project report_final

DEVELOPMENT OF SOLAR OPERATED STIRLING ENGINE

Darshan institute of Engineering and Technology

Chapter 1- INTRODUCTION

The stock of conventional fuel is limited and also the cost is high. The use of conventional

fuel also increases. So we have to find optional source of energy. The solar energy is

renewable energy and also has benefits like the low running and maintenance cost and also

pollution free. In India 300 days are clear sunny days in every year. India has a potential to

produce 30 MW of energy per sq.km. So it is better to use solar energy as a fuel.

Solar energy is more attractive renewable energy sources that can be used as an input

energy source for heat engines. So, any heat energy source can be used with the Stirling

engine. The solar radiation can be focused onto the displacer hot-end of the Stirling engine,

thereby creating the solar-working prime mover. The direct conversion of solar working

into mechanical working reduced both the cost and complexity of prime mover. According

to theory, the principal advantages of Stirling engines are their use of an external heat

source and high efficiency. Stirling engines are able to use solar energy because of cheap

source of energy. Since during two-thirds of the day, solar energy is not available, solar

hybrids are needed.

Since the combustion of the engine is continuous process in Stirling engine, it can burn fuel

more completely and able to use all kinds of fuel with various quality. According of its

simple construction and its manufacture being make the equal as the reciprocating internal

combustion engine, and when produced in a high number of units per year, the Stirling

engine would be obtain the economy of scale and could be built as a cheap working source

for developing countries. For the range of solar electric generation in 1–100 kWe, the

Stirling engine was considered to be the cheapest [1]

. However the efficiency of the Stirling

engine may be low, reliability is high and costs are low. Moreover, simplicity and reliability

are keys to a cost effective solar operated Stirling generator.

A Stirling engine is one of the examples of a broad class of heat engines which are devices

designed to convert thermal energy into mechanical energy. The internal combustion, or

gasoline, engine in an automobile is the example of the heat engine. The gasoline engine

uses the combustion of fuel inside a limited volume, whereas the Stirling engine uses an

external heat source to heat the working volume. The heat source can come from burning



fossil fuels (such as gasoline), solar energy, decaying plant substance, or whatever is

available[2]

. In fact, all the Stirling engine are requires to operate is a high temperature

difference. It is possible to run a Stirling engine by cooling one part of the engine under the

atmospheric temperature. The gas inside the cylinder of a Stirling engine is not burned or

consumed. So, in compare to the internal combustion engine, the Stirling engine does not

require an exhaust or an intake. If a clean (green) external heat source is used into the

Stirling engine, it can be an ecofriendly alternative to engines that burn and emit

hydrocarbons and other pollutants. Stirling engines also has a benefits which is limits noise

pollution because they do not require intake and exhaust valves which usually are the main

source of engine noise. Though, Stirling engines that would be suitable for automobile use

are highr, heavy, and more costly than conventional internal combustion engines. Besides,

Stirling engines require some time to heat up before they starts and the output of the engine

can‘t be changed quickly for quick acceleration and deceleration. So Stirling engines have

not yet found use in the automotive industries; they have been used as a submarine engine.

Freshly, there has been a rebirth of interest in Stirling engines as the demand for more fuel

efficient and clean engines continues to increase.

1.1. General principles

Stirling engines are mechanical devices working ideally on the Stirling cycle, or its

modifications, in which compressible fluids, such as air, hydrogen, helium, nitrogen or even

vapors, are used as operational fluids. The Stirling engine offers probability for having high

efficiency engine with less exhaust emissions in parallel with the internal combustion

engine. The earlier Stirling engines were huge and inefficient. However, over a period of

time, a number of new Stirling engine have been developed to improve the faults.

The Stirling engine operates by repeatedly totally a sequence of four steps. Each step in the

sequence is reversible and together they form the Stirling cycle. With help of understand

each of the four steps in the Stirling cycle consider two gas filled cylindrical pistons whose

chambers are connected by a thin tube as pictured in Figure 1.1.1.

The left piston has temperature TH and the right piston has temperature TC In the center of

the tube that connects the two chambers is a wire mesh that will be used to temporarily

store heat as described. For each step in the Stirling cycle of Figure 1.1.1 will be mapped to



curves on a pressure-volume plot of the Stirling cycle shown in Figure 1.1.2. The four steps

of the perfect Stirling cycle are [3]

:

(1-2) the gas in the engine is expanded at the steady temperature TH. The left piston moves

down and the right piston is fixed. In ordered to maintain a steady temperature the gas must

absorb heat QH from the source (Isothermal expansion - Figure 1.1.1a, path 1-2 in Figure

1.1.2).

(2~3) At steady volume V2, the temperature of the gas is lowered down from TH to TC. The

left piston is compressed and the right piston expanded so the total volume remains fixed.

The hot gas is passed from the left chamber to the right chamber. As the gas passes through

the split tube it delivers heat Q to the wire mesh. (Steady volume heat removal – Figure

1.1.1b, path 2-3 in Figure1.1.2)

(3-4) the gas is compressed at steady temperature TC. The right piston is compressed and

the left piston is remains equal. To maintain a steady temperature the gas releases heat QC

to the thermal source at TC. (Isothermal compression – Figure 1.1.1c, path 3-4 in Figure

1.1.2)

(4-1) at steady volume V1, the temperature of the gas is increased from TC to TH. The left

piston is expanded and the right piston compressed so that the total volume remains steady.

