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Presented work is based on an extensive CFD simulation of the exhaust stroke of a single-cylinder fourstroke internal combustion engine with the exhaust manifold attached. Since the dynamics of the exhaust flow are extremely 3D, an innovative approach to calculate the local entropy generation is developed and implemented in the discussed 3D numerical model. It allows temporal and spatial determination of critical regions and periods of entropy generation in the process with objective to reduce it.List of symbols c p Specific heat capacity (Jkg -1 K -1 ) E Exergy (J) _ E Exergy flow (W) _ m Mass flow rate (kgs -1 ) p Pressure (Pa) q * Heat flux density vector (Wm -2 ) R Specific gas constant (Jkg -1 K -1 ) s Entropy per unit mass (Jkg -1 K -1 ) S Entropy (JK -1 ) _ S Entropy flow (WK -1 )Greek symbols a Thermal diffusivity (m 2 s -1 ) eDissipation rate of turbulent kinetic energy (m 2 s -3 ) kThermal conductivity (Wm -1 K -1 ) lDynamic viscosity (kgm -1 s -1 ) q Density (kgm -3 ) U Viscous dissipation of mechanical energy (Wm -3 ) U H Entropy production term (WKm -3 )