1. ANALYZE OF KS90T SOLAR TWIN AS LOW TEMPERATURE
DIFFERENTIAL STIRLING ENGINE
In parthership with
By:
1. Dama Vara : 2014990002
2. Debby Syahera : 2014370010
3. I Wayan Surya Aryana : 2014370006
4. Lutfi Hidayat : 2014360006
5. Paskah Andreas Deo Gratias : 2014370005
MECHANICAL ENGINEERING
SAMPOERNA UNIVERSITY
i
2. ABSTRACT
A Stirling engine is a heat engine operating by cyclic compression and expansion of air or other
gas. KS90T Solar Twin LTD stirling engine is a new generation of stirling engine that has been
born to increase the effectiveness of stirling engine. This engine is noted for its high efficiency
compared to another engines. This compatibility with alternative and renewable energy sources
in which it has become increasingly significant as the price of conventional fuels rises, and also
in light of concerns such as peak oil and climate change. This paper is mainly aimed to analyze
KS90T Solar Twin stirling engine as a LTD engine. As a result, this study indicate how KS90T
Solar Twin LTD stirling engine work and how this engine look like in its orthogonal views.
Keywords: Stirling engine, KS90T-LTD, Gamma-type.
ACKNOWLEDGMENT
We wish to thank to Prof. Dr. Yunan Prawoto for many helps regarding in completing this paper.
Second, we would to thank much for another group’s suggestion who make correction to our paper.
Finally, thanks to all group members that already did hard work to contribute for the projec it.
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3. Content
Tittle ................................................................................................................................................ i
Abstract and Acknowledgment ................................................................................................... ii
Content.......................................................................................................................................... iii
CHAPTER I: Introduction ...........................................................................................................1
1.1. Background...................................................................................................................1
1.2. Problems .......................................................................................................................3
1.3. Aims..............................................................................................................................3
1.4. Benefit...........................................................................................................................3
CHAPTER II: Basic Theory.........................................................................................................4
2.1. The Principles and Works of Stirling Engine ...............................................................4
2.2. Type of Stirling Engine.................................................................................................7
2.2.1. Alpha Stirling Engine ....................................................................................7
2.2.2. Beta Stirling Engine.......................................................................................7
2.2.3. Gamma Stirling Engine..................................................................................8
2.3. Low Temperature Differential Engine..........................................................................8
CHAPTER III: Method...............................................................................................................10
3.1. Method........................................................................................................................10
3.2. Collecting Data ...........................................................................................................10
3.3. Location and Schedule................................................................................................10
CHAPTER IV: Result and Disccussion.....................................................................................12
4.1. Result ..........................................................................................................................12
4.2 Discussion....................................................................................................................14
CHAPTER V: Conclusion and Suggestion................................................................................19
References.....................................................................................................................................20
Attachment ...................................................................................................................................21
iii
4. CHAPTER I
INTRODUCTION
1.1. Background
A Stirling engine is basically an external heated appliance that make a use of a reversible
closed cycle concept in which the Stirling engine’s thermal efficiency is equal to that of the Carnot
cycle. Even Stirling engine was invented before the internal combustion engine in which it is in
1816 (Karabulut, 2000, p.71), Stirling engines were not commercialized yet at that time. The main
reason avoiding Stirling engine from being commercialized was because Stirling engine was not
competitive with those that belong to the internal combustion engine in the specs of power
produced and weight owned (Karabulut, 2000, p.71). However, even it is shown like that, there
are some aspects that successfully make Stirling engine become exist till today, which are its high
heat conversion efficiency, reliability, ability to use many fuels, and low noise operation
characteristic (Hassani, 2013, p. 1). By those characteristics, Stirling engine have been being a
demand of the effective usage of energy and environmental preservation. In fact, reducing
environmental impacts of conventional energy resources and meeting the growing energy demand
of the global population had motivated considerable research attention in a wide range of
environmental and engineering application of renewable form of energy, and among all possible
alternative energy options, solar energy is becoming more popular in the world. This is mainly
caused by the availability of plenty of sunlight in many countries (Sharma & Harinarayana, 2012,
p. 1). By that reason, a new generation of engine called LTD-SE is being developed.