The cold gas is passed from the right chamber to the left chamber. As the gas passes into

the narrow tube it recovers the heat Q stored in the hot wire mesh. (Steady volume heating

– Figure 1.1.1d, path 4-1 in Figure 1.1.2) .



Fig.1.1.1 Dual piston Stirling engine at four different stages Stirling cycle

Stirling engine at various stages of the Stirling cycle. In any real Stirling engine the

idealized Stirling cycle cannot be made. The four steps are fuzzy together and the cycle on

a PV-diagram appears elliptical. This type of engine has one little sealed piston, called the

working piston, and one higher loose fitting known as displacer piston. The role of the

displacer piston is simply to move, or displace, working gas in the engine back and forth

between a heated lower part and the upper cooled part. In the design pictured in Figure, the

lower plate is heated with the help of flame and the upper plate is cooled with the help of

water or the ambient surroundings. The two pistons are linked together such that their

movements are making 90o out of phase. That is, when the working piston is either at its

maximum or minimum height and moving gently, the displacer piston is at its halfway

point and moving at its higher speed. At position 1 of Figure, the displacer piston is in the

upper cold part which forces the working gas to occupy the hot part and be at temperature

TH. Heat is added pressure to the gas and it expands forcing the working piston to move

upwards (path 1-2 in Figure 1.1.2). At position 2 the working piston is at its maximum

height (the gas has its maximum volume V2) and is moving very gradually approximating

the steady volume path 2~3 in Figure 1.1.2. The displacer, on the other side, is moving into



the hot part causing the gas to move to the cold part. In this design, the displacer itself plays

the role of the wire mesh of Figure 1.1.1 by momentarily storing energy taken from the gas

as it cools from TH to TC. At position 3, because all of the gas is in the cold part, it contracts

(heat is removed from the gas) causing the working piston to slide down (path 3-4 in Figure

1.1.2). At position 4, the working piston is totally compressed (minimum volume V1) and is

moving gradually. The displacer piston is moving upwards forcing the gas into the hot part.

As the cool gas passes by the displacer it recovers the heat that was temporarily stored in

the displacer (path 4-1 in Figure 1.1.2). At the completion of this process the state of the

Stirling engine returns to 1 and the cycle repeats continuously.

Fig.1.1.2 Motion diagram of gamma engine of Stirling engine

The new Stirling engine is more efficient than the early engines and can required any high

temperature heat source. Hence, most sources of heat can working it, including combustion

of any combustible material, rice husk or the like, biomass methane and solar energy.

According to principle, the Stirling engine is simple in design and construction, and can be

operated very easy.

Direct solar operated Stirling engines may be of great interest to countries because of solar

energy is available in unlimited quantity. To use direct solar energy, a solar concentrator

and absorber must be used in the engine system.



The Stirling engine could be used in many applications like:

1. multi-fueled characteristic is required;

2. A very good cooling source is available;

3. Quiet operation is required;

4. Relatively low speed operation is permitted;

5. Steady working output operation is permitted;

6. Slow changing of engine working output is permitted;

7. A long warm-up period is permitted.

1.2. TYPES OF STIRLING ENGINE:

Various machine parts have been combined to provide the Stirling cycle. The cycle

provides a steady-volume process during the transfer of working fluid between the hot and

cold part of the engine, and provides a steady-temperature heating and cooling process

during compression and expansion. The compression and expansion process of the cycle

generally takes place in the cylinder (called working cylinder) with a piston (called working

piston). A displacer piston (simply called displacer) shuttles the working fluid back and

forth in the heater, regenerator, and cooler at steady volume. As shown in Fig. 1.1.2, a

displacer that moves to the cold part forcing the working fluid from the cold part causing it

to flow to the hot part and vice versa. Three different types of engine available, namely the

alpha-, beta-, and gamma-engines, are commonly used. Each engine has the equal

thermodynamic cycle but has different mechanical design characteristics.

In the alpha-engine a displacer is not used. Two pistons, called the hot and cold pistons, are

used on side of the heater, regenerator, and cooler. These pistons move uniformly in the

equal direction to provide steady-volume heating or cooling processes of the working fluid.

When all the working fluid has been passed into one cylinder, one piston will be fixed and

the other piston moves to expand or compress the working fluid. The expansion work is

done by the hot piston on the other side the compression work is done by the cold piston [4]

.

In the beta-engine, a displacer and a working piston are incorporated in the equal cylinder.

The displacer moves between the hot part and the cold part of the cylinder through the

heater, regenerator, and cooler. The working piston, located at the cold part of the cylinder,



compresses the working fluid when the working fluid is in the cold part and opens the

working fluid when the working fluid is moved into the hot part [4]

.

Fig.1.2.1Three basic mechanical engine of Stirling engine.

The gamma-engine uses separated cylinders for the displacer and the working pistons, with

the working cylinder connected to the displacer cylinder. The displacer moves working

fluid between the hot part and the cold part of the displacer cylinder through the heater,

regenerator, and cooler. In this engine, the working piston both compresses and expands the

working fluid. The gamma-engine with double-acting piston arrangement has actually the

highest possible mechanical efficiency. This engine also shows good self-pressurization [7]

.

Hence, the engine cylinder should be designed in vertical type rather than horizontal in

order to reduce disadvantage of bushing friction [4]

.

