Recent engine development has focused mainly on the improvement of engine efficiencyand output emissions. The improvements in efficiency are being made by frictionreduction, combustion improvement and thermodynamic cycle modification. Newtechnologies such as Variable Valve Timing (VVT) or Variable Compression Ratio (VCR)are important for the latter.To assess the improvement capability of engine modifications, thermodynamic analysis ofindicated cycles of the engines is made using the first and second laws of thermodynamics.The Entropy Generation Minimization (EGM) method proposes the identification ofentropy generation sources and the reduction of the entropy generated by those sources as amethod to improve the thermodynamic performance of heat engines and other devices. Acomputer model created and implemented in MATLAB Simulink was used to simulate theconventional Otto cycle and the various processes (combustion, free expansion duringexhaust, heat transfer and fluid flow through valves and throttle) were evaluated in terms ofthe amount of the entropy generated.An Otto cycle, a Miller cycle (over-expanded cycle) and a Miller cycle with compressionratio adjustment are studied using the referred model in order to evaluate the amount ofentropy generated in each cycle. All cycles are compared in terms of work produced percycle.
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