A new generation, LTD-SE, that is being developed in expecting to make a better future in
using the solar energy. The Low-Temperature Differential Stirling Engine (LTD-SE) is a kind of
Stirling engine that can run with a small temperature difference between the hot and the cold
1
5. source. By that characteristic, people believe that LTD-SE can utilize the solar energy and make
benefit of that. LTD-SE firstly developed by Kolin in 1983 (Hassani, 2013, p. 1), and now,
considering that todays’ trend is using eco-friendly energy with a high efficiency owned, the LTD-
SE is being developed and begin to be manufactured in large scale. Besides that, it is also noticed
that LTD-SE is being differed between those that have been produced previously; those that
manufactured before the LTD-SE is likely prevented by being commercialized but now LTD-SE
is being popularize regarding to its eco-friendly characteristic.
In line with LTD-SE, its differentials are also now being researched in regarding to adjust
the concept of eco-friendly to the drive mechanism used in each kind of engine. As a result of a
scientific cooperation between Moulay Ismail University in Morocco and the University of
Technology of Dresden in Germany, an LTD γ-type Stirling engine was produced. This engine
was tested and studied under a real conditions. Based on the conclusions of this study, a new
prototype of LTD-SE with walking beam drive mechanism called KS90T Solar Twin LTD is being
developed; this is beautiful, stable, easy built, and shown a high machine efficiency.
In short, considering that γ-type Stirling engine with a walking beam drive mechanism is a
new engine, so this paper aims to study both the design of the machine and the performance of
how the low-temperature Stirling engine concept in KS90T Solar Twin LTD works. A
thermodynamic analysis of the machine is also be conducted to help in finding the result of the
purposes.
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6. 1.2. Problems
Here are the problems that built up the paper:
1. What is KS90T Stirling engine?
2. How KS90T Stirling engine work?
3. What is the efficiency of the engine?
4. Is it really work in low temperatures?
1.3. Aims
Here are the aims that we want to achieve:
1. To analyze how KS90T Stirling engine work.
2. To know the design of the engine.
1.4. Benefit
There are some categories of benefit in this paper considering to whom the paper is used:
1. Group
a. Apply engineering drawing technique.
b. Understanding what is KS90T Stirling engine.
c. Knowing how KS90T work.
2. Student
a. Providing the orthogonal drawing of KS90T LTD Stirling Engine.
b. Providing a reference to the other students about KS90T LTD Stirling Engine.
3
7. CHAPTER II
BASIC THEORY
2.1. The Principles and Works of Stirling Engine
Thermal circuit with a considerable degree of simplification, consisting of a number of
thermodynamic transformations is called a theoretical circuit, the example of which is the Carnot
cycle (Fig. 1). The implementation of this course mostly impossible, because the engine forced to
have a perfect parameters. Still, this model can help in the initial stages of design, besides it can
be a simplified description of the operation of the engines. During subsequent cycles of thermal
cycle, an ideal gas is subjected to changes, in which heat exchange is conducted between the gas
and the environment (Żmudzki, 1993):
Figure 1. Carnot Cycles
Cycle 1. Isothermal compression at temperature C to D, even temperature heat source,
usually a factor that gives off heat to the cooler.
4
8. Cycle 2. Adiabatic compression from point D to A is the gas heating to achieve a
temperature at A equal to the temperature of the upper heat source.
Cycle 3. Isothermal expansion at A temperature causing reversion of gas volume to its
initial value V1.
Cycle 4. Adiabatic expansion from B to C — the working factor is expanded without
changing the heat until to achieve the cooler temperature T.