1.3. LOW TEMPERATURE DIFERENTIAL ENGINE:

A low temperature differential (LTD) Stirling engine can be o with small temperature

difference between the hot and cold ends of the displacer cylinder [9]

. This is different from

other types of Stirling-cycle engines, which have a greater temperature difference between

the two ends, and therefore the working developed from the engine can be higher.

LTD engines have two designs. The first design uses single-crank operation where only the

working piston is connected to the flywheel, called the Ringbom engine. This type of

engine, that has been showing more frequently, is based on the Ringbom principle. A short,

high-diameter displacer rod in a machined fitted guide has been used to replace the

displacer connecting rod [7]

. The second design is called a kinematic engine, where both the



displacer and the working piston are connected to the flywheel. The kinematic engine with

a normal 900phase angle is a gamma-engine

[7].

Some characteristics of the LTD Stirling engine [7]

are as given below:

1. Displacer to working piston swept volumes ratio is high;

2. Diameter of displacer cylinder and displacer is high;

3. Displacer is less;

4. Effective heat transfer surfaces on both end plates of the displacer

5. Displacer stroke is small;

6. Dwell period at the end of the displacer stroke is rather longer than the

normal Stirling engine.

7. Operating speed is low.

LTD Stirling engines gives value as demonstration units, but they immediately become of

interest when considering the possibility of working production from many low temperature

waste heat sources in which temperature is less than 1000 C

[6].

According to calculation using the Carnot cycle formula shows that an engine operating

with the source temperature of 1000C and the sink temperature of 35

0C gives the maximum

thermal efficiency of about 17.42%. If an engine could be reach for achieving 50% of the

maximum thermal efficiency, it would have about 8.71% overall Carnot efficiency. Even

the calculated thermal efficiency rather low, but LTD Stirling engines could be used with

free or low temperature sources. This engine should be selected if the low cost engines are

put into consideration.

However the particular working developed by LTD Stirling engines is low, lightweight and

cheap materials such as plastics can be used as the engine parts.

1.3.1. PRINCIPLE OF LTD STIRLING ENGINE:

The hot air engine is a simple type of engine that uses a compressible fluid as the working

fluid. Because of the working fluid is in a closed system, there are no problems with

contamination and working fluid prices. Heat transfer to the working fluid is most

important. Very High mass flow is needed for good heat transfer. The working fluid should



be that of low viscosity to reduce the pumping losses. Using higher pressure or lower

viscosity, or combinations, could reduce the high mass flow required.

The Stirling engine could ideally be a very efficient engine in upgrading from heat to

mechanical work with the Carnot efficiency. The thermal boundary of the operation of the

Stirling engine based on the material used for construction. Engine efficiency ranges from

about 30 to 40% resulting from a typical temperature range of 923–1 073 K, and a normal

operating speed range from 2000 to 4000 rpm [5]

.

1.3.2. STIRLING CYCLE:

The ideal Stirling cycle has three advantages. First, the thermal efficiency of the cycle with

ideal regeneration is equal as the Carnot cycle. During the transfer strokes, the regenerator,

which is temporary energy storage, rapidly absorbs and releases heat to the working fluid

which is passing through. So, the quantity of heat taken from the external heat source is

reduced. This results in improving the thermal efficiency(Fig. 1.3.2.1).

The second advantage, over the Carnot cycle, is obtained by adding of two isentropic

processes with two steady-volume processes. This results in increasing the p–v diagram

area. Therefore, a reasonable amount of work from the Stirling cycle is obtained without

use very high pressures and high swept volumes, as in the Carnot cycle.

Fig.1.3.2.1 Stirling and Carnot cycle



The comparison of Stirling cycle with the Carnot cycle between the equal given limits of

pressure, volume, and temperature, is shown in Fig. 1.3.2.1. The shaded areas 2C-2-3 and

1-4C-4 indicate the extra work available by replacing two isentropic processes with two

steady-volume processes. The Carnot cycle isothermal processes (1-2C and 3-4C) are

respectively, extended to process 1–2 and 3–4. The amount of work is increased in the

equal proportion as the heat supplied to and rejected from the Stirling cycle [10]

.

The third advantage has recently been found. Compared with all reciprocal piston heat

engines working at the equal temperature limits, the equal volume ratios, the equal mass of

ideal working fluid, the equal external pressure, and mechanism of the equal overall

effectiveness, the ideal Stirling engine has the maximum possible mechanical efficiency [7]

.

These three advantages that the Stirling engine is a theoretical equivalent of all heat engines

[3].

Stirling engine operation Isothermal compression process 1–2 (heat transfer from working

fluid at low temperature to an external sink): After the displacer has pushed back the

working fluid into the cold part of the cylinder, where it was cooled, it was then held steady

at its top dead center (TDC) (Fig. 1.3.2.1). This indicated the state 1 and the pressure at this

state is P1. The working piston is then being pushed from bottom dead center (BDC) to

TDC by flywheel momentum helped by partial vacuum created by the cooling working

fluid.

The working fluid is in the cold part and is under compression by working piston, which is

approaching TDC, and compressing working fluid from 1 to 2 at steady temperature. The

work done on the working fluid indicated by the area under the process 1–2.

