The recent improvement on Spark Ignition Engines has been theresult of improved engine thermodynamic cycles, made possible by advances intechnologies such as Variable Valve Timing (VVT) and Variable CompressionRatio (VCR). To evaluate the potential of these techniques a thermodynamicanalysis is made. Numerical models were implemented in Matlab Simulinkusing the laws of thermodynamics and include heat transfer, combustion,real working fluid characteristics and intake and exhaust events. The secondlaw analysis allowed the identification of inefficiency sources and directionsfor improvement. A SI engine was analysed and its processes were evaluatedby the amount of entropy generated.
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