Stirling engine belongs to a group of external combustion engines, which means that the
fuel is burned outside the engine. Flammable material or other medium are supplied to drive the
system. In this particular type of engine, temperature needed to start up the systems work. It can
be electric heating, burning candle as the application of object or a material with higher
temperature. The engine circuit may occur as a closed system, which allows for the same mass of
working gas participated in all cycles without exchanging it with the outside, so with the gas from
the outside of the engine compartment. The system allowing to better understand the Stirling
engine working is a piston engine with a single cylinder, in which a constant mass of gas is
alternately compressed and expanded, under the influence of linear progressive — return
movement of the piston (Fig. 2).
5
9. Figure 2. The movement of the single piston during closed cycle
The intense cooling of the cylinder during compression is necessary to the proper
working which assure isothermal transformation. Stopping the piston at top dead point and at the
same time providing heat allows to perform isochoric transformation 2–3 (Part 2). Isothermal
expansion is another transformation by intense heating of the cylinder 3–4 (Part 3). The cycle
closes when the piston reaches bottom dead point during the isochoric transformation 4–1 (Part
4). In fact, an engine can’t work through it in practical point of view, because it would require
the application of a specific mechanisms that allow the interrupted movement of the piston.
Think based on Figure 2, the Stirling engine should fulfill this conditions (G., 1980):
1. Continuous movement of the piston;
2. The full exchange of the mass of gas from an area in the low temperature to the high
temperature, without changing its volume (closed system);
3. There is no pressure loss in the heat exchangers and there are no internal pressure
differences.
4. The expansion process and the compression process changes isothermal.
6
10. 5. Conditions of the working gas are changed as an ideal gas.
6. There is a perfect regeneration.
7. The expansion dead space maintains the expansion gas temperature and the compression
dead space maintains the compression gas temperature during the cycle.
8. The regenerator gas temperature is an average of the expansion gas temperature and the
compression gas temperature.
Meanwhile, to get perfect regeneration can be achieved by using a material that can absorb
heat which has high heat capacity. The material used to absorb that heat called by regenerator. The
regenerator might place between cold and hot space that located inside the cylinder, however it
can placed outside. The use of this element to reduce the loss of heat energy when doing exchange
and thus increases the efficiency of the whole system.
2.2. Types of Stirling Engine
There are three types of Stiring engine based on the configuration and how it work.
2.2.1. Alpha Stirling Engine
This type of engine has two power pistons at a phase difference of 90 deg. There is a
high temperature (expansion) space and low temperature (compress) space attached to each
other. As the two pistons make the gas between both spaces go and return, the same two pistons
output power.
2.2.2. Beta Stirling Engine
In a beta type Stirling engine the displacer and power piston share a single cylinder.
Therefore, a displacer piston and power piston is supposed to have a bore of the same diameter.
By overlapping between each movement of both pistons, a compression ratio of the engine raises
7
11. and can obtain higher output than gamma type Stirling engine. However, the shaft of the
displacer and the power piston are on the same axis, therefore driving mechanism gets
complicated.
2.2.3. Gamma Stirling Engine
The Gamma engine is the simplest and easiest type of Stirling engine. This type of
configuration with double-acting piston arrangement has theoretically the highest possible
mechanical efficiency and also shows good self-pressurization (Senft, 1993). The kinematic engine
with a normal 90° phase angle is a specific characteristic of gamma configuration engine. Like a
Beta system, the Gamma system has two cylinders (sometimes there is one large and one small),
which it built-in in the different cylinder (Rizzo, 1997). Cylinders must not be parallel, but it
depend on the construction solutions. They can be construct in an oblique or perpendicular surface.
With its configuration, this type of engine can work with low heat, as compared with conventional
Beta and Alpha system. The sufficient source of heat to run the machine can be a cup of hot water.