Steady-volume heating process 2–3 (heat transfer to the working fluid from regenerator):

The displacer is moving from TDC to BDC and transferring working fluid from the cold

part to the hot part, while the working piston remains steady at its TDC, increases in

pressure as a result of expanding working fluid. The displacer is pushing the working fluid

into the hot part, passing through a regenerator which has stored heat, and already a certain

amount is being heated. Heat given up by the regenerator raises the temperature and

pressure of the working fluid from 2 to 3 at steady volume. Heat stored in the regenerator is

added to the working fluid.



Isothermal expansion process 3–4 (heat transfer to the working fluid at high temperature

supplied by an external source): After the displacer has pushed back all the working fluid

into the hot part, with a corresponding increase in pressure to the maximum position, it is

then kept at rest at its BDC. The working fluid is in the hot part and is expanding to

pressure P4, while a steady temperature process 3–4 is maintained applied at the hot part.

The working piston is being pushed from TDC to BDC by the increased pressure, and is

applying force to the flywheel, thus creating mechanical energy. This energy will be

utilized throughout the remaining processes of the cycle. The work done by the working

fluid is known by the area under process 3–4.

Steady-volume cooling process 4–1 (heat transfer from the working fluid to the

regenerator): After the working piston has reached its BDC and has supplied its energy to

the flywheel, it remains stationary and is ready to travel back to TDC under flywheel

momentum and the sucking action of the partial vacuum created by the falling pressure.

Fig. 1.3.2.2 Stirling engine operation



The displacer is moving from BDC to TDC and is transferring working fluid to the cold

part where the pressure will fall and a partial vacuum is created, through the regenerator,

causing a fall in temperature and pressure of the working fluid from 4 to 1 at steady

volume. Heat is passed from the working fluid to the regenerator.

1.3.3. Efficiency of Stirling cycle

Fig 1.3.3.1 Stirling cycle on P-V and T-S diagram



(a) The air is compressed isothermally from state 1 to 2 (TL to TH).

(b) The air at state-2 is passed into the regenerator from the top at a temperature

T1. The air passing through the regenerator matrix gets heated from TL to TH.

(c) The air at state-3 expands isothermally in the cylinder until it reaches state-4.

(d) The air coming out of the engine at temperature TH (condition 4) enters into

regenerator from the bottom and gets cooled while passing through the

Regenerator matrix at steady volume and it comes out at a temperature TL,

at condition 1 and the cycle is repeated.

(e) It can be shown that the heat absorbed by the air from the regenerator matrix

during the process 2-3 is equal to the heat given by the air to the regenerator

matrix during the process 4-1, then the exchange of heat with external source

will be only during the isothermal processes.

Now we can write, Net work done = W = Qs - QR

Heat supplied = QS = heat supplied during the isothermal process 3-4.

Heat rejected = QR = Heat rejected during isothermal compression process 1-2



Now,

And,

Thus the efficiency of Stirling cycle is same as that of Carnot cycle efficiency when both

are working with the equal temperature limits. It is not possible to obtain 100% efficient

Regenerator and so there will be always 10 to 20 % loss of heat in the regenerator, which

lowered the cycle efficiency. Considering regenerator efficiency, the efficiency of the cycle

can be written as,



Chapter 2- LITERATURE REVIEW

Pongsakorn Kerdchang, Maung MaungWin, and Sombat Teekasap, of Scientific Research

Center, South-East Asia University, presented a research paper on “Development of a new

solar thermal engine system for circulating water for aeration.” At Thailand. They

concluded that:

Uses low temperature technology, the number of Stirling engines and designs, including the

engines development, are provided and discussed. The extent of research on solar Stirling-

cycle for production has been limited to fraction of horsepower (Farber and Prescott, 1965).

The hot-air engine developed by Farber and Prescott in 1965 focused on area where air was

heated and its expansion pushes back the piston down. In the down-stroke of the piston, the

displacer moved to the left by the linkage. On the up-stroke of the piston, the displacer

moved to the right and all the hot air was at the left side of the cylinder and lost heat to the

cooling water.

An efficiency of about 9% was obtained at 100rpm with the break horsepower of about 0.2.

And after that Beale et al. (Beale et al., 1971) in 1971, considered free cylinder containing

the heavy piston which remained essentially stationary and a light displacer which moved

under the influence of pressure differential between the work part and the bound part in the

cylinder. The cylinder moved under the influence of the same pressure differential and

performs work against an external load. Since the entire pressure enclosure moved as the

unit, the free cylinder engine can deliver work from the completely sealed working gas and

since there are no internal bearing loads, or mechanical linkage or gears, etc., no lubrication

was needed. The engine should be inexpensive and should have a long life. The Fresnel

lens focused the solar radiation on the hot part of the engine and a double acting water

pump utilized the developed mechanical energy. An efficiency of about 9% was obtained at

100rpm with the working of about 149W. Stirling engine ideally could achieve the highest

possible energy conversion efficiency of all heat/working engines. Using practically any

kind of the energy, they can be employed with extremely low emissions as generator,

motor, heat pump or cooling system. In spite of all these advantages, Stirling engines still

have not made in the market breakthrough as a mass product.



