Compressed Air Car

Special Feature : Air Pollution Control Technologies Special Feature : Air Pollution Control Technologies

Compressed air car

S.S. Thipse

It is hard to believe that compressed air can be used to drive vehicles. However that is true, and the “air car”, as it is popularly known, has caught the attention of re- searchers worldwide. It has zero emissions and is ideal for city driving conditions. MDI is one company that holds the international patents for the compressed air car. Although it seems to be an environmentally-friendly solution, one must consider its well to wheel efficiency. The electricity requirement for compressing air has to be considered while computing overall efficiency. Nevertheless, the compressed air vehicle will contribute to reducing urban air pollution in the long run.

The history of compressed in Nantes in 1879). In 1892, Robert air vehicles Hardie introduced a new method of heating that at the same time served to ne cannot accurately claim that increase the range of the engine. compressed air as an energy However, the first urban transport Oand locomotion vector is recent locomotive was not introduced until technology. At the end of the 19th century, the first approximations to what 1898, by Hoadley and Knight, and was could one day become a compressed based on the principle that the longer air driven vehicle already existed, with the air is kept in the engine the more the arrival of the first pneumatic loco- heat it absorbs and the greater its motives. In fact, two centuries before range. As a result they introduced a that Dennis Papin apparently came up two-stage engine. Figure 1 shows the with the idea of using compressed air early compressed air vehicles. (Royal Society London, 1687). In 1872 Charles B. Hodges will always be the Mekarski air engine was used for remembered as the true father of the street transit, consisting of a single- compressed air concept applied to cars, stage engine. It represented an ex- being the first person, not only to in- Dr. S.S. Thipse tremely important advance in terms of vent a car driven by a compressed air Assistant Director pneumatic engines, due to its forward engine but also to have considerable Engine Development Laboratory thinking use of thermodynamics, which commercial success with it. The H.K. Automotive Research ensured that the air was heated, by Porter Company of Pittsburgh sold hun- Association of India (ARAI) passing it through tanks of boiling wa- dreds of these vehicles to the mining P. O. Box No. 832 ter, which also increased its range be- industry in the eastern United States, Pune 411044, India tween fill-ups. Numerous locomotives due to the safety that this method of Tel: (+91-20) 3023 1434 were manufactured and a number of propulsion represented for the mining E-mail: [email protected] regular lines were opened up (the first sector. Later on, in 1912, the American’s

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Figure 1: Some early compressed air vehicles

Figure 2: MDI vehicles Design of the compressed air vehicle

Compressed air engine This engine was developed between the end of 2001 and the beginning of 2002. It uses an innovative system to control the movement of the 2nd generation pistons and one single crankshaft. The pistons work in two stages - one motor stage and one intermediate stage of compression/expansion. The method was improved by Europeans, pansion of the compressed air drives adding a further expansion stage to the the pistons to create movement, replac- engine has 4 two-stage pistons, i.e. 8 engine - 3 stages. ing the burning of fossil fuel in a con- compression and/or expansion cham- ventional engine. In an air-refilling sta- bers. They have two functions: to compress ambient air and refill the storage Compressed air technology tion (currently unavailable as service stations have not been fitted yet) it is tanks; and to make successive expan- After twelve years of research and de- estimated to take between three and sions (reheating air with ambient ther- velopment, Guy Negre has developed four minutes to re-fuel. At home, with a mal energy) thereby approaching iso- an engine that could become one of 220V plug, it takes three and a half thermal expansion. Figure 3 shows the the biggest technological advances of hours. compressed air engine. this century. A French engineer by pro- CAT vehicles have significant eco- Two technologies have been de- fession, he has designed a low con- nomical and environmental advan- veloped to meet different needs: sumption and low pollution engine for tages. With the incorporation of bi-en- z Single energy compressed air en- urban motoring that runs on compressed ergy (compressed air + fuel) the CAT gines; and air technology (Figure 2). The CATS Vehicles have increased their driving z Dual energy compressed air plus (Compressed Air Technology System) range to close to 2000 km with zero fuel engines. “air car” from Motor Development In- pollution in cities and considerably re- The single energy engines will be ternational is a significant step for zero- duced pollution outside urban areas. available in both Minicats and Citycats. emission transport, delivering a com- Also, the application of the MDI engine These engines have been conceived pressed air-driven vehicle that is safe, in other areas, outside the automotive for city use, where the maximum speed quiet, has a top speed of 110 km/h and sector, opens a multitude of possibili- is 50 km/h and where MDI believes a range of 200 km. Costing next to noth- ties in nautical fields, co-generation, polluting will soon be prohibited. The ing to run, the Zero Emission Vehicle auxiliary engines, electric generators dual energy engine, on the other hand, (ZEV) range - which includes a pick-up groups, etc. has been conceived as much for the truck and van - was released in 2005. Compressed air is a new viable city as the open road and will be avail- Guy Nègre is the head of Research and form of power that allows the accumu- able in all MDI vehicles. The engines Development at Moteur Developement lation and transport of energy. MDI is will work exclusively with compressed International (MDI) cars, where the Zero very close to initiating the production air while it is running under 50 km/h in Emission Vehicle (ZEV) prototype has of a series of engines and vehicles. The urban areas. But when the car is used been in production since 1994. The two- company is financed by the sale of outside urban areas at speeds over 50 stroke engine is powered by com- manufacturing licenses and patents all km/h, the engines will switch to fuel pressed air stored in tanks at about 150 over the world. Table 1 lists the techni- mode. The engine will be able to use times the pressure in car tyres. The ex- cal specifications of the vehicle. gasoline, gas oil, bio-diesel, gas, liq-