2.3. Low Temperature Differential Engine
A low temperature differential (LTD) Stirling engineis an engine that can be run with small
temperature difference between the hot and cold edge of the displacer cylinder (Rizzo, 1997). It is
different from other types of Stirling-cycle engines, mostly Stirling engine has a greater
temperature difference between the two edges. However, the power output from the engine can be
greater because it has greater temperature difference that affect the pressure power.
LTD engines might become in two designs generally. The first design uses single-crank
operation where only the power piston is connected to the flywheel that called the Ringbom engine.
This type of engine, has been commonly spread to use, is based on the Ringbom principle. A short,
8
12. large-diameter displacer rod in a precise-machined fitted guide has been used to replace the
displacer connecting rod (Rizzo, 1997). The other design called by a kinematic engine, where both
the displacer and the power piston are connected to the flywheel. The kinematic engine with a
normal 90° phase angle is a gamma configuration engine (Rizzo, 1997).
Some characteristics of the LTD Stirling engine (Rizzo, 1997) described as follows.
1. Displacer to power piston swept volumes ratio is large;
2. Diameter both of displacer cylinder and displacer are large;
3. Displacer size is short;
4. Effective heat transfer surfaces on both end plates of the displacer cylinder are large;
5. Displacer stroke commonly small;
6. Displacer period at the end of the displacer stroke is rather longer than the normal Stirling
engine;
7. Speed operating system is low.
LTD Stirling engines provide mostly as demonstration units, but they immediately become
most interest when considering the possibility of power generation. Because the system work from
low temperature, means that’s only need heat sources less than 100 °C (B. H. Van Arsdell. . In:
Zumerchik J, 2001). A calculation using the Carnot cycle formula shows that an engine operating
with a source temperature of 100 °C and a sink temperature of 35 °C gives a maximum thermal
efficiency of about 17.42%. If an engine could be built for achieving 50% of the maximum thermal
efficiency, it would have about 8.71% overall Carnot efficiency. Even the calculated thermal
efficiency seems rather low, but LTD Stirling engines could be used with free or cheap low
temperature sources. Therefore, this engine become recommend to selected when the low cost
engines are put into consideration.
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13. CHAPTER III
METHOD
3.1. Method
We decide to use qualitative way as the method to study about KS90T Stirling Engine.
Because the main idea we get, come from problems that come up around us. Those attract us to
study about KS90T to solve the issues. Moreover the qualitative way be an effective way to us for
collecting data and the information needed.
3.2. Collecting Data
To take some information from the system, we decide to use case study with existed
product. We make analyze with the system to improve the KS90T performance. Meanwhile, we
also look up with the design. We observe the KS90T to know every detail of the component.
Furthermore, we can involve to redesign the system to get more effectiveness.
3.3. Location and Schedule
We decide to use Sampoerna University to make analyzing with the KS90T. We think of
the environment support to do analyzing and Sampoerna University might give the facilities to
support us to work. Besides, we also look at our schedule to work effectively and due in the proper
time. We use timeline to summarize every work to do. The schedule of activities detail shows as
(Fig. 3) follows:
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15. CHAPTER IV
RESULT AND DISCCUSSION
4.1. Result
Here the result we get when open the case from KS90T Stirling Engine. The data we
get come from analyze the system and study literature from existed journal.
Main Design Parameters Dimension
Plates
Flywheel
Power Piston
Displacer
Table 1: Main engine design parameters
Main engine design parameters are shown in Table 1. KS90T LTD Stirling engine is
designed in single-acting which is in gamma configuration. Since the gamma configuration Stirling
engine provides a relatively large regenerator heat transfer area and it is easy to be constructed,
this configuration act as a basic configuration in this engine KS90T LTD-SE. The power cylinder
are directly connected to the cooler plate to minimize the cold-space and transfer-port dead volume
in which, in KS90T LTD-SE the cooling water pan is a part of the cooler plate.
