Pneumatic engine

Compressed air is used to run the piston

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CHAPTER-1
INTRODUCTION
Pneumatic systems are power systems using compressed air as a working
medium for the power transmission. Their principle of operation is similar to
that of the hydraulic power systems. An air compressor converts the mechanical
energy of the prime mover into, mainly, pressure energy of the compressed air.
This transformation facilitates the transmission, storage, and control of energy.
After compression, the compressed air should be prepared …

fig.1(a) Operation diagram of a single acting cylinder

fig.1(b)Operation diagram of a double acting cylinder
pneumatic cylinder (sometimes known as air cylinders) are mechanical
devices which use the power of compressed gas to produce a force in a
reciprocating linear motion.
Like hydraulic cylinders, something forces a piston to move in the desire
direction. The piston is a disc or cylinder, and the piston rod transfers the force
it develops to the object to be moved. Engineers sometimes prefer to use
pneumatics because they are quieter, cleaner, and do not require large amounts
of space for fluid storage.
Because the operating fluid is a gas, leakage from a pneumatic cylinder
will not drip out and contaminate the surroundings, making pneumatics more
desirable where cleanliness is a requirement. For example, in the mechanical
puppets of the Disney Tiki Room, pneumatics are used to prevent fluid from
dripping onto people below the puppets.

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1.1. Scope of this work
A compressed-air vehicle (CAV) 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 use the expansion of compressed air to drive the pistons.

1.2. Significance of this work
Compressed-air vehicles are comparable in many ways to electric
vehicles, but use compressed air to store the energy instead of batteries.
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.

1.3. Objectives of this work
To obtain the rotary motion of the crank by compressed air using double
acting pneumatic cylinder. To reduce the pollution formed by burnt fuel. And
also to reduce the fuel cost. Here only compressed air is enough to get the rotary
motion. It may be a compressor or air tank with compressed air.

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CHAPTER-2
LITERATURE REVIEW
In the project, running of a double acting pneumatic cylinder by a
compressed gas. it will use the expansion of compressed air to move the piston.
In it there is no combustion engine therefore no pollution in exhaust.
Whereas in Internal combustion engines such as reciprocating internal
combustion engines produce air pollution emissions, due to incomplete
combustion of carbonaceous fuel. The main derivatives of the process
are carbon dioxide , water and some soot — also called particulate matter . The
effects of inhaling particulate matter have been studied in humans and animals
and include asthma, lung cancer, cardiovascular issues, and premature death.
There are, however, some additional products of the combustion process that
include nitrogen oxides and sulphur and some uncombusted hydrocarbons,
depending on the operating conditions and the fuel-air ratio. PM, carbon
monoxide, sulphur dioxide, and ozone, are regulated as criteria air
pollutants under the Clean Air Act to levels at which human health and welfare
are protected.
But this all has not stop the Automotive production down the ages and the
requirements of wide range of energy-conversion systems. These include
electric, steam, solar, turbine, rotary, and different types of piston-type internal
combustion engines.
At present the most used in engine in vehicles are internal combustion
engine the internal combustion engine is an engine in which the combustion of
a fuel occurs with an oxidizer (usually air) in a combustion chamber.
As their name implies, four-stroke internal combustion engines have four
basic steps that repeat with every two revolutions of the engine are as follows:
(1) Intake stroke (2) Compression stroke (3)Power stroke and (4) Exhaust stroke
Internal combustion engines require ignition of the mixture, either
by spark ignition (gasoline)(SI) or compression ignition(diesel) (CI)

