in more volatile atmospheres as they do not require electric power.

Historically, many individuals have tried to apply pneumatic motors to the transportation industry. Guy Negre, CEO and founder of Zero Pollution Motors, has pioneered this field since the late 1980s. Recently Engineair has also developed a rotary motor for use in automobiles.  Engineair places the motor immediately beside the wheel of the vehicle and uses no intermediate parts to transmit motion which means almost all of the motor's energy is used to rotate the wheel.

History in transportation

The pneumatic motor was first applied to the field of transportation in the mid-19th century.  Though little is known about the first recorded compressed-air vehicle, it is said that the Frenchmen Andraud and Tessie of Motay ran a car powered by a pneumatic motor on a test track in Chaillot, France, on July 9, 1840.  Although the car test was reported to have been successful, the pair didn’t explore further expansion of the design.

The first successful application of the pneumatic motor in transportation was the Mekarski system
Mekarski system
The Mekarski system was a compressed-air propulsion system for trams invented by Louis Mékarski or Louis Mékarsky in the 1870s. He worked in France, was born in 1843 in Clermont-Ferrand of Polish origin...

 air engine used in locomotives.  Mekarski’s innovative engine overcame cooling that accompanies air compression by heating air in a small boiler prior to use.  The Tramway de Nantes
Tramway de Nantes
The Nantes tramway is a tramway system located around the city of Nantes, France. The first tramway in Nantes opened in 1879 and closed in 1958 due to bombing damage during World War II, while the present tramway was re-introduced to the city in 1985....

, located in Nantes, France, was noted for being the first to use Mekarski engines to power their fleet of locomotives. The tramway began operation on December 13, 1879, and continues to operate today, although the pneumatic trams were replaced in 1917 by more efficient and modern electrical trams.

American Charles Hodges also found success with pneumatic motors in the locomotive industry. In 1911 he designed a pneumatic locomotive and sold the patent to the H. K. Porter Company
H. K. Porter, Inc
H. K. Porter, Inc. manufactured light-duty railroad locomotives in the USA, starting in 1866. The company became the largest producer of industrial locomotives, and built almost eight thousand of them...

 in Pittsburgh for use in coal mines. Because pneumatic motors do not use combustion they were a much safer option in the coal industry.

Many companies claim to be developing Compressed air cars, but none are actually available for purchase or even independent testing.


Impact wrench
Impact wrench
An impact wrench is a socket wrench power tool designed to deliver high torque output with minimal exertion by the user, by storing energy in a rotating mass, then delivering it suddenly to the output shaft.Compressed air is the most common power source, although electric or hydraulic...

es, drills, firearms, die grinder
Die grinder
A die grinder is a handheld power tool used to grind, sand, hone, polish, or machine material, typically metal but also plastic or wood. They are usually pneumatically driven, although versions with electric and flexible shaft drive also exist...

s, dental drill
Dental drill
A dental drill is a small, high-speed drill used during dental procedures, usually to remove decay and shape tooth structure prior to the insertion of a filling or crown...

s and other pneumatic tools use a variety of air engines or motors. These include vane type pumps, turbines and pistons.


Most successful early forms of self propelled torpedo
The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...

es used high pressure compressed air, although this was superseded by internal or external combustion engines, steam engines, or electric motors.


Compressed air engines were used in trams and shunters, and eventually found a successful niche in mining locomotives, although eventually they were replaced by electric trains, underground. Over the years designs increased in complexity, resulting in a triple expansion engine with air-to-air reheaters between each stage. For more information see Fireless locomotive
Fireless locomotive
A fireless locomotive is a type of locomotive designed for use under conditions restricted by either the presence of flammable material or the need for cleanliness...

 and Mekarski system
Mekarski system
The Mekarski system was a compressed-air propulsion system for trams invented by Louis Mékarski or Louis Mékarsky in the 1870s. He worked in France, was born in 1843 in Clermont-Ferrand of Polish origin...



Transport category airplanes, such as commercial airliners, use compressed air starters to start the main engines. The air is supplied by the load compressor of the aircraft's auxiliary power unit
Auxiliary power unit
An auxiliary power unit is a device on a vehicle that provides energy for functions other than propulsion. They are commonly found on large aircraft, as well as some large land vehicles.-Function:...

, or by ground equipment.


There is currently some interest in developing air car
Air car
A compressed air car is a car that uses a motor powered by compressed air. The car can be powered solely by air, or combined with gasoline, diesel, ethanol, or an electric plant with regenerative braking.-Engines:...

s. Several engines have been proposed for these, although none have demonstrated the performance and long life needed for personal transport.


The Energine Corporation was a South Korean company that claimed to deliver fully assembled cars running on a hybrid compressed air and electric engine. The compressed-air engine is used to activate an alternator
An alternator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current.Most alternators use a rotating magnetic field but linear alternators are occasionally used...

, which extends the autonomous operating capacity of the car. The CEO was arrested for fraudulently promoting air motors with false claims


EngineAir, an Australian company, is making a rotary engine
Rotary engine
The rotary engine was an early type of internal-combustion engine, usually designed with an odd number of cylinders per row in a radial configuration, in which the crankshaft remained stationary and the entire cylinder block rotated around it...

 powered by compressed air, called The Di Pietro
Angelo Di Pietro (inventor)
Angelo Di Pietro is an engine designer who developed the Di Pietro Motor air engine.He qualified as Congegniatore Meccanico in Avellino and moved to Stuttgart to work on the Wankel rotary engine at the Mercedes Benz research laboratories 1969 and 1970. In 1971 he migrated to Australia where he...