KS90T Solar Twin LTD Stirling engine basically make up by the acrylic plates. This
acrylic plate gives a special ability to the engine in the field of how it uses the heat supplies. This
special property let the engine to be transparent to the infra-red, in which it means that the heat
12
16. source (sunlight) can directly heat the air inside the main chamber without having to firstly heat
the plate. In line with the hot side, on the cool side, the heat can also directly radiate away into
without firstly having to pass through the cool plate.
The process of KS90T Solar Twin LTD Stirling engine in which it is cyclically heat and
cools the air inside can be shown in the cut-away diagrams below (Fig. 4 and Fig. 5) (Kontax
Engineering Ltd Company, 2012). In this case, it is important to remember that the large blue
displacer disk is moving (displacing) the air from the top of the plate to the bottoms and precisely
back again, and there is also a small black piston that actually drives the flywheel. The figure
provided also explain a different chamber; one of those chambers is the right chamber and the
other is the left chamber.
Figure 4. Hot condition
With the large blue displacer disk at the top, it is reasonable to state that, most of the air
inside the main chamber is at the bottom. By the expanding air caused by the source of heat
(sunlight), the black piston is pushed upward, in which automatically cause the flywheel to turns
around (Fig. 5).
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17. Figure 5. Cold Condition
As the flywheel turns, the displacer disk in the other chamber is moved (by means of a crank
and a connecting rod flow) to the bottom of the chamber. As the displacer move down, the air that
was initially at the bottom of the chamber rushes around the outside of the displacer to the top of
the chamber. So with the displacer at the bottom, most of the air is at the top, where it is cooled by
the cool top plate (Fig.5). As it cools, it contracts, which pulls the small black piston downwards,
and drives the flywheel around some more, and so the cycle continues.
3.2. Discussion
KS90T is a gamma type Stirling engine that use walking beam model. Walking beam
model is model of engine that use seesaw and connect with the crank, flywheels, and also the
piston. It connect the seesaw to the piston vertically to the side tube of the piston. It to minimize
the friction and maximize the movement of the piston. Like KS90T machine was made with very
high precision, moreover it chosen from high material in order to make frictionless. It important
14
18. because the system has function to convert energy from a small temperature difference to
mechanical energy—energy of movement.
Basically, the working of this machine is quite similar with the other gamma type Stirling
engine. The gamma type Stirling engine use two tube or chamber which are connected, one of
them for the piston and the other one for the displacer. The tube of displacer has different
temperature of each edge, hot and cold. Firstly, when the seesaw moves the displacer up to the
upper of the tube, the air in the tube move to the bottom of the plate. In the bottom, the temperature
of the air is increasing as the hot plate. As the air become hot, then it will expand and push the
piston so that the piston goes up. Continuously, the piston that goes up will make the flywheel
rotate, and the rotating flywheel will make the seesaw moves, then the seesaw will make the
displacer goes down. As the displacer goes to the bottom of the tube, the hot air is moved to the
upper of the tube. Next, the temperature of the air will be decreased by the upper plate, which is
the cold plate. Because the temperature of the air is decreasing, so the air will be constructed and
pull the piston down. This cycle is working continuously as long as there are temperature
difference in the end of plate. Unlike the other Stirling machine that only can move with the
temperature difference around 200K-400K, this machine can work and move with minimum
temperature different of 25K only. This can be happened because of the tiny size of the machine
and also the super low friction of the machine. As shown in the calculation:
𝑃𝑉
𝑇
= 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
105
275
=
𝑥
300
𝑥 = 1.1 ∗ 105
In the calculation shown that the difference of pressure only 0.1 ∗ 105
, a very small pressure.
15
19. 𝑃 =
𝐹
𝐴
Use weight of the whole system and assumed that friction near to zero, the equation will show as
follow:
104
=
1.53
𝐴
𝐴 = 1.5 ∗ 10−4
As shown in the calculation above, the area of the piston tube will cover 1.3*10−4
or the diameter
is only 14 millimeter. It has very small size of piston, mean that the system cover very small
machine with low friction. In the end, efficiency of this machine can be gotten with the Carnot
efficiency. Minimum efficiency of this machine is 3.4% and it can be increased depend on the
temperature difference.
