1 TRUBA COLLEGE OF ENGINEERING & TECHNOLOGY INDORE (M.P.) “FABRICATION OF BASIC STIRLING ENGINE MODEL” A MINOR PROJECT REPORT-2012 A minor project report submitted at Rajiv Gandhi Proudyogiki Vishwavidyalaya, Bhopal In partial fulfillment of the requirement as per the curriculum of BE III rd year in the Mechanical Engineering. SUBMITTED BY MANISH SOLANKI (0830ME091032) MD. UMAR KHAN (0830ME091035) ROHAN GORALKAR (0830ME091050) SUBMITTED TO: GUIDED BY: PROF. MRS. SUMAN SHARMA Asst.Prof. MR. VISHAL ACHWAL (HEAD OF DEPARTMENT) DEPARTMENT OF MECHANICAL ENGINEERING
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1
TRUBA COLLEGE OF ENGINEERING & TECHNOLOGY
INDORE (M.P.)
“FABRICATION OF BASIC STIRLING ENGINE MODEL”
A MINOR PROJECT REPORT-2012
A minor project report submitted at
Rajiv Gandhi Proudyogiki Vishwavidyalaya, Bhopal
In partial fulfillment of the requirement as per the curriculum of
BE IIIrd
year in the Mechanical Engineering.
SUBMITTED BY
MANISH SOLANKI (0830ME091032)
MD. UMAR KHAN (0830ME091035)
ROHAN GORALKAR (0830ME091050)
SUBMITTED TO: GUIDED BY:
PROF. MRS. SUMAN SHARMA Asst.Prof. MR. VISHAL ACHWAL
(HEAD OF DEPARTMENT)
DEPARTMENT OF MECHANICAL ENGINEERING
2
TRUBA COLLEGE OF ENGINEERING & TECHNOLOGY
INDORE (M.P.)
“FABRICATION OF BASIC STIRLING ENGINE MODEL”
A MINOR PROJECT REPORT-2012
SUBMITTED BY
MANISH SOLANKI (0830ME091032)
MD. UMAR KHAN (0830ME091035)
ROHAN GORALKAR (0830ME091050)
SUBMITTED TO: GUIDED BY:
PROF. MRS. SUMAN SHARMA Asst.Prof .MR. VISHAL ACHWAL
(HEAD OF DEPARTMENT )
DEPARTMENT OF MECHANICAL ENGINEERING
3
TRUBA COLLEGE OF ENGINEERING & TECHNOLOGY
INDORE, (M.P.)
CERTIFICATE
This is to certify that the project work entitled
“ FABRICATION OF BASIC STIRLING ENGINE MODEL”
has been carried out by, MANISH SOLANKI, MD. UMAR KHAN ,
ROHAN GORALKAR students of third year B.E. Mechanical Engineering under our
supervision & guidance. They have submitted this Minor project report towards partial
fulfillment for the award of Bachelor of Engineering in Mechanical Engineering of
Rajiv Gandhi Prodyogiki Vishvavidyalaya, Bhopal
during the academic year 2011-2012.
Asst.Prof.Mr. Vishal Achwal Prof. Suman Sharma Madam
Otto adiabatic isochoric adiabatic isochoric Gasoline / petrol
engines
Known Thermodynamic Cycles: TABLE: 1
14
1.4 HISTORY:
The Stirling engine were invented in 1816 by Robert Stirling in Scotland,
some 80 years before the invention of diesel engine, and enjoyed substantial
commercial success up to the early 1900s. A Stirling cycle machine is a
device, which operates on a closed regenerative thermodynamic cycle, with
cyclic compression and expansion of the working fluid at different
temperature levels. The flow is controlled by volume changes so that there
is a net conversion of heat to work or vice versa. The Stirling engines are
frequently called by other names, including hot-air or hot-gas engines, or
one of a number of designations reserved for particular engine arrangement.
In the beginning of 19th century, due to the rapid development of internal
combustion engines and electrical machine, further development of Stirling
engines was severely hampered.
Sketch of Robert Stirling of his invent
FIGURE: 6
15
LITERATURE REVIEW
16
2. LITERATURE REVIEW
The Stirling Engine is one of the hot air engines. It was invented by Robert
Stirling (1790-1878) and his brother James. At this period, he found the
steam engines are dangerous for the workers. He decided to improve the
design of an existing air engine. He hope it wound be safer alternative.