The Di Pietro motor concept is based on a rotary piston. Different from existing rotary engines, the Di Pietro motor uses a simple cylindrical rotary piston (shaft driver) which rolls, with little friction, inside the cylindrical stator.

It can be used in boat, cars, carrier
Carrier may refer to:- Science :* Carrier wave, a waveform suitable for modulation by an information-bearing signal* Charge carrier, an unbound particle carrying an electric charge* a mathematical Set over which an algebraic structure is defined...

s and other vehicles. Only 1 psi
Pounds per square inch
The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...

 (≈ 6,8 kPa
KPA may refer to:* Kenya Ports Authority* Kiln phosphoric acid, a dry process to produce phosphoric acid at high temperature in a kiln* Kilopascal , a unit of pressure* Known-plaintext attack, a method of cryptanalysis* Korean People's Army...

) of pressure is needed to overcome the friction. The engine was also featured on the ABC's New Inventors program in Australia on 24 March 2004.


K'Airmobiles vehicles were intended to be commercialized from a project developed in France in 2006-2007 by a small group of researchers. However, the project has not been able to gather the necessary funds.

People should note that, meantime, the team has recognized the physical impossibility to use on-board stored compressed air due to its poor energy capacity and the thermal losses resulting from the expansion of the gas.

These days, using the patent pending 'K'Air Generator', converted to work as a compressed-gas motor, the project should be launched in 2010, thanks to a North American group of investors, but for the purpose of developing first a green energy power system.


In the original Nègre air engine, one piston compresses air from the atmosphere to mix with the stored compressed air (which will cool drastically as it expands). This mixture drives the second piston, providing the actual engine power. MDI's engine works with constant torque, and the only way to change the torque to the wheels is to use a pulley transmission of constant variation, losing some efficiency. When vehicle is stopped, MDI's engine had to be on and working, losing energy. In 2001-2004 MDI switched to a design similar to that described in Regusci's patents (see below), which date back to 1990.

It has been reported in 2008 that Indian car manufacturer Tata was looking at an MDI compressed air engine as an option on its low priced Nano automobiles. Tata announced in 2009 that the compressed air car was proving difficult to develop due to its low range and problems with low engine temperatures.


The Pneumatic Quasiturbine engine is a compressed air
Compressed air
Compressed air is air which is kept under a certain pressure, usually greater than that of the atmosphere. In Europe, 10 percent of all electricity used by industry is used to produce compressed air, amounting to 80 terawatt hours consumption per year....

 pistonless rotary engine
Pistonless rotary engine
A pistonless rotary engine is an internal combustion engine that does not use pistons in the way a reciprocating engine does, but instead uses one or more rotors, sometimes called rotary pistons...

 using a rhomboidal-shaped rotor whose sides are hinged at the vertices.

The Quasiturbine has demonstrated as a pneumatic engine using stored compressed air

It can also take advantage of the energy amplification possible from using available external heat, such as solar energy.

The Quasiturbine rotates from pressure as low as 0.1 atm (1.47psi).

Since the Quasiturbine is a pure expansion engine, while the Wankel and most other rotary engines are not, it is well-suited as a compressed fluid engine, air engine or air motor.


Armando Regusci's version of the air engine couples the transmission system directly to the wheel, and has variable torque from zero to the maximum, enhancing efficiency. Regusci's patents date from 1990.

Team Psycho-Active

Psycho-Active is developing a multi-fuel/air-hybrid chassis which is intended to serve as the foundation for a line of automobiles. Claimed performance is 50 hp/litre.

Conger Motor

Milton M. Conger in 1881 patented and supposedly built a motor that ran off compressed air or steam that using a flexible tubing which will form a wedge-shaped or inclined wall or abutment in the rear of the tangential bearing of the wheel, and propel it with greater or less speed according to the pressure of the propelling medium.

See also

  • Angelo Di Pietro (inventor)
    Angelo Di Pietro (inventor)
    Angelo Di Pietro is an engine designer who developed the Di Pietro Motor air engine.He qualified as Congegniatore Meccanico in Avellino and moved to Stuttgart to work on the Wankel rotary engine at the Mercedes Benz research laboratories 1969 and 1970. In 1971 he migrated to Australia where he...

  • Compressed air energy storage
    Compressed air energy storage
    Compressed Air Energy Storage is a way to store energy generated at one time for use at another time. At utility scale, energy generated during periods of low energy demand can be released to meet higher demand periods....

  • Compressor
    Gas compressor
    A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...

  • Simon Ingersoll
    Simon Ingersoll
    Simon Ingersoll founded the Ingersoll Rock Drill Company in 1871.In 1905 Ingersoll-Sargeant Drill Company merged with the Rand Drill Company to form Ingersoll-Rand. Unfortunately, Simon Ingersoll never found a way to make a fortune from his rock drill and died nearly penniless.-External links:*...

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