Besides, here Beale Formula is created to help to calculate the power output of KS90T
Solar Twin LTD Stirling engine (Kongtragool & Wongwises , 2002, p. 141).
Beale Formula
P = 0.0015 pm f VP
16
20. Where P is the engine power output in Watt, pm is the mean cycle pressure in bar, f is the cycle
frequency in Hz, and Vp is displacement of power piston in cm3
.
Figure 6: Beale Number Graph
The equation can also be written as follows:
𝑃
𝑝𝑚 𝑓 𝑉𝑃
= Constant.
The resulting dimensionless parameter
𝑃
𝑝𝑚 𝑓 𝑉𝑃
is called the Beale number. This number is basically
a function of both source and sink temperatures. The graph (Fig. 6) indicates the relationship
between the Beale number and source temperature. The upper bound represent the high efficiency,
15
17
21. well-designed engines with low sink temperatures, while the lower bound represents the moderate
efficiency, less well-designed engine with high sink temperatures.
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22. CHAPTER V
CONCLUSION AND SUGGESTION
The KS90T Solar Twin LTD Stirling Engine are being analyzed. It is basically made up by
28 different kind of part in which each of them are having their specific roles within the engine.
There are three main aspects that having an important roles in how the engine works, they are the
acrylic plate, temperature, and the fluid (air) inside the chamber. The power output of KS90T Solar
Twin LTD Stirling Engine can also be gotten. It is calculated by using the Beale formula.
The Carnot thermal efficiency of KS90T Solar Twin LTD Stirling Engine is experimentally
not going to reach that of the high temperature differential Stirling engine. However apart of that
this LTD Stirling engine can use many different kind of heat source in which they are usually
ignored by human, solar heat is the example.
While making this paper, It would be advisable if:
1. There is a lab provided to support in collecting the data and making the prototype.
2. There are enough funding to create a prototype.
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23. References
B. H. Van Arsdell. . In: Zumerchik J, e. ,. (2001). Stirling engines (Vol. 3.). (J. Zumerchik, Ed.)
USA: Macmillan encyclopedia of energy.
G., W. (1980). Stirling Engines. Oxford: Oxford University Press.
Rizzo, J. G. (1997). The Stirling Engine Manual. Somerset: Camden miniature steam service.
Senft, J. R. (1993). Ringbom Stirling Engines. New York: Oxford University Press.
Żmudzki, S. (1993). Silniki Stirlinga. Warszawa: WNT.
Hassani, H. (2013). Study of a low-temperature Stirling engine driven. International Journal of
Energy and Environmental Engineering, 1-11.
Karabulut, H., Yucesu, H. S., & Koce, A. (2000). Manufacturing and Testing of a V-Type
Stirling Engine. Turk J Engin Environ Sci, 24, 71-80. Retrieved November 27, 2014,
from Stirling International: http://journals.tubitak.gov.tr/engineering/issues/muh-00-24-
2/muh-24-2-2-98073.pdf
Sharma, P., & Harinarayana, T. (2012). Enhancement of energy generation from two layer solar
panels. International Journal of Energy and Environmental Engineering, 1-9.
doi:10.1186/2251-6832-3-12
Study of a low-temperature Stirling engine driven by a rhombic drive mechanism. (2013,
November 27). doi:10.1186/2251-6832-4-40
Kongtragool, B., & Wongwises , S. (2002, October 3). A review of solar-powered Stirling
engines and low temperature differential Stirling engines. Renewable and Sustainable
Energy Reviews, 7, 131-154. doi:10.1016/S1364-0321(02)00053-9
Kontax Engineering Ltd Company. (2012). Kontax Stirling Engine. Retrieved from Stirling
Engine: http://www.stirlingengine.co.uk/Howtheywork.asp
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