After one year, he invented a regenerator. He called the “Economizer” and
the engine improves the efficiency. This is the earliest Stirling Engine. It is
put out 100 W to 4 kW. The Ericsson invented the solar Energy in 1864 and
did some improvements for after several years. Robert’s brother, James
Stirling, also played an important role in the development of Stirling
engines.
Earliest Stirling engine
FIGURE: 7
17
The original patent by Reverend Stirling was called the "economizer", for
its
Improvement of fuel-economy. The patent also mentioned the possibility of
using the device in an engine. Several patents were later determined by two
brothers for different configurations including pressurized versions of the
engine. This component is now commonly known as the "regenerator" and
is essential in all high-power Stirling devices.
During the early part of the twentieth century the role of the Stirling engine
as a "domestic motor" was gradually usurped by the electric motor and
small
Internal combustion engines until by the late 1930s it was largely forgotten,
only produced for toys and a few small ventilating fans. At this time Philips
was seeking to expand sales of its radios into areas where mains electricity
was unavailable and the supply of batteries uncertain. Philips’
Management decided that offering a low-power portable generator would
facilitate such sales and tasked a group of engineers at the company
research lab (the Nat. Lab) in Eindhoven to evaluate the situation. After a
systematic comparison of various prime movers the Stirling engine was
considered to have real possibilities as it was among other things, inherently
quiet (both audibly and in terms of radio interference) and capable of
running from any heat source (common lamp oil was favored). They were
also aware that, unlike steam and internal combustion engines, virtually no
serious development work had been carried out on the Stirling engine for
many years and felt that with the application of modern materials and
know-how great improvements should be possible.
18
2.1 PRESENTATION OF STIRLING ENGINES
2.1.1 STIRLING THERMODYNAMIC CYCLE
The Stirling engine cycle is a closed cycle and it contains, most commonly
a fixed mass of gas called the "working fluid" (air, hydrogen or helium).
The principle is that of thermal expansion and contraction of this fluid due
to a temperature differential.
So the ideal Stirling cycle consists of four thermodynamic distinct processes
acting on the working fluid: two constant-temperature processes and two
constant volume processes.
Each one of which can be separately analyzed:
Stirling thermodynamic cycle: FIGURE:8
19
Process Involved In Stirling Cycle:
1-2: isothermal compression process. Work W1-2 is done on the
working fluid, while an equal amount of heat Q1-2 is rejected by the
system to the cooling source. The working fluid cools and contracts
at constant temperature TC.
2-3: constant volume displacement process with heat addition.
Heat Q 2-3 is absorbed by the working fluid and temperature is raised
from TC to TH. No work is done.
3-4: isothermal expansion process. Work W3-4 is done by the
working fluid, while an equal amount of heat Q3-4 is added to the
system from the heating source. The working fluid heats and expands
at constant temperature TH.
4-1: constant volume displacement process with heat rejection.
Heat Q4-1 is rejected by the working fluid and temperature decrease
from TC to TH. No work is done.
20
2.2 ANALYSIS OF THE STIRLING-CYCLE
ENGINE
2.2.1 Work done by an ideal Stirling-cycle engine
The net work output of a Stirling-cycle engine can be evaluated by
considering the cyclic integral of pressure with respect to volume:
W=-∮
This can be easily visualized as the area enclosed by the process curves on
the pressure-volume. To evaluate the integral we need only consider the
work done during the isothermal expansion and compression processes,
since there is no work done during the isochoric processes, i.e.
W=-[ ∫
+∫
(4.1)
By considering the equation of state:
pV =mRT
and noting that T is constant for an isothermal process, and m is constant for
a closed cycle, then an expression for work done during an isothermal
process can be formulated:
∫ ∫
(
) (4.2)
so that by substitution of Equation 4.2 into Equation 4.1,we can evaluate
the work integral:
( ) (
) ( ) (
)
where the subscripts H and L denote the high and low temperature
isotherms respectively.
This equation can then be further simplified by noting that V4 = V1 and V3
= V2 so that a final equation for work can be obtained:
21
(
)(TH -TL) (4.3)
The work done represents energy out of the system, and so has a negative
value according to the sign convention used here.
Inspection of Equation 4.3, therefore, shows that the work output for a
Stirling-cycle machine can be increased by maximizing the temperature
difference between hot and cold ends (TH-TL), the compression ratio
(V2/V1), the gas mass (and hence either the total volume of the machine
and/or the mean operating pressure), or the specific gas constant.
Material strength/temperature considerations and practicalities such as the
overall size of the machine usually limit the amount that the temperature,
volume, or pressure can be increased.
