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The Comparison for Different Type of Drive Mechanism for Small Solar Stirling Engine 500 W in Thailand.

Eng’r. Suravut, Snidvongs*1 and Dr. Sirinuch, Chindaruksa*2

*1 Vice President, Asian Renewable Energy Development and Promotion Foundation, Bangkok, 10400, Thailand ,

airscan@cscoms.com, PhD Students, School of Renewable Energy Technology (SERT), Naresuan University, Pitsanulok, THAILAND.

*2 Physic Department, Faculty of Science, Naraesuan University, Pitsanulok, THAILAND.

Abstract

A purpose of this research is to compare the different type of drive mechanism for Small Gamma Type Solar Stirling Engine. This system was direct equipped with asynchronous motor, 500 W, as generator. There are three type of daisy chain mechanism to compare, Gear drive, Swash Plate Drive Type I (Whisper Tech), Swash Plate Drive Type II (Rotary Drive). This system will compare in term of cost, performance, and efficiency. 1. Introduction

The Author had found out from his past experience of Stirling Engine experiments. The performance of the Stirling engine depend on the fluid type, pressure, efficiency of heater tube, efficiency of cooler tube, efficiency of regenerator and friction etc. Friction is the most critical for Stirling engine. The more friction in the system it will be less power output. If we can reduce the friction of the engine it will increase the efficiency of the Stirling engine greatly.

Insolation in Thailand is varying between in 450 to 550 W/m2 daily whole year round, and the average value is at 550 W/m2 daily over the year. Friction of Stirling engine may not have direct effect to the insolation, but if the Stirling engine has less friction, Stirling engine will require less power to overcome the friction and could produce more power output. This will gain the performance of the Stirling engine up. Thus, with medium insolation as Thailand, Stirling engine could perform better.

Lot of researchers tries to improve the efficiency of the heater tube, cooler tube, regenerator, and seal to adopt higher pressure. All of these reach to maximum criterion already but to reduce the friction of the engine still far away. Stirling engine friction may come from Power Piston Seal, Connecting Rod Seal, Shaft Seal, Displacer Seal, and Type of Drive Mechanical etc. Copyright© 2007 by the Japan Society of Mechanical Engineers. All rights reserved.

The Author tries to develop the Drive Mechanism for Stirling engine which has the lowest friction. This may cause to increase the performance of the Stirling engine up to 30 %.

In this research the author will compare 3 different drive mechanism Stirling engines, with the same condition, four cylinders, power piston diameter, displacement diameter, regenerator, pressure, cooler, generator, heat exchanger, and stroke. The Daisy Chain Drive Mechanism has three different types, Gear Drive, Swash Plate Drive Type I (Whisper Tech), Swash Plate Drive Type II (Rotary Drive).

It will compare cost of manufacture, performance, and efficiency. 2. Engine Specification

The Stirling Steele engine was redesigned by enlarges. The power piston size changes from 22 mm to 48 mm, Stroke from 25 mm to 40 mm, and Volume from 37.6 cc to 289.4 cc. The power changed from 20 W at 20 psi Air to 215 W at 20 psi Air. The engine specifications shown in Table 1.

The piston sets of this engine was linked with three different type daisy chain drive mechanism, Gear Drive, Swash Plate Drive Type I (Whisper Tech), Swash Plate Drive Type II (Rotary Drive). As the engine has less crank case along with a simpler crank. It permits for a more cost effective engine to manufacture. Building four cylinders instead of single cylinder units has several strong advantages such as easy starting, good balance, smooth running even at very low speeds, increased heater and cooler surface area, and good low end torque.

Since this Stirling engine is a closed cycle device, it runs very quiet. It also has no cam shaft, lifters, push rods, valves, spring, intake or exhaust manifold, complex spark ignition or carburetor. [1]

Table 1 Engine Specification Type Gamma Acting Double Working Gas Air Max. Expansion space gas temp

650 C (+/- 5 C)

Compression space gas temp 40 – 50 C (+/- 5 C)

Ambient Temperature 40 C (+/-5 C) Thermal Efficiency 60 % Power Control Variable Pressure No. of Cylinders 4 Means Pressure 0.5 MPa Maximum Pressure 1 Mpa Bore, mm. 48 Stroke, mm. 40 Engine Displacement, cc. 72 x 4 Speed, rpm 500 - 1200 Cooling type Ethyl glycol Mechanical Output Power 215 W @ 20 psi Mechanical Output Power 550 W @ 60 psi Heat Source, Electric Heater 700 W x 4

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Source : By Author 2. Drive mechanism 2.1 Gear Drive Mechanisms

Figure 1 Gear Drive Mechanism

Source : By author

The four pistons gamma type Stirling engine, are daisy chained together with Mitter gear, Figure 1. This is done by driving the displacer via linear drive rods which are attached to the top of power pistons. The rods pass through a sealed bulkhead and the displacer cylinders are ported to power piston cylinders that are phased behind them 90°. This allows an engine that only requires one crank through per piston where other Stirling engine requires two.