A overall analysis of finite time thermodynamics of a Stirling heat engine was presented

with finite heat capacity of external reservoirs, regenerative losses and finite effectiveness

of each of the heat exchangers (i.e. a high temperature heat exchanger and a low

temperature heat exchanger) (Fette, 1995). They obtained the expressions for maximum

working output and defeated the corresponding thermal efficiency. The effect of operating

temperatures, the effectiveness of the regenerative heat exchanger on the heat transfer (QH

and QL) to and from the Stirling heat engine, the regenerative heat transfer (QR), the

maximum working power output (P) and the corresponding thermal efficiency of the cycle

have all been studied. They considered as the inlet source temperature and sink temperature

as 1300K and 300K. They also used effectiveness of each heat exchanger and each the

regenerator in the range from 0.4 to 1, and the capacitance rates of the heat source/sink

reservoirs in the range from 0.30 to 1.80kW/K. Their analysis showed that working output

and thermal efficiency were 62.55kW and 43.94%, respectively.

Bancha Kongtragool, SomchaiWongwises Fluid Mechanics, Thermal Engineering and

Multiphase Flow Research Laboratory (FUTURE), Department of Mechanical engineer

Faculty of Engineering, King Mongkut‘s University of Technology Thonburi,presenred a

paper on ―A four working-piston low-temperature differential Stirling engine using

simulated solar energy as a heat source” at Bangmod, Bangkok 10140.

They reported that:

The low-temperature differential (LTD) Stirling engine is the type of Stirling engine that

can run with a small temperature difference between the hot and cold region of the

displacer cylinder. The LTD Stirling engine is therefore able to operate with many low-

temperature heat sources. Some characteristics of the LTD Stirling engine are as given

below:

(1) Displacer to working-piston swept volumes ratio or compression ratio is high.

(2) Diameters of displacer cylinder and displacer are high.

(3) Displacer length is small.

(4) Effective heat transfer surfaces on both end plates of the displacer cylinder are high.

(5) Displacer stroke is small.

(6) Dwell period at the end of the displacer stroke is slightly longer than the normal

Stirling engine.

(7) Operating speed is low.



While the Stirling engine has been studied by a number of researchers, the LTD Stirling

engine has received comparatively little concentration. Many studies related to solar-

operated Stirling engines and LTD Stirling engines have been reviewed in the authors‘

previous works

Haneman (1975) studied the using of air with low-temperature sources. This led to the

construction of an unusual Stirling engine, in which the exhaust heat was still sufficiently

hot to be useful for other purposes. The simply constructed low-temperature heat engine

modeled on the Stirling engine was patented by White (1983). White suggested improving

performance by pressurizing the displacer cylinder. Efficiencies were claimed to be around

30%, which is as quiet high for a low-temperature engine.

O‘Hare (1984) patented a device which passed cooled and heated streams of air through a

heat exchanger by changing the pressure of air inside the cylinder. The practical usefulness

of this device was not shown in detail as in the case of Haneman‘s work. Spencer (1989)

reported that, in practice, such an engine would produce only a small amount of useful

work relative to the collector size, and would give little compared to the additional

maintenance required.

Senft‘s work (Senft, 1991) showed the motivation in the use of Stirling engine. Their target

was to develop the Stirling engine operating with a temperature difference of 20C or lower.

Senft's (1993) described the design and testing of a small LTD Ringbom Stirling engine

working by a 600

conical reflector. He reported that the tested 600

conical reflector,

producing the hot end temperature of 93 0C under running conditions, worked very well.

Rizzo (1997) reported that Kolin experimented with 16 LTD Stirling engines, over the

period of 12 years. Kolin presented a model that worked on a temperature difference

between the hot and cold ends of displacer cylinder which was as low as 15 0C.

Iwamoto et al. (1997) compared the performance of the LTD Stirling engine with a high-

temperature differential Stirling engine. They concluded that the LTD Stirling engine

efficiency at its rated speed was nearly 50% of the Carnot efficiency. However, the

compression ratio of their LTD Stirling engine was approximately equal to that of a

conventional Stirling engine. Its performance, therefore, seemed to be the performance of a

common Stirling engine operating at a low operating temperature.



SenftVan Arsdell (2001) made an in-depth study of the Ringbom engine and its derivatives,

including the LTD engine. Senft‘s research into LTD Stirling engines resulted in an

interesting LTD engine, which had an ultra-low temperature difference of 0.5 0C. It has

been very difficult for anyone to create an engine with the result better than this.

Kongtragool and Wongwises (2003b) investigated the Beale number for LTD Stirling

engines by collecting the existing Beale number data for various engine specifications from

the paper. They concluded that the Beale number for a LTD Stirling engine could be found

from the mean-pressure working method.

Kongtragool and Wongwises (2005a) ideally investigated the working output of a gamma-

engine LTD Stirling engine. Former works on Stirling engine working output calculations

were studied. They pointed out that the mean-pressure working formula was the most

appropriate for LTD Stirling engine working output . However, the hot-part and cold-part

working fluid temperatures were needed in the mean-pressure working formula.

Kongtragool and Wongwises (2005b) presented the optimum absorber temperature of the

once reflecting full-conical reflector for a LTD Stirling engine. A mathematical model for

the overall efficiency of a solar operated Stirling engine was developed and the limiting

conditions of both maximum possible engine efficiency and working output were

calculated. Results showed that the optimum absorber temperatures obtained from both

conditions were not significantly different. However, the overall efficiency in the case of

the maximum possible engine working output was very close to that of the real engine of

55% Carnot efficiency.

Kongtragool and Wongwises (2007a) also gave the performance of two LTD Stirling

engines tested using LPG gas burners as heat sources. The first engine was a twin-working-

piston engine and the second was a four working- piston engine. Engine performances,

thermal performances, including the Beale‘s numbers were presented.

