A Compressed air vehicle ( CAV ) is old concept but it becomes important because of hike in petrol prices and increase in pollution. CAV engine works on compressed air ,no mixture of fuel is required. So construction of engine may be same as conventional but some modification is needed to compensate the air as fuel fact. Obviously, these engines are pollution free. Air used is freely available in atmosphere.
A Compressed-air engine is a pneumatic actuator that creates useful work by compressed air. A compressed-air vehicle is powered by an air engine, using compressed air, which is stored in a tank. Instead of mixing fuel with air and burning it in the engine to drive pistons with hot expanding gases, compressed air vehicles (CAV) use the expansion of compressed air to drive their pistons.
Compressed air has been used since the 19th century to power mine locomotives, and was previously the basis of naval torpedo propulsion.
In 1863, Jules Verne wrote a novel called Paris in the 20th Century about a world of glass skyscrapers, high-speed trains, and air-powered automobiles.
Recently several companies have started to develop Compressed air cars although none have been released to the public, or have been tested by third parties.
Compressed Air Engine – Construction and Working :
Parts required :
1) Pressure Vessel Tank :
Tank is required to store the compressed air, actually air starts compressing in tank itself. So tank must be designed by following Design Of Pressure Vessel Standards e.g. ASME standards available for boiler and Pressure Vessel.
The storage tanks , usually circular, are commonly made from made of:
Carbon fiber in order to reduce its weight while achieving the necessary strength (a thermoplastic container surrounded by a carbon fiber shell)
Compressed air can be taken from compressor. Compressor is device which compress means increase the pressure on air from low pressure to very high pressure. We need to fill pressure vessel tank by connecting Compressor to Pressure vessel.Compressor may be of any type ,it doesn’t matter a lot but preferably Reciprocating Compressor should be used.
3) Flow control valves and flexible Pipe Lining :
Flow Control valve is used to regulate the flow of air so that pressure can be varied according the engine running conditions.
Principle Of Compressed Air Engine :
The laws of physics dictate that uncontained gases will fill any given space. The easiest way to see this in action is to inflate a balloon. The elastic skin of the balloon holds the air tightly inside, but the moment you use a pin to create a hole in the balloon’s surface, the air expands outward with so much energy that the balloon explodes. Compressing a gas into a small space is a way to store energy. When the gas expands again, that energy is released to do work. That’s the basic principle behind what makes an air car run on the road.
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. Some took this a stage further and burned fuel in the cylinder or turbine, forming a type of internal combustion engine.
One manufacturer claims to have designed an engine that is 90 percent efficient. Compressed air propulsion may also be incorporated in hybrid systems, e.g., battery electric propulsion and fuel tanks to recharge the batteries. This kind of system is called hybrid-pneumatic electric propulsion. Additionally, regenerative braking can also be used in conjunction with this system.
Advantages Of Compressed Air Engine
Main advantages of Compressed Air Engine (C.A.E.) are:
1. Major advantage of using compressed engine is that a pure compressed air vehicle produces no pollution at the tailpipe.
2. Use of renewable fuel.
3. Compressed-air technology reduces the cost of vehicle production by about 20%, because there is no need to build a cooling system, fuel tank, Ignition Systems or silencers.
4. Air, on its own, is non-flammable.
5. The engine can be massively reduced in size.
6. The engine runs on cold or warm air, so can be made of lower strength light weight material such as aluminium, plastic, low friction teflon or a combination.
7. Low manufacture and maintenance costs as well as easy maintenance.
8. The air tank may be refilled more often and in less time than batteries can be recharged, with re-filling rates comparable to liquid fuels.
9. Lighter vehicles cause less damage to roads, resulting in lower maintenance cost.
10. The price of filling air powered vehicles is significantly cheaper than petrol, diesel or biofuel. If electricity is cheap, then compressing air will also be relatively cheap.
Disadvantages Of Compressed Air Engine
Compressed Air Engine (C.A.E.) has some disadvantages, which are:
1. Less power output
2. Probability of air leakage.
3. Tanks get very hot when filled rapidly. SCUBA tanks are sometimes immersed in water to cool them down when they are being filled. That would not be possible with tanks in a car and thus it would either take a long time to fill the tanks, or they would have to take less than a full charge, since heat drives up the pressure
4. Biggest disadvantage is the energy needed to compress the air is greater than the energy stored
5. 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
6. 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.
7. 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.
Applications Of Compressed Air Engine
The compressed air engine can be used in many vehicles. Some of its applications to be used as engine for vehicles are:
Jem Stansfield, an English inventor has been able to convert a regular scooter to a compressed air moped. This has been done by equipping the scooter with a compressed air engine and air tank.
MDI makes MultiCATs vehicle that can be used as buses or trucks. RATP has also already expressed an interest in the compressed-air pollution-free bus.
Compressed air locomotives have been historically used as mining locomotives and in various areas.
Various compressed-air-powered trams were trialed, starting in 1876 and has been successfully implemented in some cases.
(e) Watercraft and aircraft
Currently, no water or air vehicles exist that make use of the air engine. Historically compressed air engines propelled certain torpedoes.
Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.