34 TECH MONITOR z Nov-Dec 2008 Special Feature : Air Pollution Control Technologies uidized gas, ecological fuel, alcohol, Table 1: Technical specifications of a Minicat vehicle etc. Both engines will be available with Mono-energy Dual-energy 2 Dual-energy 4 2, 4 and 6 cylinders, When the air tanks are empty the driver will be able to Length m 2.65 2.65 2.65 switch to fuel mode, thanks to the car’s Width m 1.62 1.62 1.62 on board computer. Height m 1.66 1.66 1.66

Engine working Number of seats - 3 3 3 Approximately 90m3 of compressed air Luggage compartment is stored in fibre tanks in the vehicle. volume Dm3 500/700 500/700 500/700 The engine is powered by compressed air, stored in a carbon-fibre tank at 30 Weight Kg 550 520 540 MPa (4500 psi). The tank is made of Engine - 41P03 41P01 41P01/4 carbon fibre in order to reduce its Power c v 25 25 50 weight. The engine has injection simi- lar to normal engines, but uses special Max. speed Km/h 110 125 140 crankshafts and pistons, which remain Urban range (zero pollution) Km 140/150 50 50 at top dead centre for about 70 degrees CO emission in urban use g/Km 0 0 0 of the crankshaft’s cycle; this allows 2 more power to be developed in the Non-urban range Km 80 1650 1500 engine. The expansion of this air pushes the pistons and creates move- Non-urban consumption ment. The atmospheric temperature is (petrol) litres - 1.8 2 used to re-heat the engine and increase CO2 emission in the road coverage. The air condition- non-urban use g/Km 0 35 40 ing system makes use of the expelled Price (from) taxes included € 9200 cold air. Due to the absence of com- bustion and the fact there is no pollution, the oil change is only necessary Figure 3: Compressed air engine every 50,000 km.

