Original scientific paper https://doi.org/10.2298/TSCI170518296T Energy, economy and pollution factor of internal combustion engine profoundly influence the development of the society. It is well known that efficiency of an internal combustion engine increases by compression ratio, and is limited due to knocking and high thermal stress development in the combustion chamber of an engine. On another side, an efficiency of internal combustion engine decreases toward the more top engine speed.

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... dering this, a concept is proposed which can change its compression ratio with speed. Variation in compression ratio is achieved by a change in stroke length through moving crank pin within the crank. In this paper the mechanism of operation and prediction of performance characteristics of variable compression ratio spark ignition engine with varying speed using quasi-dimensional combustion simulation mode is presented. It was observed that proposed mechanism provides better fuel efficiency at higher engine speed. Further, it is inferred that 3 mm increase in crank length results in 7% increment in thermal efficiency and 8% decrement in brake specific fuel consumption for 13 compression ratio at 6000 rpm.