This engine still has the same bronze bush sealed bulkhead as original designed. But at the Mitter gear instead using of bronze bushing it was changed to

bearing system. The rotation, Clock-wise or counter clock-wise, can be done by adjust a little phase angle, positive or negative, different. 2.2 Swash Plate Type 1 Drive Mechanisms

The four pistons gamma type Stirling engine, are daisy chained together with Whisper Tech Technology, Swash Plate, Figure 2. [2] This is done by driving the displacer via linear drive rods which are attached to the top of power pistons. The rods pass through a sealed bulkhead and the displacer cylinders are ported to power piston cylinders that are phased behind them 90°. This allows an engine that only requires one crank through per piston where other Stirling engine requires two.

This engine was replace bronze bushing sealed bulkhead as guide bearing with rubber seal, and replace the Mitter gear with Whisper Tech Technology, Swash Plate. This could call Positive Swash plate. It also added more bearing and universal joint. The rotation, Clock-wise or counter clock-wise, can be done by adjust a little phase angle, positive or negative, different.

Figure 2 Swash Plate Type 1

Souce : By Author 2.3 Swash Plate Type 2 Drive Mechanisms

The four pistons gamma type Stirling engine, are daisy chained together with Rotary Air Compressor Swash Plate, Figure 3. [3] This is done by driving the displacer via linear drive rods which are attached to the top of power pistons. The rods pass through a sealed bulkhead and the displacer cylinders are ported to power piston cylinders that are phased behind them 90°. This allows an engine that only requires one crank through per piston where other Stirling engine requires two.

The ideal of this engine mechanism was come from Rotary Air condition. The bronze bushing sealed bulkhead was replaced with guide bearing with rubber

seal, and replace the Mitter gear with Rotary Drum. This could call Negative Swash plate. It also added more bearing and universal joint. The rotation, Clock-wise or counter clock-wise, can be done by adjust a little phase angle, positive or negative, different.

Figure 3 Swash Plate Type 2 (Rotary) Souce : By Author

3. How to test

Friction test, Use DC motor, Minertia Encoder Motor 200 W torque 3.5 N-m, direct connects to the shaft of the Stirling engine without load and Power piston connected. Supply the motor with DC power, measure volt and current every 100 RPM until reach to maximum 1,800 RPM. Stop measurement.

Connect Power piston, Displacer Cylinder, Connecting rof, all other components. Release pressure value of Stirling engine to atmospheric pressure. Supply the motor with DC power, measure volt and current every 100 RPM until reach to maximum 1,800 RPM. Stop measurement.

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Power test, connect Stirling Engine with Torque indicator. Supply AC volt to Electric Heater, supply Air up to 0.5 MPa measure Torque, Temperature, Power. 4. Results

Table 2 shown the performance of each type of mechanism, Gear Drive, Swash Plate Type I, Swash plate Type II. This performance from the experiment at AREF laboratory, Bangkok, Thailand.

Table 2 Performance Gear Drive, Figure 4

Friction @ 1800 RPM (W) 8.9 Cost USD 950.00 Mean Time Between Fail (hrs) 2,500 How to make Easy Maintenance Time (hrs) 150 Torque (N-m) 8 Carnot Eff. % 60 Thermal Eff. % 28 Mechanical Eff. % 44 Easy to start (Count as 10) 7

Swash Plate Drive Type I, Figure 5

Friction @ 1800 RPM (W) 7.6 Cost USD 1500.00 Mean Time Between Fail (hrs) 15,000 How to make Accurate Maintenance Time (hrs) 2,500 Torque (N-m) 9.8 Carnot Eff. % 60 Thermal Eff. % 29 Mechanical Eff. % 56 Easy to start (Count as 10) 8

Swash Plate Drive Type II, Figure 6

Friction @ 1800 RPM (W) 6.1 Cost USD 1280.00 Mean Time Between Fail (hrs) 18,000 How to make Very Accurate Maintenance Time (hrs) 3,500 Torque (N-m) 10.2 Carnot Eff. % 60 Thermal Eff. % 30 Mechanical Eff. % 58 Easy to start (Count as 10) 9

Source : By Author

Gear Drive Friction Test

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500 700 900 1100 1300 1500 1700 1900RPM

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Figure 4 Daisy Chain Gear Drive Mechanism, Friction Test Source : By Author

Swash Plate Friction Test

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500 700 900 1100 1300 1500 1700 1900

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Figure 5 Daisy Chain Wisper Tech Swash Plate, Friction Test Source : By Author

Rotary Drive Friction Test

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Figure 6 Daisy Chain Rotary, Friction Test

Source : By Author

5. Conclusions All three Daisy Drive Mechanisms work well in

the test bench. All Stirling engine can be rotate Clock-wise or counter clock-wise by adjust a little phase angle, positive or negative, different.

