Compressed-air car

A Compressed air car is a car that uses a motor powerd by compressed air.

This can be combined with hybrid gasoline/diesel or electric plant and regenerative braking.

Several companies are investigating and producing prototypes and other ones, including Tata Motors, state that "the first cars should be available on the market in summer 2008."

Overview

The compressed Air car has been mentioned by Popular Mechanics and Green News as being the true car of tomorrow, with the same mileage and zero emissions as a fuel-cell car without the dangers currently associated with hydrogen.

History

Main articles: Compressed air vehicle and air engine

Technology

Compressed air cars are powered by engines, fueled by compressed air, which is stored in a tank under high pressure such as 30 MPa (4500 psi or 300 bar), following ISO 11439 . The storage tank is likely to be made of carbon-fiber in order to reduce its weight while achieving the necessary strength. Instead of mixing fuel with air and burning it to drive pistons with hot expanding gases; compressed air cars use the expansion of compressed air to drive their pistons.

Compressed air is a heavy way of storing fuel, 300l air at 300 MPa only amounts to about 12kWh (the equivalent of 1.4 liter (0.37 gallons) of gasoline). During rupture testing, the tank cracks, but does not break up, producing no splinters or fragments. In the event of a cracked tank, it is most likely to occur within the cylinder itself.

While gasoline or diesel fuel tank have the same amount of energy per litre of fuel from the first to the last litre, compressed air motors rely on the pressure within the tank, which decreases as air is drawn off.

All four major manufacturers who are developing air cars have designed safety features into their containers as opposed to hydrogen's issues of damage and danger involved in high-impact crashes. Air, on its own, is also non-flammable. Though no company has yet demonstrated the effectiveness of an imploding engine (ZAP) vs a quick release (MDI) standard, and other safety designs; it is expected that large-scale production may lead specific governments to set their own standards. It was reported on Discovery's Beyond Tomorrow that on its own carbon-fiber is brittle and splits; but creates no shrapnel.

Emission output

Compressed air cars are emission-free at the 'tailpipe', but their compressed air tanks are recharged using (typically) electric compressors and the electricity for such compressors can, in some territories, come from fossil fuels via power stations, so unless all the electricity comes from a renewable alternative source or nuclear plants, compressed air cars will still cause emissions of Greenhouse gas. However, emissions would be relocated from city streets to remote smokestacks, and it is also more efficient to burn fuel at power plants than it is to burn it in car engines. Of course a solar and/or wind recharging system can be installed in one's home or power plants, therefore eliminating the dependence of consumption of nuclear-fossil electricity.

An air motor also releases air cleaner than its intake, due to the presence of an air filter to keep contaminants out of the mechanism. Consequently, this can be viewed as air purification, instead of air pollution.

Disadvantages

Having solved most of the high pressure storage and handling problems, the main remaining disadvantages are related to the thermodynamics.

• At the supply station, compressing the air heats it, and if then directly transferred in a heated state to the vehicle storage tanks will then cool and reduce the pressure. If cooled before transfer, the energy in this heat will be lost unless sophisticated low grade heat utilization is employed (see cogeneration).
• Within the vehicle, expansion and consequent pressure reduction in the throttle or engine chills the air, reducing its effective pressure. Addition of ambient heat will increase this pressure and this addition leads to a more complex propulsion system. While an attempt was made in the Nègre system to warm the air in a long portion of the stroke at top dead center, it appears that this scheme has been abandoned due to inherent imbalances causing unacceptable levels of vibration.
• Passenger compartment heating is more difficult since the propulsion system does not provide a source of waste heat. Some form of heat pump, or more likely, an electric heater would be required.
• Limited range due to available tank technology. The air engine suffers from similar problems to hydrogen vehicles in this regard.
• Using energy to compressed air is less efficient than charging a battery with that same energy.
• Less efficient than electric motors.
• While the air engine reduces greenhouse gas emissions from the vehicle, the energy used to compress the air may not come from clean sources.
• Long refill times when compared to conventional automobiles, circa 4 Hours using a home or low-end system; a few minutes at a larger, commercial refilling station.

Advantages

The principle advantages for an air powered vehicle are:

• Fast recharge time, 3 or 4 minutes for volume transfer at a commercial refill station; hours at home or low-end station.
• Very low self-discharge rate (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). This means that batteries in operation are much more expensive than compressed air storage, and are more pollutant because a lot more pollutant material needs to be used (typical car batteries are made from sulphuric acids and lead).
• Lower initial cost than battery electric vehicles when mass produced (€3,000).
• Expansion of the compressed air reduces its temperature and heat from the passenger compartment may be cooled using a heat exchanger, providing both relief from hot weather air conditioning and increased efficiency.
• Zero pollutant emissions from the vehicle itself.

Models

Overoptimistic reports of impending production date back to at least May 1999. The MDI Air Car made its public debut in South Africa in 2002, and was predicted to be in production "within six months" in January 2004. Various companies are investing in the research, development and deployment of Compressed air cars .

Currently two companies, MDI and Energine, base the development of their projects on the principle of small cars, reducing the tare weight to the maximum. MDI also promotes larger vehicles, called MultiCATs.

