17-06-2013, 04:39 PM
Design and Fabrication of Compressed Air Engine
Compressed Air Engine.pdf (Size: 1.33 MB / Downloads: 335)
Compressed Air Engine Basics:
A Compressed-air engine is a pneumatic actuator that creates useful work by
expanding 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.
They have existed in many forms over the past two centuries, ranging in size
from hand held turbines up to several hundred horsepower. For example, the
first mechanically-powered submarine, the 1863 Plongeur, used a compressedair
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 go.
History:
a) The first compressed-air vehicle was devised by Bompas, a patent for a
locomotive being taken out in England in 1828. There were two storage
tanks between the frames, with conventional cylinders and cranks. It is not
clear if it was actually built. (Knight, 1880)
b) The first recorded compressed-air vehicle in France was built by the
Frenchmen Andraud and Tessie of Motay in 1838. A car ran on a test
track at Chaillot on the 9th July 1840, and worked well, but the idea was
not pursued further.
Disadvantages:
Like the modern car and most household appliances, 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, labour, storage,
eventually transportation to the end-user. For compressed-air cars, energy is lost
when electrical energy is converted to compressed air.
Crank shaft:
The crankshaft, sometimes casually abbreviated to crank, is the part of an
engine which translates reciprocating motion into rotary motion or vice
versa. Crank shaft consists of the shaft parts which revolve in the main
bearing, the crank pins to which the big ends of the connecting rod are
connected, the crank webs or cheeks which connect the crank pins and the
shaft parts.
Connecting rod:
Connecting rod is a part of the engine which is used to transmit the push and
pull from the piston pin to the crank pin. In many cases, its secondary
function is to convey the lubricating oil from the bottom end to the top end
i.e. from the crank pin to the piston pin and then for the splash of jet cooling
of piston crown. The usual form of connecting rod used in engines has an eye
at the small end for the piston pin bearing, a long shank, and a big end
opening which is usually split to take the crankpin bearing shells.
The connecting rods of internal combustion engine are mostly manufactured
by drop forging. The connecting rod should have adequate strength and
stiffness with minimum weight. The materials for connecting rod range from
mild or medium carbon steel to alloy steels.
Bearing:
The concept behind a bearing is very simple: Things roll better than they
slide. The wheels on your car are like big bearings. If you had something like
skis instead of wheels, your car would be a lot more difficult to push down
the road. That is because when things slide, the friction between them causes
a force that tends to slow them down. But if the two surfaces can roll over
each other, the friction is greatly reduced.
Bearings reduce friction by providing smooth metal balls or rollers, and a
smooth inner and outer metal surface for the balls to roll against. These balls
or rollers "bear" the load, allowing the device to spin smoothly.
Working of a Bearing:
As one of the bearing races rotates it causes the balls to rotate as well.
Because the balls are rolling they have a much lower coefficient of friction
than if two flat surfaces were rotating on each other.
Ball bearings tend to have lower load capacity for their size than other kinds
of rolling-element bearings due to the smaller contact area between the balls
and races. However, they can tolerate some misalignment of the inner and
outer races.
Compared to other rolling-element bearings, the ball bearing is the least
expensive, primarily because of the low cost of producing the balls used in
the bearing.