The entropy generation analysis is performed on a methane-air cylindrical microcombustor. The combustor is studied under different fuel-air equivalence ratios and two different inlet velocities. The results reveal that entropy generation due to heat transfer has the highest contribution to the total exergy destruction. Besides, the chemical and mixing entropy generations have the next greatest parts in the total irreversibility, respectively. The fuel-air equivalence ratio considerably affects the exergy efficiency of the system. This study shows that the microcombustor has the lowest irreversibility ratio near the stoichiometric conditions depending on the inlet velocity. Also the analysis shows that at Φ=1.1 irreversibility ratio abruptly rises at both inlet velocities which highlights the great contribution of entrance region in the exergy destruction. Meanwhile in the present work, it was noticed that the irreversivbility ratio reduces again when the fuel-air ratio exceeds Φ=1.1. This observation poses the possibility of operating cylindrical micro combustors under rich conditions.

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