However, it is interesting to note that the specific work output (i.e. work
output per kilogram) can be dramatically enhanced in a Stirling-cycle
machine simply by selecting a working gas with a high specific gas
constant.
One of the reasons that hydrogen and helium are so often used as the
working gas in large Stirling-cycle machines can be deduced by inspection
of the values for specific gas constants given in Table 4.1. (another reason
is the lower flow losses that occur with smaller molecule gases).
Table: Specific gas constants for a variety of gases at 300 K
Gas Specific gas constant,
R (J/kgK)
Air
Ammonia
Carbon dioxide
Helium
Hydrogen
Nitrogen
Propane
Steam
319.3
488.2
188.9
2077.0
4124.2
296.8
188.6
461.5
Specific gas constants: TABLE: 2
22
2.2.2 Heat flow in an ideal Stirling-cycle engine
The heat flowing into and out of a Stirling-cycle engine can be evaluated by
considering the integral of temperature with respect to entropy:
∫
Since the isochoric heat transfers within the regenerator are completely
internal to the cycle, i.e. -Q2-3 = Q4-1, then to evaluate the heat flows into
and out of the system we need only consider the isothermal processes.
For the isothermal expansion process in a closed cycle (where T and m are
constant, and where the subscripts H and L denote the high and low
temperature isotherms respectively):
QH= ∫
H dS
This integral can be most easily evaluated by considering the First Law of
Thermodynamics in the form:
QH=∫
∫
and by considering the equation of state:
pV=mRT n be expressed in terms of volume and temperature, and (noting
that there is no change in internal energy during an isothermal process) the
integral can be easily solved:
QH=∫
∫
H dV = 0 + ∫
H dV
giving:
QH = mRTH ln (
) (4.4)
which is a somewhat convoluted (but hopefully instructive) method of
derivation. The same expression can, of course, be obtained much more
easily by simple inspection of Equation 4.3., since the heat and work
transfers for an isothermal expansion process are equal but opposite.
23
The isothermal compression process can also be readily evaluated (noting
that V4 = V1 and V3 = V2, and where the subscripts H and L denote the high
and low temperature isotherms respectively), giving:
QL = - mRTL ln (
) (4.5)
2.2.3 Efficiency of an ideal Stirling-cycle engine
The efficiency of any heat engine is defined as the ratio of work output to
heat input, i.e.
hence an equation for the efficiency of an ideal Stirling-cycle engine can be
developed by considering Equations 4.3. and 4.4., giving:
STIRLING=
which simplifies to:
STIRLING=
this demonstrates the interesting fact that the efficiency of an ideal Stirling-
cycle engine is dependant only on temperature and no other parameter. It is
worth recalling that the Carnot efficiency for a heat engine is:
CARNOT=
and so it will readily be observed that:
STIRLING = CARNOT
or, in other words, that the Stirling-cycle engine has the maximum
efficiency possible under the Second Law of Thermodynamics. However, it
should be noted that unlike the Carnot Cycle, the Stirling-cycle engine is a
practical machine that can actually be used to produce useful quantities of
work.
24
2.2.4 Actual Stirling Engine
Actual Stirling Engine: FIGURE: 9
In real life, it is not possible to have isothermal and isochoric process
because they are instantaneous. In stirling cycle heat addition and rejection
is assumed to be instantaneous which is not possible and because of some
internal losses in friction and other the actual graph is oval shape.
25
2.3 ENGINE CONFIGURATIONS
Mechanical configurations of Stirling engines are classified into three
important distinct types: Alpha, Beta and Gamma arrangements.
These engines also feature a regenerator (invented by Robert Stirling). The
regenerator is constructed by a material that conducts readily heat and has a
high surface area (a mesh of closely spaced thin metal plates for example).
When hot gas is transferred to the cool cylinder, it is first driven through the
Regenerator, where a portion of the heat is deposited. When the cool gas is
transferred back, this heat is reclaimed. Thus the regenerator “pre heats”
and “pre cools” the working gas, and so improve the efficiency.
But many engines have no apparent regenerator like beta and gamma
engines configurations with a “loose fitting” displacer, the surfaces of the
displacer and its cylinder will cyclically exchange heat with the working
fluid providing some regenerative effect.
26
2.3.1 Alpha Stirling :
Alpha engines have two separate power pistons in separate cylinders which
are connected in series by a heater, a regenerator and a cooler. One is a
“hot” piston and the other one a “cold piston”.