Now, Kongtragool and Wongwises (2007b) presented the performance of a twin-working-

piston Stirling engine working by a solar simulator. This engine was the same as the engine

described in (Kongtragool and Wongwises, 2007a).

So, the heat source was a solar simulator made from a 1000 W halogen lamp. Comparisons

were made between the characteristics of the high-temperature differential (HTD) and LTD

Stirling engine and methods for performance improvement. However some information is

currently available on the LTD Stirling engine, there still remains room for further research.



In particular the detailed investigation is lacking into the LTD Stirling engine using solar

energy as a heat source. As a consequence, in this, the testing of the performance of a LTD

Stirling engine using simulated solar energy. The LTD Stirling engine tested in this paper is

a kinematics, single-acting, four working piston, gamma-engine. Non-pressurized air is

used as a working fluid and a solar plate fabricated from four 1000 W tungsten halogen

lamps is used as a heat source. Since the gamma engine provides a high regenerator heat

transfer area.

BanchaKongtragool a, SomchaiWongwises b, aThe Joint Graduate School of Energy and

Environment, King Mongkut’s University of Technology Thonburi, Bangmod, presented a

paper on ―A review of solar-working Stirling engines and low temperature differential

Stirling engines‖ at Bangkok 10140, Thailand. They said that:

The Stirling engine was the first developed regenerative cycle heat engine. Robert Stirling

patented the Stirling engine in 1816 (patent no. 4081). Engines based upon his invention

were built in many forms and sizes until the turn of the century. Because Stirling engines

were simple and safe to operate, run almost silently on any fuel, and were clean and

efficient compared to steam engines, they were quite popular [3]

. These Stirling engines

were small and the working produced from the engine was low power (100 W to 4 kW).

In 1853, John Ericsson construct a high marine Stirling engine having four 4.2 m diameter

pistons with a stroke of 1.5 m producing a brake working of 220 kW at 9 rpm [10]

.

The first time of the Stirling engine was terminated by the rapid development of the internal

combustion engine and electric motor. 3. The second time of the Stirling engine began

around 1937[3]

, when the Stirling engine was brought to a high state of technological

development by the Philips Research Laboratory in Eindhoven, Holland, and has

progressed continuously since that time. Initial work was focused on the development of

small thermal-working electric generators for radios used in remote areas [3,4]

. New

materials were one of the keys to Stirling engine success. The Philips research team used

new materials, such as stainless steel [7]

.

Another key to success was a better knowledge of thermal and fluid physics than in the first

time. The specific working of the small ‗102C‘ engine of 1952 was 30 times that of the old

Stirling engine[11]

.



The progress in development made by Philips and other industrial laboratories, together

with the need for more energy resources, has sustained the second time of Stirling engine

development until today [7]

.

Intensive research by Philips and industrial laboratories the development of small Stirling

engines with high efficiencies of 30% or more. In 1954, Philips developed an engine using

hydrogen as the working fluid. This engine produced 30 kW for the maximum cycle

temperature of 977 K at 36% thermal efficiency. The efficiency of the equal engine was

than improved to 38%. The experimental studies of engines of different sizes up to 336 kW

were studied[8]

.

Other attempts to more develop Stirling engines under license of Philips, were carried out

by General Motors from 1958 to 1970 [10]

.

Other licenses were granted by Philips to United Stirling AB of Malmo, Sweden in 1968

and to the West German consortium of MAN and MWM in 1967[10]

. In 1973, the

Philips/Ford 4-125 experimental automotive Stirling engine accomplished a specific

working of over 300 times that of the first Stirling engines [7]

.

Trayser and Eibling[12]

carried out a design study to determine the technical feasibility of

developing a 50 W portable solar-working generator for use in remote areas. The results of

their study indicate that it is possible to build solar-working lightweight portable, reliable,

Stirling engine at a reasonable cost. Gupta et al.[13]

developed 1 and 1.9 kW solar-working

reciprocating engines for rural applications. Engine efficiencies were found to be between

5.5 and 5.7% and overall efficiency was found to be 2.02%[17]

.

Pearch et al.[14]

proposed and analyzed a 1 kW domestic, combined heat and working

(DCHP) system. The results show that 30% of a home‘s electrical demand could be

developed and electricity cost could be reduced by about 25%. Podesser[19]

designed,

generated and operated a Stirling engine, heated by the flue gas of a biomass furnace, for

electricity production in rural area. With the working gas pressure of 33 bar at 600 rpm and

the shaft working of 3.2 kW, an overall efficiency of 25% was obtained. He expected to

extend the shaft working to 30 kW in the next step.



Dixit and Ghodke[14]

designed compact working generating systems capable of using the

combination of a wide variety of solid fuels as a local working source. The system was a

heat pipe based, biomass energy-driven Stirling engine. The macroscopic thermal design of

the engine along with the calculation of various energy losses was reported.

―Kockums‖, a Swedish defense contractor, produce Stirling Engines for the navy making

the quietest submarines in the world. This high-technology is named air-independent

propulsion (AIP). There are four submarines equipment with Stirling AIP. The models are

HMS Nacken, which was launch in 1978 and after ten years 1988 became the first

submarine equipped with AIP system, by means of a cut and lengthened by an intersection

of a Stirling AIP section, which before the installation is equipped by two Stirling units,

liquid oxygen (LOX) tanks and electrical equipment. Successful demonstration of AIP

system during many routine patrols of HMS Nacken made that Gotland, another type of

submarine, was the first submarine designed from the beginning to operate with AIP

system.