Distribution and valves To ensure smooth running and to opti- mize energy efficiency, air engines use a simple electromagnetic distribution system, which controls the flow of air into the engine. This system runs on very little energy and alters neither the valve phase nor its rise. No clutch is necessary. The engine is idle when the car is stationary and the vehicle is started by the mag- netic plate, which re-engages the compressed air. Parking manoeuvers are Gear box powered by the electric motor. The P04 pressed air tanks. The control system Gear changes are automatic, powered engine is equipped with patented vari- maintains a zero-pollution emission in by an electronic system developed by able-volume butts and a dynamic vari- the city at speeds up to 60 km/h. MDI. A computer which controls the able-volume volumetric reducer. The speed of the car is effectively continu- Articulated con-rod engines can be equipped with and run ously changing gears. The latest of The MDI con-rod system allows the pis- on dual energies - fossil fuels and com- many previous versions, this gearbox pressed air - and incorporate a reheat- ton to be held at Top Dead Centre for achieves the objective of seamless o ing mechanism between the storage 70 of the cycle.This way, enough time changes and mimimal energy con- tank and the engine. is given to create the pressure in the sumption. Its steering wheel is equipped This mechanism allows the engine cylinder. The torque is also better, so with a 5kW electric moto-alternator. This to run exclusively on fossil fuel, which the force exerted on the crankshaft is moto-alternator connects the engine to permits compatible autonomy on the less substantial. Figure 4 shows the ar- the gearbox. It has many functions: road. While the car is running on fossil ticulated connecting rod and the drive z It supports the CAT’s motor to allow fuel, the compressor refills the com- train. the tanks to be refilled.

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Figure 4: Articulated connecting rod and drive train uefied gases on some urban buses. That means that the tanks are prepared and certified to carry an explosive prod- uct: methane gas. In the case of an ac- cident with air tank breakage, there would be no explosion or shattering because the tanks are not metallic but made of glass fibre. The tanks would crack longitudinally, and the air would escape, causing a strong buzzing sound with no dangerous factor. It is clear that if this technology has been tested and prepared to carry an inflammable and explosive gas, it can also be used to carry air. z It starts the vehicle and provides meters. The car also has a small In order to avoid the so-called ‘rocket extra power when necessary. compressor that can be connected effect’ (air escaping through one of the z As an alternator it produces brake to an electrical network (220V or tank’s extremities causing a pressure leak power. 380V) and will recharge the tanks that could move the car), MDI made a completely in 3 or 4 minutes. small but important change in the design. Additional features z Because the engine does not burn Where the valve on the bus tanks are any fuel, the car’s oil only needs to of the MDI car placed on one of the extremities, MDI has be changed every 50,000 km. placed the valve in the middle of the tank z Light-weight: The vehicle has a fi- z The temperature of the clean air reducing the ‘rocket effect’ to a minimum berglass body, which makes it a expelled from the exhaust pipe is (Figure 5). light, silent urban car. The car’s body between 0 and -15 degrees and is tubular, and is held together us- can be subsequently channelled Air car in India ing aerospace technology. It can and used for air conditioning in the reach speeds up to 220 km/h (even interior of the car. Tata Motors has signed an agreement with Moteur Development International though the legal limit is 120). z Advanced features such as GSM z It does not have normal speed telephone systems, GPS satellite of France to develop a car that runs on gauges. Instead, it has a small com- tracking systems, programmes for compressed air, thus making it very puter screen that shows the speed. delivery people, emergency sys- economical to run and almost totally z Its electric system is also revolution- tems, Internet connections, voice pollution free. Although there is no offi- ary. MDI has bought a patent that is recognitions, map presentation and cial word on when the car will be com- bound to reduce the importance of traffic information can be incorpo- mercially manufactured for India, re- electrical systems in all cars. The rated. ports say that it will be sooner than later. trick consists in using a small radio z Regarding security, the seatbelt The car - MiniCAT - could cost around signal. The system makes the car system is different from what is Rs 350,000 in India and would have a 20 kilograms lighter and consider- known. One part of the belt is an- range of around 300 km between refu- ably quieter. chored to the floor of the car, like els. The cost of a refill would be about z In the single energy mode, MDI cars traditional cars. The other part of the Rs 90. In the single energy mode MDI consume less than one euro every belt, instead of being attached to cars consume around Rs 45 every 100 100 km (around 0.75 euros), that is the side of the car, is also anchored km. Figure 6 shows the proposed air to say, 10 times less than gasoline- to the floor of the vehicle. This helps car for India. The smallest and most in- powered cars. to secure the bodies of the driver novative (three seats, minimal dimen- z Its driving range is close to twice and passengers in the case of a sions with the boot of a saloon), it is a that of the most advanced electric collision. great challenge for such a small car cars (from 200 to 300 km or 8 hours z There are no keys - just an access which runs on compressed air. The of circulation). This is exactly what card that can be read by the car MiniCAT is the city car of the future. the urban market needs where, 80 from your pocket. per cent of the drivers move less than 60 km a day. Other developments in com- z The recharging of the car will be Safety features of the air car pressed air car technology done at gas stations, once the mar- The CATS air tanks store 90m3 of air at Currently some new technologies re- ket is developed. To fill the tanks, it 300 bars of pressure (four tanks have garding compressed air cars have will take about 2 to 3 minutes at a a capacity of 90 litres, and they store emerged. A Republic of Korean com- price of 1.5 euros. After refilling, the 90m3 of air at a pressure of 300 bars), pany has created a pneumatic hybrid car will be ready to drive 200 kilo- just like tanks already used to carry liq- electric vehicle car engine that runs on

