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Internal Combustion Engines

Lecture-31

Ujjwal K Saha, Ph.D.Department of Mechanical Engineering

Indian Institute of Technology Guwahati

Prepared underQIP-CD Cell Project

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Introduction

• Known as Hot air engine• Earlier abandoned due to development

of superior power-to-weight engines• Remained as academic interest due to

its unique feature during 19th century• In 1938, N.V.Philips developed small gas

refrigerating machine for production of liquefied gases

• In 1953, Stirling engine with an efficiency of 40% with specific power of 82 kW/l was invented

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The working principle

The basis of stirling engine is the same as that of all internal combustion engines i.e. the alternate compression at low temperature and expansion at high temperature of a confined working fluid.

However, the gas is heated in a radically different manner. The conventional engines burn fuel internally and intermittently whereas stirling engine burns its fuel outside the engine itself and continuously, i.e., it is an external continuous combustion engine.

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Difference

• The fuel do not enter the engine cylinder to become the working gas.

• The cyclic flow of working fluid within the engine is achieved solely through geometric volume changes and without the use of intermittently-closed valves or ports.

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Difference

An intermittent flow heat exchanger stores a large portion of heat of the working fluid after expansion and subsequently returns it to the working fluid after compression, thereby, accomplishing thermal regeneration.

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Ideal thermodynamic cycleIsothermal compression and simultaneous heat rejectionConstant volume heat addition (by regeneration)Isothermal expansion with simultaneous heat additionConstant volume heat rejection (by regeneration)

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Basic types of stirling engine

• Two-piston mechanism (Alpha type)

• Piston displacer system– Beta type– Gamma type

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Two piston mechanism

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Different configurations of two piston mechanism

Simple two piston mechanism is unsuitable for higher output engines. So came the double acting engines with following two mechanical configurations:

• In line crankshaft drive

• Circular swashplate drive

In line 4-cylinder stirling engine

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The piston displacer engine

• Two pistons—power and displacer.

• Displacer piston—heat and cools the working gas.

• Power piston—compress and expand the gas.

StirlingStirling engine is governed by the relative engine is governed by the relative motion of these two pistons.motion of these two pistons.

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Phases of the operating cycle

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Types of piston displacer engine• Beta type—single cylinder

classic sterling engine configuration.

• Gamma type—power piston and displacer piston in different cylinders.– Convenient complete

separation between the regenerator associated with displacer and the expansion and compression work of power piston.

– Larger unswept volume.– Lower specific power.– Used when the advantage of

separate cylinders outweighs the specific power disadvantage

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Phasing between power piston and displacerPower piston and displacer must be connected with some mechanical linkage to obtain the required phasing.

Types of linkages are:• Crankshaft with

displaced throws• Rhombic drive.

Two symmetrically placed connecting rods drive the power piston while the displacer piston is driven by a displacer rod extending through the power piston.

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Rhombic drive• Two crankshafts

rotating in opposite directions.

• Two synchronizing gears for timing the shafts.

• Symmetry makes even single cylinder engine balanced. No horizontal thrust as forces are balanced at yoke. Hence low frictional losses too.

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Engine parts

• Combustor and heater head.

• Regenerator.• Cooler.• Power piston and

displacer piston assembly.

• Buffer space and the rhombic drive.

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Performance of stirling engineThe stirling cycle engine is specially suitable for automotive applications because of:--

• High brake thermal efficiency.• Low noise.• Low emissions.• Specific power output comparable to Otto engine.• Desirable output shaft maximum to ideal speed ratio.

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• Multi fuel capability• Perfect balancing• Reduced exhaust emissions• Efficiency and size• Smooth and noise free engine

operation• Overload capacity• Reliable starting• No lubricating oil needed

Advantages

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Disadvantages

• Complex design due to use of rhombic drive, regenerators, heaters and coolers.

• Needs a large amount of cooling water which increases the size of the radiator.

• High cost.• Requires a blower which reduces

the engine efficiency and increases the noise.

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1.1. Crouse WH, and Anglin DLCrouse WH, and Anglin DL, (1985), Automotive Engines, Tata McGraw Hill.2.2. Eastop TD, and McConkey A,Eastop TD, and McConkey A, (1993), Applied Thermodynamics for Engg.

Technologists, Addison Wisley.3.3. Fergusan CR, and Kirkpatrick ATFergusan CR, and Kirkpatrick AT,, (2001), Internal Combustion Engines,

John Wiley & Sons.4.4. Gill PW, Smith JH, and Ziurys EJGill PW, Smith JH, and Ziurys EJ,, (1959), Fundamentals of I. C. Engines,

Oxford and IBH Pub Ltd. 5.5. Heisler H,Heisler H, (1999), Vehicle and Engine Technology, Arnold Publishers.6.6. Heywood JB,Heywood JB, (1989), Internal Combustion Engine Fundamentals, McGraw Hill.7.7. Heywood JB, and Sher E,Heywood JB, and Sher E, (1999), The Two-Stroke Cycle Engine, Taylor &

Francis.8.8. MathurMathur ML, and Sharma RP,ML, and Sharma RP, (1994), A Course in Internal Combustion

Engines, Dhanpat Rai & Sons, New Delhi.9.9. Pulkrabek WW,Pulkrabek WW, (1997), Engineering Fundamentals of the I. C. Engine, Prentice

Hall.10.10. Rogers GFC, and Mayhew YRRogers GFC, and Mayhew YR, (1992), Engineering Thermodynamics, Addison

Wisley. 11.11. Stone R,Stone R, (1992), Internal Combustion Engines, The Macmillan Press Limited,

London.12.12. Taylor CF,Taylor CF, (1985), The Internal-Combustion Engine in Theory and Practice, Vol. 1

& 2, The MIT Press, Cambridge, Massachusetts.

References

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1. http://www.mne.psu.edu/simpson/courses2. http://me.queensu.ca/courses 3. http://www.eng.fsu.edu4. http://www.personal.utulsa.edu5. http://www.glenroseffa.org/6. http://www.howstuffworks.com7. http://www.me.psu.edu 8. http://www.uic.edu/classes/me/ me429/lecture-air-cyc-web%5B1%5D.ppt9. http://www.osti.gov/fcvt/HETE2004/Stable.pdf10. http://www.rmi.org/sitepages/pid457.php11. http://www.tpub.com/content/engine/14081/css12. http://webpages.csus.edu13. http://www.nebo.edu/misc/learning_resources/ ppt/6-1214. http://netlogo.modelingcomplexity.org/Small_engines.ppt15. http://www.ku.edu/~kunrotc/academics/180/Lesson%2008%20Diesel.ppt16. http://navsci.berkeley.edu/NS10/PPT/ 17. http://www.career-center.org/ secondary/powerpoint/sge-parts.ppt18. http://mcdetflw.tecom.usmc.mil19. http://ferl.becta.org.uk/display.cfm20. http://www.eng.fsu.edu/ME_senior_design/2002/folder14/ccd/Combustion21. http://www.me.udel.edu22. http://online.physics.uiuc.edu/courses/phys14023. http://widget.ecn.purdue.edu/~yanchen/ME200/ME200-8.ppt -

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