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COMPRESSED AIR VEHICLE (CAV)
(A Practical approach with design)
Sai Chakradhar. Kommuri, Student, Department of Mechanical Engineering, QISCET, Ongole.
Email i.d:saichakradharkommuri@gmail.com contact:8143691783
ABSTRACT:
A Compressed air car is a car that
uses a motor powered by compressed air.
The car can be powered solely by air, or
combined (as in a hybrid electric vehicle).
Compressed air as a source of energy in
different uses in general and as a non-
polluting fuel in compressed air vehicles
has attracted scientists and engineers for
centuries. Efforts are being made by many
developers and manufacturers to master
the compressed air vehicle technology in
all respects for its earliest use by the
mankind. The present paper gives a brief
introduction to the latest developments of a
compressed-air vehicle along with an
introduction to various problems
associated with the technology and their
solution. While developing of compressed
air vehicle, control of compressed air
parameters like temperature, energy
density, requirement of input power,
energy release and emission control have
to be mastered for the development of a
safe, light and cost effective compressed
air vehicle in near future.
HISTORY OF CAV:
Compressed air has been used
since the 19th century to
power mine locomotives and trams in
cities such as Paris (via a central, city-
level, compressed), and was previously the
basis of naval torpedo propulsion.
During the construction of
the Gotthardbahn from 1872 to 1882,
pneumatic locomotives were used in the
construction of the Gotthard Rail
Tunnel and other tunnels of the
Gotthardbahn.
In 1903, the Liquid Air Company
located in London England manufactured a
number of compressed-air and liquefied-
air cars. The major problem with these cars
and all compressed-air cars is the lack of
torque produced by the "engines" and the
cost of compressing the air.
INTRODUCTION
Compared to batteries, compressed
air is favourable because of a high energy
density, low toxicity, fast filling at low
cost and long service life. These issues
make it technically challenging to design
air engines for all kind of compressed air
driven vehicles. To meet the growing
demand of public transportation,
sustainable with environmental
consciousness, people are in the search for
the ultimate clean car with zero-emissions.
Many concept vehicles were proposed that
run on everything from solar power to
algae, but most of them are expensive and
require hard-to-find fuels .Compressed air
vehicle project in the form of light utility
vehicle (LUV) (i.e., air car in particular)
has been a topic of great interest for the
last decade and many theoretical and
experimental investigations.
COMPRESSED AIR
TECHNOLOGY
Mankind has been making use of
uncompressed airpower from centuries in
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different application viz., windmills,
sailing, balloon car, hot air balloon flying
and hang gliding etc. The use of
compressed air for storing energy is a
method that is not only efficient and clean,
but also economical and has been used
since the 19th century to power mine
locomotives, and was previously the basis
of naval torpedo propulsion. 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 go. The air compressors
are built into them.
The principle of compressed-air
propulsion is to pressurize the storage tank
and then connect it to something very like
a reciprocating engine of the vehicle.
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. Thus,
making the technology free from
difficulties.
The air is compressed at pressure
about 150 times the rate the air is
pressurized into car tyres or bicycle. The
tanks must be designed to safety standards
appropriate for a pressure vessel. The
storage tank may be made of steel,
aluminium, carbon fibre, Kevlar or other
materials, or combinations of the above.
The fibre materials are considerably lighter
than metals but generally more expensive.
Metal tanks can withstand a large number
of pressure cycles, but must be checked for
corrosion periodically. A company has
stated to store air in tanks at 4,500 pounds
per square inch (about 30 MPa) and hold
nearly 3,200 cubic feet (around 90 cubic
metres) of air. The tanks may be refilled at
a service station equipped with heat
exchangers, or in a few hours at home or in
parking lots, plugging the vehicle into an
on-board compressor. The cost of driving
such a car is typically projected to be
around Rs. 60 per 100 km, with a complete
refill at the "tank-station" at about Rs. 120
only.
