ME433 Project:Variable Compression Ratio Engine Systems

Anthony CrawfordPh.D., P.E.

Compression ratio

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Knock Limits Compression Ratio

• Ways to mitigate knock– Higher octane fuel– Sophisticated control system– Reduced compression ratio

Theoretical VCR Benefit

• Engine Efficiency (Envera 2.2L VCR I4, a 3.6L turbo-DI V6, and a 5.7L V8 )

• Torque/Power Improved at below WOT levels

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Various VCR Systems

System Criterion 1 2 3 4 5 6 7 8 9 10Suitability for

Cont. CR Continuous VCR 2-stage VCR

Determination of Actual CR + + + + + + - - - -

Chamber Shape -- ++ ++ ++ ++ ++ ++ ++ ++ ++

Impact on Package - -- -- -- - - ++ + + +

Modification of Production o -- -- -- - - + + + +

Oscillating Mass ++ -- -- ++ ++ -- -- + + --

Friction ++ - - ++ - - o + -- oCosts o - -- -- - - o - - --

++ very low negative impact + low negative impact o moderate impact

- high negative impact -- very high negative impact

• Secondary piston– Changes clearance V

VCR that adjust the clearance volume without modifying the TDC

System Criterion 1 2 3 4 5 6 7 8 9 10

Suitability for Cont. CR Continuous VCR 2-stage VCR

Determination of Actual CR

+ + + + + + - - - -

Chamber Shape

-- ++ ++ ++ ++ ++ ++ ++ ++ ++

Impact on Package

- -- -- -- - - ++ + + +

Modification of Production

o -- -- -- - - + + + +

Oscillating Mass

++ -- -- ++ ++ -- -- + + --

Friction ++ - - ++ - - o + -- o

Costs o - -- -- - - o - - --

++ very low negative impact+ low negative impact

o moderate impact-high negative impact

--- very high negative impact

• Rotation– Moves cylinder up

VCR that adjust the clearance volume without modifying the TDC

System Criterion 1 2 3 4 5 6 7 8 9 10

Suitability for Cont. CR Continuous VCR 2-stage VCR

Determination of Actual CR

+ + + + + + - - - -

Chamber Shape

-- ++ ++ ++ ++ ++ ++ ++ ++ ++

Impact on Package

- -- -- -- - - ++ + + +

Modification of Production

o -- -- -- - - + + + +

Oscillating Mass

++ -- -- ++ ++ -- -- + + --

Friction ++ - - ++ - - o + -- o

Costs o - -- -- - - o - - --

++ very low negative impact+ low negative impact

o moderate impact-high negative impact

--- very high negative impact

• Translation– Moves cylinder up

VCR that adjust the clearance volume without modifying the TDC

System Criterion 1 2 3 4 5 6 7 8 9 10

Suitability for Cont. CR Continuous VCR 2-stage VCR

Determination of Actual CR

+ + + + + + - - - -

Chamber Shape

-- ++ ++ ++ ++ ++ ++ ++ ++ ++

Impact on Package

- -- -- -- - - ++ + + +

Modification of Production

o -- -- -- - - + + + +

Oscillating Mass

++ -- -- ++ ++ -- -- + + --

Friction ++ - - ++ - - o + -- o

Costs o - -- -- - - o - - --

++ very low negative impact+ low negative impact

o moderate impact-high negative impact

--- very high negative impact

VCR that adjust the clearance volume by modifying the TDC

• Linkage– Adjust base pivot or link length to affect TDC

System Criterion 1 2 3 4 5 6 7 8 9 10

Suitability for Cont. CR Continuous VCR 2-stage VCR

Determination of Actual CR

+ + + + + + - - - -

Chamber Shape

-- ++ ++ ++ ++ ++ ++ ++ ++ ++

Impact on Package

- -- -- -- - - ++ + + +

Modification of Production

o -- -- -- - - + + + +

Oscillating Mass

++ -- -- ++ ++ -- -- + + --

Friction ++ - - ++ - - o + -- o

Costs o - -- -- - - o - - --

++ very low negative impact+ low negative impact

o moderate impact-high negative impact

--- very high negative impact

VCR that adjust the clearance volume by modifying the TDC

• Rocking– Movement on one side generates opp. movement in piston

System Criterion 1 2 3 4 5 6 7 8 9 10

Suitability for Cont. CR Continuous VCR 2-stage VCR

Determination of Actual CR + + - + + + - - - -

Chamber Shape -- ++ ++ ++ ++ ++ ++ ++ ++ ++

Impact on Package - -- -- -- - - ++ + + +

Modification of Production o -- -- -- - - + + + +

Oscillating Mass ++ -- -- ++ ++ -- -- + + --

Friction ++ - - ++ - - o + -- oCosts o - -- -- - - o - - --

++ very low negative impact+ low negative impact

o moderate impact-high negative impact

--- very high negative impact

VCR that adjust the clearance volume by modifying the TDC

• Elastic component– Elastic components

compress at higher pressures thus reducing clearance volume and reducing compression ratio at higher loads

VCR that adjust the clearance volume by modifying the TDC

• Eccentric pivots– Effectively adjusts

link lengths System Criterion 1 2 3 4 5 6 7 8 9 10

Suitability for Cont. CR Continuous VCR 2-stage VCR

Determination of Actual CR + + - + + + - - - -

Chamber Shape -- ++ ++ ++ ++ ++ ++ ++ ++ ++

Impact on Package - -- -- -- - - ++ + + +

Modification of Production o -- -- -- - - + + + +

Oscillating Mass ++ -- -- ++ ++ -- -- + + --

Friction ++ - - ++ - - o + -- oCosts o - -- -- - - o - - --

++ very low negative impact+ low negative impact

o moderate impact-high negative impact

--- very high negative impact

Conclusions

• VCR systems have the promise to increase:– engine efficiency/power/torque– operate with multiple cycles– adjust to accommodate knock limitations of

various fuels.• Multiple VCR systems each have their own

advantages and disadvantages with regard to:– effectiveness– complexity– ability to be integrated into current engines

Key References• Pischinger, S., et. al. “Two-stage Variable Compression Ratio

with Eccentric Piston Pin,” MTZ Worldwide Edition, 2009-02.

• Mendler, C., “Envera Variable Compression Ration Engine,” US DOE report DE-FC26-05NT42484, March 15, 2011.

• Aina, T., et. al. “Influence of compression ratio on the performance characteristics of a spark ignition engine,” Advances in Applied Science Research, 3 (4): 1915-1922, 2012.