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But in today’s world, there has been a growing emphasis on the pollution
producing features of automotive power systems. This has created new interest
in alternate power sources and internal-combustion engine refinements that
were not economically feasible in prior years. Although a few limited-
production battery-powered electric vehicles have appeared from time to time,
they have not proved to be competitive owing to costs and operating
characteristics. However, the gasoline engine, with its new emission-control
devices to improve emission performance, has not yet been challenged
significantly. An approach to build an engine running on compressed air is also
a new technology and research on it is still on.
Air is compressed by an air compressor. An air compressor is a device
that converts power (usually from an electric motor, a diesel engine or a
gasoline engine) into kinetic energy by compressing and pressurizing air, which,
on command, can be released in quick bursts. There are numerous methods of
air compression, divided into either positive-displacement or negative-
displacement types.
The three basic types of air compressors are
 reciprocating
 rotary screw
 rotary centrifugal
Conventional air compressors are used in several different applications:
 To supply high-pressure clean air to fill gas cylinders
 To supply moderate-pressure clean air to a submerged surface supplied diver
 To supply moderate-pressure clean air for driving some office and school
building pneumatic HVAC control system valves
 To supply a large amount of moderate-pressure air to power pneumatic tools
 For filling tires
 To produce large volumes of moderate-pressure air for macroscopic
industrial processes (such as oxidation for petroleum coking or cement plant
bag house purge systems).
Compressed air has a low energy density. In 300 bar containers, about 0.1
MJ/L and 0.1 MJ/kg is achievable, comparable to the values of electrochemical
lead-acid batteries

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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:
 Much like electrical vehicles, air powered vehicles would ultimately
be powered through the electrical grid. Which makes it easier to focus
on reducing pollution from one source, as opposed to the millions of
vehicles on the road.
 Transportation of the fuel would not be required due to drawing
power off the electrical grid. This presents significant cost benefits.
Pollution created during fuel transportation would be eliminated.
 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.
 Air, on its own, is non-flammable.
 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.
 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.
 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 bio fuel. If electricity is cheap, then compressing air
will also be relatively cheap.

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Problem definition
The objective of the project is the use of compressed air as a source of
fuel in IC engines. For this modifications in the engine are needed. But we tried
with Double acting pneumatic cylinder
The increasing level of pollutants in the environment and the inflating
prices of petrol and diesel form the basis of study of various sources of
alternative fuels. The investigation and study of an unconventional source of
fuel carried out to establish its advantages and limitations over gasoline and to
determine its application.
The modification of four stroke engine is required to get greater power
output when using compressed air. The performance was measured using an air
compressor with air being supplied to the double acting cylinder from the inlet.
Here we need a crank shaft to convert the reciprocating motion to rotary
motion, So we use Crank shaft of a motorcycle with connecting rod.
Since it is a mini project we can't provide large budget for this so we
fitted this experimental setup in a welded stand.

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CHAPTER-3
EXPERIMENTATION SETUP
3.1. Principle
The principle behind the working of the Compressed Air Engine is the
ability of air to store energy on compression and then release the same on
expansion.
When the compressed air enters the engine through the inlet valve it
strikes the piston, which moves (reciprocate) causing first half rotation of the
crank shaft, this strikes air gets expanded which then moves to the out through
the outlet during the 2nd half rotation of the crank shaft .Thus, Reciprocating
motion of piston is converted into rotary motion of crank. The air is stored
either in cylinder or compressor.
3.2. Construction
Double acting Pneumatic cylinder is used to create the reciprocating
motion. This reciprocating motion is produced by the use of Air compressor.
Created reciprocating motion should be converted into rotary motion for the
wheel rotation or any other purposes. For this purpose Connecting rod and
crank is used.
For the complete operation of the compressed air engine so many
components are needed. They are as follows
3.2.1.Double acting pneumatic cylinder
A double-acting cylinder is a cylinder in which the working fluid acts
alternately on both sides of the piston. In order to connect the piston in a
double-acting cylinder to an external mechanism, such as a crank shaft, a hole
must be provided in one end of the cylinder for the piston rod, and this is fitted
with a gland or "stuffing box" to prevent escape of the working fluid. Double-
acting cylinders are common in steam engines but unusual in other engine
types. Many hydraulic and pneumatic cylinders use them where it is needed to
produce a force in both directions.
A double-acting hydraulic cylinder has a port at each end, supplied with
hydraulic fluid for both the retraction and extension of the piston.

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fig.2(a) double acting pneumatic cylinder design in CREO


fig2(b). Double acting pneumatic cylinder
A double-acting cylinder is used where an external force is not available
to retract the piston or where high force is required in both directions Double
acting pneumatic cylinder turn air pressure into linear motion.