The Gear Drive Mechanism is easy to make but very noisy during the operation. As the weight of gear not easy to balance so this type of mechanism can create a lot of vibration. This type of Mechanism is the cheapest one to make. The maintenance time too low, 150 hrs as the screw holding the bearing, and axial shaft always loose from vibration. The friction is about 8.9 W. The engine torque 8 N-m is quite good. Carnot efficiency is 60 %. Thermal Efficiency is 28 % and Mechanical Efficiency is 44 %. The friction test shown as Figure 4.

All piston rod of Swash Plate Drive Mechanism was installed with guide bearing on both sides to reduce friction. This type of Mechanism needs

accurate workmanship to make but it operates quite. As the parts are precision it helps the maintenance time increase up to 15,000 hrs.

As the weight of swash plate is in balance so it creates less vibration. This type of Drive Mechanism had lot of parts and complicates to make. The cost to make this system is quite high. The friction is about 7.6 W. The engine torque 9.8 N-m is quite good. Carnot efficiency is 60 %. Thermal Efficiency is 29 % and Mechanical Efficiency is 56 %. The friction test shown as Figure 5.

The Swash Plate Drive Mechanism Type 2 (Rotary Drive), all piston rods install with guide bearing on both side to reduce the friction. This type of Mechanism needs very accurate workmanship to make. It is very quite during the operation. The Stirling engine can be rotate clockwise or counter clockwise by adjust a little phase angle, positive or negative, different. The maintenance time are high, 18,000 hrs.

As the weight of Rotary drum is in balance so this type of mechanism create much lower vibration than other system. This type of Drive Mechanism has fewer parts than Daisy Chain Gear Drive but complicate to make. The cost of the system is medium high. The friction is about 6.1 W. The engine torque 10.2 N-m is quite good. Carnot efficiency is 60 %. Thermal Efficiency is 30 % and Mechanical Efficiency is 58 %. The friction test shown as Figure 6.

The Swash Plate Drive Type I (Whisper Tech) can be improved mechanical efficiency 27 % from Gear Drive Mechanism. The Swash Plate Drive Type II (Negative Rotary) can be improved mechanical efficiency 31 %.

Some modification may improve better efficiency, such as weight of linkage arm, weight of piston, type of piston seal.

Friction of Stirling engine may not have direct effect to the insolation, but if the Stirling engine has less friction, Stirling engine will require less power to overcome the friction. This will gain the performance of the Stirling engine up. Thus, with medium insolation as Thailand, average 550 W/m2 daily, Stirling engine could perform better.

ACKNOWLEDGMENTS

This research was prepared by Mr. Suravut SNIDVONGS, Vice President, Asian Renewable Energy Development and Promotion Foundation, EIT member, a PhD Student, School of Renewable Energy Technology, Naraesuan University, Pitsanulok, Thailand. The author would like to acknowledge the assistance and guidance of Asian Renewable Energy Development and Promotion Foundation Dr. Sub.Lt. Prapas Limpabandhu Deputy Minister of Foreign Affair, Mr. Sutas AROONPAIROJ and staffs, the Engineering Institute of Thailand members who provided a critical review of this research through its various stages, including Asist. Prof. Dr. Sirinuch,

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Chindaruksa, Physic Department, Faculty of Science Naraesuan University, as Advisor, Dr. Vichit, Yamboonrung, Assoc. Prof. Dr. Wattanapong Rakwichien, Asist. Prof. Dr. Mathanee Sanugansermsri, as Co-Advisor and the Naraesuan University Staffs, Pitsanulok, Thailand. Especially the Don Bosco Technical School staffs for their fabrication and construction work on the prototype. Finally, the author would like to thank the numerous industries to provide information for this research.

References [1]. The Stirling Steele engine, Ronald J. Steele, 1994. [2]. Development of Stirling Engine Generator,

Whisper Tech, 2006 [3]. Mitsubishi Air-condition Swash Plate, Rotary

compressor, 2004.

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