Air engine

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The air engine is an emission-free piston engine using compressed air. The engines are similar to steam engines as they use the expansion of externally supplied pressurised gas to perform work against a piston. Small single cylinder engines are incorporated into small toy flying airplane models.

For practical application to transportation, several technical problems must be first addressed:

As the pressurised air expands, it is cooled, which limits the efficiency (see combined gas law). This cooling reduces the amount of energy that can be recovered by expansion, so practical engines apply ambient heat to increase the expansion available.
Conversely, the compression of the air by pumps (to pressurise the tanks) will heat the air. If this heat is not recovered it represents a further loss of energy and so reduces efficiency.
Storage of air at high pressure requires strong containers, which if not made of exotic materials will be heavy, reducing vehicle efficiency, while exotic materials (such as carbon fiber composites) tend to be expensive.
Energy recovery in a vehicle during braking by compressing air also generates heat, which must be conserved for efficiency.
It should be noted that the air engine is not truly emission-free, since the power to compress the air initially usually involves emissions at the point of generation.

The principle advantages for an air powered vehicle are:

Fast recharge time
Very low self-discharge (most batteries will deplete their charge without external load at a rate determined by the chemistry, design, and size, while compressed gas storage will have an extremely low leakage rate)
Long storage lifetime device (electric vehicle batteries have a limited useful number of cycles, and sometimes a limited calendar lifetime, irrespective of use).
Potentially lower initial cost than battery electric vehicles when mass produced.

The most recent development uses pressurized air as fuel in an engine invented by Guy Nègre, a French engineer. A similar concept is currently being developed by the Uruguayan engineer Armando Regusci, an Australian Angelo Di Pietro and a South Korea Chul-Seung Cho. Despite interest in the technology, no company has yet put a vehicle using this technology into mass production. A successful vehicle would offer many of the advantages of a battery electric vehicle with the additional ability to quickly restore the stored energy - in a few minutes rather than the hours required to recharge batteries.

1 History
2 Engine design
3 Uses of air engine
4 Compressed air as an energy carrier
5 The compressed air engine as a power plant for other vehicles
6 Safety
7 See also
8 External links

[edit] History

The air engine, and its concept to use air as an energy carrier is not new. It was used in old times (19th century) to power mine locomotives. After this, it was used (and is still being used) in car racing to give the first power to the car's main power plant, the internal combustion engine (ICE).

In 1991 the inventor Guy Nègre started up MDI and invented a dual-energy engine running on both compressed air as on regular fuel. From this moment on he managed to create a compressed air only-engine, and improved his design to make it more powerful. In the 15 years he's been working on this engine, considerable progress has been made: the engine is now claimed to be competitive with modern ICEs. It is probably still not as powerful as an ICE (although depending on which model of air engine vs model ICE). Proponents claim that this is of little importance since the car can simply be made lighter, or the tanks be put on a higher pressure, pushing the engine to above a comparable ICE-engine.

Other people that have been working on the idea, among them Armando Regusci, Angelo Di Pietro and Chul-Seung Cho. They too have companies, Rugusci's RegusciAir, Di Pietro's EngineAir and Chul-Seung Cho's Energine. They are selling their engines.

[edit] Engine design

It uses the expansion of compressed air to drive the pistons in a modified piston engine. Efficiency of operation is gained through the use of environmental heat at normal temperature to warm the otherwise cold expanded air from the storage tank. This non-adiabatic expansion has the potential to greatly increase the efficiency of the machine. The only exhaust gas is cold air (−15 °C), which may also be used for air conditioning in a car. The source for air is a pressurized carbon-fiber tank holding air at around 3,000 lbf/in² (20 MPa). Air is delivered to the engine via a rather conventional injection system. Unique crank design within the engine increases the time during which the air charge is warmed from ambient sources and a two stage process allows improved heat transfer rates.

The Armando Regusci's version of the air engine has several advantages over the original Guy Nègre's one. In original Guy Nègre's air engine, one piston compresses air from the atmosphere, holding it on a small container that feeds the high pressure air tanks with a small amount of air. Then that portion of the air is sent to the second piston where it works. During compression for heating it up, there is a loss of energy due to the fact that it cannot receive energy from the atmosphere as the atmosphere is less warm than it. Also, it has to expand as it has the crank. The Guy Nègre's air 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 efficiency. In the Regusci's version, the transmission system is direct to the wheel, and has variable torque from zero to the maximum with all the efficiency. When vehicle is stopped, Guy Nègre's engine has to be on and working, losing energy, while the Regusci's version has not.

In July 2004, Guy Nègre abandoned his original design, and showed later a new design where he stated to have it invented back in year 2001, but his new design is identical to the Armando Regusci's air engine which was patented back in 1989 (Uruguay) with the patent number 22976, and back in 1990 (Argentina). In those same patents, it is mentioned the use of electrical motors to compress air in the tanks.

[edit] Uses of air engine

The Nègre engine is used to power an urban car with room for five passengers and a projected range of about 100 to 200 miles (160 to 320 km), depending on traffic conditions. The main advantages are: no roadside emissions, low cost technology, engine uses food oil for lubrication (just about 1 liter, changes only every 30,000 miles (50,000 km)) and integrated air conditioning. Range could be quickly tripled, since there are already carbon fiber tanks which have passed safety standards holding gas at 10,000 lbf/in² (70 MPa).

The tanks may be refilled in about three minutes at a service station, or in a few hours at home plugging the car into the electric grid via an on-board compressor. The cost of driving such car is projected around 0.75€ per 100 km, with a complete refill at the "tank-station" at about US$3.

[edit] Compressed air as an energy carrier

It offers an advantage over electric as there are no batteries to manufacture or discard—which is an important environmental factor. Most modern batteries can be recycled, reducing this advantage.

As with electric, it must be stressed that compressed air is only an energy vector therefore can only be as clean as its source. Compressed air technology is not as technically appealing as electric or gas/electric hybrid but it is cheap, accessible to all and available now. For infrastructure, grocery store parking spaces could be fitted with a pressure hose, eliminating the need for refueling stations, although who would pay for the energy used, and the infrastructure required, is not quite clear. The energy could be obtained through wind turbines, or mechanically from a stream without having to go through an electric stage. This would obviously have an impact on the surrounding environment. Few grocery stores have a stream, or a wind turbine, at the moment.

[edit] The compressed air engine as a power plant for other vehicles

The air engine could not only power cars (both private/taxies) but possibly also buses. Boats, self–launching sailplanes and, rather less likely, airplanes (if they're using normal propellers and not turbofans), could be powered with this engine as well.

For fans of vehicles powered by alternative energy and electricity, a successful air engine would be news as well, since they can use it to power their own transferred-emissions vehicle. They can simply buy an air engine, tankage, adapter plate, motor mounts, and other components and connect it to a new or used car chassis, as is now done for electric vehicle conversion.

[edit] Safety

As with gasoline, compressed air has its safety concerns. The primary concern is the catastrophic rupture of the tank. This could occur at fill-up, during driving, while parked, or more probably at the time of an accident. These hazards are largely addressed by providing reserve strength and by using non-shattering materials for the tank.

[edit] See also

[edit] External links

Energy Development and Use Edit
Energy development \| Environmental concerns with electricity generation \| Future energy development \| Inertial fusion power plant \| Hydrogen storage \| Hydrogen station \| Hydrogen economy \| Hubbert peak theory \| Renewable energy \| Hypermodernity \| Technological singularity \| Air engine \| Liquid nitrogen economy \| Flywheel energy storage