The compression, storage and
release of the air together are termed as
the Compressed Air Technology. This
technology has been utilized in different
pneumatic systems. This technology has
been undergoing several years of research
to improve its applications.
WORKING
The air-powered car runs on a
pneumatic motor that is powered by
compressed air stored on board of the
vehicle. Once compressed air is transferred
into the on board storage tank, it is slowly
released to power the car’s pistons The
engine that is installed on the compressed
air car, uses compressed air which is stored
in the car’s tank. The compressed air
drives the piston down as the power
stroke. At the end of the power stroke, the
compressed air is released through the
exhaust valves and the exhaust is only air.
The motor then converts the air power into
mechanical power. That power is then
transferred to the wheels and becomes the
source of power for the car. ( i.e. the
pistons were connected to the wheels
through the HERO HONDA bike’s 4
speed transmission.). This modified engine
was mounted on a rectangular
crossectional frame and a body that looked
like a curious crossbreed of a car.
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PROPERTIES OF AIR CAR
ENGINE
The properties of air car engine are:
1. Approximately 0.05 mt3
of
compressed air is stored in mild
steel tank in the vehicle.
2. The engine is powered by
compressed air, stored in the tank
at 30bar. In order to reduce weight,
The tank can be made of carbon
fibre.
3. The expansion of this air pushes
the piston and creates movement.
The atmospheric temperature is
used to reheat the engine and
increase the road coverage.
4. The air condition system can be
made use of the expelled cold air.
We only need a simple piston-cylinder
arrangement with an intlet and an exhaust.
But as we know a normal two stroke
engine contained several ports and it also
had the spark plug which we didn’t
require. So, due to the presence of ports in
a two stroke engine, it is difficult to get
required output from the engine. So,
several modifications had to be done on
the four stroke engine to suit our purpose.
The modifications comprised of:-
 Providing a suitable connector at
the cylinder head.
 Removing the spark plug from the
cylinder head.
 Modifying the cam shaft of the
engine.
1. COMPRESSED AIR TANK
Compressed air tank is one of the
most important part of these cars. These
tanks hold 0.05m3
of air to 30 bars. It is
similar to the tanks used to carry the liquid
gas. The tank enjoys the same technology
developed to containing natural gas. These
tanks do not explode in case of accidents
since there are no metals in them if made
of carbon fibre. So the selection of
material for the storage tank matters
much in safety.
2. ENGINE SPECIFICATIONS
Made: HERO HONDA
Model: CD100
Stroke: 4 stroke
No. of cylinders: Single cylinder
Displacement: 110 cc
3. THE CHASSIS
Based on design principles in
aeronautics, engine has put together
highly-resistant, yet light, chassis, zinc
rods welded together. Using these rods
enables us to build a more shock-
resistant chassis than regular chassis,
allowing quick assembly and a more
secure. This system helps to reduce
manufacture time.
4. AIR FILTER
The engine works with air taken
from the atmosphere. Air is compressed by
the off-board compressor or at service
stations equipped with a high-pressure
compressor. Before compression, the air
must be filtered to get rid of any
impurities that could damage the
engine. Carbon filters are used to
eliminate dirt, dust, humidity and other
particles which, unfortunately, are found in
the air in our cities.
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5. REFILLING
As these energies are so easy to
store Filling stations are setup as for
petrol and diesel. The filling of tank of an
air car nearly takes 3 to 4 minutes for cars.
Either, we can set up a filling equipment
too in our house, which is quite cheaper.
6. SPECIAL FEATURES
 There is absolutely no fuel
required and no combustion
in the engine cylinder.
 There is no pollution at all
as only air is taken in and
air is ejected out.
 No Heat is generated, as
there is no combustion.
 No engine cooling system
is required, like water
Pump, radiator, and water
Circulating pipes. It was
measured practically that
the engine exhaust is a
cooled air; its temperature
was measured as low as 5
degrees Celsius.
