The French company MCE-5 Development claims its MCE-5 VCR engine will usher in the mass production of vehicles that are more fuel efficient than both diesels and hybrids. Usually, internal-combustion engines with a high compression ratio make more efficient use of the energy in fuel, and also produce more power, than those with a lower compression ratio. But at high engine loads, high compression causes knock, ping, and other forms of powerstealing untimed ignition. VCR engines, however, vary compression ratio infinitely within a wide range to overcome this problem.
The idea of a variable-compression ratio is not new. There have been several engines in which the "effective" compression ratio can be changed typically by varying the valve timing. Closing the intake valve late, for example, reduces compression. Toyota employs this approach in its Atkinson Cycle Prius hybrid gasoline engine. Mazda uses it in its Millenia Miller Cycle supercharged V6, where the late timing is fixed and supercharging "fills in" throughout the range. The MCE-5 VCR engine block, which is designed to replace the traditional fixed-compression ratio block, integrates power transmission and control of compression ratio. It provides compression ratio control, ranging between 7:1 and 20:1, to each cylinder. A supercharger boosts engine peak power when needed for occasional hard acceleration or hill climbing.
French developers say thanks to its reasonable production costs, the new block could lead to a generation of fuel-efficient yet powerful vehicles.