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3.2.2.Solenoid valve
A solenoid valve is an electromechanically operated valve. The valve is
controlled by an electric current through a solenoid: in the case of a two-port
valve the flow is switched on or off; in the case of a three-port valve, the
outflow is switched between the two outlet ports. Multiple solenoid valves can
be placed together on a manifold. Here we use three port solenoid valve.

fig.3 3/2 way Solenoid valve
Solenoid valves are the most frequently used control elements in fluidics.
Their tasks are to shut off, release, dose, distribute or mix fluids. They are found
in many application areas. Solenoids offer fast and safe switching, high
reliability, long service life, good medium compatibility of the materials used,
low control power and compact design.

3.2.3.Relay sensor switch
Relays are switches that open and close circuits electromechanically or
electronically.


fig.4 Relay sensor
Relays control one electrical circuit by opening and closing contacts in
another circuit. when a relay contact is normally open (NO), there is an open
contact when the relay is not energized.

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A relay is an electromagnetic switch operated by a relatively small
electric current that can turn on or off a much larger electric current. The heart
of a relay is an electromagnet (a coil of wire that becomes a temporary magnet
when electricity flows through it). When the current is switched off, the contacts
open again, switching the circuit off. A useful property of relays is that the
circuit powering the coil is completely separate from the circuit switched on by
the relay. For this reason relays are used where a safe low-voltage circuit
controls a high-voltage circuit.

3.2.4.Relief valve
A relief valve or pressure relief valve (PRV) is a type of safety valve used
to control or limit the pressure in a system; pressure might otherwise build up
and create a process upset, instrument or equipment failure, or fire. The pressure
is relieved by allowing the pressurized fluid to flow from an auxiliary passage
out of the system. The relief valve is designed or set to open at a predetermined
set pressure to protect pressure vessels and other equipment from being
subjected to pressures that exceed their design limits.
In high-pressure gas systems, it is recommended that the outlet of the
relief valve is in the open air. If the valve is opened the pressure has to decrease
enormously before the valve closes and also the outlet pressure of the valve can
easily keep the valve open.
In some cases, a so-called bypass valve acts as a relief valve by being
used to return all or part of the fluid discharged by a pump or gas compressor
back to either a storage reservoir or the inlet of the pump or gas compressor.


fig.5(a) Relief valve fig.5(b) Cross section

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3.2.5.Connecting Rod
A connecting rod is a shaft which connects a piston to
a crank or crankshaft in a reciprocating engine. Together with the crank, it
forms a simple mechanism that converts reciprocating motion into rotating
motion.
A connecting rod may also convert rotating motion into reciprocating
motion, its original use. Earlier mechanisms, such as the chain, could only
impart pulling motion. Being rigid, a connecting rod may transmit either push or
pull, allowing the rod to rotate the crank through both halves of a revolution. In
a few two-stroke engines the connecting rod is only required to push.
Today, the connecting rod is best known through its use in internal
combustion piston engines, such as automobile engines. These are of a
distinctly different design from earlier forms of connecting rod used in steam
engines and steam locomotives.


fig.6 Connecting rod
3.2.6Crank
Engines that make their power with pistons usually need a way of
converting back-and-forth (reciprocating) motion into round-and-round
(rotational) motion—a way of driving a wheel, in other words. Most engines use
cranks to do this. A crank is simply an off-center connection that provides
energy to (or takes energy from) a rotating wheel. As the crank pushes back and
forth, the wheel rotates (or vice-versa).

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fig.7 Crank
Crank (mechanism), in mechanical engineering, a bent portion of an axle
or shaft, or an arm keyed at right angles to the end of a shaft, by which motion
is imparted to or received from it Crank set, the component of a bicycle drive
train that converts the reciprocating motion of the rider's legs into rotational
motion Crankshaft, the part of a piston engine which translates reciprocating
linear piston motion into rotation Crank machine.
3.2.7.Fork Joint
A Fork joint is a mechanical joint used to connect two rods which are
under a tensile load, when there is a requirement of small amount of flexibility,
or angular moment is necessary. There is always axial or linear line of action of
load.

fig.8 Fork joint

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3.2.8.Air flow tube
Polyethylene tubing is a flexible, lightweight, and exceptionally
durable tubing solution that is ideal for use in a broad range of applications
involving liquid and gas fluid transfer. Its inertness allows it to be
effectively used to safely transfer a vast array of chemicals, fluids, and
materials. So we use this polyethylene tube for air tight flow.

