Air car
Encyclopedia
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....
. The car can be powered solely by air, or combined (as in a hybrid electric vehicle) with gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...
, diesel, ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
, or an electric plant with regenerative braking.
Engines
Compressed air cars are powered by motors driven by compressed airCompressed 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....
, which is stored in a tank
Diving cylinder
A diving cylinder, scuba tank or diving tank is a gas cylinder used to store and transport high pressure breathing gas as a component of a scuba set. It provides gas to the scuba diver through the demand valve of a diving regulator....
at high pressure such as 30 MPa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
(4500 psi or 300 bar). Rather than driving engine pistons with an ignited fuel-air mixture, compressed air cars use the expansion
Thermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
of compressed air, in a similar manner to the expansion of steam in a steam engine.
There have been prototype cars since the 1920s, and compressed air has been used in torpedo
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...
propulsion
Marine propulsion
Marine propulsion is the mechanism or system used to generate thrust to move a ship or boat across water. While paddles and sails are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting a motor or engine turning a propeller, or less frequently, in jet...
as well.
Storage tanks
In contrast to hydrogen's issues of damage and danger involved in high-impact crashes, air, on its own, is non-flammable. It was reported on Seven Network'sSeven Network
The Seven Network is an Australian television network owned by Seven West Media Limited. It dates back to 4 November 1956, when the first stations on the VHF7 frequency were established in Melbourne and Sydney.It is currently the second largest network in the country in terms of population reach...
Beyond Tomorrow
Beyond Tomorrow (TV series)
Beyond Tomorrow is an Australian television series produced by Beyond Television Productions. It began airing in 1981 as Towards 2000, then in 1985 was renamed Beyond 2000, a name the show kept until its cancellation in 1999...
that on its own, carbon-fiber is brittle and can split under sufficient stress, but creates no shrapnel when it does so. Carbon-fiber tanks safely hold air at a pressure somewhere around 4500 psi, making them comparable to steel tanks. The cars are designed to be filled up at a high-pressure pump.
Energy density
Compressed airCompressed 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....
has relatively low energy density. Air at 30 MPa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
(4,500 psi) contains about 50 Wh of energy per liter. For comparison, a lead–acid battery contains 60-75 Wh/l. A lithium-ion battery contains about 250-620 Wh/l. Gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...
contains about 9411 Wh per liter.; however, a typical gasoline engine with 18% efficiency can only recover the equivalent of 1694 Wh/l. The energy density of a compressed air system can be more than doubled if the air is heated prior to expansion.
In order to increase energy density, some systems may use gases that can be liquified or solidified. "CO2 offers far greater compressibility than air when it transitions from gaseous to supercritical form."
Emissions
Compressed air cars are emissionEmission standard
Emission standards are requirements that set specific limits to the amount of pollutants that can be released into the environment. Many emissions standards focus on regulating pollutants released by automobiles and other powered vehicles but they can also regulate emissions from industry, power...
-free at the exhaust. Since a compressed air car's source of energy is usually electricity, its total environmental impact depends on how clean the source of this electricity is. Different regions can have very different sources of power, ranging from high-emission power sources such as coal
Fossil fuel power plant
A fossil-fuel power station is a power station that burns fossil fuels such as coal, natural gas or petroleum to produce electricity. Central station fossil-fuel power plants are designed on a large scale for continuous operation...
to zero-emission power sources such as wind
Wind power
Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, windmills for mechanical power, windpumps for water pumping or drainage, or sails to propel ships....
. A given region can also update its electrical power sources over time, thereby improving or worsening total emissions.
However a study showed that even with very optimistic assumptions, air storage of energy is less efficient than chemical (battery) storage.
Advantages
The principal advantages of an air powered vehicle are:- Refueling can be done at home using an air compressor or at service stations. The energy required for compressing air is produced at large centralized plants, making it less costly and more effective to manage carbon emissions than from individual vehicles.
- Compressed air engines reduce the cost of vehicle production, because there is no need to build a cooling system, spark plugs, starter motor, or mufflers.
