The Automobile industry is under great stress due to greenhouse gas emissions and health impacts of pollutants. The rapid decrease of fossil fuels has promoted the development of engine designs having higher fuel economy. At the same time, these designs keep the stringent emission standards in check without sacrificing brake power. Variable Compression Ratio (VCR) is one such measure. This work reviews the technological advancements in the design of a VCR engine. VCR engines can minimize possible risks of irregular combustion while optimizing Brake specific fuel consumption towards higher power and torque. An increase in fuel economy is seen for VCR naturally aspirated engines when coupled with downsizing. In addition to this, emissions of carbon dioxide decreases due to effective utilization of fuel at high loads. Since the first VCR design, there have been various modifications and improvements in VCR engine design. This paper describes the various techniques by which VCR is being implemented and provides a comparative study of original and modified technology on the basis of efficiency, engine friction, specific fuel consumption, engine rigidity and piston kinematics. The paper then reviews various historical designs which use the above mentioned techniques patented by Ford, Mercedes Benz, Nissan, Peugeot and Gomecsys and discusses their advantages. Lastly the paper explains the design, working and advantage of three VCR designs that are closer to production.
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