Chapter 3- EXPERIMENT SETUP

Fig. 3.1. Stirling Engine

The main function is shown in Diagram 1. The model consists of two parallel cylinders

which are connected by a copper tube. The working piston is open at one end between the

pressure piston and the displacement cylinder is a small air pass in which the air can

transfer. Both of the pistons work at 90 degrees angel against each other from a single

crankshaft. The hot air is made at the end of the displacement chamber (combustion

chamber).A cooler ensures that the temperature falls to ensure a good working efficiency.



The following diagrams explain the various stages

Fig. 3.1.1. working stages

A: The air placed in the working cylinder has cooled down. A slightly lower pressure is

formed and the working piston is pushed into the cylinder. The air volume is at its greatest

level. The displacement piston moves forward towards the heated area of the cylinder and

pushes the air into the cooler area. Mechanical movement follows.

B: The Displacement piston is placed at the far end of its stroke. On the way it has pushed

the hot air into the working cylinder. The movements of the two flywheels push the

working piston into its cylinder area.

C: In diagram C the working piston pushes the cooled air into the heated displacement

cylinder area just as the piston is reaching the cooler end. Then the air is heated and

expands pushing back the working piston back again. Mechanical movement follows

D: In diagram D the displacement piston has reached its top dead center and the working

piston is about to be moved to the position which shown in diagram A



3.2 LIST OF COMPONENTS AND MATERIALS

COMPONENT MATERIAL DIMENSIONS(MM)

FLYWEEL STEEL ∅55𝑋5

DISPLACER

PISTON

STEEL WIRE

AND GLASS

WOOL

∅18X85

WORKING

PISTON

ALUMINIUM ∅17X16

HOT CYLINDER CAST IRON ∅32X40

COLD

CYLINDER

TEST TUBE ∅20

CONNECTING

ROD

STEEL PLATE 120X10X2

AXLE STEEL ROD ∅5X55

COOLER ALUMINIUM 30X30X38

JOINING TUBE BRASS ∅8X50

SUPPORT AND

BASE ELEMENT

WOOD AND

ALUMINIUM

140X140



3.3 MANUFACTURING OF PARTS

3.3.1 MAKING OF CONNECTING ROD

Fig.3.3.1. connecting rod

- Cut the flat strip by 10 x 2 x 120 to length

- File its end to 90 degrees

- Then Mark out the center

- Centre punch

- Remove burr from surfaces

- Drill the holes according to dia. (3, 8 and 1,8mm diameter, open them out to 4 and 2mm

diameter)

3.3.2 MAKING OF BEARING BLOCKS

Fig.3.3.2. bearing blocks



- Remove the burr

- Mark out point

- Drill the 7mm diameter holes on marked area (Drill the pilot whole 1.6mm diameter

first!!!)

- Make internal thread. Tap the M4 internal thread –drill a 3, 3 mm hole first

3.3.3 MAKING OF FLYWHEEL

Fig.3.3.3. flywheel

- Make both of the internal M3 holes

- Then Drill out to 2.5mm dia

- Make the M3 thread on surface

- Place the axle 5 in the 5mm diameter hole

- Mark the middle of the axle

- Mark the 8 holes in flywheel

- Use Centre punch

- Drill with an 8mm pilot drill. (Carefully hold the work in a vice)

- Then Drill the 11mm diameter holes

- After that remove the burr with a countersink bit



3.3.4 MAKING OF BASE PART

Fig. 3.3.4. Base part

3.3.5 MAKING OF FLANGE

Fig.3.3.5. flange



3.3.6 MAKING OF THE COOLER

- Place the "O‖ ring in the flange and insert the borosilicate test tube in the flange

- The flange (With test tube + O ring) on the front of the cooler and then push the test tube

until it reaches a stop.

- Place the flange and cooler in a vice, remember that the test tube is upright to the cooler

and flange.

- Mark out the 4 x 2.5mm, holes in the flange on the surface of the cooler (Drill)

- Remove the cooler from the vice and add the brass tube (25) 3 x1 x18 press in the 3mm

hole (If it has too much play use a little glue)

- Now drill out 4 holes of 3, 1 diameter in the flange

- Now remove the entire burr

3.3.7 ASSEMBLE OF THE ENGINE

Fig.3.3.7. assembly of the engine

- Joint the working cylinder and the cooler with the help of glue and the joiner together

with two component glue. The glue points must be air tight and not seep into the joiner.



The distance between the cooler and the working cylinder is approximately 36mm. Check

the sizes once more before the glue sets otherwise adjust if necessary. The axis of the

cooler and the working cylinder must be placed in parallel to one another

- Now the two bushes for the flywheels (dia 7 x 1 x 7, 5) be inserted in the bearing block

and jointed in place with 2 component glue. Finally drill the two oil hole (Dia 2,5mm)

- Shorten pin to 11.7mm (Or shorter) so that it does not protrude over the working cylinder

piston (12mm dia) and rubbing on the cylinder wall.

