Continuous and Discontinuous (Stepwise) Variable compression Ratio Engine in one of the most widely acceptable methods in terms of efficiency and performance. Even though this. method was not new. it is still not ready for manufacturing due to many mechanical drawbacks such as heavy weight high inertia force heat accumulation too many component parts vibration leakage of engine oil high energy consumption low precision causes of problems for other part that work together and high cost. Today there are more than 250 patents worldwide the relate to this systim. Thus this paper presents the background of this technology mechanism categories analysis of strength and weakness and summary of highest potential mechanism pattern for line production of new generation engines.

At present in Thailand single cylinder small engines have been used generally for agriculture. This leads to large amount of fuel import while the price of fossil fuels rise continuously. The Department of Alternative Energy Development and Eff iciency Ministry of Energy decided to draft the minimum energy eff iciency standard for small engines by studying and testing specif ic fuel consumption of gasoline and diesel engines based on the JIS B 8017 and TIS 787-2551 standards respectively. Results of the experiment revealed that specif ic fuel consumption of gasoline engine was higher than diesel engines between 39% and 49% at equivalent energy supply. However the limitation of maximum and minimum energy eff iciency for gasoline engine is still necessary in order to enhance energy eff iciency of small engines manufactured in Thailand