- The rate of self-dischargeSelf-dischargeSelf-discharge is a phenomenon in batteries in which internal chemical reactions reduce the stored charge of the battery without any connection between the electrodes...
is very low opposed to batteries that deplete their charge slowly over time. Therefore, the vehicle may be left unused for longer periods of time than electric cars. - Expansion of the compressed air lowers its temperature; this may be exploited for use as air conditioningAir conditioningAn air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
. - Reduction or elimination of hazardous chemicals such as gasoline or battery acids/metals
- Some mechanical configurations may allow energy recovery during braking by compressing and storing air.
- Recent findings from Southwest Research Institute indicate that air-hybrids would allow for up to 50 percent better fuel economy and an 80 percent reduction in emitted toxins compared to conventional engines. Sweden’s Lund University also reports that buses could see an improvement in fuel efficiency of up to 60 percent using an air-hybrid system But this only refers to hybrid air concepts (due to recuperation of energy during braking), not compressed air-only vehicles.
Disadvantages
The principal disadvantage is the indirect use of energy. Energy is used to compress air, which - in turn - provides the energy to run the motor. Any conversion of energy between forms results in loss. For conventional combustion motor cars, the energy is lost when chemical energy in fossil fuels is converted to mechanical energy, most of which goes to waste as lost heat. For compressed-air cars, energy is lost when chemical energy is converted to electrical energy, when electrical energy is converted to compressed air, and then when the compressed air is converted into mechanical energy.- When air expands in the engine it cools dramatically (Charles's lawCharles's lawCharles' law is an experimental gas law which describes how gases tend to expand when heated. It was first published by French natural philosopher Joseph Louis Gay-Lussac in 1802, although he credited the discovery to unpublished work from the 1780s by Jacques Charles...
) and must be heated to ambient temperature using a heat exchanger. The heating is necessary in order to obtain a significant fraction of the theoretical energy output. The heat exchanger can be problematic: while it performs a similar task to an intercoolerIntercoolerAn intercooler , or charge air cooler, is an air-to-air or air-to-liquid heat exchange device used on turbocharged and supercharged internal combustion engines to improve their volumetric efficiency by increasing intake air charge density through nearly isobaric cooling, which removes...
for an internal combustion engine, the temperature difference between the incoming air and the working gas is smaller. In heating the stored air, the device gets very cold and may ice up in cool, moist climates. - This also leads to the necessity of completely dehydrating the compressed air. If any humidity subsists in the compressed air, the engine will stop due to inner icing. Removing the humidity completely requires even additional energy that cannot be reused and is lost.
- Conversely, when air is compressed to fill the tank it heats up. If the stored air is not cooled as the tank is filled, then when the air cools off later, its pressure decreases and available energy decreases. The tank may require an internal heat-exchanger in order to cool the air quickly and efficiently while charging, since without this it may either take a long time to fill the tank, or less energy is stored.
- Refueling the compressed air container using a home or low-end conventional air compressor may take as long as 4 hours, though specialized equipment at service stations may fill the tanks in only 3 minutes. To store 14.3 kWh @300 bar in 300 liter reservoirs (90 m3 of air @ 1 bar), requires about 30 kWh of compressor energy (with a single-stage adiabatic compressor), or approx. 21 kWh with an industrial standard multistage unit. That means a compressor power of 360 kW is needed to fill the reservoirs in 5 minutes from a single stage unit, or 250 kW for a multistage one. However, intercooling and isothermal compression is far more efficient and more practical than adiabatic compression, if sufficiently large heat exchangers are fitted.
- The overall efficiency of a vehicle using compressed air energy storageCompressed air energy storageCompressed 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....
, using the above refueling figures, is around 5-7%. For comparison, well to wheel efficiency of a conventional internal-combustion drivetrain is about 14%, - Early tests have demonstrated the limited storage capacity of the tanks; the only published test of a vehicle running on compressed air alone was limited to a range of 7.22 km.