 No air conditioning
system in the car is
required if used, the
exhaust chilled and clean
air can be recirculated
partly in the car to cool it.
 The atmospheric
temperature can fall down,
as the exhaust is a clean and
chilled air, so the problem
of pollution can be
permanently eradicated.
 Very less maintenance is
required as there won’t be
any soot formation.
 Very low cost materials
can be used, as there is no
heat involvement.
 Weight of the engine can
be reduced in the absence
of cooling system and
because of lightweight
material, which will
improve the mileage and
efficiency.
 In case of leakage or
accident, there won’t be
any fire.
 Engine vibrations were
very less and sound
pollution was also very low.
 Operating cost is ten times
less than that of gasoline
engine.
7. EMISSION OUTPUT
Since the compressed air is
filtered to protect the compressor
machinery, the air discharged has less
suspended dust in it, though there may be
carry-over of lubricants used in the engine.
The car works when gas expands.
ADVANTAGES
Compressed-air vehicles are
comparable in many ways to electric
vehicles, but use compressed air to store
the energy instead of batteries. Their
potential advantages over other vehicles
include:.
 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.
 The engine can be massively reduced
in size.
 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.
 Low manufacture and maintenance
costs as well as easy maintenance.
 Compressed-air tanks can be disposed
of or recycled with less pollution than
batteries.
 Compressed-air vehicles are
unconstrained by the degradation
problems associated with current
battery systems.
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 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.
 Lighter vehicles cause less damage to
roads, resulting in lower maintenance
cost.
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
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 oil is converted to usable fuel –
including drilling, refinement, labor,
storage, eventually transportation to the
end-user. For compressed-air cars, energy
is lost when electrical energy is converted
to compressed air.
 When air expands, as it would in the
engine, it cools dramatically (Charles's
law) and must be heated to ambient
temperature using a heat exchanger
similar to the Intercooler used for
internal combustion engines. 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 the Intercooler, 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.
 Refueling the compressed-air
container using a home or low-end
conventional air compressor may take
as long as 4 hours, while the
specialized equipment at service
stations may fill the tanks in only 3
minutes.
 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.
 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 (4 mi).
 A 2005 study demonstrated that cars
running on lithium-ion batteries out-
perform both compressed-air and fuel
cell vehicle more than threefold at
same speeds.[10]
MDI has recently
claimed that an air car will be able to
travel 140 km (87 mi) in urban driving,
and have a range of 80 km (50 mi)
with a top speed of 110 km/h (68 mph)
on highways, when operating on
compressed air alone.
POSSIBLE IMPROVEMENTS
Compressed-air vehicles operate to
a thermodynamic process as air cools
down when expanding and heats up when
being compressed. As it is not possible in
practice to use a theoretically ideal
process, losses occur and improvements
may involve reducing these, e.g., by using
large heat exchangers in order to use heat
from the ambient air and at the same time
provide air cooling in the passenger
compartment. At the other end, the heat
produced during compression can be
stored in water systems, physical or
chemical systems and reused later.
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It may be possible to store
compressed air at lower pressure using an
absorption material within the tank.
Absorption materials such as Activated
carbon, or a metal organic framework is
used to store compressed natural gas at
500 psi instead of 4500 psi, which
amounts to a large energy saving.
CONCLUSION
It’s important to remember that
while vehicles running on only
compressed air might seem like a distant
dream, but they still have public interest
due to their environmental friendly nature.
Efforts should be to make them light, safe,
cost effective and economical for deriving.
The storage of compressed air (initially as
well as during journey) with all benefits
like no heating, high energy density and
provisions to make use of cooling
produced during adiabatic expansion
during the energy release have to be taken
care off in a much more controlled
manner. Electric-powered cars and bikes
already available on the market put a
strong competition to compressed air car
not only in terms of cost but also their
environment friendly role. The technology
still looks distant but that has not deterred
inventors from working on it.
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