Join together all the connecting rod, the working piston and the shortened pin. Now the

mount it on the wooden base. On wooden base mount the bearing block with flywheels

and motor holder with washers and the screws on the base

Then join the connecting rods with the cylinder and the carrier bushes (15/18) to the

flywheels

Then Cut for square feet 30mm from the cellular foam and glue them on the base

- Now take the displacement piston in the cooler until the stop. Lay the O ring in flange

and insert the test tube into the flange. Then Insert the test tube in the cooler up to the stop

and then join the flange with 4 machine screws (test tube and cooler must be vertical with

each other. The backward and forward movement of the displacer must be free and easy to

move. Connecting rod with the screws and then use the connector block to join them.

Place the copper tube (16/3 +7mm) on the hooks to control the movement of the

connecting rods. When adjusting the flywheels on the axles it‘s necessary to see that the

working piston and the displacement piston are not stopped from the working condition.

- The two connecting rods are must run parallel to each other (Correct by adjusting the

bearing block –cooler with the working cylinder is possible)

- The "compressor‖ piston must not be stopped on the front or the back dead point in the

cylinder

- Finally the 90 degree angle between the two connecting rods and the flywheels are set as

shown in the figures



Chapter 4: RESULT AND DISCUSSION

In this project we construct alpha type Stirling engine, which has piston ( )

and according to that we design our model which is shown in upper fig.3.3.7. First we

design the engine in the creo parametric 2.0 designing software which is shown in below:

Fig. 4.1. Creo Model

Then we lubricate the all moving parts like working piston, connecting rods, joints,

flywheel, etc. with the help of thin oil. Then we heat up the displacer with the three candles.

But due to some reasons like friction, failure of regenerator and unstable joints engine can

not worked.



Chapter 5: CONCLUSION

We construct an alpha type solar operated Stirling engine in which we use atmospheric air

as a working fuel and displacer is made up of test tube then we heat up the engine by solar

radiation but due to some reasons the engine cannot work properly. Some of these reasons

are following below:

i. If Wrong lubricant used

ii. If too much friction between the parts

iii. If the displacement piston touches the front dead point in the cylinder

iv. If the displacement piston touches the rear dead point in the cylinder

v. If the displacement piston rubs on the cylinder too much

vi. If heat not enough

vii. If the displacement piston not properly wound.

viii. If the displacement cylinder does not move with the push rod- not working properly



Chapter 6: REFERENCES

[1] Bancha Kongtragool, SomchaiWongwises Fluid Mechanics, Thermal Engineering

and Multiphase Flow Research Laboratory (FUTURE), Department of Mechanical

engineer Faculty of Engineering, King Mongkut‘s University of Technology

Thonburi,presenred a paper on ―A four working-piston low-temperature differential

Stirling engine using simulated solar energy as a heat source” at Bangmod, Bangkok

10140.

[2] Bancha Kongtragool, SomchaiWongwises Fluid Mechanics, Thermal Engineering and

Multiphase Flow Research Laboratory (FUTURE), Department of Mechanical

engineer Faculty of Engineering, King Mongkut‘s University of Technology

Thonburi,presenred a paper on ―A two working-piston low-temperature differential

Stirling engine using simulated solar energy as a heat source” at Bangmod, Bangkok

10140.

[3] Pongsakorn Kerdchang, Maung MaungWin, and Sombat Teekasap, of Scientific

Research Center, South-East Asia University, presented a research paper on

“Development of a new solar thermal engine system for circulating water for

aeration.” At Thailand.

[4] Bancha congragool and somachi congwises of The Joint Graduate School of Energy

and Environment, King Mongkut‘s University of Technology Thonburi,presenred a

paper on ―A review of solarstirling engine and low temperature differential engine as

a heat source” at Bangmod, Bangkok 10140.

[5] Stine WB. Stirling engines. In: Kreith F, editor. The CRC handbook of mechanical

engineers. Boca Raton: CRC Press; 1998. p. 8-7–8-6.

[6] Van Arsdell BH. Stirling engines. In: Zumerchik J, editor. Macmillan encyclopedia of

energy, vol. 3. Macmillan Reference USA; 2001. p. 1090–95.

[7] Senft JR. Ringbom Stirling engines. New York: Oxford University Press, 1993.

[8] Walpita SH. Development of the solar receiver for a small Stirling engine. In: Special

study project report no. ET-83-1. Bangkok: Asian Institute of Technology; 1983.

[9] Rizzo JG. The Stirling engine manual. Somerset: Camden miniature steam services,

1997.



[10] Walker G. Elementary design guidelines for Stirling engines. In: Proceedings of the

14th Intersociety Energy Conversion Engineering Conference, Paper 799230. Boston:

American Chemical Society; 1979.

[11] West CD. A historical perspective on Stirling engine performance. In: Proceedings of

the 23rd Intersociety Energy Conversion Engineering Conference, Paper 889004.

Denver: American Society of Mechanical Engineers; 1988.

[12] Spend 1950—―Conventional‖ engines up to 100 kW. Sol Energy 1989; 43:197–210.r

LC. A comprehensive review of small solar-working heat engines: Part I.I. Research

since

[13] Prodesser E. Electricity production in rural villages with biomass Stirling engine.

Renew Energy 1999; 16:1049–52.

[14] Dixit DK, Ghodke SV. Renewable energy working Stirling engines—a viable energy

alternative. In: Sayigh AAM, editor. Renewable energy technology and the

environment. Proceedings of the Second World Renewable Energy Congress, vol. 2.

1992. p. 934–8.

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