Alpha Stirling: FIGURE: 10
The hot piston cylinder is situated inside the high temperature heat
exchanger and the cold piston cylinder is situated inside the low
temperature heat exchanger. The generator is illustrated by the chamber
containing the hatch lines.
Alpha type Stirling.
FIGURE: 11
27
Expansion: At this point, the most of the gas in the system is at the hot
piston and expands, pushing the hot piston down, and flowing through the pipe into the cold cylinder, pushing it
down as well.
Transfer: At this point, the gas has expanded. Most of the gas
is still in the Hot cylinder. As the crankshaft continues to turn the next 90°, transferring the bulk of the gas to the cold piston cylinder. As it does so, it pushes most of the
fluid through the heat exchanger and into the cold
piston cylinder
This type of engine has a very high power-to-volume ratio but has technical
problems due to the usually high temperature of the "hot" piston and its
seals.
Contraction: Now the majority of the expanded gas is shifted to the cool piston cylinder. It cools and
contracts, drawing both pistons up.
Transfer: The fluid is cooled and now crankshaft turns another 90°. The gas is therefore pumped back, through the heat exchanger, into the hot piston cylinder. Once in
this, it is heated and we go back to the first step.
28
2.3.2 Beta Stirling
The Beta configuration is the classic Stirling engine configuration and has
enjoyed popularity from its inception until today. Stirling's original engine
from his patent drawing of 1816 shows a Beta arrangement.
Both Beta and Gamma engines use displacer-piston arrangements. The Beta
engine has both the displacer and the piston in an in-line cylinder system.
The Gamma engine uses separate cylinders.
The purpose of the single power piston and displacer is to “displace” the
working gas at constant volume, and shuttle it between the expansion and
the compression spaces through the series arrangement cooler, regenerator,
and heater.
A beta Stirling has a single power piston arranged within the same cylinder
on the same shaft as a displacer piston. The displacer piston is a loose fit
and does not extract any power from the expanding gas but only serves to
shuttle the working gas from the hot heat exchanger to the cold heat
exchanger.
Beta Stirling: FIGURE: 12
29
Expansion: At this point, most of the gas in the system is at the heated end
of the cylinder. The gas heats and expands driving the power piston
outward.
Transfer: At this point, the gas has expanded. Most of the gas is still
located in the hot end of the cylinder. Flywheel momentum carries the crankshaft the next quarter turn. As the crank goes round, the bulk of
the gas is transferred around the displacer to the cool end of the
cylinder, driving more fluid into the cooled end of the cylinder.
Contraction: Now the majority of the expanded gas has been shifted
to the cool end. It contracts and the displacer is almost at the bottom of
its cycle.
Transfer: The contracted gas is still located near the cool end of the cylinder. Flywheel momentum
carries the crank another quarter turn, moving the displacer and transferring the bulk of the gas
back to the hot end of the cylinder. And at this point, the cycle repeats.
30
2.3.3 Gamma Stirling
A gamma Stirling is simply a beta Stirling in which the power piston is
mounted in a separate cylinder alongside the displacer piston cylinder, but
is still connected to the same flywheel. The gas in the two cylinders can
flow freely between them and remains a single body. This configuration
produces a lower compression ratio but is mechanically simpler and often
used in multi-cylinder Stirling engines. Gamma type engines have a
displacer and power piston, similar to Beta machines, but in different
cylinders. This allows a convenient complete separation between the heat
exchangers associated with the displacer cylinder and the compression and
expansion work space associated with the piston.
Gamma engine’s configuration
FIGURE: 13
Furthermore during the expansion process some of the expansion must take
place in the compression space leading to a reduction of specific power.
Gamma engines are therefore used when the advantages of having separate
cylinders outweigh the specific power disadvantage.
The advantage of this design is that it is mechanically simpler because of
the convenience of two cylinders in which only the piston has to be sealed.
The disadvantage is the lower compression ratio but the gamma
configuration is the favorite for modelers and hobbyists.
31
TECHNICAL COMPLEXITY OF TOPIC
The Stirling cycle is a highly advanced subject that has defied analysis by
many experts for over 190 years. Highly advanced thermodynamics are
required to describe the cycle. Professor Israel Urieli writes: "...the various
'ideal' cycles (such as the Schmidt cycle) are neither physically realizable
nor representative of the Stirling cycle" [
The analytical problem of the regenerator (the central heat exchanger in the
Stirling cycle) is judged by Jakob to rank 'among the most difficult and