1. ME433 Project: Variable Compression Ratio Engine Systems
Anthony Crawford
Ph.D., P.E.

2. Compression ratio

3. Knock Limits Compression Ratio
Ways to mitigate knock
Higher octane fuel
Sophisticated control system
Reduced compression ratio

4. 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

5. Various VCR Systems 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
Costs
++ very low negative impact + low negative impact
o moderate impact
- high negative impact -- very high negative impact

6. VCR that adjust the clearance volume without modifying the TDC
Secondary piston
Changes clearance V
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
Costs
++ very low negative impact
+ low negative impact
o moderate impact
high negative impact
-- very high negative impact

7. VCR that adjust the clearance volume without modifying the TDC
Rotation
Moves cylinder up
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
Costs
++ very low negative impact
+ low negative impact
o moderate impact
high negative impact
-- very high negative impact

8. VCR that adjust the clearance volume without modifying the TDC
Translation
Moves cylinder up
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
Costs
++ very low negative impact
+ low negative impact
o moderate impact
high negative impact
-- very high negative impact

9. 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
Costs
++ very low negative impact
+ low negative impact
o moderate impact
high negative impact
-- very high negative impact

10. 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
Costs
++ very low negative impact
+ low negative impact
o moderate impact
high negative impact
-- very high negative impact

11. 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

12. 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
Costs
++ very low negative impact
+ low negative impact
o moderate impact
high negative impact
-- very high negative impact

13. 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

14. Key References
Pischinger, S., et. al. “Two-stage Variable Compression Ratio with Eccentric Piston Pin,” MTZ Worldwide Edition,
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): , 2012.