fig.9 Polyethylene tube

Bill of materials

S.No Components Size Nos Material
1 Double acting
pneumatic cylinder
32*100 (mm) 1 Aluminium
2 Solenoid valve 3/2 way 1 -
3 Tube 500mm 3 Polyethylene
4 Relay sensor - 2 -
5 Relief valve - 2 Aluminium

6

Connecting rod
- 1 Mild and medium
carbon steel alloy

7

Crank
- 1 Medium carbon
steel alloy
8 Fork joint DIN71752 1 Stainless steel
table1. Bill of material

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3.3. Working
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, here we use the expansion
of compressed air to drive the piston.
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
compressed air engine.
The laws of physics dictate that unconstrained 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.
On compression, the work done by the pump gets stored as pressure
energy. This compressed air is then stored in cylinders/tanks for later use. When
this air is allowed to expand, the pressure energy of air gets converted to kinetic
energy and causes propulsion.
Compressed air engine works in two stroke such as intake and exhaust
stroke with compressed air as working fluid.
Intake: During this stroke, the piston is initially at top dead centre, inlet valve
opens and exhaust valve is closed. Compressed air enters in the cylinder during
this stroke at a specified pressure. Compressed air starts expanding exerting
pressure on the piston, pushing the piston from top dead centre to bottom dead
centre. As the piston reaches bottom dead centre the pressure of the compressed
air reduces.

Exhaust: During this stroke, the intake valve closed and exhaust valve is
opened. The piston moves from bottom dead centre to top dead centre pushing
the low pressure used compressed air out of the cylinder through the exhaust
valve. These two strokes repeat for the continuous working of the engine . The
valve positions, cam position and working of a compressed air.

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fig.10 Experimental setup

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3.4. Design calculation

At outstroke,

Force = Pressure * Area
F = p * A
=10 * 10
5
* π * 0.32
2
/4
F =80384 N

At instroke,

F = p * A
=10 * 10
5
π (0.32
2
– 0.02
2
) / 4
F = 80070 N


Torque on Crankshaft = Force * crank radii
T = F * r
= 80384 * 0.03
T = 2411.52 Nm


Power obtained = 2πNT/60
= 2π* 500 *2411.52/60
P = 126 KW

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S.NO LOAD
( N )
RADIUS
( m )
TORQUE
( Nm )
1. 80384 0.03 2411.52
2. 88400 0.03 2652.00
3. 96400 0.03 2892.00
table2. Observation of torque


3.5. Graphical representation



graph1. Pressure Vs RPM



0
100
200
300
400
500
600
700
800
900
1000
0 1 2 3 4 5 6 7
R.P.M
Pressure (bar)
Pressure vs R.P.M.

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graph2. Pressure Vs Torque



graph3.RPM Vs Torque



0
0.5
1
1.5
2
2.5
3
3.5
0 1 2 3 4 5 6 7
Torque on crankshaft (Nm)
Pressure (bar)
Pressure vs Torque
0
0.05
0.1
0.15
0.2
0.25
0 200 400 600 800 1000 1200
Torque (N m)
R.P.M.
RPM vs Torque

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CHAPTER-4
Cost estimation
S.No Components Nos Cost(Rs)
1 Double acting
pneumatic
cylinder
1 1950
2 Solenoid valve 1 800
3 Tube 3 150
4 Relay sensor 2 1900
5 Relief valve 2 150
6 Connecting rod
&Crank
1 500
7 Fork joint 1 80
Total Cost 5530
table3. Cost estimation

Conclusion
The performance of the Compressed air engine is mainly influenced by
the rotation speed and supply pressure. In the first instance, the output power
ascends sharply with the increasing rotation speed and reaches to maximum
value. After this peak, the output power drops sharply. The prototype of
Compressed air engine has a good economic performance under low speed.
When the supply pressure is 2 MPa, the maximum output power is 1.92 kW.
This is a revolutionary engine design which is eco-friendly, pollution
free, but also very economical. This redresses both the problems of fuel crises
and pollution.

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