- A 2005 study demonstrated that cars running on lithium-ion batteries out-perform both compressed air and fuel cell vehicleFuel cell vehicleA Fuel cell vehicle or Fuel Cell Electric Vehicle is a type of hydrogen vehicle which uses a fuel cell to produce electricity, powering its on-board electric motor...
s more than threefold at the same speeds. MDI claimed in 2007 that an air car will be able to travel 140 km in urban driving, and have a range of 80 km with a top speed of 110 kilometre per hour on highways, when operating on compressed air alone, but in as late as mid 2011, MDI has still not produced any proof to that effect. - A 2009 University of Berkeley Research Letter found that "Even under highly optimistic assumptions the compressed-air car is significantly less efficient than a battery electric vehicle and produces more greenhouse gas emissions than a conventional gas-powered car with a coal intensive power mix." However, they also suggested, "a pneumatic–combustion hybrid is technologically feasible, inexpensive and could eventually compete with hybrid electric vehicles."
Crash safety
Safety claims for light weight vehicle air tanks in severe collisions have not been verified.North American crash testing has not yet been conducted, and skeptics question the ability of an ultralight vehicle assembled with adhesives to produce acceptable crash safety results. Shiva Vencat, vice president of MDI and CEO of Zero Pollution Motors, claims the vehicle would pass crash testing and meet U.S. safety standards. He insists that the millions of dollars invested in the AirCar would not be in vain. To date, there has never been a lightweight, 100-plus mpg car which passed North American crash testing. Technological advances may soon make this possible, but the AirCar has yet to prove itself, and collision safety questions remain.
The key to achieving an acceptable range with an air car is reducing the power required to drive the car, so far as is practical. This pushes the design towards minimizing weight.
According to a report by the U.S. Government's National Highway Traffic Safety Administration
National Highway Traffic Safety Administration
The National Highway Traffic Safety Administration is an agency of the Executive Branch of the U.S. government, part of the Department of Transportation...
, among 10 different classes of passenger vehicles, "very small cars" have the highest fatality rate per mile driven. For instance, a person driving 12,000 miles per year for 55 years would have a 1% chance of being involved in a fatal accident. This is twice the fatality rate of the safest vehicle class, a "large car". According to the data in this report, the number of fatal crashes per mile is only weakly correlated with the vehicle weight, having a correlation
Correlation
In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....
coefficient of just (-0.45). A stronger correlation is seen with the vehicle size within its class; for example, "large" cars, pickups and SUVs, have lower fatality rates than "small" cars, pickups and SUVs. This is the case in 7 of the 10 classes, with the exception of mid-size vehicles, where minivans and mid-size cars are among the safest classes, while mid-size SUVs are the second most fatal after very small cars. Even though heavier vehicles sometimes are statistically safer, it is not necessarily the extra weight that causes them to be safer. The NHTSA report states: "Heavier vehicles have historically done a better job cushioning their occupants in crashes. Their longer hoods and extra space in the occupant compartment provide an opportunity for a more gradual deceleration of the vehicle, and of the occupant within the vehicle... While it is conceivable that light vehicles could be built with similarly long hoods and mild deceleration pulses, it would probably require major changes in materials and design and/or taking weight out of their engines, accessories, etc."
Air cars may use low rolling resistance tires, which typically offer less grip than normal tires. In addition, the weight (and price) of safety systems such as airbags, ABS and ESC may discourage manufacturers from including them.
Developers and manufacturers
Various companies are investing in the research, development and deployment of Compressed air cars. Overoptimistic reports of impending production date back to at least May 1999. For instance, the MDI Air Car made its public debut in South AfricaSouth Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
in 2002, and was predicted to be in production "within six months" in January 2004. As of January 2009, the air car never went into production in South Africa.
Most of the cars under development also rely on using similar technology to Low-energy vehicle
Low-energy vehicle
A Low-energy vehicle is any type of vehicle that uses less energy than a regular fossil fuel vehicle.Higher efficiency can be achieved by changing the vehicle's design, and/or by modifying its powertrain. Energy consumption as low as 5-12.5 kWh/100 km is achieved directly by battery electric...
s in order to increase the range and performance of their cars.
