Qip Ice 32 Variable Compression Ratio Engines

8/16/2019 Qip Ice 32 Variable Compression Ratio Engines

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Internal Combustion Engines

Lecture-32

Ujjwal K Saha, Ph.D.Department of Mechanical EngineeringIndian Institute of Technology Guwahati

Prepared underQIP-CD Cell Project


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Introduction• Need of High specific power output

accompanied by good reliability and

longer engine life.• Use of high pressure turbo charging results

induces high thermal loads.•

Turbocharger doesn’t have good adiabaticefficiency.• High peak pressure problem occurs at full

load• Can be minimized by reducing CR• But also CR should be sufficiently high for

good starting and part load operation .


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VCR engine• High compression ratio is used for good stability and low

load operation• Low compression ratio used at full load to boost the

turbocharger intake pressure• Load increases – engine exhaust increases – boost

available more• At full load turbocharger boost capacity is high so

reduction in CR is necessary for more efficiency and toreduce thermal stresses.

• Used mainly with turbocharged diesel engines-- VCR concept is beneficial at low load-- better multifuel capacity-- also spark engine can produce knock due to

sudden change from high CR to low CR.


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Theoretical Analysis• For part load and high load CR is low in VCR

than FCR• Expansion is slower at low compression

ratios.• Gas temperature is lower than the for

constant compression ratio engines for full

compression stroke and up to 500

after tdc .After this the temperature drop is slower dueto slower expansion

• Exhaust valves in VCR run hotter.• Boost pressure and mean cycle temperature

increases with load.• Both bsfc and isfc increases with load.• Pre-turbine gas temperature is higher – but

limited by metallurgical considerations.


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Methods of obtaining VCR

Va ria b le c o m p re ssio n ra tio c a n b eo b ta in e d b y a lte rin g :

• The clearance volume.• Both the clearance volume and the

swept volume.


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Various VCR Concepts• A very new and efficient method is

slidable piston head and cylinder.• Variation of combustion chamber volume.• Variation of piston deck height.• Modification of connecting rod geometry.• Moving the crankpin within the crankshaft.• Moving the crankshaft axis.• Traverse type mechanism.


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Moving Head (SVC)

high compression ratio 14:1 low compression ratio 8:1

By combining head and liners into a semimonoblocconstruction which pivots with respect to theremainder of the engine, SAAB have enabled a

tilting motion to adjust the effective height of thepiston crown at TDC.


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Variation of Combustion Chamber Volume

Typically the volume of

combustion chamber isincreased to reduce theCR by moving asecondary piston :• Ford type VCR Head:

Ford patent for

compression adjustmentusing a secondarypiston or valve.


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• Volvo/Alvar type VCR Head:

Alvarengine concept in

which each secondarypiston moves continuouslyat half crankshaft speedand could, potentially,share drive with acamshaft. Phase variationbetween the secondary

pistons and the crankshaftassembly enables therequired variation in CR.


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Variable Height Piston

Ford VCR Piston

Variation in compression height of the piston offerspotentially the most attractive route to a productionVCR engine since it requires relatively minor changesto the base engine architecture.


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Daimler – Benz VCR Piston


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Connecting Rod Geometry

Nissan VCR Engine

A popular approach has beento replace the conventional conrod with a 2 piece design inwhich an upper memberconnects with the piston while alower member connects withthe crankshaft. By constrainingthe freedom of the point atwhich the two members join, theeffective height of the con rodcan be controlled and, hence,the compression volume. All thecompound con rod designs

result in modified piston motionwhen compared to aconventional engine, since thepiston is connected to a rod

whose other end is no longermoving in a circular orbit.


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• Peugeot VCR Engine


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Movement of Crankshaft or Crankpin

• G o m e sy s V C R e n g in e in w h ic h m o v e a b le c ra n k p in sfo rm a n e c c e n tric sle e v e a ro u n d th e c o n v e n tio n a l

c ra n k p in s a n d a re d riv e n b y a la rg e g e a r.

Se v e ra l sy ste m s ha v e

b e e n p ro p o se d w h ic he ithe r c a rry the c ra nk sha ftm a in b e a ring s in a ne c c e n tric a sse m b ly o rm o v e th e c ra n k p in se c c e n tric a lly to e ffe c t aStro k e c ha ng e a t TDC .


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• Rapan VCR engine inwhich the crankshaft

main bearings arecarried in an eccentrichousing which can berotated by an actuator,via a mechanism, tovary the crankshaftposition with respectto the cylinder head.


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Traverse diesel engine T-01


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Control strategyBasic Relationship: Points 1,

2, 4, 5 lie on the plane of lowcompression. Point 3 lies on theplane of high compression.

The engine is started at lowCR and zero boost (point 1).

When the driver accelerates,load and boost increase topoint 2. When the driverthrottles back into a light loadcruise (point 3), load and boostreduce and CR increases.

When the throttle is re-opened from this condition, CRreduces as boost and loadincrease, reaching point 4 and,ultimately, point 5 (WOT).


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• Tip-in/Tip-out strategy:

Suppression of unwanted throttle input


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Accomplishments

• VCR shows the highefficiency at lowerengine power levels.

• Favorable burn rateand coefficient of

variance, which allowthe application oflean burn technology.

• Favorable andconsistent emissionlevel.


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Accomplishments

• VCR engine is verycompact and has ahigher power toweight ratio.

• VCR principle causeslow thermal and

structural loads.• bsfc of the VCR

engine is as good asthat of conventionalengine.

• VCR engine has avery less lowfrequency noise.

AVDS-1100 AVCR-1100

Gross b.p., (kW) 186.5 1100Bmep. ( bar) 10 26Displacement,(sq. cm) 18300 18300Compressionratio 22 : 1 10:1, 22:1

Weight (kg) 1385 1385Weight,kg/Gross b. p. 3.5 13.5b.p./sq. m

317 686Maximumtorque, N-m atrpm

1490/2000 3860/2000

Min, sfc,kg/gross kW/hr

0.2320.232


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• Due to use of high compression ratio atlow loads the VCR engine has a goodstarting and idling performance.

• Due to higher compression ratio atstarting and part load operation the VCR

engine has good multifuel capability .

Accomplishments


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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 YR Rogers 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://www.eere.energy.gov 3. http://www.eng.fsu.edu4. http://www.personal.utulsa.edu5. http://www.glenroseffa.org/6. http://www.howstuffworks.com

7. http://www.me.psu.edu8. http://www.saabnet.com9. http://www.osti.gov/fcvt/HETE2004/Stable.pdf 10. 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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