Energine

This South Korean company has been claiming to develop a pneumatic hybrid electric vehicle (PHEV). The CEO is the first compressed air car promoter to be arrested for fraud.

Engineers from this company have made, starting from a Daewoo Matiz, a prototype of a hybrid electric/compressed-air engine (Pne-PHEV, pneumatic plug-in hybrid electric vehicle). The compressed-air engine is used to activate an alternator, which extends the autonomous operating capacity of the car.

The Energine Corporation is a company that delivers fully-assembled cars running on a hybrid compressed air and electric engine. These cars are more precisely named pneumatic-hybrid electric vehicles.

A similar (but only for braking energy recovery) concept using a pneumatic accumulator in a largely hydraulic system has been developed by U.S. government research laboratories and industry, and is now being introduced for certain heavy vehicle applications such as refuse trucks.

EngineAir

EngineAir, an Australian company, is developing a rotary engine powered by compressed air.

K'Airmobiles

K'Airmobiles has presented two running prototypes of VPA (Vehicles with Pneumatic Assistance). Their leaders now seek to gain the means of developing several projects of urban or leisure VPP (Vehicles with Pneumatic Propulsion). K'Airmobiles propose a different technology with their VPP , which may allow a reasonable range, generally with compressed air tanks of about 50L-100L/3000 psi capacity only.

These ecological vehicles use the technology of the compressed-air engine K'Air, developed in France by a small group of researchers, which thus proposes a range of projects around an idea: that of the urban or leisure compressed-air vehicles.

K'Airmobiles is the name given to a set of projects relating to "VPA" (Vehicles with Pneumatic Assistance) and "VPP" (Vehicles with Pneumatic Propulsion), aiming to escape the constraints from thermodynamics. To do so, these models are conceived like ultra light vehicles (limited to 250 kg max.), and their consumption of compressed air was calculated to remain lower than 120 L/min., although developing a dynamic push able to reach 4kN.

Two VPA prototypes are operational today, the "K'AirBike" and the K'AirKart. Two new VPP prototypes, the one-seater "K'AirTrike" and the three-seater "K'AirMobile Max" are intended for public presentation in October and November 2007 respectively.

The technical concept of the K'Air pneumatic engines returns to direct conversion of what makes the fundamental characteristic of compressed air, namely:

• the pushing force of compressed air is exclusively exploited for conversion into kinetic energy of translation,
• itself is simultaneously converted into induced power of rotation of the axis and
• thus gives to the engine a particularly imposing torque while needing only a very low “fuel” consumption.

To simplify, one can compare the principle to that of the rotary jacks:

• the energy of the fluid (compressed air) is directly transformed into rotational movement;
• the double-acting jacks involve a pinion-toothed rack system;
• the cyclic angle of rotation can vary between 90 and 360°;
• it supports hydraulic supercharging systems.

MDI

Main article: Moteur Developpement International

MDI proposes a range of vehicles developed on an identical concept, made up of MiniCATs and CityCATs. It has entered into an agreement with Tata Motors, to produce air cars in India. MDI has proposed a range of vehicles using the same basic technology.

They have licensed 12 factories : 5 in Mexico, 3 in Australia and New Zealand, 1 in South Africa and 3 in France. MDI Andina S.A is going to sell the car in Colombia, Peru, Ecuador and Panama. ZEVCAT is going to make MDI vehicles in the United States

Psycho-Active

Team Psycho-Active (TPA) has been honored to compete in the Automotive X PRIZE . TPA is working to develop the EPOCH: a highly customizable and serviceable pneumatic / multi-fuel hybrid. At its core is the DBRE engine. The DBRE's unique characteristics allow the EPOCH to use most commercially available fuels and/or compressed air.

Quasiturbine

Main article: quasiturbine

The Quasiturbine is a prototype for a hybrid vehicle which, according to its originators, could as well function with an explosive fuel as with compressed air.

Tata

As of May 2007 Tata Motors of India planned to launch a MDI air car in 2008.

ZAP

Pictures/slides of the ZAP Motors concept were displayed at the 2007 Chicago Auto Show showing two models in testing; a two seat or a five seat hatch-back.

See also

• Air engine
• Charging station
• Compressed air energy storage
• Compressed air vehicles
• Engine swap
• Eolo Car
• Moteur Developpement International
• Plug-in hybrid
• Pneumatics
• Vaporware

External links

• Studies: Aluminum Frames, "Air Hybrids" Yield Fuel Savings (EERE).
• Compressed air vehicle group.
• K'Airmobiles - The ecologic compressed air vehicles
• K'Airmobiles - Les véhicules écologiques à air comprimé
• Fan Site and Portal to the various air-car websites
• Energine, a South Korean company developing Pneumatic Hybrid Electric Car
• ZevCat Inc., A US company that would like to sell MDI Vehicles
• ZAP Auto International
• Tata Developing Air Car.
• Compressed air vehicles hystory
• AirPoweredVehicles group
• The Air Car presented on the Beyond Tomorrow programme

News articles

• Popular Mechanics on Tata's Air Car
• Tata's Air Car
• BBC Article (2000)
• BBC Article (2002)
• Korean Air Car/Electric Vehicle
• Beyond Tomorrow Episode about the Vehicle
• The Science Channel Video Report
• MSNBC article
• Video report from 'Connected Life'