APUQ
APUQ (Association de Promotion des Usages de la Quasiturbine) has made the APUQ Air Car, a car powered by a quasiturbine.MDI
MDI has proposed a range of vehicles made up of AirPod, OneFlowAir, CityFlowAir, MiniFlowAir and MultiFlowAir. 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 torpedoTorpedo
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 in 1904.
Tata Motors
Tata MotorsTata Motors
Tata Motors Limited is an Indian multinational automotive corporation headquartered in Mumbai, India. Part of the Tata Group, it was formerly known as TELCO...
of India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
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.
Meanwhile any related articles or connections to MDI have been deleted from the website of Tata Motors, including in the archive.
Air Car Factories SA
Air Car Factories SA is proposing to develop and build a compressed air engine. This Spanish based company was founded byMiguel Celades. Currently there is a bitter dispute between Motor Development International, another firm called Luis which developed compressed-air vehicles, and Mr. Celades, who was once associated with that firm.
Energine
The Energine Corporation was a South Korean company that claimed to deliver fully assembled cars running on a hybrid compressed air and electric engine. These cars are more precisely named pneumatic-hybrid electric vehicles. Engineers from this company made, starting from a Daewoo MatizDaewoo Matiz
-M100 :The production of Daewoo Matiz started in 1998 and it was sold in South Korea and many European markets with the code name M100. The exterior design is based on the Lucciola, a Fiat Cinquecento concept by Italdesign Giugiaro which had been rejected by Fiat. The 0.8-litre gasoline engine and...
, a prototype of a hybrid electric/compressed-air engine (Pne-PHEV, pneumatic plug-in hybrid electric vehicle
Plug-in hybrid electric vehicle
A plug-in hybrid electric vehicle , plug-in hybrid vehicle , or plug-in hybrid is a hybrid vehicle which utilizes rechargeable batteries, or another energy storage device, that can be restored to full charge by connecting a plug to an external electric power source...
). The compressed-air engine is used to activate an alternator, which extends the autonomous operating capacity of the car.
The CEO is the first compressed air car promoter to be arrested for
fraud.
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.
K'Airmobiles
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 Fluid 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.
Engineair
Engineair is an Australian company which manufactures small industrial vehicles using an air engine of its own design.See also
- Air engine
- Charging stationCharging stationAn electric vehicle charging station, also called EV charging station, electric recharging point, charging point and EVSE , is an element in an infrastructure that supplies electric energy for the recharging of electric vehicles, plug-in hybrid electric-gasoline vehicles) or semi-static and mobile...
- Compressed air energy storageCompressed air energy storageCompressed 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....
- Compressed air batteryCompressed air batteryA compressed air battery stores energy in the form of compressed air and uses it to generate electricity.. A compressed air battery uses air to drive a scroll expander or other device, which in turn drives a conventional generator, to produce electricity...
- Compressed air vehicles
- Engine swapEngine swapAn engine swap is the process of removing a car's engine and replacing it with another. This is done either because of failure, or to install a different engine, usually one that is more powerful or more modern and maintainable....
- Magnetic air carMagnetic air carThe magnetic air car is a concept car. Instead of an alternative fuel source, the magnetic air car uses compressed air to propel it. The patented technology is developed by Magnetic Air Cars, Inc., a San Jose-based company who is working on the world’s first viable fuel-less car...
- Plug-in hybrid
- PneumaticsPneumaticsPneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...
External links
- Deflating the Air Car, IEEE SpectrumIEEE SpectrumIEEE Spectrum is a magazine edited by the Institute of Electrical and Electronics Engineers. The IEEE's description of it is:IEEE Spectrum began publishing in January 1964 as a successor to Electrical Engineering...
. - Scuderi Group to Present Preliminary Results on Air-Hybrid Study and Update on Scuderi Engine Prototype Testing at Washington Auto Show