36 TECH MONITOR z Nov-Dec 2008 Special Feature : Air Pollution Control Technologies electricity and compressed air. The en- Figure 5: Position of air tanks in a compressed air vehicle gine, which powers a pneumatic-hybrid electric vehicle (PHEV), works Pistones alongside an electric motor to create the power source. The system elimi- Escape nates the need for fuel, making the PHEV pollution-free. The system is con- trolled by an ECU in the car, which controls both power packs i.e. the com- Interca- pressed-air engine and electric motor. mbiadores The compressed air drives the pistons, de calor which turn the vehicle’s wheels. The air is compressed, using a small motor, Reserva powered by a 48-volt battery, which de Aire powers both the air compressor and the electric motor. Once compressed, Depositos Placa de protection the air is stored in a tank. The compressed air is used when the car needs a lot of energy, such as for starting up Figure 6: Compressed air car for Figure 7: PHEV in Republic of Korea and acceleration. The electric motor India comes to life once the car has gained normal cruising speed. The PHEV system could reduce the cost of vehicle production by about 20 per cent, because there is no need for a cooling system, fuel tank, spark plugs or silenc- ers. Figure 7 shows the PHEV in the Republic of Korea.

Well to wheel efficiency of a compressed air car We are all familiar with the standard measure of vehicle efficiency. Miles per gallon, or the CO2 emissions derived from it does not show the whole pic- source should also be considered. To hydrogen powered vehicles, com- ture. The drilling, pumping, transport- be precise, the efficiency from compressed air vehicles are not expensive ing, and refining of petroleum products pressor to wheel of the air car is calcu- and do not have a limited driving range. such as gasoline and diesel requires lated to be ~40 per cent according to Compressed air vehicles are afford- additional energy that we often over- some reports. In comparison, the effi- able and have a performance rate that look. By some estimates this “well to ciency of electric vehicles from battery stands up to current standards. To sum tank” phase adds 15-20 per cent to the to wheel is 80 per cent. If the air com- it up, they are non-expensive cars that emissions/energy use. pressor is powered by an ICE with an do not pollute and are easy to get But where does the energy go efficiency of about 40 per cent, then the around in cities. The emission benefits once it gets into the vehicle’s tank. First, overall efficiency of the air car from fuel of introducing this zero emission tech- the car must overcome the aerody- to wheel is 40% x 40% = 16%, which is nology are obvious. At the same time namic drag in order to maintain a given poor, as compared to an IC engine or the well to wheels efficiency of these velocity. For this, figures for the vehicle’s battery-electric powertrain. vehicles need to be improved. coefficient of drag, the cross sectional area and the density of air are required. Conclusion References Multiplying the coefficient of drag by The technology of compressed air ve- 1. SAE 1999-01-0623, Schechter.M., the cross sectional area results in a hicles is not new. In fact, it has been “New Cycles for Automobile en- good indicator of how aerodynamic a around for years. Compressed air tech- gines.” car is. In case of the compressed air nology allows for engines that are both 2. Internet website, www.theaircar. com. car, the electrical energy that is required non-polluting and economical. After ten 3. Internet website, www.peswiki.com to compress the air lowers the overall years of research and development, the 4. Internet website, www.mdi.lu Internet efficiency. Furthermore, environmental compressed air vehicle will be intro- website http://www.inhabitat.com/ pollution generated at the electricity duced worldwide. Unlike electric or 2007/06/01/tata-motors-air-car.

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