• The Variable Compression Ratio Engine can operate at different compression ratios, depending on the particular performance needs of the vehicle.
• The VCR technology was introduced to increase fuel efficiency under varying loads since conventional gasoline engines due to their fixed compression ratios did not achieve fuel efficiency at low power operations.
• VCR engine operates at high compression for low power levels to enable fuel efficiency benefits and operates at low compression for high power levels to prevent knock.
• VCR can be obtained by altering the clearance volume or both the clearance and swept volume.
• The usual size of VCR engine is small, about one-third the displacement volume of a conventional gasoline engine to further improve the engine’s fuel economy.
• Figure shows variation of compression ratio and peak pressure with load for VCR engine.

Advantages:

• High efficiency for lower levels of engine power
• Favourable burn rate which permits use of lean burn technology
• High compression ratio at low loads gives good starting and idling performance
• VCR engine is compact and has good multifuel capability
• Higher power to weight ratio
• Lower thermal and structural loads
• Produces very less low frequency noise