25-10-2012, 05:24 PM
COMPRESSED AIR ENGINE
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ABSTRACT
A compressed air engine is primarily an engine that uses the energy stored compressed air to do
work. Here the expansion of compressed air stored at high pressure in a storage tank occurs in
the engine cylinder to move a piston doing mechanical work. The main application of this engine
is in automobile industry where the potential energy of the compressed air is converted into
kinetic energy of the linear motion of piston and rotary motion of the crank and the crank shaft.
This motion is transferred to the wheels using usual transfer mechanisms .As the working fluid is
compressed air there is no requirement of any other fuel other than some amount of electrical
energy for compression of air in an electric compressor .The engine is free of emissions at the
tailpipe as the only exhaust is air and is environmental friendly. Even though it is below its
counterparts in power, comfort and performance, its supporters believe that altered versions of
this engine are to dominate the automobile industry in future.
INTRODUCTION
A Compressed-air engine is a pneumatic actuator that creates useful work by expanding
compressed air and converting the potential energy into motion. A pneumatic actuator is a
device that converts energy into motion The motion can be rotary or linear, depending on the
type of actuator. CAE’s are fueled by compressed air, which is stored in a tank at high
pressure such as 30 MPa. The difference between the compressed air engine and IC
engine is that instead of mixing fuel with air and burning it to drive pistons with hot expanding
gases, compressed air engine use the expansion of previously compressed air to drive their
pistons. This technology has been used by many companies like MDI (Motor Development
Industry) to develop cars and other vehicles running on compressed air engine.
PARTS
A basic compressed air engine primarily consists of a source of air under high pressure, means for
supplying air from source to engine cylinder, a cylinder system, and an exhaust system. There
are also auxiliary parts like the heater which improves the power output and efficiency of the
engine.The source is a storage tank where compressed air of pressures as high as 30Mpa is
stored. The storage tank is likely to be made of carbon-fiber in order to reduce its weight while
achieving the necessary strength. There is a cylinder having a reciprocating piston .There is
also means to supply air from tank to cylinder to drive piston.
A crank shaft is coupled to piston and is driven responsive to the reciprocating motion of
piston,suitable mechanical arrangement coupled to crank shaft supply power to
compressor, and also an independent means to supply power to compressor.
Means for supplying air to cylinder comprises: a cylinder head, an auxiliary chamber in
cylinder head, conduit means for connecting tank to auxiliary chamber, and input valve
operative to periodically admit air from auxiliary chamber into the chamber formed by
cylinder head and the top of piston, the periodicity of admission of air being
synchronized with the rotation of crank shaft. There is also an inlet valve to allow the entry of
air from the surroundings .There are also carbon filters to eliminate dirt, dust, humidity, and other
urban air impurities that could hamper the engine’s performance. There is an exhaust valve that
lets the expanded air out. A lubricant compartment is provided below the engine cylinder that
provides suitable lubrication for the engine.
That is up to 4 times less than the average vehicle and more than two times less than the
cleanest vehicle available today.
The compressed air engine works in four different modes according to requirement
Mode A: Operating with compressed air from Air Tank only in town less than 30 kph. In this
mode, high pressure air from storage tank expands in the cylinder and moves the piston. The linear
motion of piston is converted unto rotary motion of crank shaft.
Mode B: Operating with compressed air from Air Tank only which is then heated by
the heater to expand volume before entering engine. this increases the power output.
Mode C: Operating with air from the Intake which is being heated to expand volume before entering
engine. This is used on highway over 35 mph.
Mode D: Operating as in Mode C but also refilling air Tank while running.
WORKING
The compressed air from the storage tank is supplied to the cylinder system by means
of supply system. In the cylinder system the air first enters an auxiliary chamber from where it
is periodically admitted to the main cylinder. The auxiliary chamber produces some power
other than improving the overall efficiency of the engine. The compressed air which expands in the
cylinder moves the piston down. When the piston moves up the exhaust valve opens and the
expanded air is pushed out. In more evolved systems, the top portion of the main
cylinder doubles up as the compressor. the linear up and down motion of the piston is converted to
the rotary motion of the crank and crank shaft .This is transferred to the wheels by transfer
mechanisms.
Parked: It automatically shuts down the engine when the car is stationary.
At Lower Speeds: Since the Compressed Air Vehicle is running exclusively on compressed
air, it emits only air. The air expelled from the tail pipe is actually cleaner than the air used to fill the
tank. This is because before compressIon, the air is run through carbon filters to eliminate dirt,
dust, humidity, and other urban air impurities that could hamper the engine’s
performance.
At Higher Speeds: At speeds over 35mph the Compressed Air Vehicle uses small amounts of fuel–
either gasoline, propane, ethanol or bio fuels–to heat air inside a heating chamber as it enters
the engine ( again, to expand volume before entering engine). This process produces
emissions of only 0.141lbs of CO2 per mile.
ADVANTAGES
The principal advantages of an air powered vehicle are:
1) Refueling can be done at home using an air compressor or at service stations.
2) Reduced vehicle weight is the principal efficiency factor of compressed-air cars. Furthermore, they
are mechanically more rudimentary than traditional vehicles as many conventional parts of the
engine may be omitted. Some plans include motors built into the hubs of each wheel, thereby
removing the necessity of a transmission, drive axles and differentials. A four passenger vehicle
weighing less than 800 pounds (360 kg) is a reasonable design goal.